5101 250 

Flat-Plate 

Solar Array Project 

DOEIJPL-1012-99 

Distribution Category UC-63b 

Progress Report 23 

for the xiod September 1983 to March 1984 

and Proceedings of the 

23rd Project Ictegration Meeting 

Prepared for 

U.S. Department of Energy 

Through an Agreement with 

National Aeronautics and space Administration 

by 

Jet Propulsion Laboratory 

California Institute of Technology 

Pasadena. Ca!ifornia 

JPL Pubkation 84-47 
51 01 -250 

Flat-Plate 

Solar Array Project 

DOE/JPL-1012-99 

Distribution Category UC-63b 

Progress Report 23 

for the Period September 1983 to March 1984 

and Proceedings of the 

23rd Project Integration Meeting 

Frepa-ed for 

U.S. Department of Energy 

TbrauGh ar? Agreement Nith 

Iria!ional Aeronautics and Space A,..lmistration 

by 

Jet Proadson Laboratory 

Caiifcrnia lnstltute 0: Technl;!qy 

Pasx~er 3. California 

JPL P~h:~catton 84.47 
Prepared by the Ja Propulsion Laboruor). California Instituteof Technology. 

for thc U.S. Department of Encrgy through an agrccmcnt with thc National 

Aaonautics and Space Ahinstration. 

Thc JPL Flat-Phtc !War Array Projm is sponsorcd by thc U.S. Lkpartmcnt of 

Energy and is put of thc Photovo1t.w Emgy Systms Program to initiate a 

major cffon toward the development of cost-cmmpctitiw solar arrap 

This repon was prcparcd as an account of work sponsorcd b> an agcnc). of thc 

Unitcd Stat- Go\cmment. Neither thc Unitcd Statcs Gmcrnment nor any 

agene thcrcof. nor any of thcir cmpb?m. makcs any warranty. cxprcss or 

implicd, or assumes my legal IiabiMy or rcsponsibilit? for the accuracy. compkrcnas. or uscfulnas of any information. apparatus. product, or prams 

dirloscd. or rcprcvnts that its usc would not infringe pri\atdy owned rights. 

Rcfcrcncc hann to any specific commacial product. proms. or xrvize br tradc 

nunc. trademark. manufacturer. or othcrwix. docs not ncxswrily conrcitutcor 

imply its cndorscment. ra-o.nmcndation. or fa\oring b?- thc L'nitcd Stata 

Gowmmcnt or any agcnc?- thcrcof. Thc \tens and opinions of authors 

cxpresscd haan do not ncccssarily stillc or rcM chose of thc L'nitcd Stam 

Go\cmmcnt or any agcncy thereof. 

This publication rcpons on work done undcr NASA Task RE-152. Amendment 

66. DOE NASA IAA NO. DE-AIOI-76ET203)3.%. 
ABSTRACT 

lhis report describes progress made by the Flat-Plate Solar Array 

Roject during the period September 1983 to March 1984. It includes reports 

on silicon sheet growth and characterization, module technology, silicon 

material, cell processing and high-efficiency cells, environmental isolation, 

engineering sciences, module reliability and project analysis and integration. 

the 23rd Project Integration Meeting held at Pasadena, California, on March 14 

and 15, 1984. 

It includes a report on, and copies of visual presentations made at, 

iii 

NOMENCLATURE 

A 

ac 

An 

AB 

ASEC 

a-Si 

ASHE 

ASTH 

BA 

BOS 

BSF 

BSR 

C 

CER 

CPVC 

c-Si 

CVD 

CVT 

CZ 

dc 

DCS 

DI 

DOE 

EBIC 

EFG 

hpere(s1 

hgstrom( s) 

Alternating current 

Air mass (e.g., AN1 * unit air mass) 

Ant ire f lec tive 

Applied Solar Energy Corp. 

Amorphous silicon 

American Society of Mechanical Engineers 

American Society for Testing and Materials 

Butyl acrylate 

Balance of System (non-array elements of a PV system) 

Back-sur f ace fie Id 

Back-surface reflection 

Celsius (temperature scale) 

Con tro lled-environmen t reactor 

Chlorinated polyvinyl chloride 

Single-crysta 1 silicon 

Chemical vapor deposit ion 

Chemical vapor transport 

Czochralski (classical silicon crystal growth method) 

Direct current 

Dichloros ilane 

De - ion iz ed 

U.S. Department of Energy 

Electron-beam-induced current 

Edge-defined film-fed growth (silicon ribbon growth method) 

V 
EM 

EPDM 

EPRI 

EPSW 

ESP 

EVA 

FBR 

FF 

FSA 

FSR 

GE 

GFCI 

h 

HEM 

Is, 

I -v 

ID 

IEEE 

I IT 

IITRI 

I PEG 

IPEGP 

I PEG4 

IR 

IT0 

Jsc 

JPL 

Ethylene methyl acrylate 

E thy lene-propy lene-d iene monomer 

Electric Power Research Institute 

Experimental process system development unit 

Edge-supported pulling (silicon-sheet production process) 

Ethylene vinyl acetate 

Fluidized-bed reactor 

Fill factor 

Flat-Plate Solar Array Project 

Free-space reactor 

General Electric Co. 

Ground-fault circuit interruptor 

heat trans fer coefficient ; hour ( s) 

Heat -exchange method (s ilicon-crys tal ingot -grovth method) 

Short -c ircuit current 

Current-vo 1 tage 

Inside diameter 

Institute of Electrical and Electronics Engineers 

Illinois Institute of Technology 

IIT Research Institute 

Improved Price Estimation Guidelines 

IPEG, non-computerized 

IPEG, computerized 

Infra red 

Indium-tin oxide 

Short-circuit current density 

Jet Propulsion Laboratory 

vi 
K 

k 

wss 

LASS 

LBIC 

LPE 

MBE 

MEPSDU 

mgSi 

MIS 

MSEC 

m-Si 

MT 

Mw 

NASA 

NEC 

NMA 

NOC 

NOCT 

omc 

O&M 

P 

'MX 

PA& I 

P/FR 

PC 

PCS 

PC/TS 

degree(s1 Kelvin 

Equilibrium constart 

Large-area pulsed solar simulator 

Low-angle silicon sheet growth method 

light-beam-induced current 

Liquid-phase epitaxy 

Molecular-beam epitaxy 

Module experimental process system development unit 

Metallurgical-grade silicon 

Metal-insulator-semiconductor (cell configura+ion) 

Mobil Solar Energy Corp. 

Microcrystalline silicon 

Metric ton(s) 

Megawatt (s 1 

National Aeronautics and Space Administration 

National Electrical Code 

Non-mass-analyzed 

Nominal operating conditions 

Nominal operating cell temperature 

Oxygen-free hard copper 

Operating and maintenance 

Power 

Maximum power 

Project Analysis and Integration Area (of FSA) 

Problem-failure report 

Power conditioner 

Power-conditioning system 

Performance Criteria/Test Standards (SERI) 

vi i 
PMJ 

PE 

PEBA 

P It4 

PMUA 

PnBA 

PPba 

PP 

PPmJ 

PU 

PV 

PVB 

WC 

PVD 

R&D 

RCA 

RES 

RH 

RTV 

S 

S 

SAMIS 

SCE 

SEM 

SERI 

SIMRAND 

SIMS 

SMUD 

Process development unit 

Po lye t hy 1 ene 

Pulsed electron beam annealing 

Project Integration Meeting 

Polymethyl methacrylate 

Po ly on-but y 1 acrylate 

Parts per billion, atomic 

Parts per million, atomic 

Parts per million, weight 

Polyurethane 

Pho tovo lta ic ( s 

Polyvinyl butyral 

Po lyv iny 1 chloride 

Physical vapor deposition 

Research and development 

RCA Corp. 

Residential Experiment Station 

Relative humidity 

Room-temperature vulcanized 

Incident solar energy density 

second( s) 

Standard Ass emb ly -L ine Manu f ac tur ing Industry S imu la t ion 

Southern California Edison Co. 

Scanning electron microscope 

SL ,r Energy Research Institute 

- SIMulation of seeearch gd Developmerit Projects 

Secondary ion mass spectroscopy 

Sacramento Mun i c ipa 1 Ut i 1 it y Die t r i c t 

viii 
SOA 

SOC 

SOLMET 

STC 

STC 

T 

TCM 

TC S 

TEM 

RIY 

TRE I 

TTU 

U 

bf 

ucc 

uc P 

UL 

uv 

voc 

wP 

Y 

77 

=xx 

R 

State of the art 

Standard operating conditione (module performance) 

Solar radiation surface meteorological observations 

Silicon tetrachloride 

Standard test conditions 

Temper at ur e 

Transparent conducting material 

Trichlorosilane 

Transmission electron microscope 

Typical meteorological year 

Texas Research and Engineering Institute 

Texas Tech University 

Superficial velocity 

Minimum fluidization velocity 

Union Carbide Corp. 

Ubiquitous crystallization process 

Underwriters Laboratories 

U1 travio le t 

Open-circuit voltage 

Peak watt(s) 

mol X silane 

Greek letter eta: efficiency 

Greek letter sigma: lateral stress 

Greek letter omega: resistance in ohms 

ix 

r 

e 

CONTENTS 

PROGRESS REPORT 

PROJECT SUMMARY ............................ 1 

AREAREPORTS ............................. 5 

MATERIALS AND DEVICES RESEARCH AREA ............... 5 

Silicon Materials Task and 

Advanced Silicon Sheet Task ................ 5 

Device Research Task ................... 19 

PROCESS DEVELOPMENT AREA .................... 23 

PROJECT ANALYSIS AND INTEGRATION AREA .............. 25 

ADVANCED PROCESSES AREA ..................... 27 

RELIABILITY AND ENGINEERING SC'ENCES AREA ............ 29 
PROJECT INTEGRATION MEETING 

PROCEEDINGS 

INrKODUCTION ............................. 45 

PLENARY SESSIONS ........................... 47 

SUMMARY.. .............................. 47 

Array Cost Sensitivities and Goals 

(R.W. Aster, Jet Propulsion Laboratory) ............. 51 

Flat-Plate Single-Axis Tracking 

(M.R. Wool, Acurex Corp.) .................... 55 

Georgetown University Photovoltaic Higher Education 

Nat Lonal Exemplar Fac i 1 i ty (PHENEF) 

(G..J. Naff, Htighes Aircraft Co.) ................ 59 

Photovoltaic Systems Development and Evaluation 

(M.G. Thomas, Sandia National Laboratories) ........... 73 

Source-Circuit Design Considerat ions 

(C.C. Gonzalet, Jet Propulsion Laboratory) ........... 81 

Central-Stat ion Array Durability Considerat ions 

(G.R. Mon and R.G. Ross, Jr., Jet Propulsion Laboratory) .... 89 

Operations and Maintenance 

(P.K. qenry, Jet Propulsion Laboratory) ............. 97 

Technical Issues of High-Efficiency Silicon Solar Cells 

(K.M. Koliwad, Jet Propulsion Laboratory) ............ 99 

TECHNICAL SESSIONS .......................... 107 ' I- I 

HIGH-EFFIC [ENCY SILLCON SOLAR CELL RESEARCH 

(T, Daud, Chairman) .......................... 107 

High-Efficiency Solar-Cell Design Modeling 

(M.F. Lamorte, Research Triangle Institute) ........... 109 

Efficiency Est hat ion and Sens it ivit y Modeling 

(A.R. Mokashi, Jet Propulsion Laboratory) ............ 113 

Barriers to Achieving High Efficiency 

(C.T. Sah, C.T. Sah Associates) ................. 123 

MBE Growth for High-Efficiency Silicon Solar Cells 

(F. Allen, University of California at tos Angeles) ....... 131 

xiv 
Investigation of Silicon Surface Passivation by 

Silicon Nitride Deposition 

(L.C. Olsen, University of Washington) ............. 139 

High-Efficiency Crystalline Silicon Solar Cells Research Forum 

(A.H. Kachare, Jet Propulsion Laboratory) ............ ?47 

High-Efficiency Solar Cell Program: Some Recent Results 

(J.B. Milstein and C.R. Osterwalcl, Solar Energy Research 

Institute) ........................... 149 

Development and Anglysis OE Silicon Solar Cells 

Near 20% Efficiency 

(M. Wolf and M. Newhouse, University CA Pennsylvania) . . . . 159 

Surface and Allied Studies in Silicon Solar Cells 

(F.A. Lindholm, T.W. Jung and J.J. Liou, University 

of Florida) ........................... 169 

Low-Temperature EBIC Studies on Silicon Sheet Materials 

(Li-Jen Cheng, Jet Propulsion Laboratory) ............ 173 

M"crostructura1 Characterization of Annealed Silicon Ribbons 

(D.G. Ast, Cornel1 University) ................. 185 

Cryogenic Laser Calorimetry for Impurity Analysis 

(R.T. Swim, University of Southern California) ......... 195 

ENCAPSULATION 

(E.F. Cuddihy, Chairman) ....................... 197 ' L' 'e 

Encapsulation Design Analysis 

(Alexander Garcia 111, Spectrolab, Tnc.) ............ 201 

Encapsulation Materials and Processing 

(P.B. Willis, Springborn Laboratories, Inc.) .......... 217 

Photothermal Degradation of Encapsulants 

(R.H. Liang, Jet Propulsion Laboratory) ............. 245 

Po 1 per- Po 1 ymer Inter face Bond St ab i 1 i t y 

(J.L. Koenig, Case Western Reserve University) ......... 257 

Po 1 ymer -Met a1 In t e r f ace Bond St ab i 1 it y 

(J. Boerio). .......................... 271 

Predicting Electrochemical Breakdown i.n Terrestrial 

Pho tovo 1 t a ic Modules 

(G.R. Mon, Jet Propulsion Laboratory) .............. 279 

Module Flammability Research 

(K.S. Sugimura and D.H. Otth, Jet Propulsion Laboratory) .... 289 

xv 
PROCESS DEVELOPMENT AND ADVANCED PROCESSIT 

(U.H. hipold and D.B. Bickler, Chairnren) ............... 293 

Process Research of Non-Cz Material 

(C.M. Rose and R.B. Campbell, Westinghouse Advanced 

Energy Systems Division) .................... 297 

Process Research on Polycrystalline Silicon Material 

(Jerry Culik, Solarex Carp.) .................. 303 

Amorphous Metallic Layers in Si Metallization Systems 

(Marc-A. Nicolet, California Institute of Technology) ...... 313 

Met a 1 lo-Organic Dec ompos i t ion (MOD 

Met a 1 lizat ion for Photovoltaics 

(G.M. Vest and R.W. Vest, Purdue University) .......... 321 

Si lver 

A Nonnoble Front Metallization Process 

(Alexander Garcia 111, Spectrolab, Inc. .......... . . 333 

Viscosity Measurements for Thick-Film Pastes 

(J. Parker, Electrink, Inc. .................. 343 

Evaluation of the Ion Implantation Process for Production 

PE Solar Cells From Silicon Sheet Materials 

(M.B. Spitzer, Spire Corp.) ................... 353 

Laser-Assisted Solar-Cell Metallization Processing 

(S. htta and P.G. McMullin, Westinghouse ELectric Corp.) .... 365 

Ion Cluster Beam Deposition Research 

(Dennis Fitzgerald, Jet Propulsion Laboratory) ......... 377 

Large-Area a-Si Deposition Chamber(s) 

(D.B. Bickler, Jet Propulsion Laboratory) ............ 381 

Advanced Process Technologies 

(D.B. Bickler, Jet Propulsion Laboratory) ............ 385 

SILICON MATERIAL AND SHEET 

(A. Briglio, Jr., Chairman) ...................... 387 

Miniworkshop on Effects of Stress and StraiR on 

High-Speed-Grown Silicon Ribbons 

(A. Briglio, Jr., Jet Propulsion Laboratory) .......... 389 

Stress Studies in EFG 

(J.P. Kalejs, Mobil Solar Energy Corp.) ............. 393 

Advanced Dendritic Web Growth Development 

(C.S. Duncan, Westinghouse Electric Corp.) ........... 411 

Silicon Sheet Surface Studies 

(S. Danyluk, University of Illinois at Chicago) ......... 417 

xvi 
Investigation of Structural and Electrical Properties 

of Low-Angle Silicon Sheet 

(Yes. Tsuo, R.J. Hptson and J.B. Milstein, 

Solar Energy Research Institute) ................ 425 

Semicrystalline Casting Rocess Developtent and Verification 

(W.F. Regnault, Semix Inc.) ................... 429 

Electrochemical Production of Silicon 

(H.E. Bates, Energy Materials Carp.) .............. 439 

Silane Decomposiion in an FBR 

(S.K. Iya, Union Carbide Corp.) ................. 445 

JPL In-House Fluidized-Bed Reactor Research 

(COG. Hsu, Jet Propulsion Laboratory) .............. 649 

Aerosol Reactor for Silicon Processing 

(R.C. Flagan, H.K. Alam, B.E. Johnson and J.J. Wu, 

California Institute of Technology) ............... 457 

Refinement of Metallurgical-Grade Silicon by Chemical 

Vapor Transport Process 

(J. Olson, Solar Energy Research Institute) ........... 469 

MODULE AND ARRAY TECHNOLOGY 

(R.G. Ross, Jr., and L.D. Runkle, Chairmen) .............. 471 

Transparent Conducting Polymers 

(Amitava Gupta, Jet Propulsion Laboratory) ........... 473 

Analysis of Optical and Electrical Performance 

of a TCP-Coated Solar Cell 

(R.E. Daniel, Jet Propulsion Laboratory) ............ 479 

Performance Loss With Shorted Cells 

(C.C. Gontalez, Jet Propulsion Laboratory) ........... 489 

Investigation of Accelerated Stress Factors and 

Failure/JkgraJation Mechanisms 

(J.W. 'Lathrop, Clemson University) ............... 495 

Thermal Characterization of Photovoltaic Modules in 

Natura 1 Env i ronmen t s 

(L. Wen, Jet Propulsion Lsboratory) ............... 503 

Annual Energy Spectrum for Tracking Arrays 

(C.C. Gonzalez, Jet Propulsion Laboratory) ........... 515 

Suwary of Photovoltaic Performance Models 

(JPL Publication 84-81 

(J.H. Smith and L.J. Reiter, Jet Propulsion Laboratory) . . , . . 519 

xvi i 
StaridarAs : an hrergiev 

(Z.A. Prrvet. Jet Prapulsion Lahoratotv) ............ 527 

Resideqrial Array Development 

(E.C. Kern, Jr., %seachusett.s Institute af Technologv) ..... 531 

xviii 
PROGRESS REPORT 

Project Summary 

INTRODUCTION 

this report describes the activities of the Plat Plate Solar Array 

Project (FSA) from October 1983 through March 1984, including the 73rd C’Sk 

Project Integration Hectin6 (Pil4’. held on March 14 and 15. 1984. 

FSA. sponsored by the U.S. Departmcmt of Energy (DOE). has the 

responsibility for advancing solar array tcchnology whilc encouraging indust.ry 

to reduce the price of arrays to a level at rhich photovoltaic (PV) electric 

power systems will be competitive with wre conventional power sources. This 

responsibility has included dcvcloping the technology for producing low cost, 

long life photovoltaic modulcs and arrays. More than 100 organizations have 

participated in FSA sponsored research and development of low cost solar 

nodule manufacturing and mass production tcchnology. the transfer of this 

technology to industry for comcrcialization, and the development and testing 

of advanced prototype modules and arrays. Economic analyses were used to 

select, for sponsorship, those research and development efforts wost likely to 

result in significant cost reductions. Set forth here is an account of t.hc 

progress that has bccn made during t.he reportirig period. 

SIJMMARY OF PROGRESS 

Long duration tests in the conversion of silane to silicon cont.inue at 

the Union Carbide Corp. (UCC) experimental process system development unit 

(EPSDU) at Uashougal, Washington. Continuous operation of thc 

six- inch diameter fluidized bed reactor (FIR) for up to 45 hours has produced 

silicon (Si) particles up to SO0 micrometers in dianiet.cr. The maximum silane 

feed concentration was 24 mole % in hydrogen, at .in drcrage silane feed rate 

of 2 kglh. The YHH is now bcing fitted with a silicon liner to reduce 

contamination of the Si from the reactor walls. Silane continues to be 

produced in the EPSOU by the conversion of metallurgical grade Si (mgSi) to 

silane. 

In the six-inch diameter research FIR at the Jet Propulsion Laboratory 

(JPL), the conversion of up to 100% silane to Si has been demonst.ratcd without 

the formation of excessive fines. The amounts of silicon fines have bccn 

reduced by use of a secondary injection of silane. A quartz liner is being 

inserted in the YBR to reduce contamination of the Si. 

Successful experiments on the formation Si sccd particles for use in ~HHS 

continue at the California Institute of Technology. 

Hemlock Semiconductor Corp., Hemlock, Michigan, has continued 

experiments, at their own cxpense, on the conversion of tcichlorosilane (TCS) 

1 
PROJECT SUMMARY 

Metallo-organic decomposition (MOD) inks and Liquids have been formulated 

by Purdue University. Silver neodecanoate is the mozt promising material. 

Laser-assisted electroplating of copper was successfully demonstrated by 

Westinghouse. Grid lines as thin as 25 ricroneters were applied at the local 

plating rate of 12 ricrorcters per second. 

Initial experiments have been performed in a large-area uorphous-silicon 

(*r-Si) deposition research chamber at JPL. Determination of key parameters in 

-arge-area deposition chambers are to be rer5arched with the goal of achieving 

iou-cost, stable, uniform, high-quality films. 

Amorphous silicon solar cells supplied by Chronar Corp., Princeton, Yew 

Jorsey. and ARC0 Solar. Inc., Woodland Hills, California, are being used by 

Clemson University, Clarson, South Carolina, and JPL to set up performance 

wasurements baseline data for future cell and nodule measurements. 

An UFP for the purchase of .-Si and other thin-film modules has been 

issued. 

measurements and environmental testing like those of the crystalline-Si 

Block I procurement in 1975-76. 

Those modules that can be purchased will be subjected to perforunce 

Laboratory techniques to interrogate directly the chemistry of the 

interfacial chemical bond between EVA and glass and EVA and aluminum have been 

separately ddvised by J. Koenig, Case Western Reserve University, Cleveland, 

OH, and J. Boerio, University of Cincinnati, Cincinnati, OH, respectively. 

JPL developed a computer program to determine power loss from PV arrays 

due to shorted solar cells for specified module-orray electrical 

configurations. Using the program, JPL determined optimum series-parallel 

configurations for minimizing power loss for short cells, and the 

cost-effective failure level for shorted cells. 

Hot-spot testing of ARCO Solar. Inc. modules for the Sacramento Uunicipal 

Utility District CSnVD) central-station project provided data on operational 

conditions. 

appliGation tests. 

Guidelines are being developed for future central station 

Experimental modules that passed the Underwriters Laboratories Class B 

burning-brand tes:. vere developed and testea in collaboration with ARCO Solar, 

Inc. Modules **sing Kapton and fiberglass cloth as rear films passed the test. 

A res.arch forum was conducted on Array Design for Central Stations in 

Sacramei -3, California. Proceedings of the forum are in press. 

A computer program has been developed to analyze optical and electrical 

1 388s in a transparent coating polymer (TCPI-coated solar cell. Various TCP 

zharacteristics that would permit a TCP to be used as a solar cell top side 

condbctor have btm determined. 

Studies continue on a PV power system sensitivity analysis that shows the 

effects an module cost and efficiency of the many system parameters involved 

in melting the cost-to-generate goal. 

2 
PROJECT SUMMARY 

to dichlorosilane (DCS) in the process development unit (PW). Hemlock has 

tripled the output of DCS from the PW and fed it to Siemens--type reactors for 

conversion to silicon. 

Analysis and experiments coctinue on the eleCtrOChemiC81 refining of %Si 

at Energy Xaterials Corp., South tancaster, Massachusetts, and at Solar Energy 

Research Institute (SBRI), Golden, Colorado. 

A dendritic-web Si ribbon 6 meters in length was Erowa during 6 1/2 hours 

of continuous melt replenishment by Westinghouse Electric Corp., Pittsburuh, 

Pennsylvania. 

A method of measuring residual stress in Si ribbons by bonding electrical 

resistance-type foil gauges to the ribbon was demonstrated by JPL. 

gauges are bonded to the ribbon, the ribbon outside the gauges is reroved, the 

strain in the remaining ribbon is measured and the stress is calculated. 

After the 

The residual stress distribution across the width of EFC ribbon was 

determined by the University of Illinois at Chicago by use of a shadow noire 

technique that is suitable for use on rough surfaces. 

A miniworkshop on the effects of stress and strain in high-speed-6rowa Si 

ribbons was attecded by 30 participants in the comprehensive ribbon 

stress-strain effort, with open and enthusiastic exchanges of information and 

ideas on the overall study approach, results, progress and problems. 

A floating emitter Solar cell structure for high efficiency cells has 

been proposed by C.T. Sah and Associates. 

Electrically active defects in Si sheet have been detected by use of an 

EBIC technique using cryogenic cooling at JPL. 

Films of SiNx for passivating Si surfaces were deposited at 

temperatures of only lSO°C by plasma-enhanced chemical vapor deposition at 

the University of Washington. 

A new method of aueasuring minority carrier lifetime and surface 

recombination velocity in the base region of a solar cell has been developed 

at the University of Florida. 

The calibrated LBIC method has been perfected at the University of 

Pennsylvania, and microcomputer solar-cell modeling has been extended to 

include multilayered regions, the p-n junction space--charge region and the 

base region in addition to the front region. 

Simultaneous front-junction and back-junction formation has been achieved 

using liquid dopants and a belt furnace by Uestinuhouss. 

An investigation of ion implantation and annealing of non-Cz Si sheet 

materials has been completed by Spire Corp., Bedford, Hassachusetts. The 

correct annealing cycle can enhance the performance of solar cells made from a 

number of these materials. 

3 
PROJECT SUMMAR) 

Manufacturing cost analyses of a Si modules by a Japanese program and by 

a JYL program Led to significantly different results, due to different methods 

of treating capital costs. This eniphasizcs the need to understand the 

ntethodologics used in performing costing analyses. 
Area Reports 

MATERIALS AND DEVICES RESEARCH AREA 

Silicon Materials Research Task 

and Advanced Silicon Sheet Task 

INT!WDUCTION 

The objectives of t\e Silicon Yaterials Researrl?l Task and the Advanced 

Silicon Sheet Task are to identify the critical technical barriers to low-cost 

silicon (Si) purification and sheet growth that mst be overcome to produce a 

phatovoltaic (PV! cell substrate materia1 at a price consistent with FlatPlate Solar Array Project (FSA) objectives, and then to perform and support 

research and development to overcome those barriers. 

Present solar-cell technology is based mainlv on the use of Si wafers 

obtained by ID slicing of Czochralski (Cz)-grown ingots from Siemens-reactorproduced seminconductor-grade Si. 'his method of obtaining single-crystal Si 

wafers is tailored to the needs of semiconductor-device production (e .g., 

integrated circuits and discrete power and control 3evices other than solar 

cells). 

industry's development of the high-volume Si production techniques that would 

resuit in low-cost PV electrical energy. 

Re small market offered by present solar-cell users does not justify 

It is important to dovelop alternative low-cost processes for producing 

refined Si and sheet material suitable for long-life, high-efficiency solar PV 

energy conversion. To meet FSA objectives, research must be performed to 

overcome the barriers to the success of the most promising processes for 

producing large quantities of Dure Si and large areas of crystallized Si at a 

low, competitive cost. 

the sheet-growth processes, and these must in turn be suitable for direct 

incorporation into automated solar-array industry schemes. 

The form of the refined Si mst be mitable for use in 

Silicrm purification processes involving deposition of the material from 

silane and dicnlorosilane are being pursued because these two substances can 

be purified relativelv easily and, because of their high reactivitv, thev can 

be more readily decomposed or reduced to form Si than can trichlorosilane 

(TCS), which is used today in the conventional process. Research on two other 

processes that offer promise for making less-pure, solar-cell-grade Si by 

refiliement of metallurgical-grade Si (rngSi) was recently undertaken because of 

the potential for further reduction of product cost. 

FSA-funded improvements of the standard Cz ingot-growth process by 

reduction of expendable-material costs and improvement of ingot growth rate, 

together with improved slicing te:hniques, have developed the technolop so 

that larpz areas of Si can be producs.1. 

techniques, such as the semicrystalline casting process, may reduce sheet 

costs further. 

Growth of large ingots by casting 

5 
MATERIALS AND DEVICES RESEARCH AREA 

Growth of crystalline Si material in a geometry that does not require 

cutting to achieve proper thickness is an obvious way to eliminate costly 

processing and material waste. 

pulling (ESP), edgedefined film-fed growth (EM;), low-angle Si sheet (LASS), 

and dendritic-web growth are candidates for such solar-cell material. 

Growth techniques such as edge-supported 

In addition to research on processes for Si refinement and sheet 

formation, various supporting studied are under way to investigate key 

problems in both these categories. 

SUMMARY OF PROGRESS 

Silicon Material Research Task 

Semiconductor-Grade Silicon Refinement Process 

Silicon Refinement Using Silane (Union Carbide Corp.) 

The objective of this RLD program is to solve the critical problems of 

silane decomposition in fluidized-bed reactors (FBRs) for producing 

semiconductor-grade silicon (Si) for PV applications. 

tests were conducted on the 6-in.-diaaeter FBR in th- process development unit 

(PDU), for a total time of more than 80 hours. 

test duration was nearly 45 hours. In the long-duration tests, seed particles 

of 300?nicrometer mean diameter were grown to approximately 5001nicrometer 

diameter. The maximum silane feed concentration was 24 mole X, in hydrogen, 

and the average silane feed rate was approximately 2 kg/hour. A four-iii.- 

diameter Czochralski ingot was pulled from the product of the 45-hour test. 

The first 14 in. of a 16-in.-long ingot was determined to be single-crystal. 

Three long-duration 

The .ongest single continuous 

Product from the FBR was analyzed for impurities using emission spectroscopy and neutron activation analysis; results indicated that the wall 

material (Incoloy 800H) is contaminating the Si. The PDU is undergoing 

modifications to introduce a suitable impurity barricr to minimize contamination from the wall. A study of various coatings and liner materials 

resulted in the selection of a high-purity polysilicon liner as the first 

choice. A technical review was conducted at JPL with critiques from Task 

consultants J. Routbort (Argonne National Laboratory) in abrasion phenomena 

and T. Fitzgerald in fluidized-bed technology. The review confirmed the 

findings and endorsed the approactes being taken by Union Carbide Corp. (UCC) 

(silicon liner) and JPL (quartz liner; see section titled "Research on Silane 

Pyrolysis in Fluidized-Bed Reactors") to the problem of reducing wall 

contamination. Procurement of the liner system is under way. 

Silicon Refinement Jsing Dichlorosilane (Hemlock Semiconductor Corp.) 

Hemlock is investigating the critical portions of a process for making 

semiconductor-grade Si, in which DCS is made from TCS by a redistribution 

reaction using an organic ainino functional catalyst, and the DCS is then 

reduced by hydrogen to produce Si in a chemical-vapor-deposition step using 

Siemens-type reactors. 

6 
VATERIALS AND DEVICES RESEARCH AREA 

The final report on the Phase I and Phase 11 effort was distributed. 

Highlights of the work were presented in Progress Report 21. 

report on the research progam on the cold-metal-wall Si deposition reactor was 

delivered to JPL and was reviewed by cognizant JPL personnel. 

given to HeF'ock are being incorporated into the document. Highlights of the 

effort were presented in Progress Report 22. 

The draft final 

The comments 

The program in which Hemlock, at its expense, tripled the output of the 

DCS PDU to about 200 lb/hour and fed the DCS to various combinations of 

mid-sized and large-sized Siemens-type Si deposition reactors, was completed 

at the end of December 1983. The purpose of the effort was to characterize 

further the performance of the PDU and the reactors and to supply DCS for the 

coldrall-reactor program. The PDU contained to operate satisfactorily. A 

report on the program was submitted to JPL by Hemlock, and is being reviewed. 

Solar-Cell Grade Silicon Refinement Processes 

Electrochemical Refining of Metallurgical--rade Silicon 

(Energy Materials Corp.) 

The objective of this contract is to demonstrate the technical feasibility of producing high-purity Si from metallurgical-grade Si in a process 

using a Cu3Si:Si anode in a fused-salt electrochemical cell. 

The transport of Si in the Cu3Si:Si anode was considered in a diffusion 

model by the Harvard University consultant to the contract. The first 

question was whether the model is consistent with the experimentally observed 

current density and whether this density value is close to the diffusionlimited value. "le conclusion is that a deposition rate commensurate with 

three to four times the experimental maximum current density can be obtained 

without a diffusion limitation. At the higher densities the rate may be 

limited by electrochemical factors. The analysis is being extended to 

consider the diffusion of impurities through the Cu3Si:Si to the anode 

surface. 

In the experimental program, the first checkout test of the electrolysis 

cell resulted in a Si product containing a salt dispersion. 

evidence of the presence of H20, additional care will be used in the next 

test to eliminate all of the H20. 

Since this is 

The fragility of the anodes is another problem; it is being dealt with by 

using extra precautions in placing the anodes in the cell. The question of 

the effect of the extent of reaction on the electrode structure thus becomes 

additionally important. 

7 
MATERIALS AND DEVICES RESEARCH AREA 

Chemical Vapor Transport Process for Purifying Metallurgical-Grade Silicon 

(Solar Energy Research Institute) 

The objective of this research is to investigate a process in which a 

Cu3Si:Si anode reacts with HC1 to produce chlorosilanes, which are then 

decomposed on hot Si filaments to produce Si. Early results had shown the 

capability of preparing a product containin <2 ppma total impurities. 

transport rate was shown to vary as (time)' !I2, which is consistent with a 

model in which the rate is limited by diffusion of Si in the anode. 

The 

A larger reactor with a deposition rate capability of about 11 glhour has 

been constructed and is being tested. The transport rate, product purity, and 

energy use will be determined. 

Silicon Refinement Process Supporting Studies 

Silicon Particle Growth Research 

(California Institute of Technolonv 

In the program at Caltech to study he formation and grow h of Si 

particles by pyrolyzing silane, a larger, modified apparatus for the control 

of gas-phase nucleation and the growth of aerosol particles was constructed. 

The heated zone is 50 mm in diameter and 600 urm long. Ihe apparatus was put 

into operation with the intent of increasing the particle size from 0.1 micrometer to a range of 25 to 50 micrometers (mass mean diameter). Separation and 

collection of particles also is receiving increased emphasis. 

particles up to 3.5lnicrometer mass mean diameter have been grown in an 

apparatus 9 mm in diameter and 388 mm long. In preliminary experiments with 

the large apparatus, particles up to 100 micrometers in diameter (mass mean 

diameter of 9 micrometers) using 2 mole X silane were produced; however, the 

large particles were not dense. 

Previously, 

The program was extended for one year (through September 1984). This 

will enable a more thorough theoretical treatment of the final stage of 

particle growth as well as an effort to grow larger particles. 

Microwave Heating of Fluidize&-Bed-Xeactor Bed (Superwave Technology Inc.) 

A new contract to Superwave Technology Inc., Santa Clara, California, for 

a feasibility study of microwave heating of a silicon fluidized-bed-reactor 

bed in the steady-state mode was started on February 22. The first meeting on 

this effort, which is scheduled to be completed on April 30, 1984, was held at 

the contractor's facility to discuss the design of the test system and the 

requirements for demonstrating feasibility of the concept. 

8 
MATERIALS AND DEVICES RESEARCH AREA 

Research on Silane Pyrolysis in Fluidized-Bed Reactors (JPL) 

JPL is conducting FBR research with the objective of characterizing the 

deposition of Si from silnne and providing information upon which significant 

improvements in this process can be based. 

the process and basic mechanism for deposition of Si from the decomposition of 

silane onto FBR particles and to characterize the purity of the product. 

Neutron activation analysis showed heavy contamination of Si particles by the 

stainless-steel wall material. The primary mechanism was identified as 

erosion of the wall. Various wall materials, including nonmetallic liners or 

coatings, were considered to achieve high abrasion resistance and wallcontamination-free products. 

liner. 

the existing Type 316 stainless-steel reactor was established and its 

fabrication is under way. 

Work was continued to establish 

The best choice was considered to be a quartz 

A design for the support and seal of a clear fused-quartz liner for 

4 

Experiments with secondary injection of small amounts of silane at a 

point 13 in. above the distributor were conducted to increase the scavenging 

of the Si fines produced by homogeneous decomposition of silane, thereby 

increasing the efficiency of Si deposition. Reduction of fines in the exit 

filter from 10% to 6% of the total amount of Si present in the silane was 

realized, with a corresponding increase of Si product formation in the bed. 

An analysis confirmed the merits of the location of the secondary silane 

injection port. 

Effort continued to investigate the feasibility of fluid jet milling to 

prepare clean FBR seed. The jet mill is lined with a nonmetallic material to 

eliminate metal contaminants from the product seed. For feed material in a 

500- to 700-micrometer diameter range, one pass produced 15% in the desired 

range of 75 to 355 micrometers; after two passes, 28% was in the desired 

range. The results appear promising for the production of uncontaminated FBR 

seed. Fnhrirqticn nf a oolyethylene-lined device is under way. 

A report titled "Silicon Production in a Fluidized-Bed Reactor: A 

Parameter Study" was published. It summarizes the JPL effort in which a 

six-in.-diameter engineering-scale FBR for investigating the pyrolysis of 

silane to produce semiconductor-grade silicon was designed, constructed, and 

tested to establish reactor design parameters for the distributor, cooling 

aystem, heaters, silicon withdrawal system, etc. Experiments were conducted 

to establish the mass balance, silicon production rate, and particle growth 

rate. 

the seed particles as product, the remainder ending as fines that are swept 

from the FBR. It was demonstrated that up to 100% silane can be fed into the 

reactor without excessive fines formation. A paper titled "Fines in Fluidized 

Bed Silane Pyrolysis" was published in the March 1984 issue of the Journal of 

the Electrochemical Society. 

The data indicate that more than 90% of the silicon fed is deposited on 

Modeling of Silane Pyrolysis in Fluidized-Bed Reactors 

(Washington University at St. Louis) 

The objective of this effvt, which started in December 1983, is to 

develop a comprehensive model for making Si by silane pyrolyeis in 

9 
MATERIALS AND DEVICES RESEARCH AREA 

fluidized-bed reactors. 

and pilot plant data and in designing large FBRs. 

rate of Si and the particle size to the operating conditions of bed temperature, gas feed rate and composition, and solids seeding rate that will 

guarantee the minimizing of submicrometer particle formation, it is necessary 

to model the reactions of silane pyrolysis as well as fluidized-bed 

hydrodynamics. 

This model should be usaful in interpreting laboratory 

To relate the production 

The available information on homogeneous and heterogeneous pathways for 

silane pyrolysis was reviewed, and rate forms for modeling purposes were 

selected. 

and an appropriate model structure was suggested. 

The current understanding of fluidized-bed phenomena were reviewed, 

10 
SUMMARY OF PROGRESS 

Advanced Silicon Sheet Task 

Shaped-Sheet Technology 

Edne-Defined Film-Fed Growth 

(Mobil Solar Energy Corp.) 

The primary goal of this program is to develop a model for obtaining 

temperature field--residual stress -elationships applicable to Si ribbon 

growth at high speeds and to apply this model subsequently to a growth system 

that has been aodified and improved to produce low-stress ribbon at high 

speeds. 

In one subrask, a computer code developed at Harvard University to 

calculatc etress with plastic deformation in steady-state sheet growth is 

being applied to study temperature-field stress relationships. 

state is parameterized by a two-dimensional temperature field and gri.iwth 

speed. Incorporation of time-dependmt strens relaxation effects is through a 

creep law to model the impact of plastic flow on the sheet residual stress 

state. 

to predict the temperature field in a moving sheet from given system component 

temperatures (i .e., the sheet environment 

the model. This work is attempting to integrate temperature-field modeling in 

the solid, taking into account real system gexnetries with a more detailed 

heat-transfer model developed at the Massachusetts Institute of Technology for 

the die top and meniscus regions below the growth interface. 

The stress 

A second aspect of the program deals with the development of a model 

and experimental means to verify 

During this period, both modeling and experimental work were in progress 

to attempt to apply the stress analysis at a more quantitative level. 

modeling is examining stress and temperature field relationships in a search 

for low-stress growth configurations. The experimental efforts are in 

studying the high-temperature creep response of Si to provide information on 

the constitutive relationship, develop a technique to measure the temperature 

field in the sheet during growth, and develop meam to measure residual stress 

distributions. 

for the temperature field measurements. A laser interferometry technique is 

being evaluated at the University of Illinois at Chicago for residual stress 

measurements 

The 

A tempe-ature sensor based on fiber optics has been conetructeG 

Stress analysis at Harvard University examined the implicatio,i of 

non-z2ro stresses at the growth interface on model predictions. 

distributions at distances greater than about 1 mm from the interface are 

shown to be independent of the interface streee at high creep intensities, and 

the predictions based on zero in! ial streee can be used with confidence. 

This subtask at Harvard University was terminated, and the process cL transferring the computer codes to Mobil Solar Energy Corp. (MSEC) was completed. 

Using this computer code, studies cf temperature and stress field relationships in sheet growth are under way at MSEC. 

Stress 

11 
MATERIALS AND DEVICES RESEARCH AREA 

The development of finite-element models for sheet growth at HIT was also 

completed. 

growtli of 10-cmride ribbon to test certain aspects of the model with 

available experimental data on impurity segregation alid on interface shape. 

These programs for temperature and stress calculations will be applied to 

analyze the simplified ribbon growth configuration that is being constructed 

to test the stress model. 

aspects of the stress and temperature field modeling with the 10-cm cartridge 

system have had limited success. Due to :he complexity of growth environment 

at the interface, it has not been possible to use the fiber optic sensor. 

cartridge system has lacked flexibility to allow im2osition of changes in 

grovth conditions and system temperature fields in a known and controllable 

manner to study stress and temperature field relationships at a quantitative 

leve 1. 

The analysis will continue to be refined and applied to model 

During this reporting period, attempts to verify 

The 

Construction of a simplified ribbon-growth system for purposes of testing 

the stress-analysis model is nearly complete. 

installed 'n Furnace 17 after completion of creep environments. 

departures from the 10-cm cartridge system design involve simplification of 

the post-growth cooling environment by use of simple graphite insulation 

geometries. 

of these components and of the ribbon surface to give more confidence to 

temperature field specifications for the stress calculations. 

This growth system will be 

The main 

It will be possible to determine more accurately the temperatures 

In the primary creep response studies of displacement versus time for 

float-zone silicon deformed by four-point bending at 136OOC, a range of 

loads from 8.0 to 15.5 MPa maximum surface stress was used. All samples were 

(111) surface oriented, and the bending axis was 410% 

fication photomicrographs of the defect configurations produced at the low and 

high loads were obtained. Comparison of the dislocation configurations at the 

lower stresses shows that the final dislocation configurations achieved after 

10 seconds at the .wo temperatures are qualitatively similar, and the dislocation densities are also comparable for a given stress level. A one-to-one 

comparison is not possible for the high stress because the transient loading 

times are significantly shorter (approximately 4 seconds at 1215OC and 

approximately 1 second at 1360%) than for the lower stress (10-second) 

experiments. More detailed analysis of these reaponse9 is being continued. 

Low and high magniDisplacement-time curves for Cz silicon wafers stressed at 1215OC were 

also obtained. 

compared with that for EFG material at a given stress and temperature. 

material used in the experimsnts had a relatively high substitutional carbon 

level of approximately 4 x It 3ppear.s that oxygen 

exerts a greater effect on the creep response than does carkn in this range 

of concentrations. 

Creep response for all Cz samples Is significantly reduced as 

"he Cz 

atoms/cc and hig3er. 

lhese studies are continuing. 

The current design of the fiber-optic probe appears to have reasonable 

stability and reproducibility sufficient to make it useful for measurements of 

ribbon temperatures. It has been calibrated in crystal-growth Furnace 17 

under conditions that expose the fiber-optics circuit to conditions encountered 

in an actual system. The results of several calibration runs that involved 

12 
MATERIALS AND DEVICES RESEARCH AREA 

thermal cycling through the range from llOOOC to 140OOC are encouraging. 

No further work on fiter optics thermometry is being done pending testing of 

the crystal-growth system mentioned above. 

The first resihal stress distributions were obtained on EFG material 

using a shadow-Moire technique of interferometry. The experimental results 

are encouraging in that stress variations across the sample width are observed, 

which was not possible with earlier techniques. Additional testing must be 

carried out to measure the responsiveness of the technique to stress changes 

produced by variations in growth conditions. 

Dendritic Web Ribbon Growth 

(Westinghouse Electric Carp.) 

Westinghouse is conducting research on the key problems associated with a 

process for making a thin, wide-ribbon form of single-crystal Si directly from 

melt. "Dendritic" refers to the wire-like supporting dendrites on each side 

of the ribbon, and "web" refers to the Si sheet that results from the freezing 

of the liquid film between the bounding dendrites as the latter are raised 

from molten Si. 

As part of the investigation of management of the silicon-ribbon temperatare profile, initial calculations were performed to include the effect of 

heat loss by thermal conduction through the gas. It was found that even in 

the lid region, where gas conduction should be most pronounced, the conduction 

contribution was negligible. In view of these results, actual modification of 

the computer model to include gas conduction effects does not appear to be 

warranted for present purposes. 

calculating the maximum possible width of low-stress ribbon for a given thickness is being developed. Formulation of the concept is under way. 

An approach to using computer models for 

'Itro new growth configurations using dynamic control of thermal elements 

*-ore tested. The first was based on the 5460 static cor-. juration, which has 

exhibited excellent ribbon growth characteristics, and the dynamic configuration show2 promise in being able to combine t!ie enhanced growth velocity 

res,ilting frm dynamic control and the wide-growth, low-stress characteristics 

of the 5460 design. The other new dynamic configuration incorporated a lowstress top shield, &ad results were encouraging in that growth with enhanced 

velocity could be achiwed at different lid positions. 

to optimize growth for both of the new configurations. 

Further work is needed 

Westinghouse wrote the operatiq procedure for the sheet-growth machine 

that is used to produce dendritic-wb silicon ribbon and sent copies to JPL 

with complete sets of engineering drawings for the equipment (including 

control system), as a contract deliverable. 

The present contract ended on March 8. A one-year extension was 

negotiated. 

13 
MATERIALS AND DEVICES RESEARCH AREA 

Low-Annle Silicon Sheet 

(Energy Ptaterials Corp.) 

A new contract was started on March 12. The aim of the program is to 

overcome the critical barriers to the low-angle silicon sheet (LASS) ribbon 

growth of high-quality material at high linear growth velocities. Specific 

tasks of the contract involve the investigation of the parameters that affect 

the growth of single-crystal ribbon. Here the design of various silicon melt 

pump designs, cold shoe/jet configurations, and crucible and thermal modifier 

configurations will be tested in the existing furnace to optimize the growth 

parameters. 

This effort involves assembling a separate growth chamber and positivepressure facility to grow the ribbons in a clean mvironment. Throughoct the 

period of the contract, the ribbon grown under the program will be evaluated 

to test the effects of any modification made to the system. 

Another task will emphasize the growth of high-quality ribbon. 

Ingot Technology 

Semicrystalline Casting 

(%mix Inc.) 

This report period marks the conclusion of the contracted effort with 

Semix that vas a continuation of the cooperative agreement established in 1980 

with the Department of Energy. The later efforts under the agreement had been 

focused on specific research elements concerned with casting of Si blocks 

using the ubiquitous crystallization process (UCP). This focus had been 

designated in an effort to produce a program consistent with the DOE goals of 

high-risk, high-payof f research. 

Within this last reporting period several investigations were under way: 

(1) Minority carrier diffusion length in blocks. 

(2) Thermal model for UCP. 

(3) Sources of structure in cast blocks. 

The first of these efforts involves the use of laser beams to generate and 

measure the density and decay time of minority carriers in a solid brick. 

This approach provides a method of evaluating cast blocks before their 

wafering, and thus saves considerable wafering expense. In this method, one 

laser beam is transmitted through a region of the brick under investigation. 

A second beam is transmitted through a region of the brick under investigation. 

A second beam is pulsed perpendicular to the first beam at a frequency capable 

of producing significant numbers of minority carriers and with energy intense 

enough to penetrate significantly into the bulk material. Up to the present, 

lasers with a wavelength of 1.32 micrometers and approximately 1.10 micrometers have been used, respectively, for the two lasers. The variations in 

intensity of the transmitted beam are measured usiag a detector. The decay 

time of the absorption peak can be translated into diffusion length. 

14 
MATERIALS AND DEVICES RESEARCH AREA 

Ihe investigations at the time of the conclusion of the program has shown 

that the process is feasible. Measurements several centimeters &nto the bulk 

had been made, and results showed correlation with other minorit.. carrier 

lifetime measurements. At the conclusion of the development, however, the 

amount of data generated had been limited. 

from material with large variations in physical properties. 

Especially missing were results 

The second investigation still under way at the conclusion of this 

program involved the development of a computer model for describing the heat 

flows in the solidifying ir?qot as functions of heat inputs and outputs. The 

model was based on finite difference methods and included consideration of 

heat generation and volume expansion on solidification. Present state of the 

model involves description of two two-dimensional sections of the ingot, one 

in the center of each side and one through each corner. Simple but realistic 

flows were considered, and the calculated contours appear to be reasonable. 

Extensive additional development of the model is needed, including a threedimensional form, and a much vider variety of heat input and output distributions will be required before the model can be cons;&;:d to be fully useful. 

The final effort vithin the program included ocgoing studies of the 

development of structure, particularly intragrain structure, in the cast 

ingots during solidification. The details of this study are quite varied 

and complex. A number of reasonable conclusions can be drawn. The first 

conclusion relates to the development of deformation structure within grain? 

of the casting as a result of thermal stresses during ingot casting. 

differential thermal expansion and trapped liquid volumes are potential 

sources of such deformation. The deformation structure takes the form of 

dislocations that eventually configure themselves into low-angle grain 

boundaries resembling polygonization. 

Both 

Another conclusion from these microstructure studies is the deleteriois 

effect of steps and ridges on grain boundaries that appear to act as 'lockin? 

points betyeen neighboring grains. These points then result in deformatlon 

structure emanating from these points. 

More detailed studies of these and other structure studies are available 

in the literature. Because this program has now corrcluded, release of additional results from these studies is at the discretion of Semix, Requests for 

access to these and other results should be taken directly to %mix. 

Silicon Sheet Supporting Studies 

Modification of Silicon Surface Properties by Fluid Adsorption 

(University of Illinois at Chicago) 

The program on the abrasive wear of Si in the presence of various fluids 

was completed, and the draft final report idas written, submitted to JPL, and 

reviewed by cognizant JPL personnel. 

and the report is being published. A follow-on effort is planned. Ihz 

highlights of the program were presented in Progress Report 22. 

Ihe requested changes were incorporated, 

15 
MATERIALS AND DEVICES RESEARCH AREA 

An effort on masuring residual siress in Si sheet using laser interferoaaetry was started. 

interference fringes on the surface of a concentrically loaded round Cz Si 

wafer. 

residual stresses determined. 

axismetric. 

rough surfaces was used to determine the residual stress distribution across 

the width of E?G ribbon. The results indicated that each method is feasible. 

The apparatus was set up and was used to produce 

The density and distribution of the fringes were analyzed and the 

These stresses ranged from 0 to 40 HPa ali were 

Also, a shadow noire technique that is suitable for use witti 

kalysis of StressIStrain Relationships 

(University of Kentucky) 

A report titled "An Improved Analysis of the Tnermal. Buckling of Silicon 

Sheet," written by Rofessor 0. Dillon and Professor R. DeAngelis of the 

iJniversity of Kentucky, was received. 

f.,r an elastic cantilever plate subjected to a temperature profile. The 

analysis predicts a torsional buckling mode and also predicts sheet thicknesses that will result in buckling. 

The report prc:?r.ts a buckling analysis 

The elastic and plastic analyses on buckling of silicon ribbon were begun. 

Solid-Liauid Interface Studies 

(Solar Energy Research Institute) 

The aim of tbis effort is to investigate the shape and stability of the 

Si solid-liquid interface in high-speed growth techniques as functions of the 

impurity content, the thermal environment, and most important, the rapid 

solidification rate. Toward this end, SERI modified a float-zone furnace in a 

way that allows horizontal ribbon growth. 

ing a ribbon pulling mechanism, opening a side port in the furnace through 

which to pull the ribbon, and working out a silicon melt confinement system. 

Two silicon confinement methods were tried: a cold-crucible technique and 

novel method that has been submitted to JPL as a new technology disclosure for 

evaluation for possible patent action. 

several ribbon-growing experiments were attempted by did not succeed because 

the thermal environment of the new melt confinement system had not been 

optimized. The program was terminated because development of the method was 

shown to require a greater level of effort and manpower than this program has 

available. The effort was restructured for a study of the optimization of 

highly doped silicon crystals for high-efficiency solar cells. 

This involved designing and buildThe modified furnace was tested and 

Materials Properties Modification (JPL) 

The testing on the effects of light on the strength of Si wafers was 

completed. The results confirm earlier results, which indicated that the 

strength increases with increasing light intensity. 

scatter but are statistically meaningful. 

report is being prepared. 

The data still show large 

The data are being analyzed, and a 

16 
MATERIALS AND DEVICES RESEARCH AREA 

Tests were conducted by JPL on Westinghouse dendritk-web silicon ribbon 

that demonstrated the feasibility of a destructive method for measuring residual stress in sheet silicon, 

gages are bonded to Si sheet, the gages and attached Si are cut from the sheet, 

and the strain in three directions is read, allowing calculation of the 

principal stress. 

slightly rippled deformations gave relatively low values of residual stress, 

ranging from compressive stress of 200 lbfin.2 to tension stress of 

1000 lb/in,*. 

In this method, electrical resistance-type foil 

Measurements on a piece of dendritic web ribbon that had 

Research Forum 

One major FSA goal is to understand and overcome the limitations that 

stressfstrain and deformation effects are placing on the rate at which ribbon 

suitable for solar cells can be grown. 

and strain in high-speed-grovn silicon ribbons was held January 10 and 11 at 

the Westinghouse R&D Center, Pittsburgh, Pennsylvania, It was attended by 

about 30 persons, including representatives of subcontractors, DOE, SERI, and 

JPL. Its objectives were to bring together the key persons directly involved 

in the ribbon stresslstrain program, familiarize them with the latest research 

and results on this subject, exchange ideas, and assist in formulating future 

research activities. 

A minivorkshop on the effects of stress 

The miniworkshop vas successful in that there was a great deal of 

enthusiastic interchange of information and opinion, and all of its objectives 

were achieved. 

addressed to improve understanding of the stresslstrainldeformation problem. 

These include measurement of actual temperature distributions in the growing 

ribbons and in the growth environment, understanding of the dynamics of the 

lattice near the solidification zone, observation of deformation during 

growth, determination of accurate hi,;i-temperature creep data for silicon, 

integration of elastic and inelastic modeling, and systematic experimental 

evaluation of the various ribbon growth models. 

In particular, areas of research were identified that must be 

17 

Device Research Task 

INTRODUCTION 

The objective of the Device Research Task is to identify and implement 

research and development activities in the Materials and Devices Area to meet 

the near-term and 1or.g-term objectives of FSA. 

research in &:vice physics, device structure, material-device property interaction, and mzasurement techniques for physical, chemical and electrical 

evaluation 0% devices and materials. 

Task activities encompass 

Technical Approach, Organittion and Coordination 

To meet FSA objectives, efforts are nov directed toward characterization 

of various silicon-sheet materials, material-device property interaction 

investigation, and measurement techniques. 

structured accordingly. 

The program of the Task is 

The program of the Task also includes JPL in-house activities to conduct 

basic research in materials and devices characterization to support contractor 

needs and other Tasks of the Materials and Devices Area. 

SUMMARY OF PROGRESS 

Cornel1 University 

The objective of this contract is to characterize the structural, 

chemical, and electrical properties of silicon sheet material in as-grown 

and processed forms. 

Research has been concentrated on understanding the disappearance of EBIC 

contrasting of grain boundaries and dislocations when EM: material is preannealed at high temperatures before :he formation of the p-n junction. It is 

believed that the disappearance of electrical activity at these structural 

defects is caused by the formation of competing gettering centers. The most 

likely process leading to the formation of these competing gettering centers 

is the precipitation of carbon, which has not been studied as a means of 

gettering electrically active imwrities. In solar materials, precipitation 

of carbon offers an alternative to gettering by oxygen precipitation. 

based gettering should be particularly effective for those transition metals 

that are strong carbide formers. 

CarbonApplied Solar Energy Corp. 

Work has continued on refining the calibrated light-spot scan system and 

applying it to silicon solar cells made from the HEM, Silso, and UCP cast 

silicon materials. 

boundaries in various parts of these materials is being studied by this system. 

The quality of the material and the influence of grain 
MATERIALS AND DEVICES RESEARCH AREA 

Cell fabrication and analysis on cells made using silicon ribbons 

obtained from different sources is continuing. 

C. T. Sah Associates 

The barriers to achieving high-efficiency silicon solar cel!J have been 

considered and analyzed. They include: 

base and back surface field layers at the point impurity and defect centers, 

their enhancemeat due to heavy doping, and interband recombination; (2) recombination at the interface states on the front and back, and at thc metal (Si 

and Si021 Si interfaces; and (3) recombination at gross imperfections on the 

damaged cell perimeter or edge and in the bulk. 

(1) recombination in the bulk emitter, 

Research Triangle Institute 

Development of phenomena submodels have been completed and incorporated 

into the transport equations for computer simulation. 

The major point of departure of the modelling program is the analytical 

method used to analyze physical systems. 

of a physical system, the geometry is discretized into mesh points. 

one-dimensional geometry, the segments are defined by a series of parallel 

planes. 

desired. 

system, are applied to each segment, and a closed-form solution is obtained in 

each of the segments. If the boundary conditions at each of the planes defining the segments are known, then there exists a recursion relationship between 

the constants of integration of the solutions obtained in each segment. 

To obtain an accurate representation 

In a 

The segments may be taken as then as required to obtain the accuracy 

The differential equations, governing the behavior of the physical 

This method has been applied to semiconductor devices and has been shown 

to give excellent agreement between computer simulation and experimental data. 

University of California at hs hgeles 

The technique of molecular-beam epitaxy (MBE) in silicon is still in the 

developmental stages. A procedure has recently been developed at UCLA for 

growing expitaxial layers with the high doping density necessary to form a 

tunnel junction between two solar cells. 

to the bulk value, 

characteristics. Typically, the breakdown voltage is 70% of the predicted 

value but the leakage current is high bO.5 PA for 2041-diameter diodes at 

-0.5 volts). It is suspected that the poor electrical properties are caused 

by the presence of carbon at the interface. 

'Ihe mobility in these films is close 

Mesa diodes fabricated from these films show poor reverse 

lbo solar cells fabricated from the MBE-grown samples have efficiencies 

of 4.7% at AM1.5. 'his is significantly better than previous samples. 

20 
MATERIALS AND DEVICES RFSFASCH AREA 

The sharpness of profiles grown using MBE means that simple models using 

the abrupt junction approximation are applicable. Computations ‘cndicate that 

the cascade cell may be significantly more efficient than a single cell as 

long as there is no large recombination of carriers at the tunnel junction. 

Calculations show that the open-circuit voltage for the cascade cell could be 

>1 v. 

University of Florida 

A mathematical method that systematically and compactly describes response 

to transient excitation of various types has been partially developed. 

method enables comparison among all existing transient measurements for a wide 

variety of different solar cell designs, and it clarifies the inaccuracies 

resulting from many experimental techniques in wide use. Led by the mathematical treatment and related physical theory. the results obtained have been 

examined by a method apparently not used much before, using short-circuit 

current response after removal of applied forward voltage. 

This 

University of Pennsylvani-z 

The calibrated light-beam-induced current (LBIC) method has been perfected 

and microcomputer solar cell modelling has been extended to include multilayered regions as well as the p-n junction space charge region and the base 

region in addition to the front region. 

successfully applied to structures with varying doping profiles, using 

impurity concentration data obtained from spreading resistance profiles, and 

corresponding mobility values. Good fits between the measured LBIC data and 

the modelled spectral collection efficiencies could be obtained by using the 

impurity profile data, where such fits had not been obtained previously by 

single layer modelling. 

40p, 2p, and 0.3pm were evaluated for surface recombination velocity and 

minority carrier lifetime. 

The multilayer feature has been 

Devices with front-layer thicknesses of IOOpm, 

Ion-implanted solar cells with oxide-passivatea surfaces were obtzined 

and performance by the spectral LBIC method before and after rewval of the 

oxide layer showed a substantial increase of the surface recombination 

velocity upon removal of the passivation. 

The method has recently been applied to the analysis of base regions, and 

the minoritv lifetime in the layer between the high-low junction and back 

contact has been determined, as well as the lifetime in the principal, less 

heavily doped base layer. 

University of Southern California 

lhe cryogenic calorimeter has been constructed, and initial performance 

tests are in process. Theoretical studies hLve been carried OUL in parallel 

with experimental work, in preparation for planned memurements of deep-level 

21 
MATERIALS AND DEVICES RESEARCH AREA 

impurity absorption at near-IR wavelengths. 

measurements have been made on pure silicon in the near-IR as part of an 

effort to determine background absorption present. 

Room-temperature calorimetric 

University of Washington 

A plasma-enhanced chemical vapor deposition (PECVD) system has been 

assembled and is being used to grow silicon nitride films on silicon substrates. The system is based on a plasma etcher, which has been modified for 

plasma-assisted chemical vapor deposition. 

parallel plate system, substrates are supported on the grounded electrode, 

which can be heated to 350OC. 

below the grounded electrode, flow radially inward between electrodes, and 

exit through an exhaust at the center. 

30-kHz RF glow discharge is established between the electrodes at power 

densities up to 8000 W/m2. 

and ammonia. 

rate and index of refraction to growth Parameters. 

In this capacitively-coupled 

Process gases enter the reaction chamber 

To induce the deposition reaction, a 

For SiN deposition the reactant gases are silane 

Initial efforts have concentrated on relating film deposition 

Optical constants we being determined for silicon nitride films and are 

being related to film growth parameters. 

are characterized by measuring the reflectance for wavelengths between 300 nm 

and 1200 nm. These data are used to calculate index of refraction (N) versus 

wavelength, and film thickness. To date, films grown on silicon exhibit 

indices of refraction in the range of 1.9 to 2.25. 

determine both N and K versus wavelength. 

used to calculate photon transmittance into silicon. 

Films grown on silicon substrates 

Work is in progress to 

These results will eventually be 

The Si-N/Si interface will be characterized for films grown on both 

p-type and n-type silicon substrates, as well as on silicon n-p solar cells. 

Interface properties of interest are the fast-stete density, fixed charge and 

surface recombination velocity. Capacitame-based measurements will be used 

to determine fast-state density and fixed charge. 

surface recombination velocity are under consideration. 

Approaches to measuring 

22 
PROCESS DEVELOPMENT AREA 

INTRODUCTION 

The objective of the Process Development Area is to conduct research 

in critical technology areas of conventional photovoltaic device and module 

formation. Process research is grouped into three areas for reporting 

convenience: surface preparation, junction formation and metallization. 

SUMMARY OF PROGRESS 

Process research efforts have continued with an increased emphasis in 

investigation of new energy technologies. 

two for new energy technologies, one for junction formation. 

technology reports and one patent application were submitted. 

Three new contracts were awarded: 

lbo new 

Wo major items of research equipment were installed during the 

reporting period, prompted by the emphasis on higher cell efficiency and 

increased module reliability. 

Surf ace Preparation 

A no-cost contract was awarded to Solec International to investigate 

application of antireflective (AR) coatings by roller coating. JPL laboratory 

facilities will be used by Solec. .bsults will be published. 

Junction Formation 

Westinghouse Electric Corp., Advanced Energy Systems Division, has 

demonstrated simultaneous front and back dopant profiling using liquid dopants 

in both belt and diffusion furnaces. However, cross-contamination continueq 

to be a problem. Different oxide diffusion masks are being evaluated to solve 

this problem. 

Solarex Corp. has completed its poiycrystalline silicart material 

contract. Cell surfarec rere characterized by fabricating 400 minicells on 

each wafer. Lien wafers from different manufacturers were conpared, some 

similarities were found: 

voltage tnan tz control cells: excess data scatter correlates with ?hunting 

inclusions; Lhere is a strong correlation between quasi r?vti'al. recombination 

and electrically active grain and ncthgrain Poundaries. 

polycrystalline cells always have lower open-circui.: 

Metallization 

Metallo-organic decomposition (MOD) inks and liquids have been formulated 

by Purdue University. 

other metals, solvents and rheology adjusters are being examined. 

purity has surfaced as a major limitation. 

Silver neodecanoate is the most promising material, but 

Material 

23 
PROCESS DEVELOPMENT AREA 

The importance of viscosity measurement for characterization and process 

control of thick-film inks was brought out by Electrink, Inc. 

proper measurement technique and data interpretation was reported. 

A need for 

Diffusion-barrier research by Caltech is moving into exploration of 

interfacial reactions between the barriers and underlying substrate material 

or overlying metals. 

research. 

Ten technical papers were published as a result of this 

A new research tool, real-time scanning electron microscopy, was used 

to examine the controlled-atmosphere firing of the molybdenum-tin thick-film 

system. This novel approach shows great promise in interpretation of sintering phenomena. Spectrolab, Inc. used this tool to determine that the tin does 

not act as a liquid-phase sintering medium. 

24 
PROJECT ANALYSIS AND INTEGRATION AREA 

INTRODUCTION 

The objective of the Project Analysis and Integration Area (PAdI) is to 

support the planning, analysis, integration, and decision-urhg activities of 

FSA. Accordingly, PA61 supports the Project by developing and documenting 

Project plans based, in part, on the technical and economic assessments of the 

various technical options performed by PA&I. Goals for module technical 

performance and costs, derived from National Photovoltaics Program goals, are 

established by PAdI for each of the major technical activities in the Project. 

Assessments of progress toward ac)li?vement of goals are performed to guide 

decision-making within the Project. 

SUMMARY OF PROGRESS 

Analysis of Losses in a TCP-Coated Solar Cell 

PMI, in cooperation with the Reliability and Engineering Sciences Area, 

has developed a computer program to aid in the analysis of the power iosses 

found in a transparent conducting polymer (TCP)-coated solar cell due to the 

optical and electrical properties of the TCP. The program is used to cslculate the short-circuit current density (Jsc) when a silicon cell is coated 

by a TCP. 

quentia1l.y Jsc, are thickness, index of refraction, and absorptivity. The 

effect of the conductivity of the TCP will be investigated by calculating its 

sheet resistivity at varying thicknesses and the combined sheet resistivity 

of the TCP on a standard silicon cell. 

The TCP film pioperties affecting light transmission, and conseExpected power losses will be calculated using Jsc and combined sheet 

resistivities while varying the TCP properties. 

power losnes versus TCP properties will assist in the aearch for a TCP that 

will have the least possible losses. 

A parametric study of the 

Si 1 icon Cost Ana 1 ys is 

A report tit:.ed "A Probabilistic Analysis of Sili.con Cost" (JPL Document 

No. 1101-246, JPL Publication 83-94), summarizing the results of a silicon cost 

study, hha been published. 

Silicon material costs represent both a cost driver and an area where 

improvement can be made in the cost of manufacture of photovoltaic modules. 

This study analyzes the cost of three processes for the production of low-cost 

silicon that are being developed within the National Photovoltaics Ptogram. 

The costing approach is based on probabilistic imuts and makes use of two 

models developed at the Jet Roprlleion Laboratory: SIMRANTl (SIEIulation - of 

e Research -- ANd Development) and XPEG (Improved - Price - Estimation - Guidelines). 

25 
PROJECT ANALYSIS AND INTEGRATION AREA 

The costing approach, assumptions, and limitations are detailed in the 

These 

study along with a verification of the methodology. 

in the form of cumulative probability distributions for silicon cost. 

results indicate that there is a 55% chance of reaching the DOE target of 

$16/kg for silicon material. This ;.s a technologically achievable co:; basf>d 

on expert forecasts of the results Df ongoing research and development and do 

not, imply any market prices for a given year. 

The results are presented 

Photovoltaics System Sensitivity Analysis 

Work is in progress on a PV system sensitivity analysis. 

foruses on the impacts of system parameters on allowable flat-plate module 

cope and efficiency. 7lat-plate tracking, BOS efficiency, area-related BOS 

cost, capital cost, module efficiency, O&M costs, indirect costs, and insolation parameters are varied to determine allowable module cost. Early result. 

of this work were presented at DOE in January, and changes in several values 

that are used to derive FSA goals were recommended. 

This work 

A presentation in the Plenary Session (see Proceedings) describes the 

status of these deliberations on flat-plate module goals. 

Comparisons of Costing Techniques 

Since the last PIM, an opportunity arose to compare a Japanese :osting 

methodology for ainorphaas silicon manufacturing with the IPEGP model of SAMICS. 

Capital coets were treated differently in the two models, L~actinr: t.0 significant differences in cost estimates for strongly capit- --j.. csive processes 

Using the Japanese methodology, typical manufacturina . cimntes will he 

lower than SAMICS results, due to the omission of return on eqcit; Anvest.rbent 

and income taxes in those estimates. Because the overhead in the Japtwse 

method was proportional to operating cost, these estiaates were lower than 

SAMICS by 80% (l-u-,gawatt case) to 60X (100megawatt caw). 

why a costing standard ip important, and why it is necessary t9 understand the 

underlying costing methods when estirr?tes are compare? rising different methods. 

This illustrates 

26 
ADVANCED PROCESSES AREA 

Amorphous Silicon Task 

INTRODUCTION 

The objective of the Amorphous Silicon Deposition Task is to determine 

the key parameters to be used in large-area deposition-chamber designs. The 

approach is to explore the multidimensional "paraaeter space" of a-Si deposition using a highly flexible learning apparatus to approximate optlaal combinations. 

deposition chambers being designed in the PJ industry. 

Generic data generated by this procedure will be applicable to 

SUMMARY OF PROGRESS 

A large (30-in. diameter x 54 in. long) vacuum chamber has been furnished 

with a fixture (box) containing large (15 x 15 in.) electrodes for depositing 

silicon by plasma-assisted chemical vapor deposition. 

fitted with an oxidizing exhaust treatment device that conditions the effluent 

before exhausting it into the atmosphere. 

The chamber has been 

Several experiments have been performed to determine the parameters 

influencing electrode stability and unifoimity of deposition. 

SERI, the apparatus has produced a-Si depositions from pure silane that have 

good uniformity and resistance to peeling (passes the standard Scotch tape 

test). 

With the aid of 

With the apparatus now functioning, parametric experiments will begin. 

Advanced Processes Task 

INTRODUCTION 

The objective of the Advanced Processes Area is to investigate processes 

that are advanced beyond the state of the art and can be viewed as nextgeneration technologies. 

Advanced Processes include those high-risk areas associated with the 

formation of next-generation photovoltaic devices and modules or the use of 

new, high-risk process technologies. 

SUMMARY OF PROGRESS 

Process research efforts have continued with an increased emphasis in 

investigation of new energy technologies. 

one each for laser-assisted metallization and thin-film deposition. 

Two new contracts were awarded: 

27 
AD'JANCED PROCESS AREA 

Junction Formation 

Spire Corp. completed its investigation of ion implantation and annealing 

of non-Cz silicon sheet materials. 

response of different materials to identical processes. 

appropriate annealing cycle can enhance performance of many materials. 

There were significant differences in the 

Selection of the 

Metallization 

Laser-assisted electroplating of copper was successfully demonstrated by 

Westinghouse Electric Corp., R&D Division. Lines as thin as 25 micrometers 

were applied at a local plating rate of 12 micrometers per second. "his 

system is not optimized, so narrower lines and higher rates are probably 

possible. Laser pyrolysis was used to define some lines on silicon with 

spun-on silver ncodecanoate as the metal source. 

has been delayed due to environmental considerations and MY be deferred due 

to process cost Consideration. 

Iaser photolysis rese8rch 

A new contract has been signed with Superwave, Inc. Santa Clara, Calif., 

for microwave-enhanced deposition of thin films. Better control and lower 

process energy costs are possible benefits. 

28 
RELIABILITY AND ENGINEERING SCIENCES AREA 

INTRODUCTION 

The objectives of the Reliability and Engineering Sciences Area are to 

develop the reliability-durability technology base required to achieve 30-yearlife flat-plate photovoltaic modules and to develop the engineering sciences 

base required to integrate low-cost cell and module technologies into costeffective and safe arrays that meet the operational requirements of future 

large-scale applications. Elements of the first objective include failure 

mechanism identification and understanding ; module re liability predict ion 

tools; test, measurement and failure analysis technologies, and 30year-life 

materials and designs. Elements of the second objective include operational 

and safety requirements, electrical and fire safety technologies, structural 

design technologies, teaperature control technologies, and electrical circuit 

technologies. 

These item are addressed in the context of the DOE Five-Year-Plan and 

are reported herein in a structure corresponding to the organization of the 

Plan . 

SUMMARY OF PROGRESS 

Materials Research: Testing of Thin-Film Cells and Modules 

Researchers at Clemson University and at JPL are vorking with samples of 

amrphous-silicon cells supplied by Chronar Corp. and ARC0 Solar, Inc., to set 

up a performance measurements baseline fcr use with amorphous-silicon cells 

and modules. 

An RFP has been prepared for the purchase of thin-film modules, and is 

being issued to five potential suppliers of amorphous-silicon and other thinfilm modules for the procurement of a sampling of modules to be subjected to 

performance measurement and environmental testing. The objective is much thc 

same as that for the Block I procurement in 1976: t9 determine the problems 

posed by thin-film module fabrication, to establish a basis for performing 

measurements, and to assess the status of the industry. 

Collector Research: Advanced Module Development 

As a first step toward a high-efficiency module, a contract has been 

signed with Spire Corp. to de*:elop a module with an efficiency of 12% to 13% 

at NOCT. 

are near ly completed. 

The module design has been completed and cell processing experiments 

A design team has been assembled to initiate activities on the 12%- 

effici-ent $100/m2 module development. The effort is proceeding toward 

specifying a strawman design as a basis for developing a procurement plan, 

study of the tradeoff between efficiency and $/m2 is in progress to support 

selection of module design characteristics. 

A 

29 
RELIABILITY AND ENGINEERING SCIENCES AREA 

Systems Research: Module Reliability 

Reliability and Physics Studies 

1. Reliability and Durability of Electrical Insulation 

The aging deterioration of organic insulation materials subjected to 

long-term electrical stresses is extremely complex, and in an outdoor 

environment, thermal, mechanical and chemical actions may be simultaneously 

ongoing in an electrically stressed material; this way further contribute to 

insulation breakdown. Other mechanisms that can lead to electrical breakdown 

of organic insulators can originate in manufacturing defects (voids, cracks, 

etc.) and/or ionic impurities (electrochemical effects), and from aging such 

as de lamination, mechanica 1 generat ion of cracks, and chemica 1 generat ion of 

ionic components. 

With a view toward electrical insulation stability, advanced elastomeric 

encapsulation materials are being developed to be intrinsically free of 

in-situ ionic impurities, have ultralow water absorption, be weather-stable 

-oxygen), and have high mechanical flexibility. Despite these positive 

efforts toward improving insulation durability and reliability, a capability 

_of predicting the service life of organic insulation materials is not yet a 

realized technology. 

Recently, however, Spectrolab, Inc., developed a computer program to 

model the level of electrical field intensities and stresses associated with 

the geometries of encapsulated solar cells. 

technical program related to accelerated aging of encapsulation pottant 

materials, and it was desired to have knowledge of typical electrical stress 

levels to which pottants would be subjected in service. 

This was part of the FSA 

An analysis of the Spectrolab computer data led serendipiditously to an 

unexpected finding related to the dielectric strength of electrical insulation 

materials. In essence, it appears that a fundamental definition of an 

intrinsic dielectric strength of insulation materials has been identified, 

which could be stated as a basic material property independent of any test 

technique or service environment. This is similar to other pure material 

properties such as Young's modulus, index of refraction, and coefficient of 

thermal expansion. 

Future work will endeavor to validate experimentally this new dielectric 

strength concept, as part of experimental programs related to electrical 

stress aging. 

2. Electrochemical Corrosion Research 

Electrochemical corrosion characterization research continues with 

investigation of the degradation aechanisms of different 

metallization systems and system interactions with different 

30 
RELIABILITY AND ENGINEERING SCltNCES AREA 

encapsulant polymeric materials. A series of in-house tests 

subjected tvo-cell minimodules to 85OC/3% RH, 8SoC/70% RH and 

85O/C98X RH continuous exposures for 2000 h (83 days). Test 

samples included EVA, PVB and RTV encapsulation of various solar 

cells with Ti-Pd-Ag, printed Ag and Ni-solder contacts. All 

minimodule samples were aged under forward-voltage bias during the 

constant environmental tests. Data obtained from the testa, 

including I-V histories, cell capacitance, leakage current, series 

resistance and corona-inception voltage, are being reduced to 

formulate a life-prediction methodology. Another series of tests 

was initiated in January for 6OoC/70X RH, 6OoC/40X RH, 6OoC/3X 

RH and 850C/4O0C constant environments to provide lower-bound 

data for the life-prediction methodology using the encapsulant and 

metallization varieties noted above. A study of the data from these 

tests is providing a clear understanding of the physics of corrosion 

mechanisms. 

3. Reliability and Durability of Bonding Haterials 

J. Koenig has developed the laboratory techniques necessary to 

interrogate the chemistry of the interfacialschemical bond between 

EVA and glass directly. This recent accomplishment was reported at 

the 23rd PIH, at which he also showed first-ever infrared spectra of 

the interfacial chemistry. Some minor laboratory details remain to 

be completed, after which it is planned to monitor chemically the 

interface of an EVA-glass specimen that will undergo exposure to 

accelerated aging. 

Separately, J. Boerio has also achieved laboratory capability to 

interrogate directly the chemistry of the interfacial chemical bond 

between EVA and aluminum. Once a good EVA-aluminum bond is 

achieved, accelerated aging studies will begin. Boerio also intends 

to examine combinations of EVA-solder and EVA-nickel. 

4. Pnotothermal Degradation Research 

In-house photothermal degradation research has been divided into 

understanding the mechanism of degradation by monitoring and 

characterizing key intermediates, and generating a data base by 

carrying out accelerated photothermal aging of material specimens to 

validate the proposed mechanism. 

Two key chemical intermediates of polymer photothermal degradation 

outdoors have been identified as peroxy radicals and tertiary carbon 

radicals. 

previous studies were carried out at low temperature, 77K. A 

laser-flash electron spin resonance (ESR) experimental apparatus, 

capable of detecting photothermally generated, short-lived radicals 

in situ, has been set up at JPL. 

radicals have been detected at room temperature, in a polymeric 

Because of the short-lived nature of these radicals, all 

Peroxy and tertiary carbon 
RELIABILITY AND ENGINEERING SCIENCES AREA 

medium, for the first time. Studies of temperature dependence of 

the kinetics of these radicals are being conducted. 

data indicate that extremely short-lived radicals can also be 

monitored at 1OOOC. 

analytical relationship between degradation rate and magnitude of 

key stress variables, such as W, 02, and temperature. 

Preliminary 

Their decay rates will provide data on the 

Accumulation of data on photothermal aging of material specimens is 

being continued. Material properties are monitored as functions of 

photon flux, temperature and time. Exposure at a 6-sun W level has 

been completed and exposure at a 3-sun W level is being done. 

Efforts are continuing at the Polytechnic Institute of Brooklyn to 

synthesize various derivatives of 2 (2-hydroxyphenyl) 

2H-benzotriazole by condensation of the diazonium salt of 

4-methoxy=2=nitroaniline, to prepare a new and more permanent 

ultraviolet stabilizer. 

Recent modeling studies by the University of Toronto suggest that 

the best way to stabilize a polymer against outdoor degradation is 

to dissolve an additive (in very low concentration) that can trap 

peroxy radicals and also decoapose hydroperoxide. The model can now 

take into account one time-temperature variation. The useful lifetime (5% oxidation) of an unstabilized polyethylene, for example, is 

predicted to vary from a few months in hot weather (100OF) to 

almost two years in cool weather (45OF). 

have been made to monitor the model predictions regarding stabilization and the possible failure mechanisms: wrinkling embrittlement 

due to scission and/or crosslinking, discoloration and other effects 

due to buildup of unsaturated groups in the polymer. 

Preliminary attempts 

Exposure of encapsulation materials on outdoor heated weathering 

racks is continuing at Springborn Laboratories, with emphasis on 

monitoring the kinetics of stabilizer loss. 

5. Reliability Prediction and Management 

Two presentations summarizing the overall status of module reliability from both mechanisms and circuit-redundancy perspectives 

were presented at the 23rd PIM. A paper including these data is 

to be presented in a plenary session at the IEEE Photovoltaic 

Specialists Conference in May. The present work updates the reliability goals for 13 principal failure mechanisms and defines the 

research statue of each. Detailed life-prediction modeling efforts 

are nearing completion on electrochemical corrosion, and are being 

initiated on photo thermal degradation. 

32 
RELIABILITY AND ENGINEERING SCIENCES AREA 

Module and Array Engineering Sciences 

1. Circuit Analysis and Degradation Quantification 

A computer program was developed to determine the power loss due to 

shorted ce 11s for R given source-c ircuit series-para 1 le 1 conf iguration after N years with a constant yearly failure rate. The completion of this program satisfied the February milestone requirement to 

have circuit analysis tools for shorted cells operational. In addition to completing the program, the following tasks were completed 

and reported upon at the PIM: 

configurations for minimizing power loss for shorted cells were 

determined; (2) the cost-effective failure level for shorted cells 

was determined. 

(1) the optimum series-parallel 

The conclusions reported at the PIM were: 

shorted cells increases with increased 03% of paralleling and cross 

ties; (2) yearly failure rates greater than 1/10,000 lead to pwer 

losses in excess of the allocation for cell failures. 

(1) the power loss due to 

2. Operating Temperature Characterization of Roof-Mounted Arrays 

The ongoing activity has concentrated on evaluating the influence of 

environment on module thermal performance. 

on reducing uncertainties involved in NOCT testing and analytical 

predictions. Preliminary results were presented at the 23rd PIM. A 

refined methodology to take into account changes in ground reflection, ground IR emission and sky radiation was established. It was 

demonstrated that the uncertainty band can now be reduced to around 

The emphasis was placed 

l0C. 

Work is a:so under way to simplify the procedure for determining the 

NOCT of a solar-cell module. 

environmental test activity, indicates that adequate accuracy of 

measurement of NOCT can be obtained using techniques in which 

comparative measurements are made on a module and a reference plate. 

This work, which is supported by the 

3. Hot-Spot Heating with Complex Series-Parallel Source Circuits 

Hot-spot testing was completed on a panel consisting of SMUD ARC0 

Solar, Inc., modules installed at the JPL test site. 

provided data relating the degree of hot-spot heating to the 

following parameters: 

dissipated; module series-parallel configuration, and level of 

current imbalance. The data are being used to develop guidelines 

for future testing of modules to determine hot-spot susceptibility 

in central-station applications where multiparallel cell strings are 

prevalent, leading to a risk of current imbalance and severe 

The tests 

types of shadow conditions; back-bias power 

33 
RELIABILITY AND ENGINEERING SCIENCES AREA 

hot-spot heating. 

circuit design strategies to reduce the risk of hot-spot problems, 

will be presented in a paper at the IEEE Photovoltaic Specialists 

Conference in May. 

This information, along with guidelines for 

4. Bypass Diode Integration Studies 

The draft of the General Electric Co. final report on the integration of bypass diodes in photovoltaic modules and arrays is being 

reviewed. A major issue is an order-of-magnitude price difference 

for field-installed diode packages as determined by different 

organizations. Discussions with GE, Hughes Aircraft Co., and ARCO 

are progressing to resolve the issue. 

5. Module Flammability Research 

In collaboration with ARCO, a series of burning-brand tests wao 

performed on experimental modules using high-temperature, backsurface materials and improved module construction techniques. The 

purpose was to learn how different back-surface materials were 

affected and whether module construction techniques might effect 

greater resistance to flammability for hydrocarbon resin-potted FV 

modules. 

Five types of materials were evaluated: 

film, two kincis of woven fiberglass cloth, Neoprene rubber (as both 

a molded sheet and a latex coating), stainless-steel foil and 

aluminum foil. The aluminum was tested as part of a four-layer 

composite. Where the flame-resistant layer was either an electrical 

insulator or was electrically isolated from the PV circuit, the 

material was configured as a substitute back cover as well as an 

add-on layer over ARCO's present back-surface material. 

different adhesives, a thermosetting type (TS) and a pressuresensitive type (PSI, were tested for bonding the additional 

flace-proof materials to the standard back cover. 

Kapton aromatic polyamide 

Two 

Results of the tests indicate that the more promising configurations 

include softly bonded Kapton; non-wettable (by EVA), densely-woven 

fiberglass; highly crosslinked Neoprene sheet or latex compounded 

for maximum flame retardance; stainless-steel foil (24.1); and 

thick ( 1.0 mil) aluminum foil. These configurations will be 

subjected to Class B and Class A spread-of-flame tests and Class A 

burning-brand tests in the third quarter. 

34 
RELIABILITY AND ENGINEERING SCIENCES AREA 

Module Performance and Failure Analysis 

1. Solar-Ce 11 Parametric Re liab i 1 ity Testing 

During the second quarter of fiscal year 1984, FSA conducted four 

different types of cell parametric reliability testing with a 

contractor, Clemson University. At Clemson, the following four 

testing activities are under way on encapsulated and unencapsulated 

cells. 

a. 

b. 

C. 

d. 

Real-Time Rooftop Testing 

Individual cells were placed in specially designed cell holders 

and exposed to a real-time, outdoor rooftop environment. 

Results indicate differences between cell types relative to 

whether or not they are encapsulated and to various 

me ta 1 liza t ion types. 

Water-Exposure Test 

Individual cells were placed in the pressure-kersiontemperature test chamber at the U.S. Coast Guard R6D Center 

Center in Groton, Connecticut. Test results are still being 

analyzed, but initial review seems to indicate that water 

exposure of cells is less degrading than humidity exposure. 

Analysis of data is expected during the next reporting period. 

Arrhen ius-Type Temperature -Humidity Test ing 

Cells are being exposed in two separate series of temperaturehumidity accelerated-stress tests. 

humidity tests are at 80°C/85X RH and 93OCI85X RH. 

indications are that the degradation rate of cells exposed to the 

higher temperature-humidity combination (93OC/85% RH) will be 

higher. A somewhat similar test with higher humidity, at constant 

temperature, is still under way; it includes several different 

cell designs and materials. 

The two series of tem?eratureEarly 

Schottky Barrier Formation Failure Analysis 

In addition to cell testing, Clemson is involved in failure 

analysis of cells. 

accelerated stress testing of p-on-n cells is Schottky barrier 

formation on the back-side contact. 

presented at a JPL seminar and at the 23rd PIM, and will be 

presented at the IEEE Photovoltaic Specialists Conference in May. 

One potential cell failure mechanism found in 

Papers on this work have been 

35 
RELIABILITY AND ENGINEERING SCIENCES AREA 

2, Module Parametric Seliahility Testing 

The development of humidity degradation rates continues for generic 

module designs, based on comparisom of humidity testing cycles and 

humidity-temperature data from SOLMET weather tapes. Blocks I11 and 

IV minimodules subjected to endurance testing at Wyle Laboratories 

in environments of BPC, lOOOC, 85OC/85% RH, 85OC/7OX RH and 

4OoC/93% RH test levels are undergoing analysis at JPL; test data 

will be used in determining module degradation-rate curves for 

various failure mechanisms, Minimodules tested in the 850C/85% RH 

environment were returned to JPL in January for failure analysis and 

data reduction. Procurement of Block V minimodules was completed, 

providing recent EVA designs for parametric testing. 

3. Module Envirc?nental Teeting 

The environmental test activity has continued with the testing of 

Block V modules, both Group 1 and Group 2, and commercial modules of 

the same period as Block V. Testing of the Block V Group 1 modules, 

which included ARCO, GE, MSEC, Solarex Corp. (two types) and Spire 

Corp., is complete except for the large-cell Solarex modules and the 

Spire modules. 

test and Spire modules for hot-spot and 200-cycle tests have not 

been delivered. Tests of the Group 1 cormnercial modules "like Block 

V" obtained from ASEC, Photowatt International, Inc., Solavolt 

International and Solenergy Corp. have been completed. 

modules from ARCO and ASEC are nearing the end of the Block V 

testing sequence. 

Solarex has yet to complete the 200-cycle temperature 

Group 2 

Results of environmental testing performed during this period: 

BM2H 

BM2H 

BD24 

Vendor Code Quantity 

US4Q 4 

US5P 4 

4 

4 

1 

4 

4 

10 

- Test 

Twist 

T-50 

HF-10 

M- 1 OK 

HS-100 

M- 1 OK 

Twist 

Hi-potl 

Cont'y 

Results 

Satisfactory 

Discoloration (corrosion) of grids, 

interconnects, buses; also metals in 

J-box. Slinht warping of J-box 

covers. One of three cells got hot, 

had a slight yellow stain, and 

changed electrical properties. 

Module power was essentially 

unchanged. 

Sat is far, tory 

Sat ie fac tory 

Improved modules submitted for retest 

of interconnects. Four of the 10 

failed the continuity test. 

36 
RELIABILITY AND ENGINEERING SCIENCES AREA 

Vendor Code Quantity Test 

2 

LS5H 4 

4 

4 

LBMH 

LBOH 

B20H 

YS4Q 

YSSH 

E5H 

BR2H 

BQ4H 

BFOJ 

1 

4 

T-50 

HF-10 

M-1OK 

HL-1 .O 

HS-100 

Twist 

HL-1.0 

M-1OK 

Twist 

Twist 

T-200 

Twist 

HL-1 .o 

T-50 

HY-100 

T-50 

T-50 

HF-10 

HS-100 

M-1OK 

4 twist 

Results 

Sat is fac tory. 

Some delamination 4 modules: 

1, 1, 5, and 6 cell cracks 

respectively. 

1 module. 

Sat isfactory except another module of 

the 4 has marginal electrical 

degradation. 

One cell suffered 11% power loss, 2 

others satisfactory. Cell with loss 

cracked, probably by handling in teat. 

Sat is f ac tory. 

Electrically OK. 

Satisfactory. 

Sat is fac tory. 

Sat is fac tory. 

Electrical degradation 8X, visual OK. 

Sat is factory. 

Electrically sat is fac tory, 

Bus bars at one end twisted, 

intermittently shorting out the 

diode. Cells sagged and touching. 

Electrical failure after mechanical 

cyc ling. 

Sat is fac tory. 

Backside wrinkled, all modules, 

Serious delamination at frme seals 

near terminals at one ecd. 

Tedlar shrinktge, loose terminal 

housings. 

Sat is fac tory. 

Small glass crack in a corner, splits 

in white Mylar, 

5 x 10 cm delaminathi 

37 
RELIABILITY AND ENGINEERING SCIENCES AREA 

Vendor Code 

SP5H 

BWOH 

BX2H 

BX3H 

BX3 J 

BEOH 

Notes: T-50 

T-200 

HF-10 

M- 1 OK 

HS-100 

HL-1.0 

Twist 

Hi-pot 

Cont ' y 

4 

4 

4 

2 

4 

4 

1 

6 

10 

2 

3 

10 

6 

2 

4 

7 

Test 

T-50 

HF-10 

M- 1 OK 

T-200 

M- 1 OK 

'his t 

lis-100 

T-50 

Hi-pot/ 

T-200 

Cont ' y 

Cont 'y 

T-50 

T-200 

HF-10 

Results 

Back-surface delamination of areas 

near terminals extending as long as 

20 cm and generally involving several 

cells. 

Interconnect fatigue, weld separation 

(see failure analysis). 

Sat is fac tory. 

Satis factory. 

Sat is fac tory. 

Backside wrinkling and delam at 

sides, J-box and covers warped, all 

modu' 5s. 

Hipot satisfactory. Frame 

continuity : failed. 

Sat is fac tory. 

One module of 3 failed despite 

new-style grounding bracket. 

New modules submitted with additional 

frame bonding strap. Modules passed. 

Discoloration of grid lines. 

Electrically satisfactory. 

Grids, interconnects and buses 

disco lored, back sur face wrinkles. 

Extensive delamination at module 

edges, sometimes extending from frame 

seal to cells. 

= 50 thermal cycles, -4OOC to = 90°C 

* 150 additional thermal cycles 

85'C/85% RH, 20 h, then -4OOC 0.5 h, 10 cycles = 10,030 cycles at +2.4 kPa mechanical loading 

= 100 cycles of 3 cells, hot day, reverse bias, worst 

condition 

* 25-m hailstones at 52 mi/h 

= Mounting surface non-planarity of 20 m/m 

= 3000 V for 1 min 

= Current of 2 X Is, through metal frame elements. 

38 
RELIABILITY AND ENGINEERING SCIENCES AREA 

4. Module Field Testing 

Daily data collection at the JPL field test site was discontinued in 

January. Final I-V data could not be acquired due to in trumentation and array circuit control failures. All of the current weather 

and irradiance data that was stored on the hard disk was archived to 

magnetic tape. 

were also stored on magnetic tapes for use should the system be 

reactivated in the future. 

The control files that are used to schedule tasks 

Under these conditions it is estimated that if the system were to be 

reactivated it would take 40 to 60 hours to get the system back on 

line and to affect the repairs required in the instrumentation and 

array control circuits. The latter should be modified if 

reactivation is considered. 

The SMUD-type array-level hot-spot testing was completed. Data were 

obtained for seven modules that were internally wired in up to five 

different configurations and shadowed in several ways. The data 

obtained were given to the Module and Array Engineering Task for 

analysis. 

and currents of each string of cells under test, the array voltage 

and current, selected cell temperatures, irradiance data and air 

temperature, all as fucctions, of time, and detaiied temperature 

data using the infrared camera system. 

These data consisted of computer printouts of the voltage 

During this period field-test workers carried the data logger to 

Florida Solar Energy Center to take T-V curves of the modules 

installed there for JPL. 

5. Electrical Measurement Technology Development 

A formal "Procedure for the Calibration of Type I1 (Secondary 

Terrestrial Photovoltaic Devices Using a Solar Simulator Filtered to 

Closely Match Air Mass 1.5 Direct Normal Irradiance" was completed. 

F.is will be the governing document at JPL for the calibration of 

reference cells in a solar simulator until the emergence of an ASTM 

or other consensus standard. The procedure relies upon direct 

sunlight calibration of sir reference cells of varied spectral 

response which were calibrated simultanzously in June 1983. 

Special measurements on modules or secondary calibrations of 

reference cells were made for ARCO, Hughes, Solar Energy Research 

Institute (SERI), Solar Power Corp., Solec Internatimal, Inc., and 

Spire, and a special group of six reference cells was sent to SERI 

for their calibration exercise in Florida in April. 

measured included a Sanyo amorphous-silicon-cell module, a Chronar 

Corp. amorphous module and a unique module provided by TriSolar 

Corporation of Bedford, Mass. 

to Yale University, which is working on high-efficiency 

inversion-layer cell. 

Special modules 

A calibrated reference cell was lent 

39 
RELIABIL.ITY AND ENGINEERING SCIENCES AREA 

6. Failure Analysis and Reporting 

An interesting faflure analysis involved a module in which an 

aluminum bus bar extsnding across the width of the module grew in 

length during the thermal cycling and ruptured i.rrterconnects welded 

to the bar. Analysis of the pheiLomenon ascribe& the behavior to 

interactions involving (1) the superior adhesion between PlB a.rd 

both glass and aluminum. (2) the qlass transition temperature, Tg, 

of the PVB, (3) the thermal coefficient of expansion of aluminum, 

(4) the elastic limit ci the aluminum, (5) the thernal cc~fficient 

of expansion of glass, and (6) tF: range of the temperature cycle. 

There is also evidence that relatively pure aluminum may "grow" even 

during relatively moderate temperature excursions (e.g., -40°F to 

+120°F) in the absence of externally aprlied stresses. Tha 

analysis points up the need to understand thoroughly the 

interactions between materials. 

40 
RELIABILITY AND ENGINEERING SCIENCES AREA 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

RECENT TECHNICAL PUBLICATIONS 

Fourth Annual Report, Clemson dniversity, October, 1983. 

"Source Circuit Design Overview," R.G. Ross, Jr., Central-Station 

Research Forum Proceedings, Sc2ramento; California, December 5, 1983 (in 

press). 

"Hot-Spot Heating in Central-Station Arrays," C.C. Gonzalez, 

Centra 1-S tat ion Research Forum Proceedings , Sacramento, California, 

December 5, 1983 (in press). 

"Elec trica 1 Insulae ion Design Requirements and Reliability Goals, 'I R.G. 

Ross, Jr., Central-Station Research Forum Proceedings, Sacramento, 

California, December 5, 1983 (in press). 

"Lab Experience with Voltage Breakdown," G.R. Mon, Central-Station 

Research Forum Proceedings, aacramento, California, December 5, 1983 (in 

press). 

"Qualification Testing and Electrical Measurements: 

Problems," M.I. Smokler, Central-Station Research Forum Proceedings, 

Sacramento, California December 5, 1984 (in press). 

Practice and 

"Hi-Pot Qualification Test Experience," J.S. Griffith, Central-Station 

Research Form Proceedings, Sacramento, California December 5, 1984 (in 

press). 

"Breakdown of Organic Insulators. 'I E.F. Cuddihy, Central-Station Research 

Forum Proczedings, Sacramento, California December 5, 1984 (in press). 

41 



PROCEEDINGS 

INTRODUCTION 

The 23rd Project Integration Meeting (PIM) of the Flat-Plate Solar Array 

Project (FSA) of the Jet Propulsion Laboratory (JPL) was held at the Pasadena 

Center, Pasadena, California, March 14-15, 1984. The PIM theme was "LarLe 

Photovoltaic Array Technology and Cost Sensitivities .It 

In the plenary session on March 14, presentations were made on array 

cost sensitivities and goals, large-array experience, systems considerations 

for large arrays, array technology status and research, and technical issues 

of high-efficiency solar cells. 

Issues: Large PV Arrays" was held. 

On March 15 a panel discussion of "Needs and 

During the past two years much effort has been devoted to four large PV 

array designs for central-station power plants and €or a large rooftop 

design. lko 

more plants will go into operation in mid-1984, and a fifth will become 

operational in 1985. In December 1983 FSAheld a research forum on the Design 

of Flat-Plate Photovoltaic Arrays for Central Stations. As a consequence of 

these activities, this PM focused on large-array technology and related cost 

sensitivites. The advent of large panels integrated into even larger arrays 

makes it imperative that future modules be designed from an array viewpoint, 

the future module cost aqd effeciency goal5 should be evaluated in a tradeoff 

of all the factors involved in present and potential PV system cost and 

performance. 

Operational experience has been obtained from two of the plants. 

The PIM continues ts enable two-way communication between the government 

and the private photovoltaics cornunity regarding present and future 

photovoltaic activities. This exchange is required to assess recent progress; 

to identify, implement, and evaluate the integration of activities; to gain 

perspective of trends and new developments, and to guide the near-term and 

long-term planning and adjustment of priorities within the Project. 

A summary of plenary-session presentations follows. 

45 

Plenary Sessions 

SUMMARY 

U. T. Callaghan, Manager of the Flat-Plate Solar Array Project (FSA), 

opened the meeting by welcoming the pat .ipants in the Project Integration 

Meeting (PIMI, especially those representing the utilities and utility-related 

organizations. The encouraging progress and experience gained recently in the 

use of the flat-plate modules in central-station applications are vital 

achievements as photovoltaics matures. 

Mort Prince, Chief, Collector and Research Branch, U.S. Department of 

Energy (WE), presected a short discussion of the Administration's optimistic 

view of photovoltaics and of continuing strong support in Congress. He noted 

that DOE considers crystalline silicon technology as a strong contender for 

photovoltaic (PV) use through this decade, and that he believes that the 

present shcytage of polysilicon is temporary. 

A presentation Ln flat-plate module requirements for meeting National 

Photovoltaics Program goals was given by R.U. Aster of the FSA Project 

Analys'; and Integration (PAN) Area. The five-year goal of flat-plate 

collector research is to establish by 1988 technologies that industry can 

apply to scaled-up production of modules. The modules should be compatible 

with a PV system capable of generating power at $O.lS/kWh. 

parametric with module efficiencies and with balance-of-system (BOS) costs and 

efficiencies. Since Lhe 22nd PIM, when a presentation was given on this 

topic, a subject for work and discussion has been the values to be assumed in 

performing trade-off analyses: comparisons of module efficiency vs cost 

requirements for different insolation values and area BOS costs were presented. 

Module costs are 

A report on progress by ARCO Solar, Inc. in developing module, array, 

sun tracker, and associated hardware for central-station PV power plants was 

presented by J.C. Arnet: of ARCO. The Lug0 (1 MU) plant at Hesperia, 

California, and the Carrisa Plain (4 314 MU) plant in California Valley, 

California, pioneered the use of two-axis sun trackers for flat-plate 

modules. Operational experience at the Lug0 plant (15 months) and at Carrisa 

Plain (three months) has shown that they operate well and are reliable. ARCO 

is also providing the modules and atrays for the first and second phases of 

the Sacramento Municipal Utility District (SWD) central-station plant. The 

modules are integrated into subpanels in a way that reduces manufacturing, 

assembly, and installation costs. 

Progress on the first and second phases of the SWD central-station PV 

power plants, which is scheduled to total 100 MW of generating capacity in 

1993, was presented by M.R. Wool of Acurex. The first phase (1 W) of this 

plant, with single axis tracking arrays, is scheduled to be in operation in 

mid-year 1984. It is estimated that the installed cost of the first phases 

will be less than the targeted cost of $12/watt. The lower projected costs 

for future phases of the plant are encouraging. 

A comprehensive presentation on the design and the status of the 

Georgetown University Photovoltaic Higher Education National Exemplar Facility 

was presented by G.J. Naff of Hughes Aircraft Co. The 300 kW rooftop 
PLENARY SESSIGNS 

installation on a Georgetown University building in Washington, DC, is 

expected to be in operation in mid-1984. The complexity of mounting large 

arrays on a number of roofs of a multistory building and integration of the 

power system into the building was described. 

semicrystalline solar cells are being supplied by Solarex Corp. 

passed qualification testing at Jet Propulsion Laboratory (JPL). 

The 2 x 4-ft modules with 

The modules 

A summary of the Sandia National Laboratories PV Systems and 

Applications PIH, held February 14 through 16, 1984, was presented by M.G. 

Thomas of Sandia. The systems are providing data on long-term performame, 

reliability, degradation and operation and maintenance. It is essential that 

there be a comparison of predicted and actual performance to make 

assessments. Progress has been made in devising advanced-performance 

power-conditioning systems for both small and large installations. The 

performance of large utility-connected installations has been acceptable to 

the utilities. 

An overview of electrical circuit design for large PV installations and 

its influence on array reliability was presented by C.C. Gonzales of the FSA 

Re1;ability and Engineering Sciences Area. The objective of these studies has 

been to determine cost-optimum circuit-design practices that will minimize the 

effect of component ->roblems on system energy cost. The presentation covered 

the methodology for developing circuit-design options to control the effects 

of component failure and mismatch, identification of conponent failure 

mechanisms and potential solutions, some examples of design options, and the 

status of circuit-design efforts. Power losses for various types and 

frequencies of failures and strategies to reduce losses were presented. 

PV array durability for central station applications was discussed by 

G.R. Hon of the FSA Reliability and Engineering Sciences Area. To achieve 

30-year array life, the the array must be designed and fabricated with 

accepteble power degradation rates, component failure rates and little 

maintenance. Results of FSA activities in the establishment of durability 

goals, the identification of key degradation mechanisms, the status of 

degradation mechanism physics and parametric dependencies, the development of 

accelerated tests and degradation prediction models, and the identification of 

cost-effective solutions were presented. Key remaining issues were summarized. 

A summary of operation and maintenance (Obn) issues from the Design of 

Photovoltaic Arrays for Central Stations Research Forum was presented by P.K. 

'Ienry of the FSA Project Analysis and Integration Area. Past studies of 06.k 

costs have ranged from $2.00/m2 per yr to $2.50/m2 per yr. 

present knowledge of failure mechanisms and rates, it is recommended that 

$1.10/m2 per yr for fixed arrays and $1.40/m2 per yr for tracking arrays 

be used as OSn cost estimates. Better understanding of, and data on, failure 

mechanisms and failure rates are required to establish better cost estimates. 

Recently installed large arrays will provide more relevant OSn data than have 

previous small experimental arrays. Data collection and analysis is a vital 

requirement. 

Based upon 

An overview of the technical issues of high-efficiency crystalline 

silicon solar cells was presented by K.M. Koliwad, FSA Project Technologist. 

Establishment of the technologies that industry can apply to the production of 

15% efficient crystalline silicon modules is the DOE goal. The production of 

48 
PLENARY SESSIONS 

sufficiently efficient large-area solar cells using low-cost silicon sheet is 

beyond thu state of the art. The primary barriers that must be overcome are 

the inadequate quality of low-cost silicon sheet and inherent limitations of 

state-of-the-art cell structures. Extensive research is required on silicon 

sheet, understanding device physics and the design and processing of solar 

cells. 

John Day of Strategies Unlimited was chairman of a panel discussion on 

Needs and Issues: Larde PV Arrays. S.T. Carlisle of Southern California 

Edison (SCE) explained that utility's comitment to renewable energy, 

including PV. 

ARCO Solar Electric Power, Inc. (the Lug0 plant) have been good, with no major 

problems. SCE believes that more and larger PV plants are needed to gain 

long-range experience. Efficiencies must be increased because of area-related 

costs. K.U. Uatsuda of Pacific Gas & Electric Co. said that array 

efficiencies must be increased. The utilities want Federal and state tax 

credits so that they can install large systems now and not wait until PV is 

totally cost competitive. E.J. Simburger of Aerospace Corp. discussed the 

needs in five categories: capital-investment criteria, performance 

characteristics as matched with utility requirements, maturity of technology, 

the **buildability" of the system, and an accepted standard for gathering and 

analyzing performance data. U.G. Thomas of Sandia expressed a need for 

obtaining operation and maintenance experience and costs. Uartin Recchuite of 

ARCO Solar, Inc. stressed the need to continue funding SIYUD and continuing the 

tax credits until the price of PV systems comes down so that large PV systems 

can be erected during the next few years. R.G. Ross, Jr., FSA Project 

Analysis and Integration Area Manager, emphasized the need for higher 

,,~t~;ency and nigher reliability. 

The results of purchases of PV-generated electric power from 

**c-* - - 

Three presentations were made during the lat, yews period. J.F. 

Hoelscher of Solarex Corp. briefly described the plaits of his company to 

design, build and operate a central station PV plant at Adelanto, California, 

near Victorville. J.L. Young of Union Carbide Corp. described briefly the 

beginning of design work on a 3000 W/yr polysilicon plant that would bccome 

operational in this decade. R. Shoen of RSA Architects descri5ed a proposed 

solar village in the Uiddle East. There is considerable interest, in a number 

of countries, in villages using PV. 

49 

ARRAY COST SENSITIVITIES AND GGALS 

JET PROPULSION LABORATORY 

R.W. Aster 

Recommended Revision of Parameter 

Values in the Five-Year Research Plan 

ORIGINAL VALUE RECOMMENDED VALUE 

Research Goal (1982 SlkWh) 

Fixed Charge Rate 

Other Financial Parameters 

Indirec! Cost Multiplier 

BOS Efficiency 

Mod L' I e F. f f i $;e n cy Ad j us t m en t ( N 0 C) 

Arta Related BOS: Fixed 

1.Axis 

2,Axis 

Annual O&M Cost: Fixed 

Tracking 

Insolation (kWhlrn2-yr): Fixed 

1-Axis 

2-Axis 

0.1 5 

0.1 8 

1.5 

0.81 

- 

50 

- 

- 

2.28 

- 

2365 

- 

- 

No Change 

0.1 53 

No Change 

1.5 (includes M&D) 

0.865 

0.88 

50 

70 

90 

1.1 

1.4 

2250 

2700 

3000 

The Insolation Issue 

I. nas been recommended elsewhere that the insolation parameter be 

reduced from 2250 to 1623 kWh/rnZ-yr. 

This figure is an appropriate average for part of the Pacific Northwest, the 

Great Plains, along with the Mississippi River, and in the Southeast. 

However, the first major utility markets are expected to be in the 

Southwest. Southern California Edison Co. (SCE) recently announced its 

intention of purchasing 21 50 MW of renewable energy, including 350 MW 

of solar, by 1992 (Dr. L. T. Papay, V.P., Advanced Engineering, SCE). 

The likelihood of meeting PV module goals based on the parameters shown 

earlier is significant. 

The likelihood of meeting goals ba5. d on the lower insolation value is 

negligible, within the schedule given in the Five-Year Research Plan. 
PLENARY SESSIONS 

PV Module Cost and Efficiency Goals 

Consistent With 15clkWh 

0.70 

0 81) L--- 

0 

RECOMMENOEU VALUES 

0 

CD 

- 0.50 ? 60 - 

W 

& 

2 

30 - 

- 0.20 

5 

- 0.10 

OG I I I I L 0.0 

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 

MOOULE EFFICIENCY (STC AT 25"C!. % 

Sensitivity Analysis 

A report is being preja:d that gives allowable module 

costlefficiency curves, given changes in these parameters: 

* Annual insolation Fixed charge rate 

BOS efficiency Ir direct costs 

Energy goal O&M cost 

Area-related BOS cost Fixed, 1-axis and 2-axis 

tracking 

it also describes the change in PV energy cost if the following 

pal ame!ers are changed simultaneously: 

Module cost and efficiency 

Area-related 60s and power-related 60s costs 

Module cost, efficiency, and degradation rate 

Module cost, efficiency, and replacement rate 

Module cost, efficiency, and indirect costs 

52 
PLENARY SESSIONS 

Sensitivity Analysis Products 

MOOULE EFFICIENCY lSTC AT 25°CI, % 

53 

FLAT-PLATE SING LE-AX I S TRACKING 

ACUREX CORP. 

M.R. Wool 

SMUD Photovoltaic Powerplant Project 

Phase Objective 

I Technology benchmark 

and demonstration 

II Develop system design 

and PV sources 

Ill Scale up and support PV 

industry 

IV Quantity purchase to 

reduce PV cost 

2 u I 1.1 pi e :e i 00 ~ MVL' \. V 

system ! n s t al la t ion 

Size 

(MW) Year 

1984 1 

- - 

1985 1 

1987 5 

1990 20 

I Y95 73 

100 

Costs (1983$) 

($/Watt) ($MI 

12 12 

10 10 

7 35 

4 SO 

2.5 i (33 

320 

System Design Selection 

FIRST MEGAWATT 

Energy Power Cost Relative 

(GWH) (MW) ($M) Cost + Benefit 

Flat Panel 

- Fixed structure 2.2 0.63 10.9 1.14 

- Two-axis tracking 3.0 0.78 18.2 1.42 

Tweaxis Concentrator 2.7 0.74 17.0 1.46 

- One-axis tracking 2.7 0.76 11.5 1 .oo 

55 
PLENARY SESSIONS 

Verification Array Data: Typical Insolation Profile 

I---- -__ 

1,000 

800 

2 600 

0 

- 

"E 

C 

m 

0 

c. 

- 

400 - 

200 

0 

\ 

\ 

'\ 

\ 

\ 

\ 

\ 'i 

June 19,1983 /' 

0800 1200 1600 

Pacific standard time 

10 

8 

6 

4 

2 

0 

Verification Array Data: Typical 

Power and Efficiency Profile 

r June 19,1983 

5 

0800 1200 1600 

Pacific standard time 

56 
PLENARY SESSIONS 

System Cost Reductions 

Costs ($nnrattDc) Design Approach Phase I Target 

Site preparation 

Foundations and 

installation 

Panel strl; :ture and 

electrical 

Fiela wiring and power 

conditioning 

Stxiup 

contingencies 

BGS subtotal 

PV panels 

Engineering 

Total 

0.34 0.1 5 Allow terrain 

variations 

0.45 0.25 Longer span, fewer 

posts 

0.6 1 0.22 Unitize panel 

assembly 

0.58 0.34 Standardize PCIJ, 

reduce groufiding 

Costs ($/WattDc) Design Approach Phase I Target 

0.1 5 0.04 Reduce with 

experience 

2.14 1 .oc) 

5.45 1.55 At 10 percent aperture 

efficiency 

2.4 1 0.1 5 

10.00 2.70 

57 
PLENARY SESSIONS 

SMUD PV Balance-of-System Cost Progrc%s 

Site preparation 

Foundations and 

installation 

Structure 

Array electrical 

Field wiring 

PCU 8 control buiidir 

Startup 

Total $/WattDc 

SM U D PV1 

Actuals 

.34 

.45 

.37 

.24 

.16 

.42 

- .15 

2.14 

SMUDPV2 I Target 1 Estimate 

lo I i .15 

I 

.30 1 25 

I 

I .28 I .18 

,04 I .04 

.15 .15 

.19 

*41 I 

I 

1.46 1 1.00 

58 
PLENARY SESSIONS 

GEORGETOWN UNIVERSITY PHOTOVOLTAIC HIGHER 

EDUCATION NATIONAL EXEMPLAR FACILITY (PHENEF) 

HUGHES AIRCRAFT CO. 

G.J. Naff 

System Requirements and Parameters Overview 

o SYSTEN POWER AT S. 0. C. 

o SYSTEN VOLTAGE 

o POKR FACTOR 

o SYSTEPI MWlOilIC DISTORTION 

o ARR4Y POWER DEGRADATlOll 

o ARR4Y DESIGN LIFETIME 

o AVAILABLE ARMY AREA 

o ARRAY ROOFTOP 

o INSTRUNNTATION NETWORK 

o MINTEHANCE 8 MPAIR 

NO KWP 

480 yi277u 3 PHASE 60 HZ 

90 PERCENT FIINIIW 

5 PERCENT MXIBJ!! 

Efll: 3400 PERCENT VOLT - y SEC 

15 PLRCENT FIAXIWZO YEARS 

20 YEARS MINIRUFI 

ABOUT 36,000 SQ. FT. 

WATERTIGHT 

ODAS; WEATHER STATION; 

~!ODCLES/ROOF TEYP. 

/lODULi REFlOVAL, TEST EQUIP.; 

REMOTE YONITOR: SAFETY ALARMS 

39 

PLENARY SESSIONS 

36 PV Module Bipolar Source Circuit 

L 

P.V. MODULE P 

TO BRAIiCtI 

C! RCU IT PANELBOARC 

Simplified Block Diagram 

36 PV MODULE BIPOLAR I SOURCE CIRCUIT I 

P.F. CORSCTION STAT I ON 

61 

PLENMY SESSIONS 

QUALIFICATION AND TESTING OF PV MODULES 

PV Module 

FULLY TESTED BY JPL PER BLOCK V 5101- 162 

PRODUCT ION ADHEZES TO PREDETERMINED IUiNUFACTURI NG PROCESSES 

RODULES SUBJECTED TO UL790 FIRE RESISTANCE TEST 

FULL FlECHANICAL/VISUAL INSPECTION 

PREDETERMINED kCCEP1 ANCE TEST PROCEUURES 

o HUGHES-FURNISHED REFEREHCE CELL STANDARDS (DSET/ASDi #178) 

o CALIBRATED PNDULES 

o SOURCE INSPECTION/LO! SARPLES 

SOLAREX CURRENTLY DELIVERY 4% ABOVE REQUIREMENT 

Interface Control Drawing (ICD) 

o o SPECIFICkTION DEFIIYES BASIC PARAMtIERS 

0 0 INTERFACE CONTROL DMAWIiiG 

I DENT IF I ES : 

o CONF IGURAT loti 

o DINEI~SIONS 

o PARTS 

o MATERIALS 

o PROCESS SPECIFICATIOilS 

o QUALITY ASSURANCE PROVISIONS 

o o THE ICD AND SUBTICI: UOCUMUJTS MJST LE APPROVED bY HUGHES 

o o SIGNIFICANT REVISIONS TO ICD 8 SUUTlCR DOCUMENTS MUST ALSO 

BE APPROVED BY HUGHES 

63 
PLENARY SESSIONS 

Module Electrical Characteristics 

o 72 WATTS IlWMJN LOT AVERAGE AT 16.2 WILTS 

o 67 UTTS NODULE flIAllXYl AT 16.2 VOLTS 

o NASURfD AT lo00 W/w, A?! 1.5, 28OC 

o WJOO VkLT ELECTRICAL VOLTAGE INSULATION 

o 3 EWCAPSUUTED BYPASS DIODES (12 CELLS/DIODE) 

o jOURL3K CWiCTORS (UL AECOUIIZED) 

o SIZE: TWO FT. BY FOUR FT. MINATE 

Reference Cells 

o FIVE 2 X 2 CM CELLS PROVIDED BY SOLAREX 

2 EA. - SGLAREX FOR ACCEPTANCE TESTING 

2 EA. - 

1 EA, - FlOUNTED ON PHENEF ROOF 

HUGHES SOURCE INSPECTION FOR SAflPLE VERIFICATION 

o IDEIYTICAL liJ TYPE TO MODULE'S CELLS 

o FABRICATED AN3 CALIBRATED BY DSET LABORATORIES, ARIZONA 

o TO ASTM DRAFT DOCUMENT #178 "STAIUIDARU XTHOD 

FOR THE CALIBRATION AND CHARACTERIZATION OF 

NON-CONCERTRATOR TERRESTRIAL PHOTOVOLTAIC 

REFERENCE CELLS UNDER GLOBAL IRRAD!ANCE" 

64 
PLENARY SESSIONS 

Calibrated Modules 

o TWO MDULES 

o I-V CURVES GEKERATED USING EACH OF 5 REFERENCE CELLS 

EACH OF 5 REFEREKE CELLS 

VENDOR SIMULATOR 

o AVERAGE I-V CURVE GLTERPiItiED FOR EACH MODULE 

(I.E. CALIBRATED I-V CURVE) 

G CHECKED USING JPL SIPIULATOR 

Simulator Verification 

o CALIBRATED MODULE TESTED iJNDER VEiJDOR SltlULATOR 

BEFORE AND AFTER ACCEPTA’iCE TESTING DAILY 

o MTH I-V CURVESilUST AGREE HITHIN 

o ACCEPTANCE TESTING OF flODULES 0. K. 

o VERIFIES SIMULATOR/DATA ACQUISITION SYSTEM 

2X OF CALIBRATED I-V CURVE 

o HON-AGREEEIEHT - ACCEPTANCE TESTING NOT VALID 

65 
PLENARY SESSIONS 

Acceptance Testing 

0 o EACH mDULE SUBJECT TO: 

o l.ICLWl ICAL/PHY SICK INSPECT ION 

o VOLTAGE INSUUTION TEST 

<SO u WS 61 300 VDC 

USES SAMPLE OF ACTUAL SUPPORT STRUCTURE 

o DIODE VERIFICATION TEST - OPENS 8 SHORTS 

ACCEPTABLE ( I -V) CUfYE SHCilS 30 SHORTS 

DARK REVERSE VOLTAGE SHOWS :10 OPENS 

o ELECTRICAL PERF ORWNCE TEST 

I-V CURVE a 1000 W/@, An 1.5, 280C 

I a 16.2 - CURRENT GROUPS 

HUGHES SUPPLIED REFERENCE CELLS 

Conclusions 

STRIHEEIU SPEC IF ICRTIOH GUARANTEES 

ENVIRONMENTAL PERFORMANCE 

STRUCTtiRAL/PHYS I CAL INTERFACES 

ELECTRICAL PERFORMNCE 

SOLAREX CURRENTLY DELIVERING MODULES 

4% ABOVE REQUIREMEHT 

COST EFFECTIVE 

CHEAPER TO ASSURE FACTORY MODULE 

PERFORMIKE THAN TO ADJUST If4 FIELD 

66 
?LENARY SESSIONS 

ARRAY ROOFTOP DESIGN SUPPORT STRUCTURES 

o KATERTIGHT ROOF 

o AESTHETIC 

o WEIGHT - LESS THAN 10 PSF 

o SAFETY - FALLING ICE 8 SNOH 

o WALKABLE 

o GROUNDlHG 

Rafter-Pur lin Support Structure 

67 
PLENARY SESSIONS 

Typical Grid Anchor Detail 

Power Conversion and Control System 

5 

I 

I -Ai 

68 
'LENARY SESSIONS 

Electrical Protection 

o LINE FAULT 8 OVERCURRENT PROTECTION 

o ARCING DC CURRENTS (TO GROI!:ii)) - CURRENT LIMITED 

o MAGNETIC BLOW-OUT DI: iiELAYS 8 CONTACTORS 

o THEWL MAGHETli TRIP CIRCUIT BREAKERS (250VDC) 

o AIR MAGNETIC CONTACTORS - 1OOOV; 1000 AMPS 

o BIDIRECTIONAL FAULT TRIP COORDINATION 

o 

o 

AUTOMTIC ALARM RELAYS U. SECURITY TIE-IN 

SYSTEM SAFETY SHUTDOWN - CROWBARS 

o BRANCH CIRCUIT PANELBOARD ENCLOSURES (10) 

o BLOCKING DIODES 

o SURGE ARRESTORS tmJVs) 

o Ell1 FILTERS 

o REFMTE POWER FDNITORING - U, CENTRAL EHERGY CENTER 

69 



PHOTOVOLTAIC SYSTEMS DEVELOPMENT 

AND EVALUATION 

SANDIA NATIONAL LABORATORIES 

M.G. Thomas 

Systems Research and Evaluation 

SYSTEMS EXPERIMENTS ARE PROVIDING DATA OH 

o LONG TERM PERFORMANCE 

o RELIABILITY 

o DEGRADATION 

o OPERATION AND MnINTENANCE 

COilMUNlCATION IS IMPORTANT - ESPECIALLY IN SYSTEM DESIGN 

G WE NEED GOOD SUMMARIES 

3 WE NEED MAJOR EFFORTS TO SIYPLY EXPLAIN OUR RESULTS 

COMPARISON OF PREDICTED AND Ai.lUAL PERFORMANCE IS ESSENTIAL TO SYSTEMS 

DEVELOPMENT ASSESSMENTS 

o SIMPLE MODELS PROVIDE AXURATE PREDICTIONS 

o IFiPUT DATA -- ESPECIALLY INSOLATION DOMINATE .IODELS 

DATA MONITORINC AT 15 MlNUlE INTERVALS IS ADEQUATE 

o FOR ENERGY INPUT 

o LOADS (LAST YEAR) 

THERE MAY BE MORE VALUE FOR THE DSG THAN JCST THE ENEIGY IT PqODUCES 

OeM COSTS HAVE BEEN S7/M2/YR, 

THESE HAVE BEEN MAINLY UNSCHEDULED 

INCREASED PCS RELIASILITY, IN PARTICULAR, WILL GREATLY REDUCE lrlIS FIGURE 
PLENARY SESSIONS 

Utility Session Summary 

dPERATIONS 

o PV SYSTEFI OUTPUT SWINGS DU; TO CHANGING CLOUD COVER HAVE HIGH RAW RATES 

o UNDER WORST CASE CONDITIONS POTENTIAL EXISTS FOR EXCEEDING ACE CRITERIA, 

DEPENDENT ON: 

CAPACITY OF PV SYSTEfl REVITIVE TO UTILITY SYSTEM 

TYPE OF GENERATION UTILIZED FOR REGULATION (RAW RATE) 

o SlRLE SOLUTIONS AVAILABLE: 

NEATHER FORECAST; ?G 

LESS DENSE ARRAY FIELD 

GEOGRAPHIC DISPERSION 

KTER REGULATIHG GENERATION 

o PROGRAn BEING DOCUENTED FOR GENERAL UTILITY USE 

T&D IMP@CTS 

G ARENP OF :.-. . CONCERtL PRiFE XINTS OF INTEREST: 

SAFETY - NP RUN-ON OR ISLANDING 

FAULTS PROTECTION - N3 RlJh-ON, NO EFFECT ON CL~RDINATION 

MAGNITUDE AND EFFECT OF REVERSE POWER FLOW 

o HI\WrG'CS 

VERY THOROUGH DATA GATHERED AT ONE LOCATION INDICATES THAT 

HARllONIC INJECTION FRM ADVANCED PCU'S IS "IN THE N3ISE" 

MAGNITUDES SIMILAR TO ComOti HOdSEHOLD DEVICES 

AAGNITUDES SIGNIFICANTLY LESS THAN WINDOW AIR CONDITIONER 

WORK BY X RES URG TO CONTINUE AT VARYING LOCATIONS: 

AMBIENT LEVELS 

HARMON IC I WEDANCES 

PROPAGATION RECHANRB 

GENERALIZE WORK AND APPLY CORTER ANALYSIS 

o UTILITY CONTRACTS 

CONFIRtl UTILITY ACCEPTANCE OF ADVANCED Pid'S 

UT!L!TY INTERFACE ASPECTS 

ISIANDING POTENTIAL 

PROVIDE DIRECTION FOR FUTURE U-1 NORK 

74 
PLENARY SESSIONS 

PCS Session Summary 

SHALL PCS MWLOMNT STATUS 

o SEVERAL ADVANCED PERFONCE UNITS ARE COMFRCIALLY 

AVAl LABLE 

o EXCEI.LEHT PERFOMNCE UNDER DETAILED EXAnlNATlONS AND 

FIELD TESTS 

o PRESENT COSTS ARE -Sl.OO/W WITH QUANTITY PROJECTIONS 

AT $.35/W 

PCS ENGINEERING EVALUATION PRocRAl 

o EVALUATIONS hAVE ACCELERATED THE MS16# EVOLUTION PROCESS 

o OUR !JIIDERSTAND;NG OF UTILITY INTERFACE REQUIREMENTS HAS NATURED 

o NEARLY ALL PERFORRANCE PROBLEMS HAVE BEEN SOLVED BY HINOR CIRCUIT 

CHANGES (BAS I C DE 5 I GN APPROACHES ARE SOUND) 

RERA I N 1 fi JNEEDS 

o A SIflPLIFIED PCS TEST PROCEDURE IS NEEDED FOR THE USER 

o "UTILITY COMPATIBILITY IN GENERAL" SHOULD BE STMPED ON THE 

LNIT NOT NEGOTIATED AT THE SITE 

75 
PLENARY SESSIONS 

LARGE PCS DEVELOPSNT STATUS 

o LOOKING AT DESlM APPROACHES FR# 1-10 N AND 20-200 KW 

o LOOKING FOR VOLUnE EFFECTS AT LOW POWER 

o BENEFITTING FRM OTHER TECHNOLOGY EXPERIENCE FOR HIGH 

POWER (MD, FUEL CELL, BATTERY) 

o POOLING OF RESOURCES OVERCOSS HIGH FRONT-END ENGINEESING 

AND CEVELOPtEhT COSTS 

o FIELDI:IL OF AN ADVANCED s r.H UNIT BY 1986 IS POSSIBLE ~SPIUD?) 

o FUTURE POttNTIAL OF 3-4 TIES COST REDUCTION FRM 

CURRENT COSTS 

Array BOS Session 

INSTALLATION EXPERIENCE 

o SlGtllFICANT COST REDUCTION IN RESIDENTIAL BOS HAS NOT OCCURRED -- 

BUILDING BLOCK APPROACH kILL BE PURSUED 

o BASED ON "LESSONS LEARNED" WITH SNUD PV1 (t160/N2 BOS), BOS COST FOR 

SWD PV2 IS EXPECTED TO BE 190/M2 

o LUG0 FACILITY EXPERIENCED PROBLES WITH AVAllABILIPl OF DC SWITCHGEAR, 

BYPASS DIODE FAILURES, AtlD LARGE NEUTRAL CURRENTS 

o BUILDING BLOCK DESIGN RESULTED IN BOS COST REDUCTION FOR CONCENTRATOR 

ARRAY FIELD 

- BASED ON BUILDING BLOCK APPROACH, 1 N SIZE TURNKEY SYSTE! IS 

OFFERED AT PRICE OF 17,01)/'k, 

o ROOF-llOUNTED ARRAYS OFFER SEVERAL DIFFERENT AND POSSIBLY COSTLY 

BOS REQUIREENTS 

76 
PLENARY SESSIONS 

FIELD DESIGN 

o INCORPORATION OF BYPASS DIODES MY BE A SIGNIFICANT COST DRIVER -- 

STUDIES ARE NEEDED TO ESTABLISH COST EFFECTIVENESS 

o HIGH VOLTAGE CIRCUITS DO NOT OFFER ANY NEAR TEM COST ADVANTAGES -- 

LOU VOLTAGE DESIGN WOO VDc) WILL BE PURSUED FOR LARGE FIELDS 

o XTORY PROCURED PANEL ASSEFlBLlES MY OFFER AN EFFECTIVE APPROACH 

TO REDUCING INTEWDULE CONNECTION AND DIODE PROTECTION CESTS 

o PROJECTtD COS COST FOR 100 f4U NODULAR FLAT PLATE FIELD IS t52/$ 

o INTER11 GROUNDItiG PRACTICES MNUAL FOR LARGE SIZE PV FIELDS HAS 

BEEN PUBLISHED 

Remaining Issues for Large-System Development 

KEY SANDIA PROJECTS 

ARRAY FIELD DEVELOPENT - HAL POST 

PCS DEVELOPNNT - TM KEY 

What Is the Best Strategy for Electrical Protection? 

LAST YEAR'S ISSUES ANWRS 

A, GROUHDING - UHICH FWTHOD IS HOST FOR SASONABLE FAILURE RATES, NO 

REAL ECWMIC DRIVERS. SOLID 

GROONb SLIGHTLY FAVORED OVER 

RFSISTANCF fiRflIINfl 

B. FAULT PROTECTION - WHAT STRAlEGY SOURCE CIRCUIT LML 

C. MINTENANCE DEPENDENT ON FAILURE TYPE, BUT AT 

LOU FAILURE RATES, SUIEWLE FIX UPOW 

NEED (NO REGULAR SCHEDULE REQUIRED) 

PRESENT ISSUE 

DIODING - COST vs BENEFIT - CURRENT ESTIMTES ARE 

GREATER THAN UO/M WITH 1 BYPASS D!ODE/SERIES BLOCK 

(ANCWLY EXISTS BETWEEN ESTIMATE AND CURRENT FIELD 

COST TO MFACTURER FOR INSTAUATION) 

77 
PLENARY SESSIONS 

What Is the Best System Design? 

DO NOT HAVE OPTINIZED DESIGNS FOR ONE-AXIS AND 

2-AXIS TRACKING FIAT PUT€ 

RFP ISSUED FOR OPTIPIIZED DESIGNS 

What Should We Pursue in PCS Development? 

LAST YEAR'S ISSUES FWiERS -

B. VOLTAGE 400-500 VDC 400-500 V 

(DIPOLAR) ttlONOPOIA8! 

4 EXISTING CONTRACTS 

FOR INNOVATIVE DESIGNS 

PRE ;ENT ISSUE 

VOLUME ADVANTAGE VS SIZE ADVANTAGE 

COMPLEMENTARY TECHNOLOGY DEVELOPYENT 

Residential Status 

BECAiiSE A URGE AmlUNT OF DATA HAS BEEN COLLECTED FOR RESIDENTIAL 

PV SYSTEE, SUPPORT NEEDED FOR THE RESIDENTIAL PROGkM HAS 

DECREASED. HOWEVER, THERE ARE MNY UNRESOLVEO ISSUES UHICH ARE 

THE BASIS F3R THE CONTINliED RESIDENTiAL PRNM, 

78 
PLENARY SESSIONS 

Issues Remaining for Residential PV S {stems 

1. INSTALLATION COSTS - FY)DULAR APPROACH MY SOLVE 

2, RELIABILITY AND SAFETY 

3. COST EFFECTIVENESS 

4. EDUCATION 

The Residential Program 

SMLL PCS TESTINC AT SNLA 

UTILlTY TESTING OF WLL PCS AT RES'S 

mlWUR BUILDING BLOCK RFQ 

FU\MMABILITY/SAFETY TESTING AT JPL 

RES TESTING OF NEW TECHNOLOGY FY)DU?ES + PCS 

79 

PLENARY SESSIONS 

SOURCE-CIRCUIT DESIGN CONSIDERATIONS 

JET PROPULSION LABORATORY 

C.C. Gonralez 

Agenda Items 

Definition of a source circuit 

Objective of source-circuit design effort 

Methodology for developing source-circuit design options to 

control impact of component failure and mismatch 

Identification of component failure mechanisms and solution 

alternatives 

Example of the use of source-circuit design options 

Current status of source-circuit design effort 

Objective 

To determine cost-optimum circuit design practices that will 

minimize the impact of component problerns on the system 

energy cost 

81 
PLENARY SESSIONS 

Source-Circuit Definition 

u 

SOURCE CIRCUIT: 

3 PARAllEL STRINGS 

6 SERIES BLOCKS 

2 CELLS PER SUBSTRING 

1 DIODE PER SlRlES BLOCK 

Component Problems Influenced by Source-Circuit Design 

Open circuits 

Interconnect fatigue 

Cracked cells 

Short-circuited cells 

Mismatched cells 

Arcs 

Ground fault 

In-circuit 

Hot-spot cell heating 

Shadowed cells 

82 
PLENARY SESSIONS 

Component Problems and Related Issues 

I Componcnt Problem 

Opm circuits: intrrconnmt 

Shrrt4rcuitd eells 

Mitnrtchrd mils 

I GroundCult arcs 

I Incircuit ires 

Hot-spot dl heating 

Shrdawd modules 

Solution Alternatives 

Cell paralleling (parallel cell strings in modules or crossties 

between modules) 

Cell contact redundancy 

Multiple interconnects between cells 

Bypass diodes 

Cell circuit layout 

Frequent cross-strapping 

Ground-fault interrupters 

Resistance ground 

83 
PLENARY SESSIONS 

Solution Alternatives Matrix 

Cell-Paralleling and Cross-Strapping Issues 

Quantify system impact of circuit options 

Quantify system impact of failure levels 

Define cost-effective circuit 

Define allowable failure levels 

84 
PLENARY SESSIONS 

Array Power Loss 

1.0 

8 PARALLEL STRINGS A 

2 0.1 

0 

E 

bV 

U 

v) 

v) 3 0.01 

0. oat1 

0.0031 0.001 0.01 0.1 1.0 

Fsss SUBSTRING FAILURE DENSITY 

85 
PLENARY SESSIONS 

cells 

Per 

Substring 

Fraction of Power Loss After 5 Years 

vs Circuit Redundancy 

Serbs CELLS IN PARALLEL 

Blocks ' 1 4 8 16 I I 

1000 Series Cells 

460-Volt Source Circuit 

One Diode Per Series Block 

20 

10 

5 

2 

Cell Failure Rate = 0.0001 (Own-Circuit) 

Cell Failure Rate = 0.0001 (Short-Circuit)) .- 

<0.001 0.001 0.00, 0.001 

0.015 

a.012 0 051 0.026 0.016 

<0.001 0.001 0.002 0.002 - Optimum 

100 0.005 0.022 0.013 0.008 Design 

< 0.006 0.023 0.015 0.010 ikgion 

<om r.002 0.002 0.002 

0.007 0.004 

<TOG 0.012 0.009 0.006 

a001 I 0.002 0.004 0.0011 Sensitive 

500 0.001 0.004 0.003 0.002 

50 - 0.01 1 -- 0.060 - 0.025 - 

- - - - 

200 0.003 - 0.010 - - 

- - <o.002 C.006 0.007 0.008 

Top Line: ShortXireuit Failure 

Mid Line: OpmXircuit failure 

Bottom Line: lotel 

n 

1000 Series Cells 

450-Volt Source Circuit 

One Diode Per Series Block 

Cell Failure Rate = 0.0001 (Open-Circuit1 

I Cell Failure Rate = 0.001 (Short-Circuit) [ !- 

sonsitire 

Design Roglon Mid Linr: Opn-Circuit frilosr 

Bettom Linc Totel 

86 
PLENARY SESSIONS 

Analysis Results 

Optimum circuit design strategy for central stations: 

8-1 6 (or more) parallel strings; cross ties no more 

frequentfy than every 6 cells, and a bypass diode every 

15-1 8 cells 

Allowable failure levels: 

Open circuits -- 1 I1 0,000 per year 

Short circuits -- S /10,000 per year 

Comparison of Strategies 

Strategy 

A. Increased use 

of parallel 

strings 

E. Increased u5e 

of cross ties 

C. Use of bypass 

diodes 

Advantages 

1. Redundant current paths 

in case of open circuits 

2. Reduces mismatch 

losses when cell 

mismatch occurs 

1. Redundant current paths 

in case of open circuits 

2. Reduces mismatch 

losses when cell 

mismatch occurs 

1. Reduces power loss due 

to open circuits 

2. Reduces hotsspot 

heating problems 

3. Reduces risk of incircuit arcing 

Disadvantages 

1. Increased loss of power 

in case of diode turneon 

2. Increased risk of 

current imbalance 

during back-biasing 

3. Increased loss of power 

due to cell shortcircuiting 

1. Increased risk of 

current imbalance and 

hotsspot heating 

2. Increased loss of power 

due to cell shortCircuiting 

87 
PLENARY SESSIONS 

Cost.Effective Ciicuit Phsnomsnr I Problem Srstem Impact so,utionr 

Level Ourntified Derived Understood I Understood Circuit Defined Cot!iponent Problem 

Statuc Summary: Component Problems and Related Issues 

Ccrr’Effective 

fai’ure Level 

Defined 

Mirmrtched cwlls ioi6-b id@ iQ I 

Key Remaining Issues 

Shorted cells 

Quantify field failure level 

Mismatched cells 

Improve model of failure impact on system 

Ground-fault arcs 

Quantify field fai,clre level using prototype 

detector circuits 

Hot-spot cell heating 

Quantify current imbalance problom 

Improve qtdification test 

88 
CENTRAL-STATION ARRAY DURABILITY 

CONSIDERATIONS 

JET PROPULSION LABORATORY 

G.R. Mon 

R.G. Ross, Jr. 

0 bjective 

To achieve the technology base 

for 30-year array life 

Acceptable power degradation rates 

0 Acceptable component failure rates 

0 Acceptable maintenance costs 

Durability and Reliability Research Elements 

0 Establishment of durability goals 

0 Identification of key degradation mechanisms 

0 Qualitative understanding of mechanism physics 

Governing materials parameters 

Governing environmental-stress parameters 

0 Quantification of parameter dependencies 

0 Development of accelerated tests 

0 Degradation prediction models 

Mechanism degradation predidon 

System cost-energy impact anafvsis 

Identification of cost-effective solutions 

Materials of construction 

Component design features 

Circuit redundancy and reliability features 

89 , 
PLENARY SESSIONS 

I 

fixed Drop Soiling 

in Power 1 Mismatch 

Strawman Degradation Allocations: 

30-Year-Life Advanced Technology 

3% 1% I 

Cype of 

Degradation 

Constant 

O&M 

Mechanism 

Alloca tion I Specific 

Mechanism 

Voltage breakdown 0.llmilelyeart 

Glass breakage 0.002 per yeart 

Mod. open circuits 0.002 per yeart 

- 

Constant 

Degradation 

Rate 

~~ 

Cell open circuit 

Cell corrosion 

Yel!owing 

0.00001 per year 

0.2% per year 

0.2% per year 

Key Failure Modes and Mechanisms 

Electrical interconnect breakage 

Thermal cycling, wind loading 

0 Solar cell cracking 

Thermal cycling, hail impact 

0 Encapsulant delamination 

Thermal cycling, humidity, UV 

0 Encap julant physical degradation 

Temperature, humidity, UV 

Cell metallization deterioration 

Temperature, humidity. voltage 

0 Electrical insulation breakdown 

0 Optical surface soiling 

90 
PLENARY SESSIONS 

Key Durabiiity !ssues 

MECHANISM 

INTERCONNECT 

FATIGUE 

HAIL-IMPAC1 DAMAGE 

__ 

PARAMETER 

DEPENDENCIES 

QUANTIFIED 

CELL CRACKING 

i 

I 

ENCAPSULANT 

DELAMINATION 

ENCAPSULANT PHYSICAL 

DEGRADATION 

CELL GALVANIC 

CORROSION 

ELECTROCHEMICAL 

CORROSION 

ELECTRICAL INSULATION 

BREAKDOWN 

SOiLlNG I 

~~ ~ 

IIUALIFICATION 

TEST 

AVAILABLE 

LIFE 

PREOICTION 

CAPABILITY 

COST-EFFECTIVE 

SOLUTIONS 

DEFINE0 

Fatigue Information: OFHC Copper 

, 1 I Ili I I I 1 

’ HO 1 YR 5 YR 10 VR 20 YR 

owl- 100 10’ 103 10‘ 10’ 1 6 

91 
PLENARY SESSIONS 

Statistical Fatigue Curves for OFHC 1 /4-Hard Copper 

1 

i 

THERMAL CYCLE TEST DESIGN 

oo -~ - ~ . . . - . _C___-__-_.l_-T- -.---- 

PModule Interconnect Design Procedures 

ATENOOF - , DESIGN LiFt 

92 
PLENARY SESSIONS 

ae 

I-- 

z 

5 rx 

C' 

7 

Iv3 

0 

u 

cl 

U 

w 

- 

* 10: 

E 

w 

A 

u * 

cz 

uLy 

-I 

Percentage of Life-Cycle Energy Cost Increment 

Due to Doubly Redundant Interconnects 

c i 16 CuI68 SS116 Cu 

33 Cui33 INV133 Cu i 

I 1 12.5 Cui75 INV112.5 CuI I 1 I I I 

93 
PLENARY SESSIONS 

Parameter Oualif ication life 

Mechanism Dependencies Test Prediction 

Ouantified Available Capability 

0 0 0 

Interconnect 

Fatigue 

Hail Impact Damage 0 0 0 

Durability Research Status 

Cost Effective 

Solutions 

Defined 

0 

0 

0 0 I Encapsulant Physical 

t- Co .rosion 

Deg*.adation 

Cel, Galvanic 0 0 

I I Cell Cracking I 01 0 1.1 0 

0 

0 

flectrical Insulation 

breakdown 0 

0 

~~ ~ 

Elsctrochemical C irrosion I I @ rpC-lppQ 1 

3 Q 

0 I e 0 

Key Remaining Issues 

0 Electrical insulation breakdown 

Understand degradation process under bias-temperaturehumidity stressing 

Develop cost-effective design criteria 

0 Electrochemical corrosion 

Develop qualification test 

Develop cost-effective design criteria 

0 Encapsulant delamination 

Understand mechanism involved in breakdown of chemical 

bonding 

Develop experimental method to monitor interfacial 

debonding 

Develop model of physical degradation 

Develop accelerated tests, qualification tests 

0 Soiling 

Understand longevity of surface coatings 

Development of optimal performance coatings 

0 Encapsulant physical degradation 

94 
PLENARY SESSIONS 

High Operating Temperatures ~- ~ 

Major Reliability Problems 

II 

A A 

11 

ram--- 

A 

ap 

Bond Delamination 

Interconnect Fatigue 

Metallization Corrosion 

Electrochemical Corrosion 

Photothermal Degradation 

Structural Failure 

Hail-Impact Damage 

Glass Breakage 

Cell Cracking 

Voltage Braakdown 

Hot-Spot Heating 

Excessive Soiling 

Module Arcs and Fires 

Problem Area 

- 81 

L 

L 

A 

J 

T I 

1 

Reliability & Durability Developments: 1975 to 1984 

Technology 

Bond Delamination 

Interconnect Fatigue 

Galvanic Corrosion 

Electrochemical Corrosion 

Photothermal Degradation 

Structural Failure 

Hail Impact 

Glass Breakage 

Cell Fracture Mechanics 

Voltage Breakdown 

Hat-Spot Heating 

Soiling 

95 

PLENARY SESSIONS 

OPERATIONS AND MAINTENANCE 

JET PROPULSION LABORATORY 

P.K. Henry 

Summary of O&M Issues From 

Central-Station Research Forum 

Allowable O&M cost 

Various studies estimate O&M costs at $2.00/m2-yr to $2.50/m2-yr 

DOE Five-Year Research Plan assumes $2.28/m2-yr O&M costs 

Recommendation to change Research Plan O&M costs to 

$1.1 O/rnz-yr (fixed-array) and $1.40/m2-yr (tracking array) 

Array O&M strategy 

Design array to be fault-tolerant 

Array design should include some fault locating equipment 

Array design should provide for easy component replacement 

Replace modules only if necessary for safety, equipment protestion 

or overall array performance adversely affected 

Determination of failure modes, rates and O&M costs 

Failure mechanisms and failure rates of array components not yet 

well understood 

Recently installed large arrays will yield much more relevant 

O&M data than small experimental arrays 

O&M costs are not likely to be a large contributor to bus-bar 

energy costs 

97 
PLENARY SESSIONS 

EC 

FCR 

CF 

INDC 

G 

Program Goals and Economic Assumptions 

(Value Recommended for 1 -Axis Tracking) 

Levelized Electricity Cost Equation from Program Plan: 

levelized electricity cost in 

current dollars SD.15IkWh 

fixed charge rate 0.153 

general infletion rrte 0.085 

discount rate 0.1 25 

ennuel system capacity 

factor (1.axis tracking) 0.308 

indirect cost multiplier 1.50 

present worth factor based 

on a 12.5% discount rate 

and 30-year lifetime 18 

CRF 

SMSQBS 

SKWBS 

$MSQOM 

capital recovery factor for a 

12.5% discount rate end 30- 

year lifetime 

average peak isolation 

belance.of.system efficiency 

module efficiency 

BOS area.related cost 

BOS powerrelated costs 

annual O&M costs 

0.1 29 

l.OkWlmi 

0.865 

10% to 25% 

60.90 $Id 

$1 501kW 

$1.401rn*year 

(tracking array) 

98 
TECHNICAL ISSUES OF HIGH-EFFICIENCY 

SILICON SOLAR CELLS 

JET PROPULSION LABORATORY 

K.M. Koliwad 

Department of Energy Goal 

'THE FNE YEAR GOAL OF FLAT PLATE COLLECTOR RESEARCH 

IS TO ESTABUW THE TECHNOLOIGIES BY 1988 WHICH 

INDUSTRY CAN APPLY TO THE PRODUCTION OF 15% 

EFFICENT CRYSTALLINE SILICON MODULES... 88 

introduction 

h1I)DULE EFFICIENCY OF 15% (NOCT) REQUIRES SOLAR CELLS OF ECFICIENCIES 

IN THE RANGE OF 18% TO 2D% (AMI. 5 ) 

ATTAIIJhENT OF SUCH LEVELS OF SOLAR CELL EFFICIENCIES USING LARGE 

4REA AhD LOW-COST SILICON SHEET IS BEYOND THE STATE-OF-THE-ART 

IKADEQUATE QUALITY OF THE LOW-COST SILICON SHEETS AND THE INHERENT 

L 1P;ilTATIONS OF THE STATE-OF-THE-ART CELL STRUCTURES ARE THE 

PRIMARY BARRIERS 

EXTENSIVE RESEARCH IS REQUIRED TOWARDS IMPROVING THE QUALITY OF 

THE LOW-COST SILICON SHEET AND EX.TENDING THE UNDERSTANDING OF 

DEVICE PHYSICS, DESIGN AND PROCESSING 

99 
F LE N AR Y S E S S ION S 

Efficiency Limits 

BASED ON FUNDAMENTAL PHYSICAL MECHANISMS THE ABSOLUTE EFFICIENCY LIMIT 

FOR SILICON SOLAR CELLS IS ABOVE 30% 

THE BEST EFFICIENCY REPORTED TO-DATE IS 19% (AM11 

FLOAT-ZONE SILICON SHEET 

2 cm x 2 cm CELL AREA 

MlNP CELL STRUCTURE USING TUNNLING CONTACTS 

THE BEST EFFICIENCY ACHIEVED TO-DATE ON LOW-COST SILICON SHEET IS 16% 

(AM1 1 

DENDRITIC WEB RIBBON 

2 cm x 2 cm CELL AREA 

NtPPt CELL STRUCTURE 

CARRIER PECOMBINATION LOSSES WITHIN THE BULK AND AT SURFACES OF THE 

CELL LARGELY ACCOUr - FOR THE DIFFERENCE 

100 
PLENARY SESSIONS 

Primary Causes of Losses 

1. LIGHT GENRATED CURXNJ: 

CONVERS ION EFFl C If NCY 20% 

A. 

6. 

C. 

D. 

E. 

iin 

OPTICAL SURFACE PROPERTIES (REFLECTION J 

c o NTAC T c 0 VE K A I;E 

INCOMPLETE ABSORPTION (Tc!ICKt:ESS J 

RECOMBINA'i ION OUTSIDE DEPLETION REGION 

(BULK AND SURFACE, INCLUPING COMACTS J 

("DEAD LAYERS" J 

I. LIGHT GENRAED CURfENT 

I FUNDAMENTAL LIMIT IAMlI 

>, OPTICAL SURFACE PROPERTIES IREFLECTIONJ 

E. LZVTACT COMRACE 

C. INCOM?FX ABSORPTION ITHICKNfSSI 

0. RECOh\BINAii?N OUTSIDE DEPLETION REGION 

INCLUDING COMACTS I 

E. V'DEAD LAKRS" 1 

lEULK AND SURFkCc 1 

- 

I OVERALL COLL~CTIONCFF~~~~NCV 

I LIGHT GENRATED CUGRENT IAkil; 1 

2. OPEN CIRCUIT VOLTAGE: 

A. RECOMBINATIOM OUTSIDE DEPLETION REGION 

(BULK ANG SURFACE, INCLUDING CONTACTS 1 

B. BANDGAP NARROWING 

C. "CURRENT LEAKAGE" 

44 mA cm-2 

0. 91 

0. 966 0.97 

0.92 

IO 

0 86 0. 81 

0.95 I to. op 1 

o"8 I iDlSTRlEUTlOhr 

I I ASWNDI 

--- 

37.9 m~ cm-2 35.5 m~ cm-2 

3. FILL FACTOR: 

SAME AS OPEN CIRCUIT VOLTAGE :: { 

D. 

E. SERIES RESISTANCE 

RECOMB I NATION IN DEPLETION REGION 

I I 0.836 v 

1 0.60 0. Y 

t. OPfh CIRCUIT VOITAGE 

CUNDAh\ENTAL LlhlJT 

A. RECOh\BINATION OUTSIDE DEPLETION REGION 

IBUCK AND SURFACE. INCLUDING CONTACT5 I 

8. BANDCAP MRROWING 

1.0 I. 0 

-____ , C. "CURRENT LEAKAGE" 

OPEN CIRCUIT VOLTAGE. 0.661 v 0.594 V 

3. FILL FACTOR. 

FU NO AME NTAL t I hl I T - 0.96 

0.84 0.84 i: 

0. RECOMBINATION IN DEPLETION REGION 0.91 0.915 

E. SERIES RESISTANCE 0. 98 0.915 

0.80 0.80 

SAM AS OPfN CIRCUIT VOLTACt 

c. 1 1.0 I. 0 

-----_ __I__-- 

L *-. 

FILL FACTOR 

101 
PLENARY SESSIONS 

10 1 o2 lo3 lo4 lo5 lo6 

SURFACE RECOMBINATION VELOCITY 

s (cm 5-l) 

1 1 I I I I 

10 lod lo-] 

RULK NiINORITY CARRIER LIRllME T (51 

102 
PLENARY SESSIONS 

Research Approaches 

BULK LOSS CONTROL 

HIGH QUALIT" SHEET GROWTH (HIGH T 1 

BULK DEFECT PASSIVATION 

CARRIER LIFETIME MEASUREMNT TECHNIQUES IN HEAVILY DOPED THIN 

LAYERS 

SUPFACE LOSS CONTROL 

FUNDAMENTAL LINDERSTANDING OF THE ORIGIN AND NATURE OF SURFACE/ 

INTERFACE STATES 4ND SURFACE RECOMBINATION MCHANl SMS 

SURFACE RECC:JB I NATION VELOCITY MEASUREMENT TECHNIQUES 

SURFACE PP5SIVATION 

PROCtSS 

HEAVY DOPING EFFECTS 

INNOVATIVE CURRENT COLLECTION DESIGNS. (e.q. TUNNELING COWACTS, 

CHARGEAaLE TR.4NSPARENT CONDUCTING POLYMERS 1 

MODELING 

BETIER PHENOMENA SIMULATION 

PROCESS SENSITIVITY ANALYSIS 

DESIGNS FOR EFRCTIVE LOSS REDUCTION 

Summary 

ACHiEVEMENT OF 20% EFFICIENT LARGE /\REA SOLAR CELLS USING 

LOW-COST SILICON SHEET IS A DIFFICULT TASK AND IT REQUIRES: 

UEvDERSTANDING OF ALL ASPECTS OF CARRIER RECOIV.31NATION 

LOSSES 

INNOVATIVE DESIGNS AND PROCESSES BASED ON SOUND MODELING 

RESEARCH IS SHOWING PROMISING RESULTS 

103 



Technical Sessions 

HIGH-EFFICIENCY 

Reports of research 

SILICON SOLAR CELL RESEARCH 

T. Dad. Chairman 

progress in high-efficiency solar cells and 

characteriz8tion .ad rasurewnts were presented by eight Contractors, SBU, 

and JPL. 

Reu8rcb Triangle Institute reported OQ its comprehensive silicon solarcell computer modeliq. 

vith phenaaoa subrodels have been incorporated and recursion relationships 

!or arPcrica1 analysis have been set up. Both lorlewel 8ad high-level injeciion, with and witbout dipolar transport, an incorporated. 

ectivities including fabrication of solar cells for correlatioa u8s preseated. 

Various single-junction and ultijunctioa structures 

A list of future 

A. llokashi of JPL reported on efficiency estimation and sensitivity 

lodeliq. The one-dknsiolul code developed at Purdue University has been 

de operational at JPL for sensitivity arulysis of cell design paructcrs, to 

campare innovative ad conceptual designs for high efficiency, and identify 

barriers to high efficiency. 

developed at Stanford University h8s also been ude operational 8t JPL. 

capabilities and operation of these progr- were described. 

In addition, a device-processing code (SUPREX) 

The 

A repott on b8rriers to achieving high efficiency vas presented by C.T. 

Various loss mech8nisms and their limiting values were disr than 60 cdrecond and the saturation current mst be 

Sah Associates. 

cussed to show that to achieve greater than 20% efficiency, bulk recombhatioa should be 1 

reduced bel* IOm A/cd. 

New desigm of utter insulator a-p (MINP) were discussed and a new 

structure called a floating emitter cell vas proposed for 20% and higher 

efficiencies . A mo.ecular beam epitaxy (UBE) technique for uking high-efficiency 

silicon solar cells was described by the University of California at Lor 

Angeltss. Grovth apparatus and procedure were explained. Numerical analysis 

of a two-junc, :an, Cascade all-silicon cell was described. 

structures that can be obtained using MBE. 

siugle-j-wtion cells is possible if the minority carrier recombination c8n be 

solve cell leakage is to continue. 

This cell has 

Efficiency higher than that of 

lowered at the tunnel junction to below 10 4 cr/second. Further work to 

The Joint Center for Gt8dU8te Study (JCGS) presented progress in its 

investigation of silicon surface passivation by silicon nitride deposition. 

The p lasma-enhanced CVD system has been made operat ioaal, deposition variables 

have been stvidied, and optical properties of nitride films (Si#) are being 

evaluated toward a good antireflective coating. 

with t:hm Rosier method is being used for Characterization of the 

int e t Lace. 

In addition, a C-V technique 

107 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

R.H. Kachare of JPL discussed the research forum to be held July 9 

Sessions and subjects to be covered were highlighted, 

through 11 at Phoenix, Arizona, titled 'Tligh-Efficiency Crystalline Silicon 

Solar Cells." 

J.B. Milstein of SEbI described the high-efficiency silicon cell program 

at SERI. 

Be reported that H. Green in Australia has sent a cell to SERI for measurement 

that showed 19,07% efficiency, 

strated : igher than 172 efficiency. 

Details of solar cells with 172 and higher efficiencies were given. 

ASEC, Spire and Westinghouse have also demonThe University of Pennsylvania described a measurement technique for 

minority carrier lifetime 

calibrated spectral light-beam induced current (LBIC). 

by a light bear of frequency law enough to penetrate the front region only is 

used with a curve-fitting de1 to extract the information. Results on Spire 

fabricated cells with and without oxide passivation were presented. 

structuredoping profiles with modeling calculations and results were given. 

Minority-carrier lifetime values in regions of the cell during its fabrication 

and data on its degradation during fabrication were obtainable by this technique - 

and surface tecdination velocity s, using 

The current obtained 

BSF 

The University of Florida described the new technique of short-circuit 

current decay (SCCD) for and s measurement in the base region of the cell. 

This technique is based on a two-part analysis of a solar cell using Laplace 

transforms. After the higher-mode transients die out, the first-mode transient in the current of a cell gives the necessary information. Sensitivity 

analysis was presented to show data acquisition with better accuracy. 

L.J. Cheng of JPL presented work on low-temperature electron-beam induced 

current (EBIC) using a scanning electron microscope. Polycrystalline wafers 

show mre electrical activity at lower tempeatures; this gives a more sensitive 

technique for the study of defects in silicon. 

bination with respect to Fermi level were explained. In addition, a stressrelated node1 of web ribbon was presented to relate defects to growth parameters azd thenual profiles. 

Temperature effects on recomCornel1 University described its characterization work on silicon ribbon. 

Thermal annealing and electrical activity of defects were ana1ye.d. 

of carbon in EFG ribbon along with temperature cycling was evaluated. 

X-ray diffraction patterns were analyzed to obtain strain-field-related 

information. Dislocation twin interaction and coalescing of boundaries that 

may form large-angle grain boundaries after thermal treatment was discussed. 

The role 

Various 

Work on impurity analysis using cryogenic laser calorimetry was 

described by the University of Southern California. 

and method were described - 

cussed. 

Spectroscopy apparatus 

Relative advantages and disadvantages were dis108 
HIGH-EFFICIENCY SOLAR-CELL DESIGN MODELING 

RESEARCH TRIANGLE INSTITUTE 

M.F. Lamorte 

Program Goals 

1. oevelopcomprehensl 've computer models to simulate singlejwrction and multiplejunction silicon sdar cell structures shown 

in the matrix: 

2. Incorporate into the computer models the following phenomena 

submodels: 

e 

e 

e 

e 

e 

e 

e 

e 

e 

e 

e 

Effects due to - temperature 

Impurity concentration 

Defect energy levels 

High injection 

Surface states 

Front surface field 

lkck surface field 

Oxide charged insulator 

Carrier confinement 

Bandgap narrowing 

Depletion region recombination 

Surface recombination 

Series resistance 

Metal contact shadowing 

Anti-reflection coatings 

109 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

3. 

4. 

5. 

6. 

7. 

3. 

Fabricate 2 cm x 2 cm n+ p and n+ pp+ near-optimized silicon 

sdar cells 

Fully characterize the cells with respect to V,, b, Pmp vm8 b8 

q, 0 over the temperature range 25O C to 150° C. 

Assess the accuracy of the computer modeling program and 

correct phenomena submodels and/or analysis to obtain better 

than 5% agreement with experimental data. 

Determine and quantify phenomena that gives rise to solar cdl 

losses, through analysis and simulation studies. 

Obtain new cell structures and designs that minimize these 

losses. 

Accomplishments 

1. Formulation of computer simulation using the Recursion 

Relationship Method. 

2. An option may be exercised from the keyboard to use 

the nonambipdar or ambipolar solution. 

In addition to the phenomena submodels listed in Figure 2, the 

following are also incorporated into the simulation program: 

Bandgap narrowing using Fermi-Dirac statistics 

Nonequilibrium np product using Fermi-Dirac statistics 

Built-in and induced electric field components in quasi-neutral 

regions, applicable under low and high injection levels 

Photovdtage effect on depletion width 

Trap level concentration dependency on imourity 

concentration 

Composite electron and hole lifetime relationships that 

include SRH, TAA, and BBA 

Front and back svrface recombination velocities that include 

SRH, TAA, and BBA 

Electron and hole mobilities and diffusivities that are valid 

under low and high injection levels, and in nondegenerate 

and degenerate materials 

110 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

e 

e 

e 

e 

e 

e 

e 

e 

0 

e 

e 

e 

0 

0 

Recursion Relationship Method Formulation 

hmrporates a comprehensive set of phenomena submodels and 

Capability 

Combines low CPU costs of closed-form methods with high 

simulation accuracy of numerical integration methods 

Discretized into f-mesh points 

Transport equations constructed to contain a comprehensive set 

of phenomena submodels 

Appropriate transport equations applied to each mesh point 

Mesh point separations are reduced so that some coefficients in 

the continuity equationM may be considered constant at its 

mesh point 

Closed-form analytical solutions are obtained at positions 

midway between mesh points 

Value of the dependent variable at adjacent mesh points is 

governed by the analytical solution obtained in the region 

between the mesh points 

Recursion Relationship Method Execution 

f-analytical solutions are obtained which contain 2f-constants of 

integration 

Apply the 2f-boundary conditions that are appropriate to the 

field of f-mesh points 

2f-simultaneous equations result 

2f-constants of integration are solved for explicitly, and 

recursion relationships are shown to exist 

Behavior of dependent variable and derived parameters may be 

determined because the numerical value of the 2f-constants of 

integration are known 

Method is applicable to the temporal analysis in 3-dimensions 

(xO y0 z0 t, 

111 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Comparison of Numerical Integration 

and Recursion Relationship Methods 

Future Activities 

1. Complete the application of the Recursion Relationship Method 

to silicon solar cell structures and obtain the recursion relationship. 

2. Complete computer code for all phenomena submodels and 

recursion relationships. 

3. Incorporate erfc and Gaussian impurity concentration profiles, as 

well as provisions for arbitrary profiles. 

4. Debug computer program. 

5. Fabricate and characterize n+p and n+pp+ solar cells. 

6. Simulate fabricated cell structures and assess simulation accuracy and, if necessary, verify accuracy of phenomena submodels 

with experimental data. 

7. Commence simulation studies. 

112 
-4 e- N85 15263 

EFFlC l EN CY EST1 MATIO N AN D 

SENSITIVITY MODELING 

JET PROPULSION LABORATORY 

A.R. Mokashi 

Presentation 

0 bjective 

DEvnop AN EXHAUSTIVE AND cowEENsNE ANALYTICAL TOOL FOR EVALUATING lWE P€RFORMANCE OF A CRYSTAUPE SILICON SOLAR CELl OF A GIVEN OESIGN 

o COMDEF? CEU. PROCESS PARAMETERS AS NUT DATA 

o WOCZM SPIS~TTY ANALYSIS OF CELL mrcw 

PARAMETERS 

0 WAR€ NJOVATIVE AND CONCEPTUAL OESIGNS FOR 

AcHlEvpJG HIGH EFFICIENCY (MAFi 20%) 

o USEASANAIDINIDP(TIFYINGP~ERSUMIM 

CELL EFFICIENCY BELOW 20% 

113 
H IG H-EFFIC I EN CY SI Ll CON SOLAR CELL RESEARCH 

Approach 

SEARCH LITERATURE AND EXPLORE AVAILABILITY OF STATE-OF-THE-ART MODELS 

WHICH ARE APPLICABLE AND USEFUL 

ACQUIW COPES OF USEFUL MODELS 

DEVELOP A SCHEME INCORPORATING THESE MODELS 

. IMPROVEMENTS 

MODIFICATIONS 

ADD ITIONS 

i 14 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Available Models 

SOUR CEU SMUUTKIEI MODELS SCAPI0 AND SCAPZD 

0 OR. REWRD SCWARIZ AND HIS TEAM (PURDE UNNERSIM 

0 ONE OYHENSWLAND NO DB4ENSIWLCCMPUIEii COMS TO SIUUlE CONMNTIONALAND CONCENTRATOR CEUS 

0 SCAPID IS CONSIDERED SUITABLE FOR SEEMA FOR ANALYSINC CELLS USED IN 

FIATPLATE COLLECTORS 

0 A C.'PY OF SCAPID IS OBTAINED FROM PURDUE UNIMRSIM 

SCAPID IS FUNCTIONAL AT JPL 

115 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

SCAP1 D 

116 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Flow Diagram for Equilibrium Solution 

Flow Diagram for Non-Equilibrium Solution 

117 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Computer Time 

Problem Summary: Sample Run Made During the Visit 

118 
HIGH-EFFICIENCY SILICOFI S9LAR CELL RESEARCH 

Current Variation Across Cell Thickness 

During Maximum Power Point Conditions 

t- ._.....__._._________ _._t__.__.___._.__ .._.._ c -: 

. .= I- no .- 

119 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Recombination Variation Across Cell Thickness 

During Maximum Power Point Conditions 

120 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

SUPREM II (Version 0.05) 

0 SIMUUlES THE PROCESSHG W SIUCON SEMICONDUCTOR DEVICES 

0MOSTCWONLY USED PROCESSHG SlEPS ARE HANDED BY M PROGRAM 

0 HIGH NHRRAW -DIFFUSION UNDER BOTH'MRT AND OXIDIZING AMBENTS 

GAS SOURCE PllEOEPOSmON 

0 KIN YHPUNTATMN 

EPITAXIAL GRWH 

0 ETCHING AND 

0 oEposmoFI w DORD AND WORD SIUCON DIOXIDE 

0 NIMRICAL SOLUTK#J OF THE DIFFUSION UP TO FOUR IMPURITIES IS IMPEMNTED WHICH 

INCLWES HIGH CONCENTRATION AND OED EFRCTS 

0 OXIDATION OF SlUCON IS MODELED ACCORDING TO DEALCROVE EQUATION, MODIFED 

TO ACCOUNT FOR 

HIGH PRESSURE CONDITIONS AND 

0 HIGH MPURlTY CONCENTRATIONS AT THE OXIDIZING INTERFACE 

0 OUrPUT OF RESULTING IMPURITY DlSTRlBUTlONS IS 

PRINIED OR PLOTTED 

INFORMATION OBTAINED INCLUDE 

0 JUNCnON DEPTHS, 

THRSHOU) VOLTAGES 

SHEET RESlTlVITES AND 

121 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

SUFREM 111 

0 ONE DIMENSIONAL SIMULATION PROGRAM WHICH MODELS MANY INTEGRATED CIRCUIT 

FABR ICAT ION PROCESSES 

CALCULATES SELECTED ELECTRICAL CHARACTER ISTICS FROM S IMUIATED DEVICE STRUCTURE 

AND IMPURITY DISTRIBUTIONS 

0 VARIETY OF DEVICE STRUCTURES MAY BE MODELED UP TO FIVE SEPARATE LAYERS ALLOWED 

DEFAULT MATERIALS 

SiLlCUN 

POLYS ILICON 

SILICON DIOXIDE 

SILICON NITRIDE AND 

ALUM I NUM 

0 THE IMPURITIES WHICH MAY BE 

IMPLANTED DIFFUSED OR DEPOS ITED ARE 

APSENIC ANTIMONY PHOSPHORUS AND BORON 

SEEMA 

122 
BARRIERS TO ACHIEVING HIGH EFFICIENCY 

C.T. SAH ASSOCIATES 

C.T. Sah 

RATE EYASUREllENTS BY NEW CAPACITANCE 

TRANSIENT KTHOD AT TI, ZN AND Au: AND 

CONTRACTOR 

NEW CAPACITANCE TRANSIENT ETHOD FOR 

BEEN APPLIED TO MY IffURlTIES, 

CAPTURE RATES AT DOUBLE DONOR TITANIM 

CENTERS AND DOUBLE ACCEPTOR ZINC CENTERS 

OVER WIE TEMPERATURE RANGES COHPLETED, 

INPURITY CENTERS. CAPUTRE RATES AT THE TWO GOLD LEVELS 

COh'UTER-AIDED PREDICTION OF MAXIMUM ARE IN PROGRESS, 

NEW HIGH EFFICIENCY AND NEW VERY HIGH 

VERY HIGH EFFICIEEICY. PRELIMINARY DESIGN CALCULATIONS SHOW 

123 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Paraniaters Characterizing a p/n 

EQUATION 

wrwmr 

qV /kT J = JI - Jl(e J L 1. 

qV /mkT - J,(e J 

1 Junction Solar Cell 

- 1) 

- 1) 

m = 1 + 2 Space Charge Layer 

m=2 High Level QNR's 

m=4 Surface Channel 

m 2 + 4 Resistive Shunts 

m Avoid nonideal recombination 

Maintain low injection levell 

components (THEY GIVE LOW FF, 1 

0.. J, = 0 

J = JL - Jl(e qV J /kT - 1) 

124 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Parameters Affecting the Performance of 

High-Efficiency Silicon Solar Cells 

HIGH EFFICIENCY SILICON cVn JUNCTION 

SOCAR CELL CHARACTERIZATION PAR!HTER 

J = J~ - J~ eqv /kT - 1 

m J' = 32 m~/cm2 at AMI (89 rnw/cm2) 

6 J1 qpBsB t qflESE where: 

BASE (Thin: 

EMITTER (Thin: 

PI 

- 

m FOR A An1 29% CELL 

125 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

VOC FF EFF J1 % ‘B N~~ 

mV x rnA/an cm/s us ~i/cm~ 

650 ,8375 13,88 2,OE-13 128 39 lI7E12 

680 ,8410 20,56 9,4€-14 55 83 6,5Ell 

700 ,8445 2l,26 4.3E-14 27 186 3,6E1! 

720 ,8460 21,90 

LIMITS none * 

Performance and Requirement of 20% 

Silicon BSF p + /n/n + Solar Cells 

126 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Emitter Recombination Limitations 

127 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

BSC VFE SCT 1 3d 

0 

BSC VFE SCT 2 

. 

128 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

129 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

1. Material physics 

G&* * *E* Ti ~&;p,D*e 

N,,(x,t) a%,+ 

*it 

Material Chemistry 

2.Device p 

Device, Design **- - -mu-.** 

3. Fabrication Technology 

4. Ret i 

QWk. * 

I30 
P E85 15265 

MBE GROWTH FOR HIGH-EFFICIENCY 

SILICON SOLAR CELLS 

UNIVERSITY OF CALIFORNIA AT LOS ANGELES 

F. Allen 

PURPOSE: 1. TO UTILIZE THE EXTREME DOPANT PROFILE 

CONTROL POSSIBLE WITH MBE TO GROW 

SILICON SOLAR CELLS OF HIGH EFFICIENCY 

2. TO MODEL BY COMPUTER A CASCADE SILICON 

CELL WITH TWO JUNCTIONS IN SERIES AS A 

MEANS OF GETTING LARGE D.C. VOLTAGE AND 

HIGH EFFICIENCY 

UCLA Silicon MBE System as of 12/13/82 

WARTS 

CRYSTAL 

SAMPLE LOhDING 

PORT I WVlEWPORT I 

131 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Silicon MBE for Solar-Cell Growth 

ADVANTAGES: 

COMPLETE DOPANT CONTROL TO - 108 

ARBITRARY PROFILES 

ABRUPT CHANGES 

FROM 10E13 TO > fOElO~rn-~ n-TYPE (Sb) AND p-TYPE (Gd 

CAN PROVIDE VERY SHALLOW FRONT SURFACE FIELD 

AND VERY DEEP BACK SURFACE FIELD 

CAN GROW TANDEM CELLS CONNECTED BY TUNNELJUNCTIONS 

CURRENT LIMITATIONS : 

0 HIGH REVERSE LEAKAGE AT JUNCTIONS (UCLA) 

LOW GROWTH RATE (3&/sec UCLA) 

0 TOTAL DEPTH OF €PI-LAYER: < 5 r(lCR0NS 

HIGH COST PROCESS-STILL BEING DEVELOPED 

FINE TUNING NEEDED TO GET HIGH'LIFETIME 

UCLA Program Results in Past Year 

1. MBE CELL GROWTH 

0 12 WAFERS GROWN FOR JPL 

0 ONLY 2 OF THESE SURVIVED TO MAKE FINISHED 

CELLS WHICH COULD BE TESTED 

RESULTS: 

0 SIMPLE PROFILE 

0 GROWN BY SOLID PHASE EPITAXY 

0 PROCESSED AT JPL 

SAMPLE 

I6 +lo9 +110 -10 

-1 

---- Vodv) 0.46 0.49 

Jac(mA/cm') 14.6 13.8 

FF 0.71 0.7 1 

9% 4.7 4.8 

ANNEALED IN H, AT 75OOC FOR 1 HOUR 

132 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Problems in MBE Growth Thus Far 

1. HIGH REVERSE CURRENT AT JUNCTIONS 

PROBABLE CAUSES: 

*IMPURITIES: SlMS SHOWS C, Mo, Cu 

DISLOCATIONS: DEPEND UPON ATOMICALLY CLEAN 

SUBSTRATE BEFORE GROWTH 

RFMEDIES 

1. IDENTIFY IMPURITIES AND ELIMINATE THEM 

BELL LABS RESULTS ,(J.C. BEAN) SHOW re -30 uSEC 

AT JUNCTIONS ARE POSSIBLE 

(IN 5 X Id5 7sr)ATIRfAi.) 

133 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Higher q Possible With Cascade Cell 

MODEL: ONE SHALLOW JUNCTION NEAR SURFACE 

SECOND DEEP JUNCTION BENEATH FIRST 

FIRST JUNCTION p-DOPING HIGH 

SECOND JUNCTION p-DOPING LOWER 

FRONT AND BACK SURFACE FIELDS 

(NOT PENETRATING YET) 

IDEA: HIGH ENERGY PHOTONS PRODUCE HALF OF ALL 

PAIRS IN 1st 2.5 MICRONS 

THESE ARE MOST EFFICIENTLY COLLECTED 

IN SHALLOW (2 MICRON) JUNCTION 

REST OF LOWER ENERGY PHOTONS PRODUCE 

PAIRS DEEP IN SAMPLE, COLLECTED BY 

DEEP JUNCTION 

134 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Fraction Generated versus Depth 

CELL 

0 20 

TUNNEL JUNCTION 

1 

vo 60 eo 100 

DEPTH IMICRONS: 

CELL 2 

r CELL 1 CELL 2 

135 
H IG H -E FFlC i E NCY SI Ll CON SOLAR CELL R ES E ARC H 

Parameters for Calculations 

0.1 5X10E17 

b.? 9X 1 OE 16 

* 1.5X 1OE 16 

3 4.5X 10E15 

10 1.25XlOE15 

10.9 

19 

27 

31 

36 

52.2 2.5 

105 6 

164 10 

193 12 

232 15 

NA = 10E2Ocm-3 

W" 

(JJ 

0.05 

0.12 

0.28 

0.47 

0.93 

rp = 0.49s 

S's ON OUTER SURFACES = 10E4 cmla 

S'S AT TUNNEL JUNCTION= 0 

WIDTH OF n+LAYERS = 0.2 y 

136 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

UCLA Program Results in Past Year 

2. COMPUTER MODELLING OF CASCADE CELL IN SILICON 

(P. SPARKS) 

*REASONS FOR INVESTIGATING 

.UP TO TWICE Voc POSSIBLE 

SLIGHTLY HIGHF!? Ti POSSIBLE 

.COULD GHOW BY MBE-USE TUNNEL 

JUNCTION TO CONNECT CELLS IN SERIES 

Efficiency of 100 pm Si Solar 

1e.s 

18.0 

17.5 

H 

>. 

V 

Y 

2 17.0 

i W 

b 

Cells 

CASCMU CELLS 

SINGLE CELL' 

lS.04, , , 1 

0.1 0.3 1 3 10 

RESISTIVITY OF REAR BASE (ohm-cm) 

(FRONT BASE P = 0.1 ohm-cm) 

137 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Other Progress With UCLA MBE Process 

1. DEMONSTRATED POWER OF SOLID PHASE EPITAXY 

DEPOSIT AMORPHOUS SILICON ON CLEAN SUBSTRATE AT ROOM TEMP. 

WITH DOPANTS AS DESIRED 

@REGROW IN SITU AT S7OoC 

RESULTS: 

GOOD (BULK) MOBILITY 

0 GOOD CRYSTAL OUALITY 

0 No AND NA LEVELS UP TO > 1 OE 18 cfri3 FOR 

FIRST TIME : TUNNEL mor 6s NOW POSSIBLE 

NO DOPANT SMEARING n+ P+ n+ 

li iiir 0 GREW FIRST TRIANGULAR BARRIER 

DIODES IN SILICON WHICH WORKED -I I- 50 A 

Future Effort of UCLA Group 

DEMONSTRATE AND EVALUATE TUNNEL JUNCTION 

NEE LD FOR TANDEM CELL. 

(APPEARS TO HAVE NO PROBLEMS-DOESN'T 

DEPEND ON HlQH QUALITY CRYSTAL 

AT JUNCTION-NEEDS ONLY ABRUPT n++-p++ TMNSITION) 

*DEMONSTRATE A CASCADE CELL USING SUCH A TUNNEL 

JUNCTION WITH Voc HIGHER THAN POSSIBLE WITH 

A SINGLE CELL. 

CONTINUE TO WORK TO ELIMINATE IMPURITY CAUSING 

LEAKAGE PROBLEM. 

138 
INVESTIGATION OF SILICON SURFACE PASSIVATION 

BY SILICON NITRIDE DEPOSITION 

UhlVERSITY OF WASHINGTON 

L.C. Olsen 

Other Contributors 

DR. BILL ADDIS 

DR. WES MILLER 

GLEN DUNHAM 

ERIC EICHELBERGER 

DAN DOYLE 

Objectives and Approach 

0 WECTIVES 

TO EVALUATE THE USE OF SILICON NITRIDE DEPOSITED BY 

SURFACES. 

PLASMA-ENHANCED CVD FOR PASSIVATI3N OF SILICON 

APfWOACH 

TASK 1 - SIN FILM GROWI'H BY PECVD 

ESTABLISH PECVD SYSTEM 

DEVELOP PROCEDbRa:S FOR SiN FILM GROWTH 

TASK 2 - FILM CHARACTERIZATION 

OPTICAL CONSTANTS 

PHOTON TRANSMISSION AND PHOTOCLJRRENT AYALYSIS 

TASK 3 - CHARACTERIZATION OF SiN/Si INTERFACE AND 

IMPACT ON SOLAR CELL PERFORM4NCE 

INTERFACE STATE DENSITY AND FIXED CHARGE 

SURFACE RECOMBJNATION VELOCITY FROM ROSIER METHOD AND 

THEORETICAL STUDIFS CONCERNING SOLAR CELL PERFORMANCE 

PHOTORESPONSE ON SILICON CELLS 

139 


HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

SiN Deposition Variables 

GAS FLOW RATES 

NH3/SiHI GAS FLOW RATIO 

PLATEN TEMPERATURE 

RF POWER 

' CHAMBER PRESSURE 

Measurement of lndes of Refraction 

3f SiN Films on Silicon 

MEASURE R VS A 

VALUES OF NI VS i AND K, VS. I ARE KNOWN 

ASSUME Kt - 0 IPARTCULARLV COOD APPROXIMAnON 

FOR A >SO0 nml 

Df3E-E d AND N. VS. A 

olrton -- 

TIM. a..m, K. Q ,,, -*ssum N. I CONSTANT OVER 30 nm RANGE FOR 

A -400 nm AN0 DETERMW d FROM R VS A DATA 

-TMENDETEWMN, VS A 

Measurements of Optical Constants 

of SiN Films on Quartz 

R 

7- 

t OF WAVELENGTH ?\I / 

MEASURE 1 VS A AND R VS A 

DETERMINE d USING LONG WAVELENGTH R AND T DATA 

w 

USE COMPUTER ANALYSIS TO DETERMINE N, AND a, vs I 

BASED ON KNOWN VALUES OF N, VS A. d AND EXPERIMENTALDATA FORR ANDTVS A 

i 

T 

142 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

1 80 - - 

Silicon Nitride as an Antireflection Coating 

170 

100 ! I I , 

1 I I 1 I I I 1, 

L) BARE SILICON 

n FOR 790 !% FILM ON 

SILICON: N--2.0 @ 500 nm 

5 

20 c c) 

0 

300 450 600 750 900 1050 1200 

WAVELENGTH fnml 

Index of Refraction vs Wavelength 

2.20 

380 420 460 500 540 500 620 660 700 740 

WAVELENGTH lnml 

CMAMBER WAS EVACUATED MORE 

CAREFULLY FOR SN47 RELATIVE TO 

SN46 

143 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

SiN Film Index of Refraction vs Growth Parameters 

.- \I . - 1 -- 

0 1000 2000 3000 

RF POWER Iw!rn’) 

I 

B, 223. 

t’ 

E21- 

5 

z 20. 

&22. 

w 

a 

0 

1.9 - 

0 

SiH. INH I 

/ 

SUBSTRATE TEMPERATURE = 270’C SUBSTRATE TEMP€RATURE = 270 ‘C 

GAS FLOWS (sccm) GAS FLOWS (rccrn): SiH. = 10, Ar = 30 

AND NH. VARIED. 

RF POWER = 1225 w/rn* 

10 I 10 

Calculated AM 1 Photocurrent 

INDEX LAYER 1 AM1 PHOTOCURRENT (mAkm*) 

OF ~ THICKNESS j 1 TOTAL AREA WITH i 1 AR LAYER , 

I STRUCTURE REFRACTION ( A 1 j ACTIVE AREA 4% SHADOWING 

1 38.5 37.0 

838 35.29 ~ __ 33.89 ~ ~ - - 

I SINGLE , 1.9 .. 34.07 ’ LAYER , 2.0 ; 

2.1 35-41 - - ~ 33.99 __~~. ~..

2.2 35.18 33.77 

I 

i 

I 

DOUBLE 

LAYER i 

COMPUTATIONAL APPROACH: 

(1 I EXPERIMENTAL RESULTS FOR INTERNAL PHOTORESPONSE OF SHALLOW JCT 

12) PHOENIX AM1 IRRADIANCE SPECTRUM 

(3) PHOTON TRANSMllTANCE CALCULATED WITH COMPUTER CODE FOR MULTIPLE 

SILICON NIP CELL 

LAYERED STRUCTURE 

144 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Density of States Measurement 

VOLTAGE OISTRIBUTON IWUIO. 

I- + ax iwsi 1 

C. 

I1I.C. CrnIICl 

v = *w - 

WHERE 

I c LBS ams - arc - ass ~ dms 

HIGH FREDUENCY CAPACITANCE 

dV dVms - dais 

_e!k*K!sc 

.e!k 

co CD 

+ 

t 

-c 

c ' : C.' . Co' 

CD = C~IWSI + DATA ANALYSIS 

- DETERMINE C, FROM C VS V AT V < 0 

1 ' 4. ctioosE y. AND CALCULATE v 

CALCULATECVS VFOR~~~ ~ o 

DETERMINE ams = am, - ass AS FUNCTION OF ws BY COMPARING EXPERIMENTAL RESULTS 

Oms Con V 

D, GIVEN BY 

FOR c vs v TO THEORETICAL RESULTS FOR c vs v WITH ams - o 

dc4 d% 

k' d., d., 

C versus V for SiN Film on p-Type Silicon 

500 

400 

- 

a 

y 300 

2 

D 

- 

2 

: 200 

V 

100 

0 

FILM 84SiN2 

1 I 1 I I 

- 10 .- 8 - 6. - 4. - 2. 0.0 2.0 

GATE VOLTAGE 

145 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

DCF @ MDGAP (ern 'eV ~ '1 . 1 

GROWTH PARAMETERS 

AFTER ESTIMATED'" 

s-% 

SiN GAS FLOW (sccm) RF POWER AS HEAT 

FILM (Ar,NH,, SiH.) (wlm') DEPOSITED TREATMENT," 

SiN-2 80. 7.0, 2.8 163 1.0 x 10" 1.0 x 10" 500 

25 

SiN-40 , 30, 70, 10 1223 9.2 x lo1' 8.1 x 10" 4000 

SiN-42 1 30. 10, 10 816 1.7~10~' 1.3~10'~ 6500 

SiN-47 72. 48. 24 1223 1 9.1 x10" 9.0~10~~ 4500 

SiN-29"' 54, 54. 18 1468 <5 x 109 __ 

Midgap Interface State Density for SiN/pSi Substrates 

(1 )FILM SiN-29 HAS A 50 A THERMAL OXIDE. 

(2) 500 "C FOR 30 MINUTES IN ARGON 

(3) S IS ESTIMATED FROM 

S = 0 VTH Dss - 2kT 

Surface Recombination Velocity: Rosier Method 

w- S 

BASED ON SOLAR CELL 

STRUCTURE 

ASSUMING Lp ') 1,. THE INJECTION CURRENT 

I,, = D k&+ expw 

0, 

IF CURRENT SENSITIVE TO VGN, THEN: 

-INJECTION CURRENT DOMINANT AND SENSITIVE TO S 

-IF KNOW NI, AND n?, CAN DETERMINE S 

146 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

H I G H- EFFl C I EN CY CRY STALL1 N E SI LI CO N 

SOLAR CELLS RESEARCH FORUM 

JET PROPULSION LABORATORY 

A.H. Kachare 

Pre-PIM Modeling Meeting 

DEVICE PHYSICS IS umurooD 

RESEARCH IN HATERIAL SCIENCE IS WELDED 

--- HEAVY DOPING EFFECTS 

--- INTERFACES 

REASUREnENTS NEEDED FOR 

--- SURFACE - INTERFACE PARAHETERS 

--- MINORITY CARRIER LIFETIME IN THIN LAYERS 

INNOVATIVE DEVICE DESIGNS WEED FURTHER RESEARCH 

High-Efficiency Silicon Solar Cell Research 

A “FLOAT EMITTER” CELL STRUCTURE HAVING) 2011; EFFICIENCY WAS 

PROWSED 

BARRIERS TO ACHIEVE HIGH EFFICIENCY CELLS YERE DISCUSSED AND 

PERFORMANCE LIMIT WAS BROUGHT OUT 

SERI’S HIGH EFFICIENCY CELL ACTIVITIES WERE REPORTED 

. . . ASEC 16. K 

, . , WESTINGHOUSE 17.2X 

. , , SPIRE 18.1X 

LBlC AND SCCD TECHNIQUES TO MEASURE s ANDY IN EfllTTER AiiD 

BASE LAYERS SHOW PROWISE 

147 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

GROWTH AND CHARACTERIZATION OF SI3N4 AS A SURFACE PASSIVANT 

IS IN PROGRESS 

Low TENPERATURE EBIC PROVIDES BETTER UNDCRSTANDING OF AS-GROWN 

AND PROCESS-INDUCED DEFECTS IN LOW-COST SILICON SHEETS 

ETCH PIT STUDY HAS IDENTIFIED TWO STRESS REGIONS ACROSS 

AS-GROWN WEE 

INTERACT13NS OF DISLOCATIOFS YiTH TWIN AND CARBCM WIlH GE IN 

ANNEALED EFG WERE EXPLAINED 

FSA Project Research Forum 

ITLE: H Isn-Err IC I ElCT CRTSTALL I NE SILlCOl SOLAR CELLS 

DATE : JULY 9-11, 19R4 

LOCATIOW: TnE POINTE. PHOENIX, ARIZONA 

I OVERVIEW 

II HIGH-EFFIC IENCY ColcEPrs 

111 SURFACE-INTERFACE EFFECTS 

IV BULK EFFECTS 

V ~(ODEL ING 

VI HI Gn-Et Flc IENCI DEVICE PRoctrslNe 

148 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

High Efficiency Solar Cell Program: 

Some Recent Results 

J.B. Milstein and C.R. Osterwald 

Solar Energy Research Institute 

1617 Cole Boulevard 

Golden, Colorado 8040 1 

ABSTRACT 

All of the I-V measurements discussed in this talk were performed in the PV Devices and 

Measurements Branch at SERI, and were carried out at 28OC and AM1.5 using the SERI 

X-25 simulator. 

Roughly one year ago, SERI measured cells, fabricated by Rosa Young and co-workers at 

Oak Ridge National Laboratory under SERI auspices, which demonstrated 16.5% 

conversion efficiency. At that time, these cells were the most efficient silicon cells that 

we had seen. Others have claimed higher efficiencies prior to that time, which we do not 

dispute; however, such cells were not made available for our measurement. An account 

of the results of Young, - et a1 is reported in Applied Physics Letters 43(7), 666-668 (1983). 

In May, 1983, K.S. Ling c$ Applied Solar Energy Corporation provided us with six cells, 

each approximately 4cm in area, to be tested at SERI. Results of these tests were 

reported at the Photovoltaics Advanced Research and Development 5 th Annual Review 

Meeting, May 19-21, 1983, in Denver. Three of the six cells demonstrated in excess of 17% 

efficiency; the group ranged from 16.7% to 17.1%. The detailed results are presented in 

Table 1 below. SERI did not financially support the work performed by ASEC in 

fabricating these cells. 

In August, 1983, a group of 1 ern2 solar cells fabricateu by A. Rohatgi at Westinghouse 

Electric Corporation HhD Center, under SERI Subcontract No. XB-3-02090-4, were 

measured. Three cells demonstrated 17.1% efficiency, two 17.0%, and one 16.3%. The 

details of our observations are presented in Table I1 below. 

In September, 1983, a group of 4cm2 solar cells fabricated by M.B. Spitzer at Spire 

Corporation, under SERI Subcontract No. 28-3-02090-3, were measured. One cell 

demonstrated 18.0% efficiency, two 17.6%, and one 17.5%. These cells were remeasured 

at JPL on three additional simulators, with the cooperation of Bob Weiss, Bob Meuller 

and Gerry Crotty (all of JPL). It was found that the 18.0% cell had degraded (fill factor 

was reduced from 80.0 to 78.0%), but the other measurements were confirmed. 

Subsequently, the loss in fill factor was reconfirmed by measurement at SERI. The 

reason for this loss is unknown. In November, 1983, two additional Spire cells from the 

same batch were measured at SERI, and exhibited 18.0% and 17.9% efficiency. These 

results are summarized in Table III below. 

In December, 1983, a series of MINP silicon solar cells fabricated by M. Green and cw 

workers at the Solar Photovoltaic Laboratory, University of New South Wales, 

Kensington, Australia, were tested at SERI. Seven cells, each approximately 4 cm2 in 

area, were provided for these tests. One cell exhibited 19.1% conversion efficiency, two 

19.O%, one 18.8%, two 18.7%, and one 18.1%. These results have been corroborated by 

tests performed at Sandia National Laboratory. The efforts at UNSW have been 

supported by the Australian Government and by NASA-Lewis. Details of the test results 

ate presented in Table IV below. 

149 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

On March 6, we measured several 4cm2 MINP solar cells fabricated by Larry Olsen and 

coworkers at the Joint Center for Graduate Study - University of Washington under SERI 

subcont act XB-2-02090-5. The best cell measured exhibited V ,=636 mV, Jsc=31.1 

mA/cm , FF=.787, -fficiency=15.6%. Visual comparison of this &vice with those of 

Green indicates that the single antireflection coating used by JCGS is less effective than 

the double coating used by UNSW. 

Measurements of reflectance exhibited by double layer antireflection coatkgs have been 

performed at Westinghouse by Rohatgi and at SERI on the UNSW cells by us. The 

observed reflectances are very similar, with integrated reflectivity from 4000 2 to 

11000 1 of 5% or less. Theoretical models have been developed at Westinghouse which 

give predictions that conform closely to the observed data. These results are presented 

below. 

H 

We feel that a number of significant observations should be made. First, excellent 

results are being attained by a number of different research groups, using a variety of 

approaches, not all of whom are financially supported by SERI. Second, the Request for 

Proposals No. RB-2-02090, "Research on Basic Understanding of High Efficiency in 

Silicon Solar Cells," which SERI issued in March, 1982, was motivated by the conception 

that an "existence proof" (Le. a demonstratable cell which exhibits efficiency exceeding 

17% by the largest amount practicable) would provide strong impetus for research by nonSERI supported groups based on knowledge that research on high efficiency cells can be 

fruitful. Hopefully, such activity will be fostered by the attainmer.t and dissemination of 

results such as those described here. Third, SERI has expressed an interest in testing 

highly efficient cells whether or not they have been fabricated with SERI support. We 

are pleased to assist the PV community by providing this service, and hope that this offer 

will be acted on by additional successful groups. 

Further information on the details of fabrication of the cells we have discussed can be 

obtained from the groups who have performed the research, and will undoubtedly be 

discussed in the near future in the professional literature. 

150 
HIGH-EFFICIENCY SOLAR CELL PROGRAM : 

S3ME RECENT RESULTS 

SOLAR ENERGY RESEARCH INSTITUTE 

J 8. Milstein 

C.R. Osterwald 

FZ Si N+P W6 

SAMPLE: SO2053 VOC = 0.6202 VOLTS 

DATE: MAY 13 1983 15:55 Jsc = 34.75 rnA/cm^2 

TEMP - 

AREA - 

0.15 

0.10 

0.05 

0 

-3.05 

-0.10 

28.0 c FILL FACTOR = 79.33 X 

4.056 cm-2 EFFICIENCY = 17.10 X 

OOL 0000000 PIN" -nrmvLnKlb ... ....... 00000000000 

Ill 

Table 1. Results of Measurements on ASEC Cells, May 1983 

I 4.070 14.75 620.7 78.05 16.84 

2 4.062 14.58 6111.6 79.88 1i.09 

3 4.068 31-72 619.6 79.24 17.05 

I 4.062 34.02 621.8 79.92 16.90 

5 4.010 33.86 622.8 79.11 16.68 

6 4.051 34.75 020.2 79.13 I? IO 
HIGH-EFFICIENCY SILICON SOLAR CEI-L RESEARCH 

’51 n+pp+ HIEFY-4-5 

SAMPLE: SG2 183 VOC - 0.6042 volts 

DATE: AUG 5 1983 15: 38 Jsc = 35.60 mAicm’2 

TEMP - 28.0 C 

AREA 1.010 ern-2 Efficiency = 17 11 % 

Fill factor = 7 r4 % 

40.0 

35.0 

30.0 

25.0 

20.0 

15.0 

10.0 

5.0 

0 

-5.0 

-10.0 

-15.0 

-20.0 

00 OOOOOGO run n N IT V Ul b 

0000000000 

II 

.. .. 

Table 11. Results of Measurements on Westinghouse Cells, 

August 1983 

Sa nple 

1) 

HIEFY -4-4 

-5 

-6 

-7 

-8 

-U 

Are? 

(cm ) 

J 

(m lFc m 2) 

1.01 3s .5 604 79.6 

1.01 35.6 604 70.5 

1.01 3s .9 60: 78.6 

1.01 35.4 604 79.7 

1.01 35.3 603 79.8 

1.01 35.5 601 76.1 

n 

(e ) 

li.1 

1i.l 

Ii.0 

17.0 

16.3 

17.i 

152 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Table 111. Results of Meastiiements on Spire (r elis, 

September 1983 

Sample 

I 

SD2219 

SD2220 

SD2221 

SD1222 

November, 1983 

Sample 

I 

SD22:O 

SDP253 

sn2?52 

Are! 

(cm 1 Js 

mhcm2 

4.01 15.7 618 

4.00 36.1 522 

4.01 36.3 616 

4.01 16.0 619 

Are! 

(cm 1 

4.00 36.0 620 

4.nO 16.0 621 

4.00 16.2 622 

FF n 

(%! (a 1 

80.f 11.6 

BL .I 13.3 

78.0 11.5 

19.1 17.6 

FF n 

(B 1 ($1 

78.0 11.4 

80.1 I;.$ n0.1 18.0 

Si n+pp+ 32C 

SAMPLE: SO2253 VOC = 0.6221 volts 

DATE: OCT 28 5983 15: 14 JsC . 36.15 nA/cm-2 

TEMP - 28.0 c Fill FdCtGr = 60.06 % 

AREA - 4.000 cn-2 Efficiency - 18.01 4: 

0 

.05 -. 

-0. io 

0.15 

0.10 - 

0 

Q 

E 

Y m 0.05 

tZ 

w 

3 

U 

a 

a i! 

153 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Si PE MINP #176 

SAMPLE: SO23 19 VOC = 0.6526 volts 

DATE: DEC 22 1983 11: 13 JSC = 36.01 mA,'cm-2 

TEMP - 28.0 c Fill factor = €32.14 % 

AREA = 4.068 ern-2 EfficienLy - ~9.0- X 

0.15 

0.10 

1- 

G 

E 

- m 0.05 

tz 

W 

U 

U 

3 

i) 

0 

-0.05 

-0.10 

xx 

am 0 E€ v1 

>- H 

00 ~000000 Nn NFIVlllIDf\ 

00000000G0 

ti 

.. .... 

VOI. TAGE (vo 1 t. ?I 

Table IV. Results of Measurements on UNSW Cells, 

December 1983 

129 4.09 660 34.5 

120 4.01 640 36.1 

78 4.01 543 36.r) 

1399 4.08 650 36.2 

1366 4.08 65 2 36.3 

I77 4.08 653 16.0 

1i6 4.01 65 3 36.0 

79.8 18.1 

81.0 18.7 

80.8 18.; 

80.0 111.8 

80.2 19.0 

80.8 19.0 

81.1 19.i 

154 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Si MINP 

SAMPLE: 84SiNP4 Voc - 0.8383 volts 

DATE: MAR 8 1484 la 12 JSC - 31.10 mA/cm'2 

TEMP - 

AREA - 

0.14 

0.12 

0.10 - 

0.06 a 

Q 

c 0.01 

z 

w 

a 0.02 

a 

3 0 

0 

-0. OP 

-0.04 

-0 - 0. 

28.0 C Fill fmctoc 78.72 X 

3.970 cm'2 Efficiency - 15.58 X 

000000 

00000000000 

111 

2IymqIoIpb ... .-._... 

VOLTAGE (VOl tS) 

155 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

- 

0.m - . t 

0.m 1 

0.0s 

1' 

\' 

wavmlongtn (urn) 

XI. , I I 1 1 I 

a5 Retlectivdy Impmvcment 50% 

- 

XI. , I I 1 1 I 

a5 Retlectivdy Impmvcment 50% 

- 

156 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

lsoreflectivity Curves 

157 

DEVELOPMENT AND ANAYLSIS OF SILICON 

SOLAR CELLS NEAR 20% EFFICIENCY 

UNIVERSITY OF PENNSYLVANIA 

M. Wolf 

M. Newhouzw 

Calibrated Spectral LBlC 

I " 

I .- I' 

I " 

I 

I- +I 

PRECEDING PAGE BLANK NOT FILXED' 

159 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

I 

Surface Recambination Minority Carrier Lifetime 

Vel oci t y 1 

S ns 

cm E-’ Layer 11 Laytr 21 Layer 3 1 f 

1. The calibrated spectral LBIC method when applied to an individual region uses exclusively wavelengths which do not 

penetrate beyond the layer under investigation. 

ms Error 

2. The method operates only in the short circuit condition to 

eliminate influences of the other regions of the device, 

including the junction space charge region, from affecting the measured data. 

100 0.06 10 10 

0.66 1 1 

0.06 0.4 0.4 

1.7. to4 0.07 1 10 

0.7 0.7 0.7 5 1.6.10 

3. As far as possible under the constraints of point l., a 

wavelength range with widely varying absorption coefficients 

is used to gain sensitivity for differentiation- between 

surface recombination and bulk recombination, or, when a 

layered region is involved, between the properties of the 

i nd i vidual 1 ayers . 

1.74 

2.18 

3.79 

2.09 

0.95 

Front-Layer Parameters of Spire Cell 4400-208 

4. lo5 

- 

1 2.0 

Sinqle Layer 

5 

After 10s Hf etch 

0.3 

1 

1.2.10~ 

3. IO7 

0.94 0.3 

0.06 1 

3.96 

7.54 

(slope does not 

match mil) 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

In ''thin'' regions of high performance, only a "maximum surface recombination velocity" and a "minimum bulk lifetime" can 

be determined, which lie at the threshold to the "saturation" of 

the collection efficiuncy. Actual values could be more favorable, 

but do not improve the spectral collection efficiency. 

Good cells with the usua1,under 0.3 m thick front layer, 

fall into this category (Spire cell with oxide layer.) After 

removal of the oxide layer, a 2-order of magnitude increase of 

the surface recombination velocity from the prior "maximum" was 

clearly observable, Le. , the collection efficiency is no 

longer saturated. 

161 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Spreading Resistance Analysis: 

Alloy-Regrowth BSF Structure, 2 Models 

101'- . . .-- 

0 ._ e 

? 3 1 5 . lOEPTM - m*r#a 

162 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

CELL a-002 FRONT LAYER BASE LAYER FIT 

x RUNS 

I I I 

MEASUREMENTS 

I 1 

FRONT REGION SE5 110ns IlOm - 1- I- 2,2 

6ns 16ns 12.5~9 13.4 BASE REGION -I- IK5 11Ons 1100ns 6ns 16ns 11.3~~ 5.5 

WHOLE CELL K5 Ilona '6~ s 6ns 16.. 11.5~~ 6,s 

I I 1 I 1 .I 

CELL 37-3 I' '\ 

'\ 

I I '\ 

I I MEASUREMENTS 

As a first, it has been possible to determine the minority 

carrier lifetime in the alloy-regrowth layer between the high/low 

junction and the back surface. For this purpose, windows have 

been etched into the back metallization, and the calibrated spectral LBIC method applied to the back of cells. Modeling this 

layer by 3 sublayers according to the spreading resistance profiles 

or as one layer with constant impurity concentration (dashed line) 

yielded the same results. 

voc 

co P'D f MEAS'D 

MI RV 

1 

- 1- 

I 

- I530 I - 

593 I 598 

I 

I 

I 

-I 

I 

- I163 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Beyond the alloy - regrowth layer properties, the minority 

carrier life-time in the less heavily doped layer of the base 

can be determined in this measuremant. 

region"). All the data can then be corroborated by measurement 

from the front surface. (Labelled "whole cell"). 

(Data labelled "base 

Where the spectral collection eff icienty saturates, a comparison of the calculated open circuit voltage ( or saturation 

currentwith the measured one can indicate the need for an increase of the minority carrier lifetime value (or decrease of the 

surface recombination velocity, if the layer is very thin 

so that surface recombination dominates over bul k recombination) 

so as to match the measured open circuit voltage (see cell W2- 

002 measurements) 

164 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

S STAGE 

ORIGINAL WAFER 

AFTER EPI-LAYER 

DEPOSITION 

AFTER SOLAR 

CELL COMPLETION 

Measured Minority Carrier Lifetimes 

at Various Stages of Processing 

CELL TYPt 

AT Tu UTE 37 w2 

SUBSTRATE DOPING (cm-') 1.6 E i6 'I E 16 

EPI-LAYER DOPING (~m-~) 2E17 ?E17 

1 IN WAFER (US) 450 120 

7 IN WAFER (US) 3-8 1-2 

f IN 2Pm THICK 

€PI-LAYER (PS) -20 10-20 

1 IN WAFER (US) 20 1.5 

EPI-LAYER (US) 0 I002 6 

f If4 2Um THICK 

1 IN ALLOY-REGROWTH 

LAYER OF BASE (ns) 2.6 6 

The method has enabled the determination of the minority 

carrier lifetimes in all regions of solar cells at various stages 

of the process. It has permitted the observation of lifetime 

degradation occuring in various process stases. 

165 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Experimental cal ibrated spectral LBIC data can give improper 

rewl ts if, e.g. , an absorbing layer (AR, passivation oxide) overlays the active area of the cell. 

adjusted to match the open circuit voltage yields significantly 

larger collection efficiency values than measured. The particular 

cell has a thick, absorbing oxide layer. 

In this example, the lifetime 

166 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Limits of Calibrated Spectral LBIC 

THEN : 'actual 'mear'd. 

('tot 'bulk ' "surface 

'9UrfaCe If 'bulk << 'surface.) 

'actual 'rnaas*d. 

'actual ' 'rncar'd. 

- RELIEF: (FOR FRONT LAYERS) : 

IF jo,front a li3 'o,bare: 

HIGHER VALUES FOR 7, LOWER FOR -s 

CAN DETERf .NED* 

1. If the layers are thin and surface rccombination domin?tes, 

only the surface recombination velocity can be re1 iably determined. 

2. 

values for 'I and s by the LBIC method. The actual values may be 

more favorable and can, in some cases, be determined from the 

saturation current. 

The collection efficiency can saxrate, leading to 

167 

" 

@ai SULFACE AND ALLIED STUDIES IN SILICON SOLAR CELLS ---- 

UNIVERSITY OF FLORIDA 

F.A. Lindholm 

T.W. Jung 

J. J. Lmu 

* TUO-PORT moML---LINEaRITY 

NQW SCR C VI- w8 NEW OCWD 

169 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

I(0.s) I(XONB'S) 

Fig. 1 Two-port network representation for hole densit) and hole 

current (density) dt the tw edger of the n-type quasi-neutral bJse 

resion. 

Fiytre A-1 

(a) For t c 0. switch 5 is closed. 5 is open. converse1 for t > 0; the 

junction space-chdrge reglbn is defined %y x < x : ..,. (3j charge denslty 

dt t = O+. (c) char density for C of thePorder of'\ dtcic~;~;; r:!:::':Y 

time. (d) the .totd?current is x-independent hut 15 essentially mdjoritycarrier COWJ-CCIO current In the two quasi-neutral reqions and 1s 

displaccnwnt currert in the space-charge reyion fo t of the order of a dielectric relaxation Lime. (e) electrons and holes drift Out of the soace- charge region in a trrnsi tine. (f) the resultlng excess hole density in th? 

space-chapqe repian after a transit tim has IdPSed. 

170 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH OF Pc,.. .. 

a m --- 

'ground n 

I I i PULSE ! 

R1 

Fiq. 2 The electronic switching circuit used in the SCCO nethod. The 

circuit elements are switching transistor 1s 2N3906 the ulse 

generator 1s HP 8004. and the 10gdrlthnlC dmpllfier con;iSts o? the 

usual configuration of an Operdtlonai amplifier (8urr-Brown 3500C) 

connected to node 8 through 3 100 ohm reSlStor and across which (between 

nodes 8 dnd C) two oppositely directed swltchlng diodes (iN914) 

constitute the feedback loop. 

t- t 

tu0 

171 
ORiW!.$t. t”.‘.‘. . 

OF PO22 QC.. .-. , HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

P 

Estimated Lifetime of the Minority Carriers, T 

159 us 

MEASUR 

CURREW I 

RATI0.R 

1-7 t 

25 US 

OR161* 

‘FIRST ~DE(o)”DIFFUSlor(O-)) 

0.7 

ED 

IT I ~ / 

THIS IS A CHART WERE YE CAN ES:iMATE 

IS 350 h AND ITS D, IS 12 cn/s 

LIFETIME OF THE MINORITY CARRIER YlTH 

61yEN T AND R- THE DEVICE THICKHESS 

61 us 

7 MEASURED DECAYIW6 TIME COYSTAwT.T, 

I53 us / 35 us 

PROQRAMH~TIC 8s FUTURE -I 

LXTLND =-PORT WETHOD8 

IRRfiDXATXON 

tXTEND SLNSITSVITV b -CURACY 

172 
LOW-TEMPERATURE EBIC STUDIES ON 

SILICON SHEET MATERIALS 

JET PROPULSION LABORATORY 

Li-Jen Cheng 

Contributors 

JACK COLLIER 

KATHY OUtlAS 

flARlV LEIPOLD 

ANDY HORRISON 

BRYAN SU 

THEN NGUYEN 

Contents 

* ETCH PTT PA- ON 

EBIC-SEM: Electron-Beam-Induced Current 

n' 

P 

173 


HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Advantages of Low-Temperature EBlC 

BEITEX SPATIAL RESOLVPIW 

a Reduction of thermal emission 

- CAPABLE OF OBSERIiING MORE DEFECTS 

a Fermi level change 

a Reduction of thernal e~lSSlOn 

Temperature Effects on Recombination 

Ecl+ 

LOW 

m-seune 

I 

E ; + 

t 

i 

E, 

E ,-• 

I 

! - t 

I 

176 




{IGY-EFFICIENCY SILICON SOLAR CELL RESEARCH 

EBlC Scan 

-14 -120 -100 -so -60 -4 -20 

1.0 

0.8 

W 

1 5 a4 

8 

az 

a0 

I,lllllIllll 

20 Y) 60 80 100 1201 

Temperzture Dependence of EBlC Contrast 

of Dislocations in Web Ribbons 

181 
HIGH-EFFICIENCY SILICON SOLAR CELL PESEARCH 

0 

s 

C 

C 

v) 

c, 

ii 

I 

.' . 

*. . ,. :. *. . .- * .. ri * 

m 

FW 

182 
HIGH-E~FICIENCY SILICON SOLAR CELL RESEARCH 

r- MAJOR SLIP PUNES 

of WEB 

(I. 0. 1111) PUhES) 

NATURE 

OF 

STRESS 

fEWfILE 

tncna 

m 

I ail) I 

I 

I 

I 

I 

I 

I 

DIRECTIOlr IMTERCWlS 

GROWTH AXIS UEI SURfrrcE 

WITH RESPECT TO al 

PARALLEL * 

x 

PARALLEL X 

FERPEI*)IcuLAo 

PERPErOICULAR - 

I 

I 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

[a I 

TOP VIEW 

Possible Movement of Three Major Slip Planes Under Stress 

183 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Explanation 

SOLID-LIQUID 

POSSl SOURCE 

by RUCTUATIONIN 

TEMPERATURE 

GRADIENT AM 

GRW AXIS 

w 

THERMAL COIYTRACTION 

DUE TO SllFRYSS 

Of THE DWRlE 

AND THE coNcAvf-Mmy 

SOLI 0-LIW ID 

uyy FUICNAMIN 

Conclusions 

I) Snona tnat fmo alstln~ulU180la rtnss raQlocrr .cross rillcon 

aenarltlc we8 rlooonr may :Itst arrlng tM cooling procmrs 

of tw growth. 

1 84 
MICROSTRUCTURAL CHARACTERIZATION 

OF ANNEALED SILICON RIBBONS 

CORNELL UNIVERSITY 

D.G. Ast 

Agenda 

8) Electrical Activity of grain boundaries 

.................... Role of carbon. 

8) Basic studies of grain boundaries 

------------------- Strainf iel d, expansion/contract ion 

e) Interaction of dislocations with twins 

------------------ Twins as obstacles to plastic relief. 

185 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Basic Idea 

Annealing time (hr) 

0) Assemble data for kinetic disappearance of EBIC contrast 

0) Check kin2tics for compatability with C diffusion 

Long range cffort: 

0) Use DLTS to check for formation of C related states. 

186 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Electrical Activity of Grain Boundaries 

Joint study with Mobil ----- effects of pre-anneal ing 

0) Pre-anneal ing greatly reduces electrical dctivity 

0) Present model 

Formation of competing aettering centers by C 

Collection of kinetic data to verify C hypothesis 

0) Present status 

0) Long range effort 

Study of a C based gettering system as an alternative 

to (conventional) 0 based gettering system. 

C should be especially efficient in gettering those 

transition metals whick are known to be good carbide 

formers; e.g. Ti, W, b, Fe. 

C is naturally preseat in solar materials grown in 

graphite crucibles. 

187 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Basic Studies of Grain Boundaries 

Comparative study of the width and strainfield 

of grain boundaries in Ge and Si. 

Approach is to fabricate grain boundaries by 

grwing bicrystals and by high T sintering 

Width and contraction/expansion of crystal lattice 

at grain boundary measured by diffraction techniques. 

Study completed---- draft written up. 

Major results 

past boundary 

noticeable contracted in Ge. 

generally expanded but can be explained with covalent 

bond model. 

* Strain field extends about 5 to 10 lattice spacings 

* Lattice in boundary plane is slightly contracted in Si 

* Contraction is specific to Ge,Si as gb in metals are 

188 
HIGH-EFFICIENCY SILICON SOLA6 CELL RESEARCH 

Strain Fields and Widths of Grain Boundaries 

Basic idea: 

0) Treat grain boundary as a slab of thin material with a 

different lattice constant from bulk. 

matrix matrix 

Fourier transform (i .e. diffraction pattern): 

),iRod of matrix 

Rod of grain boundary. 

189 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

I-- 

190 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Geometry 

0) Real 1 ife complications: 

* Unwanted presence of small tilt components 

* Boundary not parallel to (004) planes. 

Results to date: 

Mtll Angle Streak Boundary Streak Boundary CSL 

Length (A.") Width Shift Contrlctln. S: 

Si 16 0.088 11.63A 

Si 22 0.10 10.0 

Si 37 0.060 16.7 

Si 45 0.108 9-2 

0.4% 25 

0.37% 13 + 

0.4% 5 

0.4% 

Ge 22 0.07 14.29 2.0% 13 - 

191 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Twin-Dislocation Interactions 

0) Coherent twins are major planar faults in solar material. 

They are present in high concentrations in EFG. 

0) During annealing (e.g. during formation of p-n junction) 

or during cooldown (after heater) stress relief by 

dislocation motion can be limited by twins. 

0) Twins accumulating many dislocations dissociate into 

small angle grain boundaries and coherent twins. 

0) Small angle grain boundaries coalesce to form large 

(20 to 30 degree) angle grain boundaries. 

0) Study completed-------- draft written up 

Dislocation-Twin Interactions 

0) Very c-lcx ---- out of scope of a lSmin 

pnwntat ion. 

0) An exrrgle rill be provided to Illustrate 

the ksic prwetdure used to Mtrtigate 

the various possible dislocation 

wchrnius. 

Matrix fwi n 

*) Vectors transfered from left to right lust 

be expressed in the twinned coordinate system. 

*) The various diswcirtion rerctlons posslble urt them 

be cxulmd. 

192 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

I have looked at the individual step:, 01' the reaction of dlslOCdtlOn3 

uith out of p1ar.e &urgers vectors. 

To repeat the notation: 

The tiin plane is (1 1 1) 

Incominq jislocdtions move on (1 -1 -1)oId plane 

htgoinb .penetrdti?g) diSlOCatiOnS move on the (1 -1 -1)neu plane. 

The relation of the new and old (111) ylane is such thdt they hdve 

a common corner [O 1 -11. 

The overdll redction uas: 

1/2[1 0 11 ------------------------, . 1/6[-1 -4 -11 

(refered to old COOrdAnate system) (same vector in tuinned coordinates) 

Thus it appeared that overall, a complete aislocdtion uith an out of plane 

Burdersvector could cross the tuin prvided there uas enough strnin energy 

relief to generate a partial dislocation. ~. 

The individual steps of this procLss are as follouh. 

The incoming dislocation is dissociate0 into tu0 partials, uith the 

leading partial pressing against the twin pla?e: 

1/2[1 0 11 ------------------. --> 1/6[1 -1 21 + 1/6[2 1 11 

(on (1 -1 -1) old (Both on ( -1 -1) Old) 

The leading 231 tlal transf'ers across the tuin pla.ie and, in the twin 

coordinate system appears in neu notation as: 

1/6[1 -1 21 ---------> 1/18[-1 -7 21 

((1 -1 -1)Old) ((1 -1 -1) new) 

It dissociates during the crossing proces.' into the following compownts, 

expressed in the twinned coordinate systcm: 

193 
HIGH-EFFICIENCY SILICObi SOLAR CELL RESEARCH 

l/ldi-l -I Z] ---------------> 1/6[ -1 -Z 11 + 1/16 [-2 1:J 

The Iirst term on the right side is d 3liSSile partial on the new (1 -: -1) 

plane and will glide away. The second term is dn inleresting producr. :r is one Lfrird of a glissile pdrtidl in the (111) plane. It has a very scall 

strdin field and rrmlnas me SOmeWhdt of Marks sub LJSC vectors In Sij33i 5 

tuisL o'>undories. The energy of the redction, if primit;vely analysea :n 

first order dS be1r.g proportional to the byuare of the Burgersvector is: 

1/b < 116 + 1/54 

The redction does require some energy, 6UT VERY LITT1.E. IT REGUIRES LE2b 

LNEAC:' THAN CONVEkTIf& A PARTIAL OF A IN PLANE BV DlSLOCATIONI INTC A 

CLISSlLE PAHTIAL AND A STAIHtlkOU : 

1/6 < 1/6 + 1/!U 

Furthermore, both Croducts of this reaction are glissile and ui 

relievin; the stress at the tip of the pile up against the twin 

The trailing partial requires more energy. Again the first stc? 

transform this partial from the untwinned L'J the twinnea system 

l/b[211] ------------------- ' 1/1H[-2 -5 -51 

The dislocation on the right dissociates Into: 

1/1&[-2 -5 -51 ------------- > 1/'6[-2 -1 -11 + 1/9[-2 1 11 

The entrgy required, tredted in the square mechanism i?: 

1 mcve .Wdy 

plsre. 

is t3 

1/b i l/b + 1113.5 

It is somewhat higher than that of d classical stairod (which in this iase 

cdn not form). 

Still, the total energy for both steps is still lower than taking a diss0cia-r: 

dislocation uith in plane Burgersvector and moving it on the twin plant Oy 

making tu0 stairrods. 

The first step of the reaction requires so little energy that it occurs likely quite ofLen. I have not considered any further reactions of cne 

1/18[-2 1 11 product, which is glissile in the tuin plane uith dls1oca:lons 

which mil(ht be already in the twin plane (SP and FP). Nor have I consliered 

the fractional steps associated with this dislocatlon. 

bince there is a "phase shift" in the twin boundary, the leading parrial 

of the lncoming dis1oca:ion (defined in such a ury that the dislocatior. Is 

ssociated uith an intrinsic SF) will emerge on the other side of the tvln 

bundary as an extrinsic SF. 

194 
Laser 

CRYOGENIC LASER CALORIMETRY 

FOR IMPURITY ANALYSIS 

UNIVERSITY OF SOUTHERN CALIFORNIA 

R.T. Swimm 

Calorimetric Spectroscopy 

Benm 

Sample 

Laser 

Chart Recorder Nanovoltmeter 

Sample 

Heating and Cooling Data 

195 
HIGH-EFFICIENCY SILICON SOLAR CELL RESEARCH 

Ca I o ri me I ric spec troscc py - 

car& n& replace: 

moss spectroscopy 

deep level transient spectroscopy 

but can replace : 

relative transmission spectroscopy 

(for low - obrorption samples) 

196 
. i 

ENCAPSULATION 

4 ', ,- 

. 

1% 2 ' 

E.F. Cuddihy, Chairman 

Spec trolab, Inc. 

The basic FSA contract with Spectrolab, Inc,, on encapsulation engineering 

has been completed. The presentation suurited highlights, key findings, and 

major technologies accomplished under this contract. 

the Spectrolab, Inc. presentation below. It was announced that a detailed 

final report is in preparation. Spectrolab investigated the interrelationship 

betwen encapsulation material properties and module performance features 

involving opt ica 1, struc tura 1, thermal, and e lee tr ical isolation behavior. 

The analysis also included the effects of encapsulation amterial interchange, 

and encapsulation design options on umdule perfonaance, 

These are detailed in 

Springborn Laboratories, Inc. 

Springborn Laboratories, Inc. presented an updated sunry of its work 

related to materials development and accelerated aging test results. 

items: 

e.g., 10SoC, and possibly to as low as 9OoC, but there are not yet enough 

experimental data to define the lower temperature; (2) the protective additives (W absorbers, antioxidants, etc.) formulated in the current A-9918 

encapsulation-grade EVA are subject to physical loss at elevated temperatures, 

such as those that may be associated with module rooftop applications. To 

counter this, Springborn is exploring advanced EVA formulations containing 

chemically bound additives . 

Two key 

(1) copper and EVA are chemically incompatible at high temperatures, 

Jet Propulsion Laboratory 

Accelerated aging almost always involves raising the exposure temperature 

of test specimens, to accelerate aging reactions. The question then arises as 

to the upper temperature limit allowable for accelerated testing. The criterion is that increases in temperature should accelerate the same mechanisms of 

aging operative at intended service temperatures, but should not alter uechanisms or introduce new mechanisms. JPL's sophisticated, laset-probe technique 

for spectroscopic identification of reaction mechanisms occurring in test 

samples as a function of temperature was described. This technique will be 

used to determine the allowable upper temperatures for accelerated aging of 

materials such as EVA. Some preliminary data for a model pottant compound, 

poly-n-butyl acrylate, were presented. 

University of Toronto 

J. Guillet was unable to attend. His presentation was cancelled. 

197 
ENCAPSULATION 

Polytechnic Institute of New York 

Otto Vogl was unable to attend, but a sunry and update of his scheduled 

presentation vas given by a colleague, A.C. Albertsson. 

chemical synthesis of advanced polyleric and reactive stabilization additives 

for polyreric materials, such as EVA. These additives, such as protective 

UV-absorbing agents, are resistant to high-temperature physical losses. 

Vogl carries out 

Dau Corning 

E.P, Plueddeunn is the primary developer of all of the €SA adhesion 

promoters and primers for bonding the various material components of modules, 

such as EVA to glass. 

found in more detail in a recent JPL publication "Chemical Bonding Technology 

for Terrestrial Photovoltaic nOdules" (JPL Document No. 5101-232, JPL 

Publication 83-86). 

self-priming EVA. 

Plueddemann sumarited his vork to date, which can be 

A major item vas the status of his current work on 

Case Uestern Reserve University 

J. Koenig of Case Western Reserve University and J. Boerio (see below) 

have developed the technology to investigate a chemically bonded interface, 

€or direct chesical information on both bonding and aging mechanisms. The 

technology is based on Fourier transform infrared tecnniques (FTIR). Koenig 

presented the first FTIR spectra of the bonded interface between EVA and 

glass, using the EVA-glass primer system developed by Pleuddemann. Eventually 

this technique will be used to track interfacial aging for rate data and life 

assessment. 

University of Cincinnati 

J. Boerio's efforts are identical to those of J. Kuenig, except that the 

emphasis of his study is on polymers and metals, such as EVA and aluminum, 

These interfacial chemistries can be quite distinct from those between EVA ad 

glass, for example. Boerio presented interfacial spectra of the bonded interface between EVA and aluminum, using an experimental metal primer system 

developed by Plueddemann. Bonding EVA to aluminum is complex, and Boerio's 

interfacial studies are providing clues to stable, high-strength, long-life 

inter f ac ia 1 bonds . 

Je C Propu 1s ion Laboratory 

The role of polyvinyl butyral (PVB) as a direct, causative agent of 

module electrochemical corrosion was described by G.R. Mon of JPL. 

contains ionic impurities that, in combination with absorbed water at high 

humidities, result in the PVB functioning as a solid-state battery electrolyte. 

The high-humidity, high-temperature (85Oc, 85% RH) behavior of PVB in modules 

having silver metallization grids was described and compared with that of other 

metals, and also with other pottants su,ch as silicones and EVA. The latter 

PVB 

198 
ENCAPSULATION 

two pottants were found not to exhibit similar electrochemical behavior. 

on theoretical considerations and experimental data, an electrochemical lifepredict ion mode 1 was deve loped and described . Based 

Jet Propulsion Laboratory 

The flambility behavior of modules fabricated with hydrocarbon pottants 

such as EVA and PVB was described by R.S. Sugimra and D.H. Otth of JPL. The 

a790 flalplability test consisted of a burning brand resting on the giaas surfaces of modules. Localized surface heating caused glass fractures, internal 

thermal decomposition of the pottants to volatile liquid and gaseous praiucts, 

and high-,emperature softening or melting of conventional module back-cover 

materials. pressure acting against a decreasing 

mechanical strength of the back cover caused rupture of the back cover, 

permitting an outward venting of the volatile liquid and gaseous decomposition 

products, which ignited upon contact vith oxygen of the air and an open flame. 

Some preliminary flaamability tests with modules fabricated with experimental 

high-strength, more-temperature-resistant back-cover materials showed promise. 

A buildup of internal g. 

199 

ENCAPSULATION DESIGN ANALYSIS 

SPECTROLAB, INC. 

Alexander Garcia 111 

Acknowledgements 

DESIGN, ANALYSIS, AND TEST VERIFICATION OF ADVANCED ENCAPSUIATION SYSTEMS 

JPL CONTRACT 1955567 (ED CUDD I HY, TECHNICAL HON I TOR 1 

JOINT EFFORT OF SPECTROLAB AND HUGHES AIRCRAFT COHPANY 

J. F. COAKLEY .. THERNAL, OPTICAL ANALYSES 

L. B. DUNCAN - STRUCTURAL ANALYSIS 

I, R. JONES - PROGRAPI NANAGEMNT 

J. I. KALLIS - ELECTRICAL, THERBAL ANALYSES 

D. C. TRUCKER - ELECTRICAL 

Objectives 

0 ANALYTICAL METHODOLOGY 

0 VERIFICATION 

0 DESIGN AIDS, MASTER CURVES 

0 RESEARCH DIRECTION 

0 TCM 

PRECEDING PAGE ELAiW NOT FJI.MYD 

201 
ENCAPSULATION 

Today's Topics 

0 STRUCTURAL ANALYSIS 

- DEFLECTION 

- THERRAL 

0 OPTICAL 

0 THERMAL 

0 ELECTRICAL ISOLATION STUDIES 

Objective and Approach 

0 DEVELOP METHODOLOGY TO ANALYZE PHOTOVOLTAIC ENCAPSULATION 

SYSTEM DESIGNS 

0 APPROACHED USING FIVE MODELS 

- STRUCTURAL DEFLECTION ANALYSIS 

- THERMAL STRUCTURAL ANALYSIS 

- THERMAL ANALYSIS 

- OPTICAL ANALYSIS 

- ELECTRICAL AFIALYSiS 

0 VERIFY MODEL BY TEST 

0 VERIFY MODEL BY COMPARISON TO EXACT SOLUTIONS 

202 
ENCAPSULATION 

1 w e v) 

I 

t 

2 

N 

m 

Concept No. 1 

Module Concept 

TEMPERED GUS 

EVA CRANE GUS 

CELLS 

CRANE GUS-EVA 

AL/ACRYL IC 

0 

1 2.5 CM (0.9843 IN.) 

f FRAME 

10.3 CH (4,055 IN,) 

SQUARE CELLS 

1.3 m (0.0512 IN,) 

t/ CELL SPACING 

I,- 1.2 KETERS -I (47,244 IN,) 

203 
E NCAPS ULATlO N 

Structural Analysis Objective 

DEVELOP REDUCED-VARIABLE MSTER CURVES TO EMBLE DESK-TOP 

CALCULATION OF SOLAR CELL STRESS 

e WIND PRESSURE LOADING 

TEMPERATURE EXCURS IONS 

Assumptions 

ANALYSIS : 

LARGE DEFLECTION THEORY (NONLINEAR) 

e STRESSIDEFLECT ION ANALY s I s OF UNST I FFENED FLAT PLATES 

UNDER PRESSURE LOAD ING 

SMALL DEFLECTION THEORY (LINEAR-ELASTIC) 

e TEHPERATURE EXCURSION AND DEFLECTION ENCAPSULATION 

SENSITIVITY STUDIES 

0 RIB DESIGN CONCEPTS 

Structural Analysis Results 

e FINITE ELEMENT ANALYSES WERE PERFORMED TO PREDICT SOLAR CELL STRESS 

e MASTER CURVES WERE DEVELOPED TO PREDICT SOLAR CELL STRESS As A 

FUNCTION OF SOLAR CELL, POTTANT, AND STRUCTURAL PANEL PARAMETERS 

204 
E NC APS U LATl ON 

9 

8- 

7- 

6- 

3 

2 

1- 

Parameter Limits 

lllllllllllllll111~ 9 

-8 

-7 

E-50000 - 6 

E-10000 - 

118 INCH THICK, TEMPERED GIASS 

(E POTlANT MODULUS, PSI) 

------ ---- 

-4 E =5000 

E-2500 

E lo00 -3 

!I

E =500 -2 

111111111111111II11, -1 

STRUCTW~AL PANEL POTTANT CELL 

ESP: 0,75-30 MSI Ep: 0.5 - 2.5 KSI E,: 5 - 30 MSI 

Ts,: 0.04 - 0,25 IN. 1,: 0.001 - 0.020 IN. 1,: 0,005 - 0,015 IN. 

asp: 7-24 ulN/IN/oc 0,: 1 - 12 UIN/IN/OC 

Thermal Stress Analysis (AT = 100OC); 

Glass Superstrate Design 

0: 

n 

x 

U 

E 

2 

0 

v) 

OOTlED LINE -ALLOWABLE CELL STRESS IN TENSION 

205 
ENCAPSULATION 

?I 

Thermal Stress Master Curve 

c NQtL. t Sc = TENSION -0 

a0 c - Sc 1 COUCRLSSION 

*si c 

'a 

0 

Q 

cn 

k 

e 

r u A 

206 

- . 

- 

SCT - SOCAR CELL MAX. 

EC = MOQULWOF SOLAR CILL, fPS0 
ENCAPSULATION 

to3 

3 

2 

102 

10' 

Pressure Stress Master Curve 

Scp - SOLAR CELL MAX PRESSURE STRESS. (KSI) 

- 

- 

- 

- 

- 

- 

- 

- 

c 

- 

- 

c 

- 

I I 1 Illlll I I I1 Illll I I I I1 Ill 

ssp STRUCTURAL PANEL MAX STRESS. (KSll 

ESp - MOOULUS OF STRUCTURAL PANEL. (PSI) 

tsp - THICKNESS OF STRUCTURAL PANEL, (IN) 

tp THICKNESS OF POTTANT (MIL) 

Ep 0 MOOULUSOF POTTANT (KSII 

Ec - MOOULUS OF SOLAR CELL, (PSI) 

tc \- THICKNESS OF SOLAR CELL, (MIL) 

Le - LENGTH OF SOLAR CELL, (IN) 

10-5 104 10-3 

REDUCE0 VARIABLE (t/C)p f11Et3~sp 

NOTE USE cunvE A FOR PRESSURE < io PSF USE CURVE a FOR PRESSURE - so PSF 

FOR INTEAMEOIATE LOAOS. INTERPOLATE LINEARLV BETWEEN A AND 9 

Conclusions - Structural Analyses 

0 VIABLE MASTER CURVES 

10-2 

0 THERMAL/HYGROSCOPIC EXPANSION COEFFlClENTS 

0 MODULUS OF POTTANT 

207 
ENCAPSULATION 

Optical Analysis: Objectives and Constraint 

0 OBJECTIVES 

- RADIANT ENERGY TRANSMISSION THROUGH ENCAPSULANT AND FRONT 

COVER LAYERS 

- RADiANT ENERGY ABSORBED IN CELL, ENCAPSULANT, AND FRONT 

COVER 

- GENERAL APPLICABILITY 

-- CELL MATERIALS AND TYPES 

-- ENCAPSULANT AND FRONT COVER MATERIALS 

-- SPECTRUM OF RADIATION SOURCE 

0 CONSTRAINT 

- NORMAL INCIDENCE 

- AM1,S SOLAR SPECTRUM USED IN ALL CASES STUDIED 

Optical Analysis: Assumptions 

0 ANALYSIS STRICTLY APPLICABLE TO SPECULAR SURFACES 

-- INCIDENT RADIANT ENERGl FLUX CONTAINS DIFFUSE COMPONENT 

0 CELL POWER CONVERSION EFFICIENCY DECREASES WITH TEMPERATURE (.5%/OC) 

0 SCATTERING, IR EMISSION IGNORED 

0 ZERO-DEPTH CONCENTRATOR PHENOMENA 

-- ACCOUNTED FOR IN COMPUTER PROGRAM 

-- NEGLIGIBLE FOR CLOSELY-PACKED SQUARE CELLS 

0 ANTI -REFLECTION COATINGS TREATED As IDEAL QUARTER-WAVE F! LMS 

0 ANTI-REFLECTION COATINGS DO HOT AESORB HEAT 

0 OPTICAL AND THERMAL PHEWMENA ARE UNCOUPLED 

208 
ENCAPSULA'I'ION 

Power Conversion Efficiencies - Silicon Cells 

WAVELENGTH, A 

AR-Coating Reflectance vs Wavelength 

(Coating Optimized for Encapsuiaflt-Silicon Interface) 

WAVELENGTH, >, MICRON 

209 
ENCAPSULATION 

Ratio of Power Input to Power Output vs AR Coating Thickness 

0.10 - 

P OUTPUT 

P INPUT 

0 

0.05, 0 0.02 0.04 t (MICRONS) 0.06 0.08 0.1 I' 0.12 I 

Optical Analyses Conclusions 

0 TRANSMITTANCE ' 0.45 RICRONS 

0 AR/TEXTURING CRITICAL 

210 
ENCAPSULATION 

Thermal Analysis Philosophy and Assumptions 

o OBJECTIVE - 

o COhSTRAINTS - 

o ASSUWPTIONS - 

PROVIDE FLEXIBLE THERNALIIOPTICAL PROGRAN FOR EVALU 

OF ENCAPSULATION DESIGNS CONSIDERING 

-- VARIABLE NUMBER OF LAYERS 

-- VAalABI !AVER MATFRILL, TU!C~YFSS 

-- VARIABLE VOLWETRIC OPTICAL PROPERTIES 

AND SURFACE PROPERTIES 

PROVIDE FLEXIBLE DESIGN TOOL No EDGE EFFECTS OR 

INTCRWNNECIION PHENOMENA ARE INCLUDED IN THE DEL 

CELL SIZE -- 

-- HODULE SIZE 

RADIAT:VE HEAT loss COMPONENTS HODELLEI: THROWH 

SFEClF ICATION OF GROUND AND SKY TEMPERATURES 

CONSIDER Oric CEI.L CENTQALLV LOCATED in NODULE 

Module Energy Balance - Superstrate Design 

SINGLE CRYSTAL CELL 

SKY (19.9%) 

-AIR (15.3%) 

WIND - 

-AIR (14.7%) 

GROUND (1.1%) 

-GROUND (14.1%) 

T N 

GLASSCOVER LAYER 

NO IRON 

POWER(o) y. 

ELECTRICAL 

OUTPUT 1.32 10.9 

ABSORBED 

REFLECTED 

TOTAL 

8.18 67.7 

-- 

2.59 21.4 

12.09 100.0 

~.~.:.:.~..:.~.:.~..~.~.~ ............... ~,!.~.:.:.:.:.:.~GRou~~~:.:.:.~~:~~~.:~.:~~~~~:~~~~~.~~ ...... :.:.z- .......... . . i. . . ..'... . . . . .... . 

211 
EN C A?SU LAT I ON 

Solar-Cell Temperature vs Backside Emissivity 

(Glass Superstrate Design) 

a2 0.6 1.0 

EM I ss IV ITY 

Thermal Analyses Conclusions 

0 Enissivirr P~RE CRITICAL THAN THERWL RESISTIVITY 

212 
ENCAPSULATION 

Electrical Analysis 

3 

I 

3 

c 

c 

2 - 

3 

0 

w 

POTTANT 

LOCATION OF 

MAXIMUM 

FIELD CEU 

UNES OF 

FORCE 

Objective 

DESIGI4 GUIDANCE TO PREVENT 

BREAKDOMI 

0 CELL EDCE/CORNER Rmius 

0 POTTANT THICKNESS 

0 CELL TMICKNESS 

‘GROUND PLANE 

Electrical isolation Studies 

0 FINITE ELEPIENT %DEL 

0 ELECTR I CAL/TMERMAL ANALOGY 

0 NASTRAN 

213 
ENCAPSULATION 

Therm a I - Elec t r i c a I An a I og y 

THERMAL PARAMETER 

TEMPERATURE T 

THERM/+L CONDUCTIVITY k 

TEMPERATURE GRADIENT TT 

HEAT FLUX 

INTERNAL HEAT GENERATION q 

-kVT 

ELECTRICAL PARAMETER 

POTENTIAL V 

PtRMITTIVITY € 

ELECTRIC FIELD 1&-V" 

ELECTRIC DISPLACEMENT 6 = 

CHARGE DENSITY i P= T.5 

Formula for Family of Solar-Cell-Like Shapes 

R / 

CELL tc 

I 

POlTANT 

t 

t 

tp 

GROUND PLANE 

% 'A Em=-(l+5) V ($ -1) 

tP 

FOR tp/tc >2 

214 
ENCAPS'JLH I ION 

Electrical Analysis Results 

0 FINITE ELEMENT UETHOD DEVELOPED AND VERIFIED 

0 ELECTRICAL STRESS INTENS IF I CAT I ON SEVERE ONLY FOR 

-- VERY SHARP CORNERS 

-- VERY THIN CELLS 

0 FOR EXTREHE GEOMETRIES, 

-- FINITE ELEMENT METHOD INACCURATE 

-- SIHPLE FORMULA DEVELOPED 

Electrical Analyses Conclusions 

0 VISIBLE ELECTRICAL M~DEL 

0 REAL WORLD VALUE OF R NECESSARY 

Conclusions 

0 VIABLE STRUCTURAL RASTER CURVES 

0 THERMAL GUIDELINES 

0 ELECTP~CAL hDELlNG TECHNIQUE 

0 ELECTRICAL BREAKDON MOST PROMISING FOR FUTURE 

FRUITFUL RESEARCH 

215 

ib NE13 13;JbY 

ENCAPSULATION MATERIALS AND PROCESSING 

SPRINGBORN LABORATORIES, INC. 

P.B. Willis 

POTTANTS 

OUTER COVER FILM 

~UBSTRATES 

PNTI -00 I LING TREATMENTS 

ULTRAVIOLET STABILIZERS 

FABRICATION CONCEPTS 

PDHES IVESIPR IMERS 

PHELu 

(TECHNOLOGY &~E.s) 

@PTlMl ZED t??TER I ALS FORMULATION 

~TERIALS LIFETIME AND AGING STUDIES 

FIELD EXPOSURES 

21 7 
ENCAPSULATION 

Module Components (Essential) 

0 PLUS ADHESIVES WHERE NEEDED 

SU,RFACE 

TREATHENTS 

OUTER r ’ COVER 

POTTANT 

b BACK 

COVEf? 

GPSKET 

A. ELIf1INP.TEE IN SUPERSTP-4TE DESIGN 

218 
ENCAPSU LATl ON 

Candidate Polymer Encapsulation Materials 

SlimTE: 

POTTANTS: 

wm. COVERS: 

POROUS SPACER: 

BACK COVER: 

GASKETS; - 

LOA0 BEARING TOP COVER 

SODA - LIE GLASS (LOW IRCN) 

EWIP.NICAL STRESS RELIEF, ELECTRICAL ISOLATIM, 

CELL POSITIOIIIWG, ENVIROWIQHTAL ISOLATION, 

CORROSION BARRIER 

ETHYLEHVVINYL ACETATE (RIA) 

ETHYLENVnnHYL ACRYlATE (UA) 

ALIPHATIC POLYURETHANE (W) 

MINATKM TYPES 

CASTIE TYfB 

3 

mytaum ACRYLATE) (BA) 

PROVIMS HARD SOIL RESISTPMT SURFACE, UV 

SCREENIHG, MECHANICAL BARRIER 

ACRYLAR 22417 

NOW-SCREENING TYPES? $.%;Xi, FEP 

PROVIDES FIXED SPACING FOR MECHANICAL, ' 

DIELECTRIC ISOIATION: EVACUATION PATH 

WRING LPMIHATION 

CRANEGLASS (NON-WOVEN GIASS CLOTH) 

MECHANICAL BARRIER, ELECTRICAL ISOIATION 

@sSIVITY FOR COOLING flli3UI.E 

KORAD 63O00, TEDLAR 150BS3WH 

SCOTCHPAR 20CP - WHITE (POLYESTER) 

OTHER WHITE FILE? 

WM RUBBER 

(PAWLING RUBBER CO,) 

219 
ENCAPSULATION 

Sealants 

FUNCTION AND PROPERT I E3 : 

PREVENTS INTRUSION OF RAINWATER 

0 SELF HEALING 

0 INEXPENSIVE 

WEATHERABLE 

NOW-STAINIFG (NO SoLvmrs) 

e APPLICABLE! 

SELECT IONS : POLY SULF I DES, BUTYLS, U RfM ANES , OLEF TNIACRY L I C COPOLYHERS 

BUTYLS MEEr ALL CRITERIA EXCEPT APPLICATION 

AUTWTIM TWO-PART URETHANES MY BE BEST CHOICE 

0 MORE WORK NEUED 

220 
E NC APS U LATlO N 

Pottant s 

0 RECEIVED GREPTEST EPPHAEIS TD DPTE 

0 C@NSIDEP€l! T(! BE POST CRITICAL CPPPONENT DUE 

T@ PE8U IPEMNTS CF : 

0 CPTICPL TRPllSPPPEtlCY 

LOW fl(VD'1LUZ (STPESS RELIFF) 

0 LOP SOFTENING (PELT) PC'It'T 

BELOV SOLDER FLN P@It!T 

0 LOP (MELT) VISCPSITY 

LOW STRESS CN CELLS 

P.ESIPTANT TO LIGHT ANI! HEkT 

0 LOK6 LIFE 

0 HO SUODEN CHPNGE IN PECHPFICAL P'OPEPTIES 

(CLASS TRAHSITIOtl TEHPEPkTURE) 

D I ELECTR IC STPENGTt! 

0 PCITPGLE FOP. VOLURE PWJCTIOtl 

0 I!(' CREEP AT CPEPPTIHG TU'PEPATI'RES 

(CUPJIELE) 

0 LOP COST 

FORK t!!.S PESULTEI! I# C@W€PCCPL EVPLUPTI!?tl PRODUCT 

(SPRIliGEOPt! RIA P 901.8) 

WHERE IRE YE NOIJ? 

YPEPE PRE YE G@It!C? 

221 
EN CAPSULATION 

History of EVA (Springborn A-99 18) 

ETHYLENE/ETHY L PCRY LATE 

PLASTI c I ZED PVC 

lxlmmuw 

HIGH I~ELT Visc~r'fv 

THERMOPLASTIC 

ETHYLENE/PROPYLENE/DI ENE N~T WEATHERABLE 

ETHYLENE/PROPYLENE NOT WEATHERABLE 

STYRENE/BUTADl ENE NOT HEATHERABLE 

i?NOMER PROCESS TEMPERATURE HIGH 

~OLYVINYL ALCOHOL FATER SOLUBLE 

IHERMOPLASTIC URETHANE 

Y I TON" PQLYMERS 

ETHYLENE/!~ETHYL ACRYLATE 

HIGH COST 

FEW GRADES, HIGH VISCOSITY 

VEfY HIGH COST 

&rlYAmE RE'€LPANY GRADES AVAILABALE 

WIDE RANGE OF PELT FLOWS 

EASY TO PROCESS 

LOW COST HANDLING/PROCESSING (?I 

THERMOPLASTIC (No CREEP 

RESISTANCE) 

ULTRAVIOLET SENSITIVE 

OX IDATION SENS I TIVE 

GOOD ADHESlVE PROPERTIES 

0 NEED TC FORMULATE A PV PODULE GRADE 

222 
ENCAPSULATION 

BASE RES IN SELECT I ON : 

0 MUST BE OVER &3CX V!NYL PCETETE FOR ACCEPTABLE TRANSPARENCY 

0 VERY HIGH (-45: VIPIYL ACETPTE) APPEAR TO EE LESS STAELE 

(HFPT LIGHT) 

FINAL GRADE SELECT I ON : 

EYLtwi 

EY 101-25 

EY 902-30 

UE 645-35 

UE 638-35 

ELVAX 250 

ELVAX 170 

ELVAX 240 

u? UELLMm 

us I 4@ 7,s 

us I 4P 70.0 

us I 33 48,O 

us I 31 24.0 

DUPONT 33 43,O 

DUPONT 36 G,7 

DUPONT 28 43'0 

CHOICE: ELVA)! 150 Bi!Imiu 

. PI MI^^ 7 VP FQP clwn OPTICPL 

, HIEVEST MELT FLOP THPT FAY STILL 

BE EXTR.U3ED EASILY (HANDABLE) 

, LOYEST VISCO$ITY AND LOYEST STRESS 

Otl CELL STRIF!G DURING LAMINPTIOK 

223 
ENCAPSULAT!ON 

224 
ENC4PSULATION 

- E-E-€-E-€-€-€-€- VA-E-Vr-VA~-VA-Vi-E-E-VP 

- 

ETHYLENE SECTIM fiTwLem1rn b.CETPTE SECTION 

FIE1 PERCXIDE CPCICE: LUPERWL - 101 (LUCIM'L CW.) 

CURES THRCilCE A GWf5 WLY! 

ADVANCED FERCXIDE STUDY: WPEPSOL TEEC (LUCIWL CORP. 1 

CUP.@ THPCUGH EcM WE PWC VINYL PCETATE 

mFWaQi(iEL P. 

TDIMPSTURE, oc lMO 1400 lSo0 1w 

Tin€, MIR. IC 3 2 1 

4. LPECRATCRY CURES It' PLPTEN PRES$ 

225 
ENCAPSULATION 

I +mi 

226 
ENCAPSULATION 

cumm 

ELVAX 150 

LUPERSOL 101 

CYPSORE UV-53lA' 

FJlJGARD -P 

TIWW 77I?* 

LUrnSPL TBEC 

LEKL 

100 

1.5 

0.3 

0.2 

0.1 

1.5 

EU)#flOhl 

POLYMR 

CURING AGENT 

UV SCRENEI? 

PWTI OX IMNT 

HIHDERED WINE LIGHT STPE. 

HYCROPEROXIDE DECOPOSER) 

(FREE RADICAL TRAP AND 

(REPLACES LUf'ERS@L 101) 

MTRUSIOW: (EASY) 

STCRAGE : 

SCREY - LDPE 

BARREL - EQ0C 

DIE - 75% 

VD - 24:l 

MJDULE PEPFCIPR4YCE PT 50%: EXCELLENT 

COfT (SPPINGEORN) : $0.35 PER SOUARE FOOT 

P. THIS COMBINATION PARTICUURLY EFFECTIVE; HALS PROTECTS UV-531 

???? OXIDATION. 

(ALLE~I, JCPS, V27, 276~ (1982)) 

227 
EN CAPS U LATl ON 

EVA 9918 - STPND9PD CIALUATl@t! GRADE 

EVA 15295 - "FAST CUCE' GRADE 

G@AL: THIRTY YEARS SERVICE LIFE 

- 0 H@umYcuKNoN? 

CMmITIMI x E?Bow(Ty 

Rs/4 9OC 49,lXJ HRS. SUPFACE 

OTHERS 

THERTAL, %? 8,000 HRS. OPTICAL 

t€CWt!ItpL 

THERTAL, 13?C 3,003 HRS. ECHBYIVL 

OPTICAL 

RS/4 HPTER 10,0[10 HRS. ANY 

RS/4 89C 8,W HRS. ANY 

RESULT 

CRACKING 

No CHASE 

SLIGHT YEUW 

M CWGE 

102 RE?!AIIY 

742 REMIN 

NO CHAM 

N@ CHANGE 

0 DEGRADATION HOTICED ONLY IN EXTREE C@NDITIONS 

a NEE@ FOP !EANI!4GFUL SHORT TEfM TEST 

228 
ENCAPSULATION 

Accelerated Aging Test Program 

amm RanmER#L &INt 

229 
EN CAPSULATION 

Outdoor Photothermal Reactors 

(BT) 

7O'C NoQwlQmHus 

wc m 10s-c 

WA AB928 

mImd AT: 

230 
ENCAPSULATION 

EVA Aging 

231 
ENCAPSULATION 

muAlIoN 

EVA 9918 

EVA 9918 

EVA 9918 

EVA 9928 

aVPx8L-m 

ELvm 

EVA 9918 

e 

0 

0 

232 
ENCAPSULATION 

Outdoor Photothermal Reactors: Module Results 

mm 

WC 

M'C 

WC 

0 

e 

TIE - 

233 
ENCAPSULATION 

Outdoor Photothermal Reactors 

UCEWL dR: 

2 34 
ENCAPSU LATl ON 

Pottan t s 

ADVANCED FORMUIATIONS CANDIDATE ADDITIVES : 

uv-2098 

uv-2308 

Plop! 79-4005 

78-6121 

UV-!346 

HOETPVII! f!-20 

CHIMKORF 944 

P -2590-EF 

PYERICPII CYPNAPIIDE 

AMEFICAN CYANAVIDE 

!iATI@NAL STPPCH 

KPTIONPL STPYCH 

AMEP I CAI! CYPIIPMIDE 

AflEP!CL;, HCIECHST 

CIEP GEIGY 

GEORGIA PPCIFIC 

UV SCREEN 

UV SCREEV 

UV SCREEN 

UV SCPEEF! 

FPLS 

HPLS 

HPLS 

HPLS 

JEPCTIVE 

PClLYttERIC 

REACTIVE 

POLYMERIC 

POLYMEPIC 

PEACT IVE 

POLYMERIC 

POLYMEP I C 

TP BE USED YITH: 

LUPERSOL TBEC LUCID ICL PEPOXIDE CURING AGENT 

NO PDDITIONAL ANTIOXIDPr!T AJDD - 

HPLS CCMFCUNK PPPEPP TO 2E SUFFICIEtlT 

0 FUTURE FORMULATICNZ \'ILL UYE THPEE CCYPONENTS: 

TBEC, UV SCREEN, tlPLZ 

235 
ENCAPSULATIOP 

Advanced Formulations 

EVA 14747: C?KTAINS U4-m CMWED 

e m1STAN-r m rnYSIS 

(Urn - 1,500 HOURS - mc) 

OPT - WC 2,003 HIE MILLIE 

236 
ENCAPSULATION 

TItlE AtID 

I?duL;iE CDNDITION 

GLPSSIRES INITEDLAR' 

7OoC EVP 9918 1 

3,000 HP5, EVA 16713 P. 1 NO CHANGE 

EMP 16717 

EVP. 14747 J 

90% EVA 9918 SOME COLOR FLOP 

3,000 HRS, NOR COPPER 

NO CHANGE 

!?/A 16718 A 

EW 16717 

EVA 14747 

l0S0C 

3,000 HPF, 

EVP 9018 SNEPE COPPER RXN 

DEPOLYVEP IZAT I OH 

DEW11 NATION 

EVP. ;67!8 A SLIGET COLOR (CQPfTf? 

EM! 16717 SLIGHT COLOR (COPPER 

EVA 14747 SLIGHT CO'.@R (COPPEP 

EVA 16718 A: TBEC, UV 2098, TINUVIN 770 

€!A 16717: TBEC, UV 2098, TINUVIN 770 

EVA 14747: LUPERSCL 101, UV 2098, TINUVIH 770 

A. TEDLAR 150 BS 30 WH/68040 ADHESI~S 

237 
ENCAPSULATION 

Adhesion Experiments 

EVA A9298 0.25 u? 

ZdoK) 0.05 29 

€'/A EE5/ 0.25 3l 32 

26030 cj 10.9 3.5 

m m/ 0.25 7.4 58 

Z4EO 0.8 49.3 39.3 

238 
ENCAPSULATION 

Antisoiling Experiments 

SUWACE CdMISTRY 

0 HARE 

SmMTH 

0 HYDROPHOBIC 

0 OLEOPHOBIC 

0 ION FREE 

0 LO\ SURFACE ENERGY 

SURFACE IHVESTIGATED 

SUNADM GLASS 

0 

0 ACRYIAR (ACRYLIC FIM 1 

TEDLAR (100 BG 30 UT) 

TREPTWNTS REMAIIIIK 

L-1668 FLUOROSILANE (31) 

0 E-382C PERFLOUPODECPNCIC ACID/ 

SILANE (MW CGRW!G) 

239 
ENCAPSULATION 

Soiling Experiments 

240 
EN C A PS U LAT i 0 N 

241 
ENCAPSULATION 

242 
E NCAPS Cl LATl ON 

Additional Activities 

243 
E NC APS U LATl ON 

Conclusions 

Future Work 

244 
PHOTOTHERMAL DEGRADATION OF ENCAPSULANTS 

JET PROPULSION LABORATORY 

R.H. Liang 

Objectives 

DEVELOP MECHANISTIC MODEL TO PREDICT LIFETIM 

OF ENCAPSUMNTS WITH RESPECT TO PHOTOTHERMAL 

DEGRADATION 

DEVELOP VALID ACCELERATED PHOTOTHERMAL 

TESTING PROCEDURES FOR EVALUATION OF 

EN CA P '5 U LAMS 

Mechanistic Model 

I DEGRADATION I 

1 

I NTERMED I ATE S DEGRADATION 

DEGRADATION 

Approach 

! TUDY MECHANISMS OF PHOTOTHERMAL DEGRADATION 

PYOTOTHERMAL AGING OF MATERIAL SPECIMENS 

PHOTOTHERMAL AGING OF TWO-CELL MODULES 

245 
EN CAPSULATION 

Mechanistic Studies 

STATUS 

LASER-FIASH ESR ( ELECTRON SPIN RESONANCE 1 APPARATUS 

IN OPERATION 

KEY DEGRADATION INTERMEDIATES IDENTIFIED 

TIME, TEMPERATURE AND LIGHT FLUX CORRElATlON 

I NIT I ATED 

246 

ENCAPSULATION 

Time Profiles md Intensity of Peroxy Radical 

as a Function of Light Intensity 

a). 100% b). 465% c). 26% d). 12% 

PERCXY RADICAL IG iec II c P1 

248 
EN CAPS U LATlO N 

In-Situ Steady-State ESR Spectrum of Photoirradiated 

PnBA at Room Temperature in Air 

SIMULATED TERTIARY 

f PEROXY 

249 
t- N CAPS C I LA 1-1 ON 

In-Situ Steady-State ESR Spectrum of 

Photoirradiated PnBA at 23OC in Vacuo 

Time Profile of Tertiary Rqdical at 2S°C in Vacuo 

LIGHT OFF 

E - 

v) 

L E - 

LIGHT OFF 

E - 

v) 

L E - 

c - -- 

LICM ON L--- 

TIME - 

2 50 
EN CAPS ULATICN 

Half Life of Radical Decay as a Function of Temperature 

TE hl PER ATU RE I HALF LIFE 1 sec ) 1 

3.9 -+ 0.4 

55"C 4.6 f 0.6 

15 C 2.9 _+ 0.6 

Temperature Dependence of Rate Constants for 

Photoinduced Crosslinking of PnBA in Vacuo 

251 
ENCAPSULATIOW 

Photothermal Aging of Material Specimens 

AGING PARAMETERS 

00 UV - 0 SUNS, 2 SUNS, 6 SUNS 

0. TEhlP. - 75°C. 85°C. !05’C. 120°C. 135°C 

SAMPLE CONFIGURATIQr3 

0 EVA - SUNADEX /EVA I PYEX 

TEDLAR /EVA I PY REX 

PnBA - SUNADEX I PnBAl PY EX 

STATUS 

SUPADEX I EV4 PYREX 

0 0 6 SUNS AT 35‘C. 105‘C. lZO-‘C. 135’C COhlPLETED 

0. 0 SUNS AT 85’C. 105’C. 12O’C. 135C COMPGTED 

0. 2 SUNS AT 85’C. 120’C I?! PROGRESS 

0 SUNADEX i PnSA I PYREX 

0. 6 SUNS A7 85’C, 105’C, 120’C, 135-C COMPLETED 

252 
ENCAPSULATIOb 

Transmittance Spectra of SunadexlEVAIPyrex 

at 6 Suns and 1 2OoC 

VJAVELENGTH, nn 

Transmittance Spectra of SunadexlEVAIPyrex 

100 T I I I 

ViAVELENGTH. nm 

253 
ENCAPSULA llON 

Transmittance Spectra of Sunadex/EVA/Pyrex 

at 2 Suns and 120°C 

Loss Of Transmittance of Sunadex:EVA/Pyrex 

as a Function of Time at 1 20°C 

0 8 
ENCAPSULATION 

Photothermal Aging of 2-Cell Modules 

STATUS 

CHARRCTERIZAT!!X OF CER-G COMPLElED 

TEMPERP.TURE RANGE 55% TO 120°C 

UV FLUX 6 SUNS To 15 SUNS 

TESTING AT 60°C. SS"C, 120°C AND AT 6 SUNS 

INITIAlED 

255 

POLYMER-POLYMER INTERFACE BOND STABILITY 

CASE WESTERN RESERVE UNIVERSITY 

J.L. Koenig 

Infrared Surface Spectroscopies 

Reflectance 

specular diffuse 

Diffuse Refmtance Optics 
ENCAPSULATION 

140. 

120. 

p. 

R 

E 

N 

5 40. 

I 

1 

Y 

20. 

0. 

Silane Coupling Agent 

0 OCH3 

II I 

CHZ = C - C - 0 (CH2I3 Si - OCH3 

I I 

CH3 OCH3 

8-MPS 

Approximate Surface Coverage 

% w/w 

0,001 

0,OI 

0, ro 

i,O 

layers 

0,05 

0153 

51 3 

53 

f 0,269 m2/g qlass 

>; 

0 

9 

x 

0 

X 

0 

258 
EN C B.PS CI LATlO N 

ICU. - 

1100. - N 

1 

E 

I2 

1 

E 

I 

N 

1 

: 80. - 

060.- 

5 90. - 

5 

I 

1 

y 20. - 

MPS/Amine Modified Glass 

0 

0 

0 

0 

0 1 I 

I I I I I I I 

*O 

0. 

1 

MPS/Amine Modified Particulate Glass 

0.m 

0.06 - 

0.04 - 

1 

INCER3ING LOFDINGS 

( 0.016 - 3.00 l.EICHT PERCENT 1 

-0.02 

i8m 1750 1700 1650 1600 1 

WWMBER (CW 1 ) 

259 
ENC APSU LATl ON 

0.5 .' I I I 

Acid Wash 

H H 

0' 0' 

1 GLASS [ c2Izrl GLASS 

260 
E bi CAPS U LAT IO N 

0. 35 

0. 30 

0.25 

0.20 

0.15 

0. 10 

0. os 

0.00 

Acid Washed 

50 layers rt, 

/ VI -- _. I I I I I I 

3200 3100 3000 2QOO 2800 2700 

YAVENUWBER tCM-1) 

261 
ENCAPSULATION 

Base Washed 

0. 60 

0. so 

0. 40 

0. 30 

0. 20 

0.10 

3. 00 

hydrothermal tr. 

- 

- 

si lane modified 

. 

-0.10 -/- I I I f 

3200 3100 3000 2300 2000 2700 

WAVENUMBER (CW- 1) 

262 
ENCAPSULATION 

Sunadex Glass 

0. 40 

0.39 

0.20 

0. 10 

0. 00 

-0.10 

50 layers 

- hydro t h e rm a I t r 

3200 3100 3000 2900 2e00 2700 

WAVENUMBER (Cn- 1) 

263 
EN CAPS U LATlO N 

1.241 

0. .9?3 

0.705 

0. 437 

0. 168 

-0. 100 

Pristine Glass (DRIFT) 

3800 3180 2SfjO 1940 1320 700 

cn- I 

2 64 
ENCAPSULATION 

3 

265 
ENCAPSULATION 

I. -.%I 

1-39? 

1.015 

0.644 

Silane Modified Glass (DRIFT) 

100 layers thick 

-0. 100 

3800 700 

266 
ENCAPSULATION 

Composite Interface 

Silane ot gloss 1 EVA 

interface 

I 

=CI 

EVA /gloss '\ composite 

loss 

305t 3000 2950 2900 2850 2800 2750 

UAVEHUWBERCCM-I) 

267 
ENCAPSULATION 

0. 

7. 

8. 

3. 

4- 

3. 

2. 

1. 

0. 

Silane at gloss/ EVA 

inter foce 

Silone on substrate 

I \ surface 

=‘“r 

3020 3000 2900 2960 2940 2920 2900 2990 2960 

1.4 

1. 2 

1.0 

0. e 

0. 6 

0. 4 

0.2 

0.0 

-0.2 

C=O STRETCHING 

EVA19 lass composite 

Silane modified glass 

Silane at EVAIglass interface 

\ 

! BOO 1700 1760 1740 1720 1700 1600 1860 

VAVENUMeFR (CM-1) 

268 
ENCAPSULATION 

In-Situ Composite 

16. 

1 c. 

12. 

10. 

a. 

5. 

-. 

2. 

0. 

c=o 

I I I 1 I I 

4000 3500 3000 2500 2000 1 so0 1000 500 

YAVENUMeER CCM- I > 

269 
ENCAPSULATION 

EVA-Glass Composite 

35. 

30. 

2s. 

2c. 

1 s. 

IO. 

5. 

G. 

i 

-5. 1 1 I I I i I 

3100 3D50 3000 205G 2900 2850 2800 2750 

2 70 
ENCAPSULATION 

POLYMER-METAL INTERFACE BOND 

J. Boerio 

15272 &>- 

STABILITY 

Strategies 

Ellipsometry for Determining Stability 

of Polymer-Metal Interfaces 

271 
ENCAPSU LATl ON 

Sample Cell for In-Situ Ellipsometry 

of Metals Exposed to Water 

272 
EN CAPS U LATlO N 

In-Situ Ellipsometry for Aluminum Undergoing 

Hydration in Water at 4OoC 

2 73 
EN CAPS U LATlO N 

Infrared Spectioscopy for Determining 

Chemistry of Polymer-Metal Interfaces 

Active Component in A-I 1861 Primer 

2 74 
ENCAPSULATION 

Transmittance IR Spectrum of 7-MPS Monomer 

I 

1 

. 

I 

I 

I 

I 

1 

1 I 

1 

I 

+: 

to00 WOO 1600 1400 1200 1000 UIO 600 

4 

CY 

IR Spectra of y-MPS Films With Three Different 

Thicknesses Deposited cn Aluminum Mirrors 

1u 

0.6. 

0.126s 

275 
ENCAPSULATION 

IR Spectra of (A) Thick and (6) Thin (Monolayer) 

Films of 7-MPS on Aluminum Mirrors 

N 

0.021. 

1s 

1.. ,a. :. 1,. 

I.... 

1800 1600 

C k 

1400 1200 1000 800 

CY -l 

1000 800 

t1800 1800 1400 1200 

c h14 

2 76 
EN C A PS U LAT IO N 

I I t I I 1 . I 1 I I I I I I I I 

1800 1 eo0 1400 1200 1000 a00 

-1 

CM 

Conclusions 

1. ELLIPWETRY IS EFFECTIVE FOR NE OF POLYNWETAL 

IwTERfACES, 

2. IR IS EFFECTIVE FOR UENISTRY OF INTERFACES, 

Futuie Work 

1. APPLY THESE TEWIWES TO INIEIIFACES LIEEN EVA AND 

OTHER ETALS SuQl AS NI AND Cu. 

2. ME REC'*?KNDATIQIs RR 2WER FO~lAT1ON AND 

APPLICATIW OF PRIERS FOR BONDING EVA TO rnMs. 

277 

PREDICTING ELECTROCHEMICAL BREAKDOWN 

IN TERRESTRIAL PHOTOVOLTAIC MODULES 

JET PROPULSION LABORATORY 

G.R. Mon 

The Problem 

The Mechanism 

Elect roc hemical Corrosion Mechanism 

I -Y 279 

PRECEDIISG PAGE BLANK NOT FILMED 
ENCAPSULATION 

Experimental 

Test Specimen Geometry 

X 
ENCAPSULATION 

Parameter Dependencies 

Electrical Conductivity, PV8 

1l.C 

281 
ENCAPSULATION 

Y 

Y -I 

10-l'- 

Electrical Conductivity, EVA 

I I I I I 

282 
ENCAPSULATION 

Normalized Cell Power Output vs Interfacial 

Charge Transferred in 1944 h of Test Exposure 

Conclusions From Experiment 

Under conditions of the experiment, median time to cell failure occurs 

aver the passage (between cell and frame) of about QT = 4 coulombs 

of charge per 10 cm of interface 

Ni-solder metallization appears to be the most stable, and silver paste 

seems to be the least; EVA affords the greatest protection against cell 

corrosion, unprotected PVB the least 

The electrical conductivities of PVB and EVA are known in the T-RH 

ranges experienced by deployed modules 

283 
EN CAPSULATION 

Design Algorithm 

0 Life prediction 

Determine median cell life for each series cell 

Determine failure rates for each cell 

Determine failure rates for each module 

Determine the number of modules that fail each year 

Least life-cycle costing 

Determine the break-even cost of delivered energy 

Establish decision-making criteria for selecting among 

various cost-performanco alternatives 

Life Prediction: Median Cell Life 

For several sites around the country, SOLMET weather data give daylight 

hours per year that a module experiences at various T - RH combinations 

Use SOLMET data plus 0-data for the proposed encapsulation to generate 

E ai q; the yearly cl.arge transferred, then, is 

Qy = V(Eq - 7i)K coulombsIyear 

The median time to cell failure is 

QT (= 4 coulombs) ?M = years 

QY 

284 
E NC APS U LATl ON 

0 

2 

303 

519 

531 

SOLMET Weather Data: Hours per Year at T /RH 

Combinations Listed (Insolation > 5 mW/cm 22 ) 

0 0 

0 0 

0 0 

34 0 

182 c 

- 

cd imp. 

't 

85 

15 

65 

55 

45 

35 

25 

15 

5 

05 

15 

65 

55 

45 

35 

25 

15 

5 

85 

15 

65 

55 

45 

35 

25 

15 

5 

- 

0 

0 

0 

0 

33 

I 15 25 

0 0 0 

0 0 0 

0 0 0 

0 0 0 

3 0 0 

1;; I 1;; 

61 72 

0 0 

0 0 

0 0 

101 

39 

0 0 0 

106 15 

80 78 

78 60 

0 0 

0 0 

0 0 

ANWMT Rn. 'I 

1;; I 1;; 

61 72 

0 0 

0 0 

0 0 

106 15 

80 78 

78 60 

0 0 

0 0 

0 0 

0 0 0 

4 0 

104 10 

PVB EVA 

r 

16 

0 

0 

0 

0 

0 

0 

- 

0 0 0 0 

::: I 31: I 22: I a! 

- 

15 

0 

0 

0 

0 

0 

0 

3 

3 

- 

10 

0 

0 

0 

0 

0 

0 

28 

92 

48 

0 

0 

0 

0 

2 

151 

1 

0 

- 

- 

-- 

0 

1 0 

210 

0 0 

0 

0 0 

0 

0 

0 

23 

6 

0 

The Quantity Coiq for PVB and EVA at Selected Sites 

SITE 

6.80 X I ALBUllUERllUE 3.16 X lo-' 

4.54 x 10-5 

2.06 x 10-4 

1.84 x 10-7 

5.91 x 10-7 

285 
ENCAPSULATION 

Median Time to Failure Exhibiting Dependency on Site, 

Encapsulation, Voltage and Cell-to-Frame Distance 

I 1 AOUNO CELLS IN PVB ROUND CELLS IN EVA 

'Y. 

YEARS 

TU. 

YEARS 

OB0 

I RECfAlGULM CELLS IN PUB I RECTANGULAR CELLS IN EVA I 

I 8 - 10 cm t - 0.114 a I TI. 

YEARS 

TIY. 

YEARS 

286 
1 CAPS ?I LAT IO N 

Life Prediction: Cell Failure Statistics 

Assume log-normal failure statistics, i.e., the logarithms of the times 

are normally distributed 

The probability that a cell fails in the tth year is 

t-1 t ZM 

u = 1.3 is assumed based upon values determined by other 

investigators of similar problems 

Life Prediction: Module Failure Statistics 

Assumptions 

Only module edge cells, r in number, fail electrochemically 

All cells of a particular module experience the same module 

operating voltage: the mean of the module terminal voltages 

The probability that a module fails in year t, conditimal upon its not 

having failed before year t, is 

qt = 1 - 11 - PCELL(t)Ir + 

The actual module failure rate - the probability that a module fails in 

year t - is 

t- 1 

Qt= 1- Qi *qt t >1 

Q1 = q1 

[ i=l ] 

For an N-module series source circuit, the yearly average module failure 

probability is .N 

287 
ENCAPSULATION 

Yearly Average Module Failure Rate vs Years of Operation 

YEARS Of OPERATION 

Conclusion 

Module electrochemical breakdown rates are predictable! 

2 88 
MODULE FLAMMABILITY RESEARCH 

JET PROPULSION LABORATORY 

R.S. Sugimura 

D.H. Otth 

ARC0 SOLAR, INC. 

J. Arnett 

K. Lewis 

Introduction 

Objective: 

Approach: 

Phase I: 

Phase II: 

Develop the technology base required to construct fire-ratable 

modules 

Explore new materials of construction and module 

configurations to achieve increased tire resistance 

Assess fire-resistance capability of current PV module 

designs 

Perform parametric tests to characterize flammability 

Phase 111: Hypothesize and test improved construction techniques that 

lead to increased fire resistance 

289 
ENCAPSULATION 

r 

I& 

Spread-of-Flame Burning Brand 

1 Time Distance Size 

Background 

I i Class A 1 10min 6 ft 

1 Class B 10 min 8 ft 

1 Class C 4 min 13 ft 

I 

! 

Tests for Fire Resistance of Roof Covering Ma’xials, UL-790 

Spread-of-flame test-distance that flame has spread. No flaming or 

Burning-brand test - until flame, glow and smoke disappear. No 

glowing brands of roof material 

sustained flaming on underside, production of flaming or glowing 

brands of roof material 

I 

1 12 x 12 x 2 114 in. 

6 x 6 x 2 114 in. 

1 112 x 1 112 x 25132 in. 

290 
ENCAPSULATION 

Chronology 

Exploratory testing (June. 1980; August, 1981 1 

GlasslsiliconelCRES pan (Bfk 111) 

SylgardF RP back (Blk 111) 

Glass/siliconelPan-L-Board (Blk IV) 

GlasslEVAIT (Blk IV) 

Fiedings 

Silicone modules are inherently fire resistant 

EVA modules are highly flammable. mav not be fire ratable 

Manufacturers' testing (1 983) 

Parametric testing (January. 1984) 

27 burning-brand tests 

9 different manufacturers 

3 different encapsulantsl8 different back surfaces 

Parametric testing: findings 

Difficult to maintain module integrity 

Glass shatters due to thermal stress 

Penetration of back-surface material is disastrous 

hydrocarbon encapsulants are highly flammable 

Heating from brand is highly localized 

Joint ARCOlJPL test program (February, 1984) 

Fabricate and test experimental modules 

High-temperature back-surface materials 

Improved module construction techniques 

291 
ENCAPSULATION 

ARCO-JPL Flame Retardant Test Program 

II I I 

Mbmiwllrdl 

Ts F 

Ps P 

P 

Ts P 

Ps F 

F 

Ps F 

Ts F' 

- 

- 

F 

1s Q 

- 

Summary 

Temperature measurements indicate that materials with high 

thermal stability are required to maintain back-surface integrity 

Avalrbb hqh-temperature materials are potentially effective 

in this apmtion 

Future Work 

Complete burning-brand effort 

Analyze data 

Nominate candidate materials 

Identify cost tradeofis 

Start spread-of-flame research 

292 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

M.H. Leipold and D.B. Bickler, Chairmen 

Presentations on 11 on-going process developeats were made during the 

technology session. 

forution, thick- and thin-film deposition and hydrogen passiwation. 

Areas being inwestigated are metallization, junction 

Vestinghouse Electric Corp. Advanced Energy Syst- Division reported on 

s~ltaneous junction formation using liquid dopants. 

f8bricated using n-:ype dendr! ic web. 

front junction was a major problem. 

be one 8pproach to a solution. 

during simultaneous firing. 

taneously fired cells were measured. 

A p+nn+ cell was 

Cross-doping of phosphorus into the 

Earlier fomation of a harder glass will 

Desired diffusion profiles utre obtained 

Efficiencies up to 12% yere found when skime munt of LBIC (laser-beam induced-current)-imaged grain-boundary 

activity has little or no effect on space-charge recombination or fill factor, 

according to Solarex Corp. Continuing work on large-grain polycrystalline 

silicon (Stmix and Uacker) has also shown that there is a strong correlation 

between quasi-neutral recombination and electrically active grain and subgrain boundaries. Mditional findings were: Voc of polycrystalline cells 

is 20 to 60 rV lover than that of single-crvstal cells; large data scatter 

correlates with inclusions; rost Voc scatter is accounted for by .JQ~ 

variation. 

cells, vas just starting. 

hother contractual effort, hydrogen passivation of polycrystalline 

Caltech diffusion barrier studies continue to produce results and have 

attracted interest fra industry and other R&D laboratories. Certain 

amorphous wtallic layers can be very stable at high temperatures. 

concern in selecting amorphous metallic layer constituents are crystallization, reaction with underlying silicon or reaction with overlying metal. 

Rules for selecting amorphous film con6tituentr are: 

plus a metalloid; use two transition metals with low solubility and that have 

a deep eutectic; use two transition metals of different crystallographic 

structure. Films are formed by ensuring a ra-;dom atomic arrangement and using 

low-temperature deposition with high heat dissipation. Potential solutions to 

reactivity of amorphous metallic films are: Use an intermediate layer; use 

early transition metals with high reaction temperatures with silicon; nitrogen 

containing alloys show promise; ternary alloys show promise. 

Areas of 

Use a transition metal 

"he HOD (metallo-organic decomposition) work at Purdue University continues to provide interesting results. Many organic compounds and rheology 

adjusters can be used to form the HOD inks. 

need for fairly high-purity organic precursors so that all organics break down 

at essentially the same temperature. Ink requirements for screen printing 

are' 

at low shear rate; be pseudoplastic and thixotropic. 

also being studied for compatibility and boiling point. 

baseline procesaes with silver neodecanoate are being pursued: 

xylene and solvent exchange, solution with toluene and solvent exchange, and 

Experimental work has shown the 

have very low vapor pressure; have viscosity in the range of 100-500 Pa 

Available solvents are 

Three different 

solution with 

293 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

solid compound plus additive. 

investigated. Important parameters are: purity of ingredients, heating rate 

between 70% and 22S°C, and air flow. 

is not fully understood, dense films with good adhesion and conductivity have 

been produced. 

Different furnaces and air flows are also being 

Although the mechanism of adhesion 

Spectrolab Division of Hughes Aircraft Co. has continued research into 

molybdenum-tin combination has adequate conthe non-noble front aetallitation system of molybdenum-tin-titanium hydride. 

Sotme interim conclusions are: 

ductivity; shunting is never a problem; solderability is a major problem; more 

work is needed on vetting phenomena; a cellulosic vehicle is best. 

analytical technique is being used to obtain real-time and videotaped visual 

SFW data that can be used to examine ink behavior during firing. 

of research findings has been gained by using fully described inks from 

Electrink, Inc., instead of proprietary formulations from vendors. 

A new 

More control 

Electrink, Inc., has been examining viscosity measurements as a means of 

process control of thick-film printing. 

convenient to make and can be reproducible. 

production application and are a means of correlating composition and condition of the ink. Three different viscosity conditions can be found: Newtonian 

(viscosity is constant with varying shear rates); plastic (viscosity decreases 

with increasing shear rate); dilatent (viscosity increases with increasing 

shear rate!. Thixotropic materials have an additional constant to define 

liquid structure restoration rate for disrupted states. 

of viscosity measurements for thixotropic materials requires scheduled measurements and close temperature control. 

rheology may be calculated from three or more measurements at different shear 

rates with an iterative computer program. 

Generally, viscosity measurements are 

The measurements do relate to 

Cod -producibilitv 

Constants relating to material 

Ion implantation of non-Cz silicon sheet materials was studied by Spire 

Corp. Materials examined were: Wacker Silso; Solarex Semix; Crystal Systems, 

HEM- ?lobi1 Solar EFG, and Cz controls. Ihe ion-implantation process was 

held coirJcant; annealing processes tried were one-step thermal, two-step 

thermal, three-step thermal and pulsed electron beam annealing (PEBA). 

Analysis of the one-step anneal at 85OOC shows EFG improved; *mix relatively unchanged and HEM, Cz and Silso somewhat degraded. 

two-step anneal at 850% shows EM; much improved; Semix, Cz and HEM relatively unchanged and Silso slightly degraded. Conclusions are: use of ion 

implantation allows tailoring of thermal annealing process to a specific 

material; ;-or. implantation and rapid thermal annealing can be used successfuily for ~ ..?ction formation. 

Analysis of the 

., iszr-assisted solar-cell metallization processes are being developed by 

the h6D Division of Westinghouse Electric Corp. Potential advantages of laser 

deposition techniques are high resolution, no photolithography, clean and con- 

.dmination-free, in-situ sintering, and low contact resistance. Three processes are being investigated: pyrolytic deposition (thermal decomposition of 

liquid or gas phase), photolytic deposition (photodissociation of vapors and 

solutions), and laser-assisted electroplating. Results of laser pyrolysis 

were encoxaging; lines of silver were formed by decomposition of a spun-on 

silver 2eodecanoate film provided by Purdue University. 

p-qs’ble problem in this process. 

mut is ready to use for titanium and tin depositions. 

Adhesion is still a 

Laser-assisted gas-phase photolysis equipEarly results of 

2 94 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

laser-enhanced electroplating of copper have been exciting. 

wide line has been achieved with a 12 micrometerlsecond local plating rate. 

A 25-micrometerIon cluster beam (ICB) deposition research is being pursued at JPL. The 

intent of the research is verification of Japanese work, investigation of PV 

applications other than metallization (such as dielectric and semiconductor 

deposition) , and characterization of ICB as a function of source parameters. 

A number of changes have been made in the ionizer chamber to achieve more 

reliable operation. A crucible nozzle is being considered for better collimation of tire beam. Other changes being investigated are cluster detector, 

substrate heater, and operation of ionizer at higher temperatures. 

Another JPL research effort is a program for SERI. The parameters 

governing large-area deposition of amorphous silicon are being established. 

Tests have been run on plasma stability vhile voltage, pressure and electrode 

spacing are varied. 

to corner effects, electrode spacing, silane feed rate and velocity, and substrate influence (aluminum, silicon or glass). 

Deposition uniformity is also being studied with regard 

New contracts to explore the technology of advanced processes have been 

let for two excimer laser energy sources and one microwave source. 

to apply energy selectively to achieve process improvements has already been 

seen in other research efforts. 

detailed assessment of a new technology and thereby validate claims of large 

processing improvements or cost reductions. 

The ability 

An additional benefit is the ability to get a 

295 

PROCESS RESEARCH OF NON-CZ SILICON MATERIAL 

WESTINGHOUSE ADVANCED ENERGY SYSTEM DIVISION 

C.M. Rose 

R.B. Campbell 

Contract Information 

Objective: Investigate High-Risk; High-Payoff 

Improvements to @ Baseline Process 

Sequence 

Time Period: November, 1983 - March, 1984 

Funding: JPL Funds Used for Engineering Effort 

Only; Technician and Material Costs 

BorneBy 0 

Contract Tasks 

Evaluate Feasibility of Simultaneously Forming Back & Front 

Junctions of Solar Cells Using Liquid Dopants on Dendritic Web 

Silicon 

Compare Simultaneous Diffusion to Sequential Diffusion 

Test of Belt Furnace for Diffusion Process 

Develop Process Control Parameters and Sensitivities 

Perform Cost Analyses 

297 
!'!?XES DEVELOPMENT AND ADVANCED PFJCESSES 

Approach 

N-Type Dendritic Web Silicon 

Liquid Phosphorous Dopant for Back N'N Junction 

Liquid Boron Dopant for Front P+N Junction 

investigate Several Resistivities of Web 

(0.5 Q-CM to 5.0 0-CM) 

Investigate Various Suppliers Dopants and Masks 

Potential Benefits 

Fewer Processing Steps 

Less Opportunity for Contamination During Processing 

Less Costly Process 

HOWEVER 

Process Requires N-Type Dendritic Web Due 

to Diffusion Constants of Dopants in Silicon 

298 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

DRIVE BORON AN0 

WOSWOROUS 

OXIDE ETCH 

I 

Junction Formation Process Steps 

0 

00.0. 0 

Initial Results 

Diffusion Time - Temperature - Ambient Gas 

Determined for Desired Sheet Resistivity and 

Junction Depth 

Temp = 95OoC ? 20' C 

Time = 20 Min ? 5 Mil 

Gas Ambient = N2 for Most Dopants 

2 99 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Simultaneous Diffusion 

Junction Depths of P+N and N'N Satisfactory 

Xj (P'N) - 0.2 - 0.4 /IM 

Xi (N'N) -O0.4-O.6/1M 

Maximum Efficiency - 12% 

Cross-Doping of Phosphorous into Sun Side 

of Cell Confirmed by: 

Sheet Resistivity Measurements 

Spreading Resistivity Measurements 

n -t n Back Junction by Simultaneous Diffusion 

(491 25-21A) Xj = 0.8pm 

0 0.5 1.0 1.6 2.0 2.6 3.0 

DISTANCE INTO CELL (pM) 

300 
PROCESS DEVELOPMENT AND ADVANCE3 PROCESSES 

p + n Front Junction by Simultaneous Diffusion 

I I 1 1 I J 

0 0.125 0250 0.376 0.W 0- 0.750 

DISTANCE INTO CELL (pM) 

Belt Furnace Test 

0 Initial Test at Radiant Technology Corp. 

Proper Temperature Obtained 

Proper Junction Depths Obtained 

Cells Showed Effect of Cross Doping 

301 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Solutions to Cross Doping 

Form Impermeable - Harder Glass 

from Diffusant Source 

Use of Si02 Masks as Diffusion 

Barriers 

Sequential Diffusion 

Process Sequence for N-Type Web Adapted 

from P-Type Web Sequence 

Back Phosphorous Doped Junction Diffused First 

Front Boron Doped Junction Diffused Second 

Cell Efficiency Range 12.0 - 14.5% (20 CM2 Cell) 

Xi e 0.4 - 0.8 PM 

Xj e 0.2 - 0.3 /.iM 

Average Cell Efficiency 3 13% 

Process Control Parameters and Sensitivities 

Three Resistivities of Silicon Web Being 

Tested (0.5 Q-CM; 1 .O Z1-CM; 5 n-CM) 

Other Process Sensitivities will be Studied 

When Cross Doping Solved 

Conclusions 

Sequential Diffusion of N-Type Web Yields 

Cells with Average Efficiency > 13% 

Cells Up to 12Y0 Obtained with Simultaneous 

Doping af N-Type Web 

Diffusion Masking will be Required to Prevent 

Cross Doping 

302 
PROCESS RESEARCH ON POLYCRYSTALLINE 

SILICON MATERIAL (PROPSM) 

SOLAREX CORP. 

Jerry Culik 

PROPSM Programs 

o IDENTIFY RCHANISPIS LIHITING CELL PERFORHANCE (SHORT-CIRCUIT 

CURRENT. OPEN-CIRCUIT VaTAGE. FILL-FACTM. PEAK PWR) IN 

-NiQ-GRAIN. CAST. POLYCRYSTALLINE SILICON SHEET MTERIAL . 

a DEVElGP SOLAR CELL FAEPICATION PROCESSES. CWATIBLE rI:H CIMTING 

iltc~Nlws. 79 ItPROVE PERFORWNCE (GETTERIS). 

0 DEVELOP A PASSIVATION PROCESS (HYDROGENATIOIY) . INCLUDING PROCESS 

SENSITIVITY INALYSIS. 

303 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Dark I-V Analysis Summary 

flINI-CELL UAFERS t4-1166 AND 7!-OlEITOP 

OUASI-NEUTRAL (BULK) RECOPBINATION (J~o) VARIES FROH s x 10-9 wcd .J 

1 x 10-8 nAIcn2. THAT IS. EFFECTIK flINOIlY-CARRIER DIFFUSION LENGTH 

:'?.!?KS BY FACTOR OF TWO. 

SUE CELLS HAVE JQNO GFfEATER THAN 2 X 10-8 nA/CH2. 

MAJORITY OF CELLS LOSE LESS THAN 10 hV DUE TO EXCESS SPACE-CHARGE 

(JUNCTION) RECOnBINATIOfI (JSCO): FEU CELLS LOSE ME THAN 20 nV. 

HOST OF Voc SCATTER IS ACCOUNTED FOR BY Jmo VARIATION. 

DETERHINE CAUSE Q JQNO VARIATION 

- LIGHT-BEAW INDUCED CURRENT (LBIC! - 800 Ntl 

- DEFECT (SECCO) ETCH 

- CORRELATE STRUCTURE WITH ELECTRICAL CHARACTERISTICS 

304 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Minicell Evaluation 

1. FABRICATE 400 PHOTODIOOES (ON 5 M CENTERS. 0.19 & AREA) ACROSS loCfl X 

10Ch POLYCRYSTALLINE SILICffl WAFERS USING MESA STRUCTURE FOR ISOLATIW. 

2. KASURE ILLUHINATED I-V CIURACTERISTICS ACROSS WAFER. 

3. LOCATE ARZAS WHICH SUFFER FROW REDUCED VOC ANDlOR FILL-FACTDR. 

4. MTERHINE CAUSE: 

0 SHUNT CONDUCTANCE. 

0 

0 

0 LIGHT-SPOT SCANNING TO LOCATE ELECTRICALLY ACTIVE GRAIN AND SUBDARK I-V ANALYSIS FOR JQO. Jso. AN0 N-FACTOR. 

DEFECT ETCH OF SERIAL WFER FOR DISLOCATION CONTENT. 

GRAIN BOUNDARIES. 

illuminated I-V Characteristics 

SCll-1 241 30.3 (0.4) 580 (15) 61.7 (9.2) 

(SINGLE-CRVSTAL) 

71-0lE. TOP 294 23.9 !!?.6) 562 (16) 66.3 (5.7) 

71-01E. MOME 255 27.9 (0.8) 560 (19) 63.9 (7.2) 

71-01E. 8OTTOn 271 26.1 (0.5) 520 (42) 55.5 (9.6) 

C4-108 287 28.2 (1.9) 540 (55) 56.9 (11.0) 

C4-1160 329 29.4 (1.6) 559 (14) 64.6 (3.3) 

UACKER SILSO 308 27.5 (0.8) 551 (19) 63.6 (5.2) 

MEAN (STANDARD DEVIATION ABOUT MAN 1 

MEASURED AT 135 nWlCR2. AMO. 25% 

o Voc OF POLCRYSTALLINE CELLS IS 20 TO 60 MV LOWER THAN 

SINGLE-CRYSTAL . 

0 EXCESS SCATTER IN VOC AND FF OF 71-01E180TTOn AND C4-108 

CORRELATED WITH INCLUSIONS (RESISTIVE SHUNTS 1. 

305 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

LBiC Scans, Wafer C4-116B 

306 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

LBlC Scans, Wafe; C4-1168 

307 
PROCESS 0RtGIN.X 

OF POOR DEVELOPMENT AND ADVANCED PROCESSES 

LBlC Scans, Wafer 7 1 -0 1 E/TOP 

308 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

ORIGINAL P.'&': .A 

LBlC Scans, Wafer 7 1-01 E/TOP OF POOR ~UitLr'l 'i 

309 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Summary of LBIC results 

STRONG CORRELATION BETWEEN QUASI-NEUTRAL RECMBINATION AN0 ELECTRICALLYACTIVE GRAIN AN0 SUB-GRAIN BOUNDARIES. 

WNT OF LBIC-IMGED G.B. ACTIVITY HAS LITTLE OR Et0 EFFECT GN SPACECHARGE RECOWBINATION OR FILL-FACTOR. 

ISOLATED CELLS HAVE EXCESS Jsco FRM 'DEFECT' THAT IS NOT RESOLVED BY 

LBIC. 

Limiting Mechanisms 

FOR SOHE UAFERS. Voc AND FF SCATTER ARE DUE TO INCLUSIONS. WHICH ACT AS 

RESISTIVE SHUNTS. 

FOR OTHER MFERS. CRYSTAL STRUCTURE CONTROLS WASI-NEUTRAL RECOneINATfON 

AND THEREFORE Vw. FF. AND Jx. 

THERE DOES NOT APPEAR TO BE A STRONG CORRELATION BETMEN STRUCTURE AND 

SPACE ,CHARGE RECOHBINATION. 

LOUEST Jmo IS 5 X 10-9 flAlc$, WILL LIMIT Vw TO ABOUT 585 HV (IDEAL 

DIOOE, FGR Jsc - JL - 30 tWCfl2). 

310 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Hydrogenation 

0 FABRICATE SARLE SET. 

0 LOCATE AREAS THAT CONTAIN CELLS WITH LOW Vw. HIGH JQNO. ELECTRICALLYACTIVE G.B. (LBIC). 

0 HYDROGENATE - DC PLASM 

0 EVALUATE ANY CHANGE IN GRAIN BOUNDARY ACTIVITY AND JQNO BY DARK I-V 

CHARACTERISTICS AND LBIC. 

311 

-* 

-pig 15277 An 

P PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

AMORPHOUS METALLIC LAYERS 

IN Si METALLIZATION SYSTEMS 

CALIFORNIA INSTITUTE OF TECHNOLOGY 

Marc-A. Nicofet 

- WHY AMORPHOUS METALLIC LAYERS? 

- FORMATION OF SUCH LAYEkS 

- PROPERTIES OF SUCH LAYERS: 

CRYSTALLIZATION 

REACTION WITH SI 

REACTION WITH METAL OVERLAYER 

- CONTACT WITH SUCH LAYER AS DIFFUSION BARRIER 

- PROBLEMS, OUTLOOK 

PRECEDING PACE RLANK NOT m,hfED 

313 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Amorphous Layers as Diffusion Barriers 

in Metallization Systems 

ADVANTAGES 

- NO GRAIN BOUNDARIES 

NO RAPID DIFFUSION PATHS 

LOW ATOMIC DIFFUSIVITIES 

- REDUCED REACTIVITY 

- MANY CHOICES 

FLEXIBILITY, OPTIMIZATION 

DISADVANTAGES 

- METASTABLE 

- AT LEAST TWO ELEMENTS 

MANY CHOICES 

- PROPERTIES = F (DEPOSITION PROCESS AND PROCEDURE) 

COMPLEX, NEW IN DEVICE TECHNOLOGY 

- R8D, TOLERANCES, TESTING 

314 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Formation of Amorphous Metallic Layers 

- RULES FOR SELECTION OF ELEMENTS AND COMPOSITION 

M/R L 10% 

LOW SOLUB 1 L 1 TY I OF[ DEEP EUTECTIC 

TRANSITION METAL + MtTALLOlD 

TWO TRANSITION METALS 

TWO TRANSITION METALS OF DlFFFffcdl STRUCTURE 

- RULES FOR F~RMATION PROCESS 

RANDOM ATOMIC ARRANGEMENT 

LOW ATOMIC MOBILITY: LOW T 

LOW HEAT 

FAST HEAl DISSIPATION 

OUR PROCESS 

RF DIODE SPUTTERING (13.56 MHZ) 

MAGNETRON TARGET (3") 

( Bi:KAPLATE ) + (PARTIAL COVER SHEET 

OF B 

GAS: AR OR AR~,~ + N0.1 

Sheet Resistance of Amorphous Ni-W Layer 

on Si02 and Si Substrate 

am. t t+ poly. 

a 

so' VACUUM ANNEALING 

@ t#@ 2M rn Y) In IQI w 100 

ANNEALING TEMPERATURE (.C 

315 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Sheet Resistance of Amorphous Ni-N-W Layer 

on Si02 and Si Substrate 

ANNEALING TEMPERATURE (.C 1 

316 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

NI&, 

NI&~Y~ 

Crystallization and Reaction With Si > 

625-650 650 I 

I 

I 

I 

725-750 i 600 I 

TREF < Tc (EXCEPT FOR W IN NI-I-W) 

CRYSTAUIUTIOU SLOWER THAN REACTION 

(A) ALLOY RETARDS REACTION WITH (SI’ 

T, 2 T, (UtCEPT FOR MI-N-W) 

CRYSTALLIUTION INDUCES REACTION 

31 7 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Mstallurgical Stability of Amorphous Ni-W Layer on 

Si (1 00): Penetration of Ni Into Si (Monitored by BS) 

318 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Metallurgical Stability of Am c~hous Ni-N-W Layer 

With AI Overlayer: t .. Analysis 

P C (1/2 T,'C HI 

( PQCH2) 

FE45W55 400 

Mol-xNI, 

N'36W64 

30<x<60 

Contact Resistivities of Amorphous RF-Sputtered 

Metallic Thin Films 

N+s 1 I P+SI 

(AS-DEPOSITED * T, 1/2 HI .- - 

oml + 0.2 3+1 

1*2 1+2 

I 1-2 1 + 0.4 

319 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Schottky Barrier Heights of Amorphous 

RF-Sputtered Metallic Thin Films 

'B (1 

nOl-xNI, 11 AS-DEPOSITED 

500 !I 3o<x< 60 

NI#~ I I AS-DEPOSITED 

400 

450 

MS I 

0.61 

0.65 

0.68 

0.63 

0.65 

0.65 

0.64 

PSI 

- 

0.42 

0.42 

0.45 

0.43 

0.43 

N 

1.08 

1.01 

1.05 

1.W 

1.08 

1.15 

Problems, Solutions and Outlook 

PROELMS 

- RINIHIZE REACTIONS OF hORPHoUS LAYERS 

WITH SUBSTRATE 

WITH OVERLAYER 

SOLUTIONS 

- INTERHEDIATE SILICIDE LAYER 

- EARLY TRANSITION NETAL ALLOYS 

- HlGH TREF'S 

- N-CONTAINING hORPnOUS ALLOYS 

- TERNARY bWRPHoUS ALLOYS 

OUTLOOK 

SOnE PROBLEMS 

PRONIS~NG RESULTS 

MANY POSS 1 B 1 LIT TES 

320 
METALLO-ORGANIC DECOMPOSITION (MOD) 

SILVER METALLIZATION FOR PHOTOVOLTAICS 

4 

PETAL HETERO-ATOH 

ION (O,',N,P,AS) 

- 

PURDUE UNIVERSITY 

ORGANIC 

RADICAL 

G.M. Vest 

R.W. Vest 

MOD Film Processing 

ComON SOLVENT 

+ 

RHEOLOGY ADJUSTORS 

II 

+ 

PRINT, SPRAY, DIP, ETC. 

+ 

HEAT 

321 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Silver Neodecanoate 

Subs t 1 twnts 

R1 CH3 

R2 ’ CH3 

R3 ‘ CH6H13 

X Abundance 

31 

67 

2 

322 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

323 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Molecular Design Criterion 

1. As the Choln Length of tk Organlc Radical Increases: 

a) the salubllltv of the conmiin!! ;n orsanlc 

solvents lncrmscs; 

b) the metal content of the comoound decreases. 

2, The SolubllltY of the Comund Increases If the Oroonlc 

Radical is Branched. 

Sllver Cmund Fomlo n/o AFI T~ (Oc) 

(theo) 

Horo-tlethyl Succinate CH300C-$H4 . COOAg 45 230 

y5 

;r 

2-Eth~1 butyrate C2H5 - C - COOAg 48 235 

H 

CqHg - C - COOAg 

I 

2-Eth~1 hexonoote I 

c2H5 

Neoventanoa te 

Neodecanoote 

43 235 

52 230 

38.6 230 

324 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

325 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Ink Requirements for Screen Printing 

1, Very Low Vawr Pressure 

2. Viscosity 130-500 Paes at Low Shear Rate 

3. Pseudoplastic 

4, ThlXOtrODiC 

Solvents 

Comnerc i a 1 Chemical Boillns 

Name Ham Formula Point 

Butyl carbi to1 2- (2-butoxy- CH3 (CH2 )3 * O'CH2- 236-249' 

ace tat e ethoxy) ethyl CH2 O-CHZ-CH~COOCH~ 

acetate -. 

a -TerD i ne0 1 a -Terpl neo 1 CH3(C6H8)C(CH3)20H 217-218' 

Phenyl ether Diphenyl ether (C6H5)20 259' 

Dodecane Dodecane CH3( CH2 110CH3 215-19 

.- 

Dialyme 2-1WthOxy ethyl (CH30CH2CH2)20 162' 

ether 

TrlglYme 

- ~~ -~ ~ ~ 

Trl ethylene CH30CH2CH20CH2CH20- 216' 

glycol dlWthYl CH2CH20CH3 

ether 

bl 

Neodecanoic Acld Neodecanalc Acld R2-C-COOH 250-?Y0 

326 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 
-- 

PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

328 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Ink Formulating 

-5.0 - - 

-10.0 - - 

- 

- 

-250 - - 

-30.0 - - 

-350 - - 

1 

METHODXylene Solution of Sllver Neodecanocte Plus Addttlve 

Solvent Exchonae In Rotovamr at 4O-6O0C 

t!EU!UL 

Toluene Solution of Silver Neodecunoate Plus Additive 

Solvent Exchange in Rctovamr at 25OC 

l!mDRL 

Solid Silver Neodr -noate Plus Additive 

329 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Firing 

1. muffle Furnace at Constant TerrPeroture cnd Stili Air 

2. Ruffle Furnace w!th ilme-Temwrature Proormlns and 

Controlled Air Flow 

3. Belt Furnace with Varlable Tlme-Term)erature Profiles 

and Natural Convectlon 

4. Comblnatlons of No. 1 and No. 3 

Results on AI203 Substrates (2) 

- ~ 

Sheet Firing Sequence 

Ink I Tap. OC time bin) Type of Surface Line Resis:. Resfst. 

Furnace Appearance Adhesion Lkfin. tcin) (s:-crn) 

9 200-350 10°/oln 1 silvery poor poor 0.113- 

350 20 surface 0.1i2 

ufth vetloo 

tint 

11 200 1o0/min 1 brownish poor excellenr * 

150 30 black uith LO if not 

oily terture fair smudged 

!' 100 IS 1 brovnirh poor') poor.) nor 

200-3M 10°/rnin srw ausured 

350 45 

20 70 15 1 brwnirh W 0.460- 

200 10 sw lo& 0.001"- 5.M 

200-250 10°/min to 0.012" 

2 50 10 excellent 

350 30 

21 60 30 I dull good fair 0.189 22.72 

200 20 yellovirh 0.020" 

225 20 rilver 

310 30 

21 60 30 I whitish poor fait 0.062 7.46 

200 20 rilver t0 

225 20 fair 

350 30 

350-100 30°/mln 

500 12 

21b) 60 40 1 brownish good fair 0.280- 

2oc m grey yell- 0.626 

350 30 

- 

a) good La excellent on g1a.r 

b) printed md fired on Si 

3 30 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Summary: Appearance 

1, Pyrolysis Products Can Produce a Dark Surface Fllm 

2. Purlty of All Ink Inoredlents 1s Very Imrtmt 

3. Heating Rate in the Range 70-229C IS rmrtant 

4. Air Flow Rate Is Imrtant 

5. Surface Film Can Be Rmved BY LlMt Burnlshlng or 

Heatma 10 ntnutes at MOOC. 

Summary: Adhesion 

1. Low Tenoerature Solvent Rmvo1 is of Prime Imrtance 

(15-30 mlnutes at 60-7OoC required for oresent Inks) 

2, Heatlna Rote in tne Ranse 100-250~~ 1s imrtant 

3. A1r Flow Rate is Imrtant 

4. Maxlmm Tenwrature Is Imrtont 

5. Possible Long Term Adhesion Problem 

6. Mechanlsm of Adheslon is Not Understood 

331 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Summary: General 

1. Cenerlc Cmunds ore Essential 

2. HIM PurltY Ran Mterlals are Very Inportant 

3. Prooer Tlm-Tenperatwe Processlng Is Crltlcal 

4. RID Silver Shows treat Prmlse for Low Tenuerature 

Metal1 lzat Ion 

332 
A NONNOBLE FRONT METALLIZATION PROCESS 

SPECTROLAB, INC. 

Alexande- Garcia 111 

Objectives 

0 OPTlMlUTlON, EVALUATION AND ~f3ONS3tATlON OF A 

NOVEL NETALLIZATION SYSTEM 

0 ~/SN/TIH SYSTEM 

0 IT0 CONDUCTIVE AR SYSTEMS 

Approach 

0 SCREEN PRINTING 

0 AIR FIRING 

0 REDUCING ATMOSPHERE 

0 CONDUCTIVE AR COATING (IT01 

333 
PROCESS DEVELOPMENT AND ADVANCED ?ROCESSES 

New Pastes Investigated 

0 Mdl3 PASTE 

e BORANE-PYR IDINE 

0 AG NEODECANATE 

0 4G RESINATE 

0 IN RESINATE 

Front Metallization Pattern 

symm About 

e 

2.040 

- f 

3 I 

0.125 

Typ Specin, 

of 17 GZLC 

lzncs 

-008 w-5e 

To1 nor.-c.; 

2.040 -1 

I 

334 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

8403 h 

335 
PROCESS DEVEL 'JPMENT AND ADVANCED PROCESSES 

R4n3 7 

336 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

+ 

+ 

1 0 

7 

X 

+ 

+ 

c 

C 

1 

1 

m 

r? 

7 

337 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

ORIGINAL P5.5.i -> 

OF POOR QUALII’Y 

+ 

+ 

+ 

+ 

+ 

3 K 

< 

L 

Iz 

Y 

K 

u 

u 

a 

a 

SPECTROUB o c fomu xai 

erum cIu~wtA DATZ 11-16-83 

SERIAL NO. 1QB?-sb 

E CELL E MODULE 0 PANEL DESIGNATION: 

SOURCF. DSUN S3TUNGSTEN OXENON 

0 UNCOLLIMATED 

TESTTEMP.: %.-7 

TEST NO.-PROC. NO.- 

vninc~ (VOLTS x 

338 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Paste N, Electrink No. F-80 

FORMULATION 

- I TW X BY WEIGHT 

TITANIUM HYDRIDE (Til421 * 45 

NOLYBDENUM METAL POWDER 16.06 

TIN METAL POWDER 64,24 

BORANE PYRIDINE 5,OO 

VEHICLE V-38 14,25 

VEHICLE V-38 

-TERPINEOL 43,62 

BUTYL CARBITOL ACETATE 43.62 

ETHYL CELLULOSE N-14 9,76 

THIXATROL ST 3.00 

Paste M, Electrink No. F-82 

FORMULATION 

I TEN 2 -- BY WEIGHT 

MOLYBDENUM OXIDE (floO3) 17,572 

TIN METAL POWDER 64.907 

TI TAN I UM RES I NATE I 002 

VEHICLE V-44 17,519 

VEHICLE V-44 

O-TERPINEOL 70.54 

CARB~TOL ACETATE 4,17 

TR ICHLORJETHYLENE 19.20 

ETHYL CELLULOSE 6,09 

339 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

t 

+ 

4 K 

+< L 

c 

Y 

B 

E 

2 

0 

+ 

+ 

340 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

New Analytical Technique 

0 CONTROLLED ATMOSPHERE SEM 

0 VIDEO TAPE PICTURE As SAMPLE Is BEING HEATED 

a VARIOUS GASES AVAILABLE a 5 TORR 

Cont rolled-At mosp here SEM 

Si ANN ING 

CHAM BE R 

...... ..... * 

34 1 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Conclusions 

* %/SN HAS ADEQUATF CONDUCTIVITY FOR SCPEEN PRINTING 

0 SHUNTING Is NCVER A PROBLEM 

0 SOLDERABILITY A MAJOR PROBLEM 

0 %RE WORK NEEDED ON WETTING PHENOMENA 

0 CELLULOSIC VEMICLE BEST 

Results 

0 VARIOUS ADDITIVFS UNSUCCESSFUL ON IMPROVING ADHESIVE 

0 SEM PESULTS SHOW TIN Docs NOT WET SYSIEM AT Low TEMPERATURE 

342 
VISCOSITY MEASUREMENTS FOR THICK-FILM PASTES 

ELECTRINK, INC. 

J. Parker 

343 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

a 

I 

......... 

...... - ...... 

__ .. .-. 

. .-.. 

.......... , . --:- ;.- : I '. .......... , - .--- . - *-' .. ...- ... .._-_ L.. ....... .... 

I. 

... ............ .... ,I. e. 

.......... .....-. - 

! .... ........ !:.- -. -. .. 

I 

.-. 

.. 

.. 

..... .-. - .- l%+&t&NtO.f. ~ ..... ... -. . * .. .. ._.._ ........... ..*.*- .. .. .. - ...... ....... ....... . .- . 

. - ,-. .- . . - -. - . . - . - -. . -. ._ .. 

344 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Non-Newtonians 

345 
PROCESS DEVELOPMENT AND ADVANCED PSOCESSES 

Log Viscosity vs Log Speed 

... 

346 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Thixotropic Materials 

b )? 4 + cs 

34 7 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Viscosity Procedure 

tne ink suples snould be a minimum of 3 inches deep and a minimum 

of one bncn in diameter. rfter ZY hours or mgre of atanding the sam- ple snoulo bo brought to and ~aintainod at ZS C = .3 C. 

Usrnq a Ioveled Brookfield RTV viscometer uith a no. 7 Spindle and 

stutrng with a Spindle spmed of 2.S rpm. viscosity measurements are 

to be ..(Io after tne indicated times in the follouing sequence of spindle 

so~oosr 

order spad 

no. rp. 

L 2.5 

2 5.0 

3 LO 

Y 20 

S LO b 5.0 

7 2.5 

equilibrrua noto 

time. minutes t. -. -k> 

LO 

LO after standing 

LO 

LO no measurement 

L 

b after stirring 

L 

the ten minute pmriod at 20 rp. sorves to stir the ink in the vicinity of 

tne spindle. No measurement at 20 rpm is required. 

Acceptable viscosrty value ranges are tabulated below. 

speed after stmding af ter sti rring 

rP= centipoise centipoise 

2.5 L7SiOOO 2 20.000 LLO*OOO z 20.000 

5.0 LOS.000 2 LSvOOO 75~000 2 LS1000 

LO 70.000 2 LO*OOO 55*000 2 L0.000 

Viscosity measurements should be made for tu0 different samples from a batch of ink. Tha average values for the tu0 samples should fall uithin 

the above viscosity ranges. 

348 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

t w -so 

349 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Log Viscosity vs Log Speed 

2 A 4 

Loo 3raro 

350 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Conclusions 

2. 

3. 

351 

EVALUATION OF THE ION 

FOR PRODUCTION 

IMPLANTATION PROCESS 

OF SOLAR CELLS 

FROM SILICON SHEET MATERIALS 

SPIRE CORP. 

M.B. Spitzer 

0 bject ives 

0 APPLY THE ON IMPLAI\ITATION PROCESS TO 

PRESENT-DAY MATCQl ALS AND FABREATE 

CELLS 

0 INVESTIGATE TEMPERATURE EFFECTS 

0 COMPARE THERMAL ANNEALING TO PULSED 

ELECTRON BEAM ANNEALING 

Status of Program 

TECHNICAL WORK COMPLETE 

CELL DELIVERIES COMPLETE 

FIRST DRAFT OF FINAL REPORT 

APPROVED BY JPL 

PREPARATION OF FINAL COPY IN 

PROGRESS 

353 
Pr ,OCESS DEVELOPMENT AND ADVANCED PROCESSES 

Anneals Investigated 

0 ONE-STEP 

2 HOURS AT EITHER 550, 65C, 750, OR 85Q'C 

0 TWO-STEP 

15 MIN AT EITHER 550, 650, 750 OR 850% 

FOLLOWED BY 1 HOUR AT 550'C 

0 THREE-STEP 

550.C-2 HRS. 

850 'C- 15 MIN. 

55O'C-2 HRS. 

0 PULSED ELECTRON BEAM ANNEAL 

SPI-PULSE 7000 

-1 J/cm2 

-50 psec PULSE WIDTH 

3 54 
PROCESS DEVELOPMENT AN3 ADVANCED PROC€SSES 

IMPLANT FRONT 

Cell Process Sequence 

PHOSPHORUS 

NOTE: NO AR COAT:NG, NO BSF 

HEM, SEMlX AND 

dlLSO ONLY 

EVAf'nRATE 

FRONi METAL 

Ti-Pd-Ap 

LIFT-OFF 

AND SINTER 

400 'C 

S9W TO 

1 2crix 2cm 

I 100 mW/cm* 28% 

355 
PROCESS DEVELOPMENT AND AuVANCED PROCESSES 

J, Analysis of One-Step Anneal 

t 

. PEW ‘55o’C 650’C 750% 850.c 

Spectrp’ “->sponse for Cz Controls Processed 

W. ’. J Single-Step %Hour Anneal 

n 

Ip 

Y 

I .o I 

I Ion em CZ SOLAR CELLS 

2-hr. ANNUL 

403 600 800 1000 

WAVELEI. 3TH (nm) 

356 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

External Quantum Efficiency of EFG Cells Annealed 

With a Single-Step Pvocess and With PEBA 

1.0. 

0.8 

0.6 

0.4 

0.2 

0 

EF6 RlOWU 

tk. ANNEUS 

- 

- 

- 

- 

4oc’ 600 800 1000 

357 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

SlLSO 

- ONE-STEP 

ANNEAL 

Spectral Response of Silso Cells 

Processed With One-Step Annealing 

0) 

400 600 800 IO00 

WAVELENGTH (nm) 

Js, Analysis of Two-step Anneal 

1.2 

1.1 

0 

3 

a 

1.0 Y 

A 

e 

fa .9 oz 

.8 

CZ 

HEM 

SlLS 

PEBA ' i 550'C 650'C 750'C 850% 

358 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

0.6 

0.4 

0.2 

0 

n * 

> 

0 

z 

Y 

w 

I! 

LL 

LL 

w 

5 

tz 

U 

3 

0 

J 

a 

a 

z 

W 

F 

X 

W 

- 

- 

* 

- 

External Quantum Efficiency of Cz Control 

Cells Annealed With a Two-step Process 

0.8 

WVELENGTH (nm) 

External Quantum Efficiency of EFG Cells Annealed 

A 

ap 

> 

0 

z 

Y 

w 

2 

LL 

LL 

Y 

I 

3 

Iz 

a 

3 

0 

4 

a 

z 

a 

W + 

X 

W 

With a Two-btep Process and With PEBA 

0.8 

850.C 

0.6 - 750.C 

PEBA 

0.4 * 

0.2 - / 

/ 

0 

400 600 800 1000 

WAVELENGTH hm) 

359 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

I .o 

0.8 

External Quantum Efficiency of HEM Cells 

Annealed With the Two-step Process 

SJLSO 

. TWO-SfEP ANNEALS 

- 

PEBA 

WELENGTH (nm) 

Spectral Response of Silso Cells Processed 

With a Two-step Tnermal Anneal 

WVELENGTH (nm) 

360 
, 

IMPLANT voc 

ENERGY (mV) 

5 keV 508 

(20 CELLS) (25) 

4436- If 53 1 

10 keV 52 1 

4387- 1 tf 534 

15 keV 520 

(20 CELLS) (18) 

4335-2b 536 

(15 CELLS) (13) 

ROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Jsc FF Ef f Eff x 1.41 

(mA/cm2) (%I (%I (%I 

23.0 65.9 7.71 10.9 

(0.3) (2.5) (0.67) (0.9) 

23.0 71.3 8.7 1 12.3 

23.3 68.9 8.39 11.8 

(0.5) (4.9) (0.88) (1.2) 

23.4 75.9 9.48 '3.4 

23.5 69.2 8.47 11.9 

(0.2) (3.8) (0.77) (1.1) 

23.5 73.1 9.23 13.0 

Average AM1 Performance of the 

PEBA-Processed Cz Control Group 

- 

MATERIAL "oc JSC FF Eff Eff x 1.4 

(No. OF CELLS) (mv) (m!/cm2) (%I (%I (%I 

Cf (15) 52 1 23.3 68.9 8.93 11.7 

BEST CZ 534 23.4 75.9 9.48 13.3 

HEM (15) 525 22.3 70.9 8.29 11.6 

BEST HEM 53 1 22.8 73.1 8.87 12.4 

- 

SILSO (15) 519 21.0 

B€ST SILSO 542 21.5 

NOTES: INSOLATION WAS AM1, 100 mW/cm2. Tt28.C. STANDARD DEVIATION 

SHOWN IN MRENTHESIS. THE BEST CELL IN EACH GROUP IS ALSO 

INDICATED. 

69.5 

73.3 

Pulsed Electron Beam Annealing 

of Silicon Sheet Materials 

361 
PROCESS DEVELOPMENT AND ADVANCED PROCt3SES 

Conclusions 

0 USE OF ION IMPLANTATION ALLOWS TAILORING 

OF THERMAL PROCESS TO A PARTlCULAR 

SHEET MATERIAL 

0 EFG IS IMPROVED AFTER HIGH TEMP 

0 SlLSO IS DEGRADED AFTER HtGH TEMP 

HEM AFFECTED MOST AT 550-750 C 

0 SEMlX APPEARS INDEPENDENT OF PROCESS TEMP 

0 CZ IS DEGRADED BY PROCESSING AT 750 C 

0 ION MllPLANTAilON AND RAPlD THERMAL 

ANNEALING CAN BE SUCCESSFULLY EMPLOYED 

FOR JUNCTION FORMATION 

362 
PROCESS DEVELOPMENT AND ADVANCED PFiOCESSES 

SPECTRAL RESPONSE OF HEM SOLAR CELLS 

ANNEALED WITH A ONE-STEP PROCESS 

ONE-STEP ANNEAL 

0.8 

0.6 

0.4 

0.2 

0 

400 600 800 1000 

WAVELENGTH (nm) 

363 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

SPECTRAL RESPONSE OF SEMIX CELLS 

PROCESSED WITH A ONE-STEP ANNEAL 

I .G 

0. a 

0.6 

0.4 

0.2 

0 

SEW% 

ONE-STEP ANNEAL 

650.C 

400 600 800 1000 

WAVELENGTH (nm) 

364 
tt N8 5 

LASER-ASSISTED SOLAR-CELL 

METALLIZATION PROCESSING 

WESTINGHOUSE ELECTRIC CORP. 

S. Dutta 

P.G. McMullin 

Milestone Chart 

Tasks/Milestones 

- 

1. Conduct literature Search On Current StateOf-The Art her Metallization Schemes 

2. Assemble And Test Each Of The Following Systems: 

2.1 Photolytic metal deposition using a 

focused CW UV laser 

2.2 Photolytic metal deposition using a 

mask and UV flood illumination 

2.3 Pyrolytic metal deposition using a 

focused CW laser 

3. fabricate Fifty Solar Cells 

4. Characterize The Cells And Determine The 

Eff ects Of Transient Heat On Solar Cell 

Junctions And On Bulk Lifetime 

5. Compare Economics Of laser Assisted 

Processing With Competing Technologies 

Pieliminrry Report 

Final Report 

6. Support Meetings 

7. Provido Documentation 

15282 

M 

365 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

A Convent iona I Metal I iza tion Sys tern 

Employs A Sequential Multistep Process: 

Photolithographic Pattern Definition 

Film Deposition 

Laser-Assisted Metallization 

Techniques Are Essentially 

One-Step Processes: 

laser-Surface Interaction 

Resulting In 

localized Film Growth 

Potential Advantages of Laser Disposition 

Techniques for Photovoltaic Systems 

High Resolution 

No Photolithography 

Clean And Contamination - Free 

ln-Situ Sintering 

low Contact Resistance 

366 
PROCESS DEVELOPMENT ArVD ADVANCED PROCESSES 

Laser-Assisted Deposition Techniquss 

Pyrolytic Deposition (Thermal) 

laser Chemical Vapor Deposition (LCVD) 

Laser Deposition From Solutions 

Photolytic Depositioir (Non-Thermal) 

Laser Photodissociation Of Vapors 

laser Phoiodissociation Of Solutions 

laser Assisted Electroplating 

367 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Experimental Setup for Laser-Assisted Electroplating 

Argon-Ion 

laser 

Copper 

Plating Solution 

Silicon Substrate (Cathode) 

' Anoae 

368 
PHOCESS DEVELOPMENT AND ADVANCED PROCESSES 

Photolytic Deposition 

Laser-Induced PhobdscDmpositbn of Gas-Mae Organometallic Compounds: 

This Technique is FunBmenblly Different from Thermally Based 

laser Procases 

Phaions 

.Mal condcr.scs 

on Illuminated 

Regions of Substrde 

Forming Wemed Film 

369 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Experimental Setup for Laser-Assisted Photolysis 

HeNe laser 

x-Y 

Translation 

3 70 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Experimental Setup for Laser-Assisted Electroplating 

.Copper 'Anode 

Plating Solution 

Silicon Substrate (Cathode) 

371 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Laser Power Dependence of Electroplated Spot Size 

Plating Current = 1 mA 

Dwell Time = 5 sec 

3 a 5 6 

Laser Power ( watts) 

Summary of Laser-Assisted Electroplating Results 

Novel Technique For Greatly Enhancing local Plating 

Rates - Yield Fine-line, Directly-Written Patterns With 

Excellent Adhesion 

Multiple Rapid Laser Scans Yield Finer, More Even Line 

And Higher local Plating Rate Than Single Slow Scan 

(Same Total Exposure Time) 

Plated Linewidth Depends On Laser Power, Plating 

Current, And Electrolyte level 

25 pm linewidth And 12 pm/sec local Plating Rate 

Obtained 

372 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Laser Pyrolysis of Spun-on Metallo-Organic Film scaca-~-bswBam Ar+ 

-1 

-1- 

Spun-On Silver 

Neodecanoate Film 

- Silicon Substrate 

Sample Base Temperature laPC 

Focussed Laser Spot Decomposes Spun-On Film 

Silver Metallization Patterns are formed by Direct-Wrling 

373 
PROCESS DEVELOPMENT AND ADVANCED PRXESSES 

l(10 

90 

-80 

E 

1 

40 

Laser-Deposited Line Width vs Laser Power 

I 1 1 I I I I I I I I I 

o Film Spin Speed =2OOO rpm - 

0 Film Spin Speed =loo0 rpm 

- - 

I I I I I I 1. 

1 2 3 4 5 b 7 

Laser Power ( watts) 

1 2 3 4 5 b 7 

Laser Power ( watts) 

3 74 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Status 

Laser-Assisted Gas-Phase Photolvsis 

Sample Chamber And Gas-FilVPumping Station 

Initial Deposition Of Titanium And Tin Planned 

Designed And Constructed 

laser- Enhanced Electroplating 

Exciting Early Results Using Copper Plating Solution 

25 pm Linewidth And 12 pm/sec local Plating Rate 

Achieved 

Laser Decomposition Of Spun-On Metallo-Organic Films 

Ability To Rapidly laser-Write Solar Cell 

Metallization Pattern Demonstrated 

Adhesion Being Studied 

375 

r'N85 15283 

ION CLUSTER BEAM DEPOSITION RESEARCH 

JET PROPULSION LABORATORY 

Dennis Fitzgerald 

Objectives and Present Plan 

OBJECTIVES 

TO VEHIFY CLAIMED RESULTS OF JAPANESE WORKERS WITH RESPECT TO 

METAL DEPOSITION ON SILICON- 

* TO INVESllGATE OTHER PV APPLICATIONS OF ICB SUCH AS DIELECTRIC 

AND SEMICONDUCTOR DEPOSITION. 

O TO CHARACTERIZE ICB BEAM AS A FUNCTION SOURCE PARAMETERS. 

PLAN 

O FABRICATE/TEST ICB SOURCE FOR SILVER DEPOSITION. 

0 DEmsiT SILVER CLUSTERS ON SILICON AND GLASS SUBSTRATES FOR 

EVALUATION AND DETERMINATION OF PROPER DEPOSITION PARAMETERS. 

(PULL TESTS, CONTACT RESISTANCE, UNIFORMITY, DEPOSITION RATE). 

O DEPOSIT SILVER CLUSTERS THROUGH HASK TO METALLIZE FRONT OF 

SOLAR CELL AND MEASURE I-V (PERFORHANCE, FILL FACTOR, ENVIRONMENTAL DEGRADATION, ETC.) 

Ion Cluster Beam Assembly 

IONIZER GRID 

IONIZER FILAMENT 

RADIATION SHIELD 

4Nfin" 

Fb!iuffbn 

CARBON CRUCIBLE 

CRUCIBLE HEATER 

WATER COOLED JACKET 

VACUUM FLANGE 

377 

PRECEDING PACE BCANK NOT m,?,mn 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Problems and Solutions 

IONIZER FILAMENT WIPE SIZE INCREASED AND SPRING WOUND TO PRClTECl 

CRUCIBLE HEATER DESIGN CHANGED TO PROVIDE BETTER SCPPORT FOR 

TOP CRUCIBLE SUPPORT ELIMINATED TO REDUCE HEAT LOSS AND VAPOR 

ELECTRON BEAM SUPPLY MODIFIED TO PROVIDE BETTER MATCH TI; LOAD 

REQUl REMENTS. 

LOWER CRUCIBLE SUPPORT BEING MODIFIED TO PREVENT ARCS DURING 

AGAINST -YERMAL AND MECHANICAL STRESS. 

FILAMENTS AT OPERATING TEMPERATURE (2400OC). 

CONDENSAT ION ON SUPPORT STRUCTURE. 

E-BEAM OPERATION. 

VAPOR CONDENSATION ON STRUCTUHE SURROUNDING CRUCIBLE IS A WASTE 

OF MATERIAL, CONTAMINATES RADIATION SHIELDING AND INSULATORS, AND THE VAPOR CAUSES aRcs IN E-BEAM REGION - CRUCIBLE NOZZLE 

BEING CONSIDERED FOR BETTER COLLIMATION OF MATERIAL. 

ICB Experimental Setup 

VACUUM 

CHAHBER 

/ I ! I /- SUBSTRATE 

SHUTTES/rll RROR 

CRUCIBLE THERWC9UPLE 

378 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Results and Discussion 

" CLUSTER FORMATION HEQUIRES CRUCIBLE PRESSURE IN RANGE OF i 1G i'l loftti 

(1350°C TO 1550°C FOR SILVER). 

' PROBLEMS PRECLUDED OPERATION ABOVE !400°C. 

" SILVEH DEPOSITION AT 1400°C LOOKED UNIFORM FAILED TAPE PULL lEST 

' CUHRtNT ICB MODIFICATIONS SHOULD PERMIT OPERATION AT MUCH 

' EARLY EXPERIMENTS INDICATE N€ED FOR CLUSTER OETECTOR TO IDENTIFV 

NAY ALSO HEQUIRE SUBSTRATE HEATER TO MAKE PROPER BOND OF NlAL 

(IONIZEH 50OV/200~A, 3Kv ACCELERATION, SUHSMTE AT 50°C). 

HIGHER TEMPERATURESPRESENCE AND SIZE OF CLUSTERS. 

TO SUBSTRATE. 

3 79 

LARGE-AREA a-Si DEPOSITION CHAMBER(S) 

JET PROPULSION LABORATORY 

D.B. Bickler 

Objective 

Determine key parameters to be used in large-area 

deposition-chamber designs 

Approach 

Explore the multidimensional "parameter space" of a-Si 

deposition using a highly flexible learning apparatus to 

approximate optimal combinations 

Milestone Chart 

5HJ 

V 

V 

JASC 

A 

5 

V 

A 

V 

V 

c 

I 

I 

I J JA 

L 

381 
PROCESS DEVELOPMENT AND ADVANCED PROCESSES 

Electrode Tests 

STABUTY 

voltagerange 2O%tolrn% 

osP=iw min to 2in 

Opreszpure OAttOrr to 2torr 

Plasma Stability 

srpply Pletr mrmnt (lm) 

I 1 I I 

.O 0.5 1.0 1.5 2.0 2.S 

mwro (m 4) 

382 
PROCESS DEVELOPMENT AND ADVANCED PRC SSES 

Silane Utilization Cost Influence 

080wistts outpn0846eff. 

*. oAtlOO% sUareuQ&athn, 

osilaecocst cxi7tol~Wg 

lo9 Cm2 x Qs x 10 *Cm x 233 g/m3 x 32/28 = I33 g sw, 

@ 100%: (17- lB/g x L33g /80 w = (.om8 to .0166~iW 

0 4%: ( 1 x= a.071 toA16)WW 

Depositior? Di1ernm.a 

383 

ADVANCED PROCESS TECHNOLOGIES 

JET PROPULSION LABORATORY 

D.B. Bickler 

Material Application Methods 

oMetau-Oeoorrposr 'tiun (M 0 0 )- fihrs 

Energy Sources 

OlAmerS 

0- 

RF 
PROCESS DEVELOPMENT AND ADVnNCED P9CCESSES 

Processing Techniques 

*Fkdrctbnaf"anmmmbs" 

New Contracts - -e) 

386 
SILICON MATERIAL AND SHEET 

A. Briglio, Jr., Chairman 

Eleven presentations were made covering research on processes for 

refining silicon (Si) and on Si shaped-sheet technology. 

A report was presented by JPL on the FSA-sponsored miniworkshop oa the 

effects of stress and strain in high-speed-grm Si ribbons, held January 10 

and 11 at the Westinghouse R&D Center, Pittsburgh, Pennsylvania. 

Hobil Solar Energy Corp. reported on its work to develop an understanding 

of strebs generation in Si sheet growth and to define configurations for 

growing low-stress ribbon at high speeds by the edgedefined film-fed growth 

(EFG) process. 

as lw as 105OOC. 

One finding was that significant creep occilrs at Cemperatures 

Westinghouse Electric Corp. described its program to investigate the 

dendriticlreb Si ribbon-growth process. Emphasis is currently being placed on 

the Dodeling and experimental evaluation of hardware configurations that use 

dynamic positioning of the critical elements during growth to obtain the best 

conditions for producing low-stress ribbon at high speeds. 

The University of Illinois at Chicago presented results of its study to 

determine nondestructively the residual stresses in Si sheet, using laser 

interferometry for polished surfaces and Wire interferometry for rough 

surfaces. Using these techniques, residual stresses ref? measured i- a 

Ctochralski wafer and in EFG ribbon. 

The Solar Energy Research Institute (SERI) described results obtained 

from a study of low-angle Si sheet, using a combination of secondary electron 

imaging, electron channeling, and EBIC techniques in a scanning electron 

microscope. Correlations of the structural and electrical properties of 

defects in the sheet material were obtained. 

Semix Inc. reported on defect analysSs of semicrystalline Si and thermal 

analysis of the ubiquitous crystallization process (UCP), which produces this 

material. The studies showed that a degraded structure can form in the solid 

behind the crystallization front due to thermal stresses, and as a result the 

local photovoltaic properties can be adversely affected. 

Energy Materials Corp. reported on two efforts. One is for a scaledvp 

demonstration of a fused-salt electrochemical cell for refining metallurgicalgrade Si. The system was operated in its first test, and examination of the 

product revealed that water was present, indicating incomplete drying of the 

system before the test. 

of the PIM, is for continuation of development of the low-angle silicon sheet 

(LASS) process that had been previously supported by SERI. 

involved, status, and plans were described. 

The other program, which had just started at the time 

The technology 

387 
SILICON MATERIAL AND SHEET 

Union Carbide Corp. (UCC), presented information on its research on 

pyrolysis of silane in fluidized-bed reactors (FBRs) to make Si. 

duratiorl tests (one of nearly 45 hours) were made to demonstrate operability 

and determine product purity. 

the reactor wall; modifications are being made to improve purity. 

LongThe results showed metallic contamination from 

JPL described results of its research on deposition of Si from silane in 

FBRs. As with the UCC tests, JPL results showed contamination of the product 

by the wall material, and appropriate changes are being made to prevent this, 

Scavenging of fine particles produced in the FBR was shown to be feasible by 

secondary injection of small amounts of silane above the distributor. 

Caltech described progress in a study of the formation and growth of Si 

particles by pyrolysis of silane in free-space reactors, with the aim of controlling the process to avoid or minimize the generation of fine particles. 

Significant increases in particle size were obtained. 

SERI reported on its investigation of a process for refining metallurgicalgrade Si by a chemical-vapor transport process, in which a Cu:Cu3Si anode 

reacts with HC1 to form chlorosilanes, which are then decomposed on hot Si 

filaments to produce pure Si. 

sured, and the results support the hypothesis that the transport is limited by 

diffusion of Si in the anode. 

The Si transport rate in the process was mea388 
SILICON MATERIAL AN0 SHEET 

A. Briglio, Jr., Chairman 

MINIWORKSHOP ON EFFECTS OF STRESS 

AND STRAIN IN HIGH-SPEED-GROWN SILICON RIBBONS 

JET PROPULSION LABORATORY 

A. Briglio, Jr. 

HELD JANUARY 10, 11, 1984 AT YESTIN6HOUSE R 8 D CENTER, PJTTSWIR6H, PA. 

sEconn sTREss/siRAin MINI-UORKSHOP in nE HELD 

' 1ST UAS IN YOHHBER 1982 AT HOBlL SOLAR ElER6Y COUP., YALTHAII, MA 

THIRD MINI-UORKSHOP EXPECTED TO BE HELD IN LATTER HALF OF 1984 

' 60AL OF STRESS/STRAIW PUNRAM: UNDERSTAND AND OKRCOllE PUWm OF STRESS AID 

STRAIN THAT IS LlMlTlU6 RATE AT WHICH SI RIBBONS Of SUITAME OUAllTY FOR MARIN6 

SOUR CELLS .CAN BE GROWN* 

' PURPOSE OF WORKSHOP 

ACOUAINT PARTICIPANTS YITW YnRK THAT IS 601Y6 [#I 

OPEN DIRECT COMUNICATIOWS MTIIEEU PARTICIPANTS 

IMNTIFY ASSWPTIONS lUW6 USED IN UORK, TO ASSURE A COeWlON BASE 

IDWlfY WORK MEED TO UNDERSTAND STRESS/STRAIW PROBLEM 

389 
SILICON MATERIAL AND SHEET 

STRESWSTRAIN MINIWORKSHOP 

Agenda 

JANUARY 10, 1984 

OPENIN6 RERAFKS * - * * * * - . * - * A- HOROISON 

WELCW - - - ~ ~ - * * * * - * * - - DR. JOHN HUM (ACTIN6 MNA6ER, YLSTIN6HOUSE R 8 D CENTER) 

STRESS BUCKLIN6 MODEL ............... STRAIN-RELATED DEFECTS ............... -1 PROF. OSCAR DILLON (UNIV. OF KENTUCKY) 

JPL STRESS/STRAIN MEASUREMYTS ON SILICON RIBBON . . 1. O'DONNELL (JPL) 

ROB11 SOLAR'S STRESS/STRAIW PROCRAH * - * * * - * * - DR. J. KMEJS (HOB11 SOLAR EWERCY cnw.) YON-DESTRIKTIM DETERRINATION OF RESIDUAL 

STRCSSES IN SHEET SILICON * - * - * - - * - - * PROF. S- LANVLUK/DR- A- ANDONIAN 

(UNIV- OF ILLINOIS AT CHlCA60) 

STRESS/STRAIN NODEL * - - - * * * * - * PROF. J. HUTCHINSON (HARVARD UWIV.) 

JANllARY 11, 1984 

WESTIYQOUSE STRESS/STRAIW APPROACH * * * * * - - DR- R. SEI?ENSTICKER/DR* S*-Y. LIEN 

(VESTINGHOUSE ELECTRIC CORPS 1 

CENERAL DISCUSSION . * - * * * - OPEN 

FUTURE RESEARCH ACTIVITIES DISCUSSION - * - - * OPEN 

SWIARY REVIEW OF MEET116 - * - * * - - - DOE/SERI/JPL PERSOWMEL 

390 
SILICON MATERIAL AND SHEET 

' STRESS BUCKLING MODEL (DILLON) 

UNIV. OF KY DEVELOPIN6 BUCKLlN6 MOM1 FOR SI RIBBONS 

CALCULATED THICKNESS AT WHICH MICKLINS OCCURS, ASSWIN6, FOR EXAMPLE: 

TEMPERATURE IS FUNCTION OILY OF DISTANCE MOM6 RIBBON LENCTH 

MATERIAL IS ELASTIC WITH CONSTANT MATERIAL PROPERTIES 

' 

' 

OBTAINED RELATIONSHIP OF CRITICAL THICKNESS (THICKNESS BELOW WHICH RIBBOW BUCKLES) 

VS WIDTH. RESULTS ARE REASONABLY CONSISTENT WITH WESTINCHOUSE EXPERIMENTAL RESULTS 

NEW BUCKLING ANALYSIS DESCRIBED YlTH EQUATIDYS lNwKVlN6 VARIOUS BUCKLING MOMS, 

EXTENDIN6 INTO ION-LINEAR RATERIAL BEHAVIOR 

' STRAIN-RELATED DEFECTS (M AN6ELIS) 

CALCULATION OF DISLOCATION DEWSITY 

CALCULATION OF STRESS/;;RAIN RELATIONSHIPS AS FUNCTIONS OF SUCH VARIABLES AS 

TENPERATURE, DISLOCATIJN DENSITY, OXYCEN COWTENT, AND STRAIN RATE 

JPL STRESS/STRAIN MEASURERENTS ON SlLlCoY RIBBON (O'DONNELL) 

' DENDRITIC WEB RIBBON 

' 

' 

RESIDUAL STRESS MEASURED BY USE OF STRAIN QGES ON DEFORMED RIBBON 

WITH ONE SARPLE OF DEFORMED RIBBON, MEASURED RESIDUAL STRESSES RAIINC FRON 

200 PSI IN COMPRESSION TO 1000 PSI IN TENSION 

EFG RIBBON 

' 

' DETERMINED DISLOCATION DENSITY BY IMA6E ANALYSIS 

RESOLUTION OF WHETHER OBSERVED RIBBON DEFORMATIONS ARE ELASTIC OR PLASTIC AND 

CORRELATIflN WITH GROWTH CONDITIONS AI. - NEEDED 

HADE VAR IOUS REASUREMENTS INCLUDING SURFACE PROFILES LEN6THWISE AND ACROSS 

R I EBON 

MOBIL SOLAR'S STRESS/STRAIN PROGRAM (KALEJS) O 

' GOALS: DEVELOP UNDERSTANDING OF STRESS-GENERATION MECHANISM IN SI SHEET 6ROWTH 

AND DEFINE M WIRUM - STRESS GROWTH CONFIGURATIONS FOR ~MI-PR-THICK, IO-CM-WIDE E!G RIBBON 6RMIIMG AT 4 CM/MlN 

' CREEP STUDIES, TEMPERATURE FIELD MODELING AND MEASUREMENT, RESlDUAL STRESS 

REASUREMENT 

CREEP STUPIES (FOUR-POINT BENDING TESTS): 

TERPERATURE * REASURING SYSTEM USING FIBER OPTICS BEING DEVELOPED 

' SIGNIFICANT PLASTIC FLOW EVEN AS LOW 

AS 10SO't. 

' 

NQN-DESTRUCTIVE DETERRINATION OF RESIDUAL STRESSES IN SHEET SILICON (DANYLUK, ANDONIAW) 

' METHOD OF DETERMINING RESIOUL STRESS BEING DEVELOPED, INVOLVINlr: 

' 

' 

' ANALYTICALLY COWPUTE DEFLECTION 

APPLY EXTERNAL LOAD TO SILICON SARPLE 

EXPERIMENTALLY REASURE DISPLACEMENT IISING LASER INTERFERMETRY 

0 RELATE DIFFERENCE BETWEEN REASUREO AND COMPIITEO DEFLECT IONS in RESIDUAL STRESS 

' SCHEME FOR USING LASER INTERFERMETRY BE1 WC DEVELOPED FOR EXPERIMENTAL REASURERNT 

OF DEFLECTIONS, USING Mol RE PATTERNS 

391 
SILICON MATERIAL AND SHEET 

STRESS/STRAIN MODEL (HUTCHINSON) 

SIMPLIFIED MODEL DEVELOPED FOR BEHAVIOR OF STRESSES VERY NEAR MELT INTERFACE 

MODEL SOLVED FOR DIFFERENT VALUES OF STRESS AT THE CROYTH INTERFACE 

BEYOND ABOUT 0.1 CM FROM 6RWTH INTERFACE, LATERAL STRESS AT RIBBON CENTERLINE IS 

INDEPENDENT OF IYITIAL STRESS. 

SI AT INTERFACE BEHAVES AS FLUIDINITIAL STRESS 6ETS RELAXED VERY OUICKLY* IN EFFECT, 

' WESTllCHOUSE STRESS/STRAIN APPROACH (SE IDEISTICKER/LIEN) 

APPLICATION OF CMPUTER MODELS TO 6ROYTH SYSTEM DESlCN (SEIDENSTICKER) 

TEMPERATURE MnML - CMPUTES TENPERATURE ALWC WEB RIBBON 

STRESS MODEL - CALCULATES THERMALLY 6ENERAlED STRESS IN NEB RIBBON 

BUCK1116 MODEL - STRESSES FRDM STRESS MODEL SERVE AS INPUT DATA TC BUCKLINC MODEL, 

WHICH CALCULATES THE CRITICAL BUCKLINC CONDlTlOYS FOR A CROyIH6 NEB CRYSTAL. 

INELASTIC PROCESSES ARE NOT INCLUDED IN THIS MODEL AT THIS TIME 

BUCKLlN6 PREDICTIOWS ARE IN 600D A6REERENT WITH OBSERVED CROYTH BEHAVIORBY USE OF MODELS, NEW GROWTH CBNFICURATIONS HAVE BEEN DESICYED. 

INCREASED WIDTH OF UNBUCKLED RIBBON FRM 2.8 CM (WIDTH PRODUCED BY MOST 

SUCCESSFUL EMP I R ICALLY DES I6NED CONF I6URAT I ON 1 TO 5 8 CM 

THESE HAVE 

IDENTIFICATION OF WORK NEEDED in UNDERSIAWD RIBBON STRESS/STRAIW PROBLEM 

NEED TO UNDERSTAND BETTER THE REGION ADJACENT TO LIQUID - SOLID INTERFACE 

NEED TO HAVE ACCURATE HICH-TEMPERATURE CREEP DATA OF SILICON 

SYSTEMATIC EXPERIMENTAL EVALUATION OF MODELS IS REOUIRED 

ACTUAL TEMPERATURE DESTRIBUTION IN 6ROWIW6 RIBBONS AND IN 6RWTH ENVIRONMENT 

AROUND CRYSTAL NEEDED, FOR DEVELOPMENT OF ACCURATE MMLS OF CRMlTH PROCESS. 

REOUl RES DEVELOMENT OF TEMPERATIIRE-REASUR IW6 TECHNIOUES 

392 
STRESS STUDIES IN EFG 

MOBIL SOLAR ENERGY CORP. 

J.P. Kalejs 

. . -. 

TE(HI(OLOGY 

ADVANCED MATERIALS RESEARCH TASK 

EONTRACTOR 

MOBlL SOLAR ENERGY CORPORATION, CONTRACT 

I NUMBER 956312 

I - GOALS 

0 DEVELOP UNDERSTANDING OF MECHANISM OF 

STRESS GENERATION IN SILICON SHEET CIROUTH 

AND DEFlNE MINIMUM STRESS GROWTH CONFIGURATIONS FOR 200 pM THICK 10 CH WID€ 

EFG RIBBON GROWING AT 4 CH/MIN, - 

Projects 

STATUS 

VERIFICATION OF STRESS MODEL IS 

UNDERWAY IN AREAS OF: 

0 CREEP LAW STUDIEb. 

0 TEMPERATURE FIELD MODELING 

t 

AND MEASUREMENT. 

0 RESIDUAL STRESS MEASUREMENT. 

TEMPERATURE-STRESS FIELD 

MODELING IS IN PROCRESS, 

0 STRESS ANALYSIS FOR VERTICAL SILICON SHEET GROWTH 

(HARVARD UNIVERSITV), 

0 RESIDUAL STRESS MEASURENENTS (UNIVERSITY OF ILLINOIS), 

0 TEMPERATURE FIELD MODELING USING t-V DATA AND 

INTERFACE SHAPES (HIT). 

0 CREEP LAW STUDIES FOR T 2 lM)o°C, 

FIBER OPT I CS TEMPERATURE SENSOR DEVELOPMENT. 

393 
SILICON MATERIAL AND SHEET 

/ 

oo = 0 (no creep) Y 

I 

/ I 

I 

601 / .. 

- - 

/ 

intarface p 

I 

I 

0.2 

- I (a) 

- 

-30 - - 

Stress Analysis Program 

0 IMPACT OF INTERFACE STRESS BOUNDARY CONDITION 014 STRESS DISTRIBUTIONS HAS BEEtl EVALUATED, 

(I SEHSITIVITY ANALYSIS IS IN PROGRCSS TO EXAMINE STRESS DEFENDENCE 

ON : 

- WIDTII, GROWTH SPEED, 

- CREEP LAW, 

- POST-GROWTH TEflPERRTURE FIELD, 

0 GROHTH CONFIGURATION IS UNDER DEVELOPMENT TO t'YALUA? 

- TEMPERATURE FIELD MDEL, 

- FIBER OPTICS THERMETRY, 

- STRESS MOEL. 

Simplified Model Predictions 

3 94 
SILICON MATERIAL AND SHEET 

Thickness-velocitv curves for 10 m cartridge system with cold shoes at a face 

heater temperature settin9 of 1431OC. 

dashed line is for a contlnuously imposed 

velocity Chdnge that temiiiated in a ribbon 

pull-out or neaiscus bwak at the hlsl~est 

speed. 

lhe 

(b) 

Eaperiaental (envircant) vertical tonpcrrture profile in IO cm ETG rartridqe 

and calculated ribbon disti4butlon. 

395 
SILICON MATERIAL AND SHEET 

lsnpcrature profiles used In Stress mrlysis: 

1. EFG system. 2. fdealired system. 3. finite element 

mode' alack body rrdfation. 

396 
SILICON MATERIAL AND SHEET 

m i I 

I 

I 

i i 

MOT 

i 

IJ 4 E 

sheet ~18th icm) 

Variatlm of peak u 3 dmin, ad (b) 4%/ain for flnitr c?mt black body rMiatim 

aodcl, and la, creep intmslty rtpresmtation. Pofnt (1) is 

wevim calculations for En system at 6 dnin md la, crrcp 

intensity. 

with rieth of sheet at gcath speeds of (a) 

397 
SILICON MATERIAL AND SHEET 

a- 

- 

Creep Law Studies (Four-Point Beriding) 

0 RULTIPLE LOADING - DEFECT STUDIES. 

0 SINGLE LOAD TRANSIENT CREEP STUDIES, 

e ORIENTATION AND IMPURITY DEPENDENCES. 

398 
SILICON MATERIAL AND SHEET 

Schematic of Stress Distribution 

c (SEC) 

(111) FZ SILICON CREEP RESPONSE AT 1215OC FOR LOADS 

1. 8,6 /PA, 2. 12.7 MPA, AND 3. 15-6 RPA WITH 

(110> BENDING AXIS 

OF : 

3 99 
SILICOF\j MATERIAL AND SHEET 

m 

- 

- c 

Y 5 -1 

U 

c 

ci 

c 

I 

t 

-2 

1 I I 1 

I I 1 1 

2 4 

t (scc) 

(711) FZ silicon creep response at 1?60°C for loads of 

1. 8.0 !Pa, 2. 12.0 HPa. 3. 14.9 HPa. anO 4. 15.5 ma. 

with g110, bending axis. 

400 


SILICON MATERIAL AND SHEET 

(111) SZ -ilicon creep response at bo temperatures with (110, 

bendfnp axis: 

1. 1215’C. 11.0 MPa. 

2. 1215’C. 13.5 HPa. 

3. 1360OC. 7.0 Wa. 

4. 1360%. 12.0 MPs. 

5. lWO°C; 15;5 NP;; 

6. 13W0t. 15.5 MPa, Cs = 1 x 10” at/cc. 

403 


SILICON MATERIAL AND SHEET 

Creep Law Studies 

0 SIGNIFICANT CREEP AT 1051)~~. 

0 PRIMARY CREEP LIKELY TO OWINATE ABOVE 1200~~. 

0 STRESS LIKELY TO SELECTIVELY ACT ON ORIENTATIONS WITH 

HIGHEST RESOLVED STRESSES ON GLIDE PLANES TO: 

- RAPIDLY GENERATE 106-107/~+’ DISLMATIONS BY 

MULTlPLICATlONe 

- FINAL SLIP BAND CONFIGURATION AND RESIDUAL STRESS 

IS FUNCTION OF STRUCTURE (E.G., ORIENTATION AND 

PARALLEL BOUNDARIES), I~RPURITY CONTENT, AND SLIP 

BANDS ACTIVATED. 

406 
SILICON MATERIAL AND SHEET 

Schematic of Optical Thermometer 

Optlal ffbo? bund10 

to dotoctor 

Coolln9 50 in 

HZO Out 

1 .O II dl~ltor 

wrtt rod 

n 

40 7 
SILICON MATERIAL AND SHEET 

Sensor Development Status 

0 uATER-COOLED PRO6E HAS BEEN CONSTRUCTED AND TESTED 

IN FURNACE ENVIRONMENT. 

0 SOHE NON-REPRODUCIBILITY (t 3-5OCI HAY HAVE 

MECHANICAL ORIGINSa 

0 EXPERIMENTS ON TIP CONFIGURATION AND COATINGS ARE 

PLANNED, 

0' SIGNAL STRENGTH SHOULD BE ADEQUATE WITH 0.25 Wl TIP. 

Low Stress Growth Configuration 

0 10 QI CARTRIDGE WITH COLD SHOES FOUND NOT TO HAVE REQUIRED 

FLEXIBILITY FOR 

- OPERATING VARIABLE/DESlr.N CHANGES, 

- TESTING 3~ FIBER OPTICS SENSOR. 

0 DESIGN AND FABRICATION OF GROWTH CMFIGURAT!ON UNDERWAY: 

- LOWER HEFF TO INCREASE FLEXIBILITY, 

- SIMPLIFY POST-GROWTH COOLING PROFILE TO FACILITATE 

ANALYSIS AND TEMPERATURE HEASUREHENTa 

408 
SILICON MATERIAL AND SHEET 

Future Work 

0 COWTINU€ TWERATURE-STRESS FIELD RELATIONSHIP 

STUD I ES , 

0 DEVELOP GROWTH SYSTvl FOR STRESS RODE1 

EVALUATION. 

0 CONTINUE YIELD STRESS STUDIES. 

409 

I N85 15286 J2 5 

ADVANCED DENDRITIC WEB GROWTH DEVELOPMENT 

WESTINGHOUSE ELECTRIC COW. 

C.S. Duncan 

Long-Range Goals of Program 

lonn Ranne Goals Of Program: 

Continuously-Melt-Replenished Growth Period Of 

65 Hours With An Area Rate Of Growth > 25 cm2/Minute 

length Of Web Crystal Greater Than 10 Meters 

Dislocation Density less Than 10 42 /cm 

Resistivity Of Web In Range Of 1 To 3 Ohm-cm P-Type 

Terrestrial Solar Cell Efficiency > 15% 

Principal Tasks of Current Phase of Program 

Develop Computer Specifications For low-Stress Web 

Growth Configurations Having Thermal Elements In 

Fixed Position. Correlate With Experimental Web 

Growth. 

Develop Computer Specifications For Web Growth 

Configurations Incorporating Dynamic Positioning Of 

Thermal Elements. Correlate With Experimental Web 

Growth 
SILICON MATERIAL AND SHEET 

I’ Elastic Region 

\ I ,4 Buckling Stress and Widt9) 

( Residual Stress and 

Silicon Web Area Growth Rate and Ouality are Determined by 

the Temperature Profile in the Crowing Web 

Buckling and Web Width (Elastic Region) 

- Goal 

Attain low Buckling Stress And Increased Width Of 

Unbuckled Growth 

Status 

Major Reduction Of Buckling Stress Has Been 

Achieved 

Computer Models Have Been Developed And Applied 

Model Predictions Have Been Verified By 

Width Has Been Increased 80% Since Application 

To Define Growth Configurations 

Experimental Web Growth 

Of Models 

412 
ILICON MATERIAL AND SHEET 

Current Activitv 

0 

0 

0 

Model Application And Experimental Verification 

Are Continuing With Goal Of Further Increases In 

Width 

Experimentally Developed Techniques Are Applied 

To Obtain Improved Growth 

Residual Stress Is Monitored For All New Growth 

Configurations 

413 
SILICOhJ MATERIAL AND SHEET 

Velocity and Residual Stress (Plastic Region) 

- Goal 

Attain Increased Growth Velocity While Maintaining 

Low Residual Stress 

Status 

Important Increase In Growth Velocity Has Been 

Achieved 

Computer Models Have Been Applied To Define 

Growth Configurations 

Model Predictions Of Velocity Have Been Verified 

In Experimental Web Growth 

Gas Conduction Effect Found To Be Of Negligible 

Significance Near Growth Interface 

Split Width Measurement And Calculation Verified 

Velocity Has Been Increased 55% Since Application 

Of Models 

Current Activity 

Dynamic Positioning Of Lid Relative To Growth 

Interface (LIN) For Velocity Improvement 

Dynamic Positioning Of Portion Of Lid And Shield 

Assembly For Control Of Heat Loss Above Growth 

Interface And Velocity Improvement 

Design Of lids As A Control Of Temperature Profile 

For Reduction Of Residual Stress And Enhancement 

Of Growth Velocity 

Residual Stress Monitored For All New Growth 

Configurations 

414 
SILICON MATERIAL AND SHEET 

Variation of Web Velocity With LIN 

J 

1.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 

LIN. cm 

Lid Design for Increased Velocity 

Factors Which Can Affect Velocity: 

0 Lid Thickness 

Lid Temperature 

Width Of Growth Slot 

Profile Of Growth Slot (Beveled, Etc) 

Placement With Respect To Adjacent Shields 

And Melt 

415 
SILICON MATERIAL AND SHEET 

Residual Stress Measurements 

Residual Stress Is A Critical Factor In The 

Development Of Higher Velocity Growth Configurations 

Split-Width Measurement Was Shown To Give Good 

Estimate Of Maximum Residual Stress In Silicon Web 

Crystals Based on Detailed Measurements 

Split-Width Method Is Routinely Used To Evaluate 

Residual Stress In New Configurations Of Web Growth 

New Configurations for Web Growth Defined by 

Computer Modes and Verified Since Last PIM 

Two Static Growth Configurations (5503, J517) 

Three Dynamic Growth Configurations 

(RE435, RE443, RE453) 

Summary 

Model-Defined Advanced Concepts For Web Growth 

Configurations Have Been Defined And Verified In 

Experimental Web Growth 

'0 Major Increases In Achieved Width And Velocity Hate 

Resulted From These Concepts 

416 
SILICON-SHEET SURFACE STUDIES 

UNIVERSITY OF ILLINOIS AT CHICAGO 

S. Danyluk 

Objective 

Ibn-datructlrr dttmlMtlOn of mlkl str.osa 

In short srtlons of sheet slllcon 

Dwelopd a Laser Interfenmetry Tachnlque (for 

pollslud surtacal and 

wlled a shadow klr6 tachnlqur (for rough swfaca) to Ltemlne drflrtlonr In sheet 

sll Icon. 

me1op.d an atulysts if rxtractlng resldurl 

strasa from wrsured deflectlons of clrcular 

wafers and short rectmgular rlbbons. 

Residual Stress 

Dtflnltlon of Resldurl Stress - Stress that UIrtr In the slllcon 

shnt after mprocarlng.m 

TIlrrmd bradtent -Z 

1. Residual stresses redlstrlbute after cuttlng, pollshlng. etc. 

2. Out-of-plane resldual stresses are lmedlately wldent since 

they producr buckllng (potato Chlp); In-plane resldual stresses 

are not wldent and so must be neasured. 

3. The nom1 resldual stresses are zero at the surfacer slncr 

these are "free." 

4. Normal resldual stresses decrease to zero near the ends of I 

rlbbon. The decrease occurs In a length that 1s about equal 

to the width. 

41 7 
SILICON MATERIAL AND SHEET 

41 8 
SILICON MATERIAL AND SHEET 

Plate Analyrls: 

d'w ZA (curvaturr at xO--to be detemined rxpairntrlty) dx' 

M applied lldent 

Eh'b 0 0- 12(1-u') 

u deflection at xo 

419 
SILICON MATERIAL AND SHEET 

I 

t I 

o-2r 1 

l....,....L........~.,..,....,....'...r) 

'. i 

0 I 

E. , mimental Nondestructive Technique 

for Measuring Residual Stresses 

1. Short sctton of ribbon (2b = L) 

2. Heterogeneous In-plane residual stresses are present-are zero 

at surfacer. 

3. External normel stresses are zero. 

4. Thickness is unlform. 

420 
SILICON MATERIAL AND SHEET 

Experimental Results 

Rbbfl Solar: 

Sgeciwn No. Growth Sp8W (cn/atn) 

47R1-3 1.15 

blR1-1 2.00 

4lR1-2 2.00 

blR1-b 2.25 

421 
SILICON MATERIAL AND SHEET 

)r 20.5'' .d 5 \" .i a" K =3fl x: 3.5* 
ILICON MATESIAL AND SHEET 

4 

423 
SILICON MATERIAL AND SHEET 

424 
"85 1- 15288 

I N V E ST I G AT I 0 N 

PROPERTIES 

OF STRUCTURAL AND ELECTRICAL 

OF LOW-ANGLE SILICON SHEET 

SOLAR ENERGY RESEARCH INSTITUTE 

Y.S. Tsuo 

R.J. Matson 

J.B. Milstein 

Considerable research is being conducted in low-t?os: polycrystalline semiconductors in 

!he photovoltaic solar cell industry. We have found that the combination of secondary 

electron imaging (SEI), electron channeling, and electron-beam-induced current (EBIC, 

a1.m knoan as charge collection scanning electron microscopy) techniques in a scanning 

electron microscope (SEMI is quite useful for correlating morphology, crystallographic 

orientations, and electronic quality of individual grains in polycrystalline semiconduc tor 

samples. It is also possible to obtain quantitative information about the minority Carrie: 

diffusion length of individual grains and the minority carrier recombination velocity at 

grain boundaries using the EBIC line scan method. The high spatial resolution obtainable 

with electron channeling and EBIC techniques and the ability to select between the SEI, 

EBIC, and electron channeling modes in the SEM make them far superior to conventional 

structural and electrical characterization techniques in studying small-grained 

scmiconduc tors. 

These techniques have been applied to the studies of low angle silicon sheets. Low-angle 

silicon sheets (LASS) that are pulled almost horizontally from the melt at very high 

speeds, up to about 400 cm /rnin, were assessed. Large areas of single-crystal silicon are 

occasionally grown by the LASS method. However, single-crystal LASS sheets contain 

many defects which may result from the unusually high growth speeds, and from 

apparently unusual modes of crystallization. 

2 

Experimental Method 

A JEOL JSM 35C SEM with a selected area diffraction component attachment was used 

in the experiment. An IC specimen holder was modified to operate at the 9-mm working 

distance required for optimal electron channeling in this microscope. A GW Electronics 

Model 103B specimen current amplifier was used for EBIC imaging and a Keithley Model 

427 current amplifier was used for digital quantitative EBIC images and linescans. The 

G W Electronics Model 130 backsca ttered electron imaging (BE11 detector and electronics 

were found to be optimal for acquiring clear electron channeling patterns (ECP). 

Restrained by a short working distance, the BE1 unit, rather than the SEI unit, was used 

in a topographical mode to image topographical features. 

Different approaches can be taken to perform both electron channeling and EBIC analysis 

on the same area, depenctng on the requirements of the experiment. If the individual 

grains are relatively large and easy to locate, then the ECP work is done to establish the 

orientation of the grains; then, after a Schottky barrier device is made out of the 

material, the EBIC siudy is performed. Since the electron beam of the SEM is a constant 

current source, the EBIC line scan traces and images reveal spatial variations in the 

cnarge collection efficiency of the Schottky barrier device. To measure the effective 

sclrface recombination velocity of minority carriers at a grain boundary, an EBIC line 

scan normal to the boundary is obtained. To be quantitatively useful, a digital line sca 

425 
SILICON MATERIAL AND SHEET 

using a calibrated current amplifier, a computer, and a plotter are used to record the 

natural log of the EBIC signal as a function of distance. The minority carrier diffusion 

length within each grain can also be measured by scanning the beam perpendicular to the 

edge of the front contact pad and recording the EBIC current as a function of distance 

from the contact pad. 

By switching between ECP, BE1 ai 2BIC while moving across the material, the location, 

topography, electrical quality, crystalline orientation and even the crystalline quality can 

be correlated for polycrystalline materials. Evaluating tne crystalline quality requires 

measuring the relative peak heights (ECP contrast) and the shape of the peaks (ECP 

linewidths) shown by ECP line scans (intensity vs. scan angle) normal to the crystalline 

bands. 

Applications 

Complementary electron chenneling and EBIC were first used in the study of ESP silicon 

sheets grown at SERI. 

Ti-s EBIC/ECP technique was applied to LASS samples grown at the Energy Materials 

Corporation. Probably because of the unusually high giowth speed-the single-crystal 

LASS samples studied were grown at the speed of 210 cm /min--the defect structures we 

observed in these samples were rather unusual for single-crystal silicon. In addition to a 

relatively high density of electrically active dislocation networks, they also contain what 

appear to be inclusions. The sample has been chemically etched to reveal the defects. 

The electron channeling patterns indicate that some of these inclusions are actually 

silicon crystals with orientations identical or very similar to the rest of the crystal. The 

superposition of the ECP taken at the center of a defect and the SEI of the location of 

the ECP at a high magnification is shown. The dark lines of the SEI show that the 

stacking faults occur along 220 planes. An EBIC micrograph of the same area is 

shown. The sample was mechanically and chemically polished to remove etch pits before 

being fabricated into Schottky barrier devices for EBIC studies. The EBIC images clearly 

illustrate the electrical activity of the various defects. They also show electrically 

active dislocations that were not revealed by chemical etching. In addition, our study 

showed that large, electrically active dislocation networks exist under the dendrites that 

appear on the top surface of LASS sheet during growth. Such information is not only 

useful from the device point of view; it also provides insight into the mechanisms of 

growth in the LASS process. 

The LASS ribbon studied contains both polycrystalline regions and a large single crystal 

region. In this ribbon (about 6cm x 24 cm in size) which represents perhaps 40 seconds of 

growth, one sees the spontaneous nucleation of the single crystal region, "stable" growth 

of single crystal material to dimensions of several centimeters width by over ten 

centimeters in length, and termination of single crystal growth. We belive that much 

information regarding these processes may be abstracted from the ribbon by careful 

study. 

By comparing regions of LASS material which are clearly polycrystalline with the single 

crystal region, we have discovered a number of remarkable features which we have not 

seen reported in standard texts which treat defects in semiconductors. in the 

polycrystalline regions, we find defects which extend throughout the thickness of the 

ribbon. In the single crystal region, we observe surface features on the upper surface of 

426 
SILICON MATERIAL AND SHEET 

as grown ribbon which are reminescent of structures commonly observed in flux-grown 

crystals which float on the surface of the molten flux. These features, which are readily 

seen in an optical microscope, appear to be crystallographically oriented hillocks bounded 

by crystallographic facets, with depressed central regions. Photos will be shown. To the 

naked eye, however, these features appear to be finely spaced oriented dendrites, which 

grew at an angle to the pull direction. 

By the use of EBIC, ECP and SEI, we have examined defects in the single crystal region 

which also extend through the entire thickness of the ribbon. Some of these defects 

enclose crystalline regions which are oriented identically or nearly identically 4th the 

crystal, while others are definitely polycrystalline. In both instances, we observe that no 

apparent degradation of the crystal structure in the direction of the macroscopic growth 

direction has occurred. It is well known that, for example in Czochralski growth, such 

growth accidents rrpidly lead to loss of structure. Our observation leads us to suspect 

that in LASS growth, the conception of aT( interface which simply proceeds in the growth 

direction is incapable of explaining all of the features seen. Accordingly, we postulate 

that the defects observed are generated by a moie complex process, in which growth 

occurs behind the macroscopic interface (or leading edge). In the hypothesized process, 

there are liquid regions behind the growth front which close by lateral growth from 

aa:acent solid regions. These "lakes" of molten material are first confined from below by 

a thin layer of solid silicon, which traps a pool of liquid silicon. When the pool freezes, 

the surface growth a:tifacts are formed, by virtue of the fact that silicon expands on 

freezing. As the layer which isolates the pool from the remainder of the melt is closed, 

defects sucn as dislocations and stacking faults are produced, which are observed by the 

methods indicated above. We observe the defect structures on the bottom surface of the 

ribbon as well. By comparison of optical micrographs taken at the Same magnification on 

both surfaces, we can see that these unique structures maintain their character, but are 

somewhat larger on the bottom surface as compared to the top surface. This behavior is 

consistent with the hypothesis that the ribbon continues to grow in the thickness 

direction after the growth front has moved away, taken with the conception of local loss 

of structure as growth proceeds downward into the melt similar to Czochralski growth. 

This picture is also consistent with the "popcorn effect" previously reported by Energy 

Materials Corporation. 

conclusion 

By using a combination of secondary electron imaging, electron channeling, and EBIC 

techniques in a SEM, we have correlated the structural and electrical properties of 

defects in low-angle silicon sheet material. This technique has proven quite useful in 

correlating the structural and electrical properties of highly defected or polycryst:: line 

semiconductor materials. 

42 7 

SEMICRYSTALLINE CASTING PROCESS 

DEVELOPMENT AND VERIFICATION 

SEMIX INC. 

W.F. Regnault 

Principal Areas of Research 

o DEFECT ANALYSIS OF SEMICRYSTALLINE SILICOJ 

o THERHAL MODELInG OF THE UCP 

Investigation of Structural Defects Within Grain Volumes That 

Affect Efficiency of Semicrystalline Silicon Solar-Cell Materials 

PURPOSE: 

TO DETERMINE THE NUCLEATI3G MECHANISMS OF A JISLOCATIOd SUBGRAIN STRUCTURE OCCASIOMLLY FOUID IN SGiICRYSTALLIdE SILICOlJ 

APPROACH : 

TO PERFORM X-RAY TJPOGRAPHIC, OPTICAL, AND EBIC 

STUDIES On SEVERAL SAMPLES OF UCP MTERIAL 

X-Ray and EBIC Measurements 

OBJECTIVES: 

TO DETERMIaE THE RELATIVE CRYSTALLOGRAPHIC ORIENTATIONS OF NEIGHBORIIG GRAINS 

TO XTERMINE THE INTERNAL DISLOCATION STRUCTURE OF 

THE CRYSTALLITES 

TO CORRELATE THE OBSERVED DISLOCATION STRUCTURE WITH 

THE ELECTRICAL RESPONSE OF THE MATERIAL 
SILICON MATERIAL AND SHEET 

Optical 0 bservations 

OBJECTIVE : 

TO DETERPlIE THE ORIGIi4 OF IRREGULARITIES ALONG THE 

HIGH AiiGLE GRAN BOUNDARY OF NEIGHBORIHG GRAIiuS 

Conclusions 

o THE DISLOCATION STRUCTURE WILL ADVERSELY AFFECT THE 

LOCAL PHOTOVOLTAIC PROPERTIES OF SEMICRYSTALLINE 

MTERI AL 

o THE SUPGRAIN STRLlCTllRE ARISES FdOM IRREGULARITIES IN 

THE HIGH ANGLE GRAIN BOUNDARIES OF HEIGHBORING GRAINS 

o GRAIN BOUNDARY KINKS ARE FORME9 BY GRAM IMPINGEMENT 

AND BY A RELAXATION OF A CURVED BOUNCARY INTO A LOWER 

ENERGY STATE COMPRISED OF STRAIGHT LINE SEGIENTS 

WHEN TWO GRAINS ARE IN A SECOND ORDER TWIN REL4TIONSHIP, TfEY SHARE A COMMON SLIP DIRECTION, UNDER APPLICATION OF A SUITABLE STRESS, BOTH GRAINS CAFl SIMULTANEOUSLY RESPOND BY SLIPPING ALOtiG THIS COMMON DIo 

RECTION 

o THE DRIVING FORCES ARE LIKELY TO ARISE FROM HIGH TEMPERATURE THERMAL STRESSES 

Thermal Analysis of UCP 

PURPOSE: 

TO DEVELOP A CPlPUTER SIMULATION OF THE UBIQUITOUS 

CRYSTALLIZATIOil PROCESS IN ORiIEli TO MODEL THE TIIE 

DEPEiJDEilCE OF THE SOLIDIFICATION FRONT ANT) TO AID 

Id TiiE STVJY OF THE TEMPERATURE DISTRIBUTION WITH 

,lil IJGOT 

APPROACH : 

TO IIZITE A TWO DIMENSIONAL FINITE-DIFFEREI~CE NDEL 

USI,;; TiiE IilPLICIT ALTERMTIIYG DIRECTIOI$ SOLUTIN 

TO THE TRAiiSIGYT HEAT CO!IDUCTION EQUATION 

430 
ILICON MATERIAL AND SHEET 

Mathematical Symmetry Elements for Finite 

Element Analysis of UCP Ingot 

Features of the Model 

o TAKES IdTO ACCOUilT VOLUHE EXPAilSION UW# FREUIEiG 

o IiKLUDES EFFECTS FROM THE RELEASE OF LATENT HEAT OF 

FUSIO# 

Differential Equation 

x= 

YT= 

KFPCP = 

1- 

HORIZONTAL COORDINATE, CM 

VERTICAL COORDINATE, CM 

TIME, SEC 

TEMPERATURE, OC 

THERMAL CONDUCTIVITY, J/SEC crl OC 

RATE IF HEAT GENERATION DUE TO LATENT HEAT REL 

J/SEC CM3 

DENSITY, GM/CM3 

SPECIFIC HEAT, J/GH OC 

45 

4 31 
I 

SILICON MATERIAL AND SHEET 

Boundary Condition 

ALLons THREE IMPORTANT CASES : 

1. INSULATED SURFACE AT PL~FIE OF SYMETRY 

2, SPECIFIED FLUX p (J/SEC CM~) 

d= A= 0 

INTO THE flEDrUM': 

A=O 

3, SURFACE INTERACTS WITH SURROUNDING FLUID AT 

TEMPERATURE TS, WITH HEAT - TRANSFER COEFFICIENT H CJ/SEC cd OC) 

ds H 

fi= H Ts 

E,G, FOR^(= 0,00568,13= 8,07, 

Ts = 3.07 = 14210 C 

o I 00568 

Physical Properties, etc. 

KP= 

To = 

E= 

HCP - 

HF = 

H*= 

0,67 J/w SEC OC 

2.5 GR/CR3 

0,917 J/QR Oc 

1420° C CPOURING TEMPERATURE^ 

U03 J/GH LATENT &AT] 064 CAL/GM~ 

0.1 GRACTIONAL EXPANSION ON FREEZING] 

1Q,8 CH (HALF INGOT WIDTH) 

16,s CH [INGOT HEIGHT) 

432 
SILICON MATERIAL AND SHEET 

Test Conditions 

Ono Cross Section of the Ingot 

CASE I, LOSS OF HEAT OUT OF THE BOTTOM 

CASE 11, EQUAL LOSS OF HEAT FROfl BOTTOM MD SIDES 

433 
SILICON MATERiAI. AND StiEET 

Run 1 

-c = 0,00568 J/SEC CH~ OC 

@c = 8.07 J/SEC CH~ 

= 0 

% = 0 

To = 14200 C 

(INITIAL TEMPERATURE) 

4 34 
SILICON MATERIAL AND SHEET 

435 
SILICON MATERIAL AND SHEET 

MD * 0 

B, = 0 

Run 2 

To = 1420° C 

AT = 100 SEC 

T~~~ = 21600 SEC (6 HOURS) 

WB = 0 

a, = -1 

436 
SILICON MATERIAL AND SHEET 

lo 

5 

C 

4 37 
SILICON MATERIAL AND SHEET 

Status 

A TWO DIHEISIWL CWUTER BOKL HAS El DEVELOPED 

,EO TO ESTABLISH rx TRUE BOUNDARY CIXU~ITIOI~S WITHIII 

A UCP FUR'IACE 

4 38 
ELECTROCHEMICAL PRODUCTION OF SILICON 

ENERGY MATERIALS CORP. 

H.E. Bates 

Program Objectives 

DESIGN AND BUILD CELL TO PRODUCE sq GdMR 

DETER'IINE OPERATING CO((DITI0wS AND RUN CELL CAI 

43 HOURS TO PRODUCE 2KG OF SI - 

THEORETICAL ANALYSIS AN; NODEL OF ANODE IMPURITY 

' AND SI DEPLETION BEHAVIOR, CORRELATE WITH EXPERIRENTAL 

OBSERVATIONS 

0 ANALYZE ECONOMIC POTENTIAL OF LARGE SCALE PRODUCTION 

Background 

PROCC5S IHVENTED AND DEMONSTRATED BY JERRY OLSON OF S.E.R.1. 

. KEY ELEMENT IS cU3sI - SI ANODE 

LOW TEMPERATURE (N1goooC) FASRICATION OF k - SI ANODE 

439 
SILICON MATERIAL AND SHEET 

Electrorefining Process Schematic 

PRIHARY SI 

HATRIX: 

CU3SI + SI 

ANODE ELECTROLYTE 

SI 

GATWE 

Experimental Procedure 

DRY SALT nlxTuRE: 35OOC + 19-3 TORR 

0 MELT SALTS AND PRE-ELECTROLYSIS REMOVAL OF IMPURITIES 

SILICON ELECTROLYSIS: 100 rU/Cl? 

ANALYZE ANODE (STRUCTURE, IMPURITY DISTRIBUTION), 

ELECTROLYTE PURITY, DEPOSITED SILICll(r 

440 
SILICON MATERIAL AND SHEET 

Progress 

SYSTEM CWPLETED, 

b ANODES (20d5X1CM) SXCESSFULLY FABRICATED 

BY CASTING. 

SIGNIFICANT PURIFICATION OBTAINED BY SLAS 

FORPIATION WRING ALLOYING, 

0 INITIAL RODE, OF ANODE BEHAVIOR DEVELOPED, 

SYSTEM SUCCESSFULLY OPERATED FOR FIRST 

EXPERIRENT - RESULTS BEING ANALYZED. 

44 1 
SILICON MATERIAL AND SHEET 

Copper-Silicon Anode Impurity Content 

IMPURITY 

- (PPRW) 

B 

AL 

P 

CA 

TI 

V 

CR 

PlN 

FE 

NI 

ZN 

SN 

PB 

cu 

1005 

IO4 

,005 

.07 

NR 

IO1 

2 

I02 

9 

2 

255 

30 

15 

- 

Cu-SI ALLOYS 

EXPECTED 

(10) 

-650 

(10) 

- 50 

(120) 

(50) 

(100) 

(60) 

1000 

2 (25) 

- 180 

- 20 

- 10 

- ACTUAL 

6 

5 

0.6 

084 

2 

5 

2 

3 

100 

1 

1 

0.4 

0,8 

0 IMDICATES TYPlCAL VALUES, AFTER HUNT AMD bSAJ 

442 


SILANE DECOMPOSITION'IN AN FBR 

UNION CARBIDE CORP. 

S.K. lya 

- ~~ 

TECHNOLOGY 

POLYCRYSTALLINE SILICON RgD 

APPROACH 

SILANE DECOMPOSITION IN A FLUIDIZED 

BED REACTOR 

CONTRACTOR 

UNION CARBIDE CORPORATION 

GOALS 

0 DEMONSTRATE PROCESS FEASIBILITY. 

0 DETERMINE OPERATING WINDOW. 

0 CONDUCT LONG-DURATION TESTS, 

0 DEMONSTRATE SILICON PURITY, 

REPORT DATE 

MARCH 15, 1984 

STATUS 

0 LONG DURATION TESTS WERE CONDUCTED TO 

DEMONSTRATE OPERABILITY AND DETERMINE PURITY1 

0 PRELIMINARY PRODUCT PURITY FROM METAL WALL 

REACTOR WAS ESTABLISHED. 

0 FBR PRODUCT WAS MELTED AND SINGLE CRYSTALLIZED, 

0 PDu MODIFICATIONS TO IMPROVE PROCliCT PURITY ARE 

I CURRENTLY IN PROGRESS* 

Run Summary: Long-Duration Tests 

0 3 LONG DURATION RUNS WERE CONDUCTED WITH TOTAL RUN TIME 

OVER 80 HOURS. 

0 LONGEST SINGLE RUN WAS FOR 45 HOURS WITH VOLUNTARY SHUIIJOWN. 

- 300,~ SEED GROWN TO 500~~ PRODUCT 

- AVERAGE SILANE FEED RATE 2 KG~R 

- MAXIMUM SILANE FEED CONCENTRATION 221! 

- BED TEMPERATURE 600'C - 700'C 

. - u/u, 3.5 - 580 

- COMPLETE SILANE CONVERSION WITHIN THE BED 

- ON LINE PRODUCT WITHDRAWAL WAS DEMONSTRATED 

- FINE POWDER 5 - 6% OF SILANE FEED 

- POWER CONSUMPTION 15 KWHIKG 

445 
SILICON MATERIAL AND SHEET 

Long-Duration Run: Mass Balance 

> PRODUCT OUT 

56,9 KG. 

> POWDER OUT 

3,7 KGi 

SILICON IN 

79.3 KG. 

INITIAL BED WEIGHT 33.5 KG 

SILICON IN 79.3 KG 

TOTAL 112.8 KG 

.- 

FINAL BED WEIGHT 57,6 KG 

PRODUCT OUT 56.9 KG 

POWDER FROM FILTERS 3.7 KG 

TOTAL 118,2 KG 

ERROR IN MASS BALAMCE = 4,6% 

Preliminary Product Characterization 

FARTICLE PROPERTIES 

0 500,~ MEAN PARTICLE DIAMETER 

0 100 LB/CFT, BULK DENSITY 

0 SMOOTH, ROUNDED SURFACE 

0 FREE FLOWING 

PARTICLE HORPHOLOGY 

0 DENSE DEPOSITION LAYER 

0 LAYERED RING-LIKE GROWTH STRUCTURE 

@ GROWTH LAYER THICKNESS OVER 10O)JUM 

PARTICLE PURITY 

@ EMISSION SPEC AND NAA DATA SHOWED MET ALL;^ 

CONTAMINANTS (FE, CR, N!) FROM REACTOR WALL, 

@ PARTICLES WERE MELTED AND SINGLE CRYSTALLIZEDi 

446 
SILICON MATERIAL AND SHEET 

Product Purity improvement Plan: PDU Modifications 

SEVERAL REACTOR LINER AND SPRAY COATING OPTIONS WERE 

EVALUATED. 

HIGH PURITY POLYSlLlCON LINER WAS CHOSEN AS FIRST CHOICE# 

WITH QUARTZ LINER AS A BACKUP, 

LINER WAS DESIGNED AND ORDERED. 

PRODUCT WITHDRAWAL SYSTEM WAS REDESIGNED TO ENABLE COOLlNGr 

SCREENI!IG, AND BAGGIPG WITHOUT MANUAL HANDLING OR EXPOSURE 

TO ATMOSPHERE.. 

Future Plans 

PDU MODIFICATIONS COMPLETED - I (J, 1984 

0 HIGH PURITY EXPERIMENTS CONDUCTED - 11 8 111 B, 1984 

0 SEED GENERATION METHOD TESTED - 11 8 111 a, 1984 

e TFCHNICAL AND ECONOMIC ASSESSME~ST - IV Q, 1984 

44 7 

JPL IN-HOUSE FLUIDIZED-BED REACTOR RESEARCH 

JET PRO?ULSION LAB9RATORY 

G.C. Hsu 

Metallic Impurities (ppmw): Neutron 

Activation AnalysidLLL (1 1 /83) 

J& RllN & 

109 ~SCEII) 

111 (sctn) 

111-4P 

ill-np 

115P-1 

ll5P-2 

115 I*c.Ol rl 

115 Inmr 

115 INGOT B2 

1.; 

4 

16C 152) 

'iS(171) 

31(171) 

46(171i 

n.7 

0.2 

0.3 

TOTAL 

l.imuEm 

107 

266 

190 

275 

*REACTOF. WALL MATERIAL S.S. 316: co 17x FE 701 NI 121 RO 2.51 nN 2t SI 11 

449 
SILICON MATERIAL AND SHEET 

Stainless Steel 

Reactor 

Silicon iarbtdc 

Coated Graphite 

Reacto- 

-- 

,‘irconicm Oxide 

Variovs Wall Materials for FBR 

(rich Si tube) contamination -Relattvely trpensire construction 

-Iton-uniform coatInside Surface of ing 

graphite tube is -600d heat -Posstble carbon 

coated rich Sili- transfer contarinatton 

con Carbide. -Expensire conInside Surfacr of contraination 

struction 

-Posstble zirconium 

Disadvantages 

Ouartz Liner-7-nStainless Steel cally sealed 

Reactnr 

The hardness of SS 

surface is tncrrascd by treating it in a liquid 

cyanide bath. 

sion - 

6as dtstrtbu- 

-Possible migration tor. expanded 

 expen pen st re of attrlltc iapur- head. and withprocess itits from hot 55 drawal asreably 

surface will be treated 

- by this process 

LiQuid Nitriding 

- 

450 
SILICON MATERIAL AND SHEET 

Quartz Liner System for 6-in. FBR 

COMPONENTS : 

@ STOP RING 

@ SEALING RING 

@ QUARTZLINER 

@ 01 STRI BUTOR HOLDER 

@ DISTRIBUTOR HOLDER SUPPORT 

@ PNEUMATIC CYLINDER SUPPORT 

@ PNEUMATIC CYLINDER 

@ US DISTRIBUTOR 

@ SILICON WITHDRAWL 

@ KINETIC CAMPLER 

@ HYDROGEN PURGE 

d 

451 
SILICON MATERIAL AND SHEET 

Reaction Paths for Silane Pyrolysis in FBR 

INCORPORATION 

of 

CVD HOGENEOUS FINES CVC 

ON ON SEED ON 

A FINES 

Si 

NUCLEI CLUSTER 

Conditions for Incorporation of 

Homogenous Fines Onto Seed Particle 

@ TERPERATIIRE TARRANN TERPERATIIRE ( 610.C FOR SI' 

TAMANN TIIPERAIURE 0.52 X (BULK EL1116 POINT IN *K) 

- DEFINED AS INDEX FOR suRt.'cE RoniLiiy 011 .YETTAIIILITV 

@ IN 'HE PRESENCE FC SILANE RFACTION 

- CVD REACTlOl IS NEEDED TO SEAL FINES AFTER ADSORPTION 

@ SIZE OF FINE PARTICLE IS RALL ENOU6H FOR SIICCESSFIIL ADSORPTION 

452 
SILICON MATERIAL AND SHEET 

Fines Incorporation and CVD 

SCHEMATIC REPRESENTATION OF THE CONTINUOUS NUCLEATION 

OF GROWTH CONES IN "EGENERATIVE DEPOSITS' 

'PYROCYTI" CARBON DEPOSITIONL.F. COFFIN, JI. Am. CERAM-SOC. 47, 473 (1964) 

Locations of Secondary Silane Injection 

for Enhancing Scavenging 

n TERPERATIIRE > TARRAIN TEMPERA. IRE 

0 PRIRARY SILANE 1NTRD~llCf9 FROR THE IlISTRIRllTnR MILL DEPLETE AFTER 

I? INCHFS 

o AT THE 13-IN. incaiinh, THE R~XIRIIR VZE n~ FINE PARTICLE IN fi~s 

PHASC IS LESS THAN 1 pq 

:A> 13-INCH ABOVE THE DISTRIRUTOR 
SILICON MATERIAL AND SHEET 

Scavenging Experiment (JPL 6-in. FBR) 

Scavsnging Experiments 

X OF FINS 6 FEED C; 

5X 2.6X 

+ n.ix -lX 

4 54 
SILICON MATERIAL AND SHEET 

Jet-Mill Grinding of Silicon Particles 

(Si Fed Into 2 Opposing Jets, Single Pass) 

o, 15 

5 DESIRED FRACTION (-355 pm TO +75 rm) 

I 1 1 

'8 10 15 20 

TOTAL NITROGEN FLOW RATES, SCFM 

Jet-Mill Grinding of Silicon Particles 

Isr PASS YIELD 2ND PASS YIELD' 

SI ZE FKACT IONS (OVERALL ) 

OVERSIZE (+ 355pm) 

*is5 P FRACTION WAS RECYCLCD 

FEED SIZE: -?07/*500rr 

N FEED RATE: 12 SCFR 

S?LICON FEED RATE: 40 6RARSflIN. 

455 

.. '\ 

b. 

AEROSOL REACTOR FOR SILICON PROCESSING 

CALIFORNIA INSTITUTE OF TECHNOLOGY 

R.C. Flagan 

M.K. Alam 

B.E. Johnson 

J.J. Wu 

A Free-Space Reactor System for Production of Silicon 

PRECEDING PAGE BC4NK NOT PII.h4FD 

457 
Processes in Silane Pyrolysis Reactor 

-EOl406ENEOUS GAS PEASE REACTION 

-HOHOGENEOUS NUCLEATION 

-HBTBROQFYEOUS CONDENSATION 

-HETEROGENEOUS REACTIONS 

-COAGULATION 

Silane Pyrolysis (Ring & O'Neal, 1982) 

k9 SiH2 -> surface - SiHz 

k 

SiH4 -103 surface - SiHd 

kll 

SiHZ -surface --> surfrce-SiHZo 

kl2 surface - SiHz SiH4 -d surIace - SiHj + SiH30 

SiH3- SiH4 k13 > SizHg He 

H2 SiH 3' H* SiH4 k14 , ............. 

erp[-S9600/Rf) sec'l kl 

458 
SILICON MATERIAL AND SHEET 

Homugeneous Nucleation 

CRITICAL NUCLEUS 

NUCLEATION RATE (CLASSICAL THEORY 1 

Particle Growth 

-CONSIDER THE ONION CARBIDE SYSTEM 

0.2 TO 1 MICRON PARTICLES WERE ?RODUCED, 

ACCOUNTING FOR >801 OF THE MASS AT THE REACTOR 

OUTLET 

THIS coiinEsPoiDs TO 1014 TO 1016 PARTICLESIM~ 

GROWTH Of THESE ?ARTICLES TO 10 MICRON SIZE 

REPUIRES INCREASING T E MASS 01 EACH PARTICLE BY 

A FACTOR OF 103 TO 10 I 

IN omn TO SUPPLY sorrrcIenT SILICON, THE SEED 

103 TO 105 

A&ROSOL MUST BE DILUTED WITH SILANE BY A FACTOR OF 

-CAI ADDITIODAL DCU PAITICLB IOINATIOD BI ?IBVllTBD 

AT TlI RRDOCRD ?ARTICLE COICBlTIATIOI? 

Aerosol Reactor for Growth of Large 

Silicon Particles by Silanc Pyrolysis 

1. OENERATE SEED ?ARTICLES DY ?YROLYSIS OF A 

SMALL AMOUNT OF SILANE. 

2. MIX SEED mom win rnrnnny SILANE rLow, 

AMOONT OF SILANE IS surrmcwt TO GROW THE 

LIMITING NOMBER CONCCNTRATION SOCH THAT THE 

DESIRED SIZE 01 PARTICLES FROM THE SEED. 

3. REACT THE SILANE AT A RATE WHICH IS CONTROLLED 

SOCH THAT THE SEED ?ARTICLES SCAVENOS THE 

CONDENSIBLE VAPORS RAPIDLY CNOUGH TO INHIBIT 

romcn NOCLEATION. 

459 
SILICON MATERIAL AND SHEET 

Reduction of Overall Nucleation Rate 

TOTAL FRACTIONAL CLEARANCE VOLWE 

AVERAGE NUCLEATION RATE 

4 60 
SILICON MATERIAL AND SHEET 

Silane 8 Carrier Goa 

I 

Seed 

Reactor 

1% Silane r' Primary 

Reactor 

1 

I 

Si I icon 

Carrier Gas 

"2 

461 
SILICON MATERIAL AND SHEET 

Temperature Profile and Reaction Kinetics 

in the Aerosol Reactor 

""I== - 

0 0.2 0.4 0.6 b.3 I .O 

TIME (stc.) 

Particle Growth in the Silicon Aerosol Reactor 

'i 2 

1 c 

41 I I I 

2 Ye 

/ 1 

1 

.O 

0 0.2 0.4 0.6 0.8 1 .o 

TIME (sec.) 

462 
SILICON MATERIAL AND SHEET 

Total Clearance Volume Fraction in the Reactor 

- 

0 

c. 

to 

Y 

10= 

IO2 

10’ 

loo 

0 0.5 I .o 

TIME (sec.1 

* I I I I I I 1 A 

Mass Distribution of Silicon Aerosol in a High-Temperature 

Reactor at 900K Without Seed Aerosol (Silane Concentration 1 %) 

0. 

too 10’ 

diameter (pml 

463 

<-6 
SILICON MATERIAL AND SHEET 

Mass Distribution of Product Aerosol After Reactin 1 % 

Silane With Reduced Seed Concentration (2.7 x 10 Bo /m 3 ) 

10” 100 IO’ 

diameter (pm) 

PTce Mass Distribution of Aerosol After Reacting 2% Silane in 

of Seed Aerosol (Total Seed Concentration 1.02 x 10 !m ) 

dp (microns) 

464 
SILICON MATERIAL AND SHEET 

Silicon Losses in the Reactor as a Function 

of Input Silane Concentration 

percent si !me 

Comparison of Characteristic limes of Silane 

Reaction With Residence Times in Reactor 

lo2 

IO' 

IO0 

lo" 

lo" 

T(sec) 

.8 1.0 1.2 1.4 

WK/f 

465 
SILICON MATERJAL AN0 SHEET 

B I I I I I I I I 

0 t 234 56 7 B9 

TIME (sed 

E 10s 

n 

466 
SlLiCON MATERiAL AND SHEET 

0 I 2 3 4 56 7 0 9 

TIME (sed 

467 

?479 / REFINEMENT OF METALLURGICAL-GRADE SILICON 3 

BY CHEMICAL VAPOR TRANSPORT PROCESS 

SOLAR ENERGY RESEARCH INSTITUTE 

J. Olson 

Reactor Schematic 

- Thermocouple 

A C FiIamwl Power 

7W'C 

1OSo'C 

Si + 3HCI=HSiCt, + 1/2H1 

Transport Rate Measurement 

Conductance of r rlllcon filament rlth length L. uldth Y, and thlcknerr X lr: 

c.I dn where o lr the 

electrical conductlvlty 

where R is the mars 

transport rate and p the 

mas# denrlty of rillcon 

v If 

I 

x -3 I Mt 

Real-the. ln situ =aaurementa of the filrmcnt Conductance reveal that the 

tranrport rate varies with tlme sa t-*I2. 

Ira r model of r tranrport procear that 1r llmlced by dlffuslon through a 

depletlon layer the thicknerr of which increaser vith tlmc sa tl/*. 

Thlr tlmc dependence can be derived 

469 
SILICON h;?A.TfZiAL AND SHEET 

e 

E 

(I) 

c 

0 

0, 

0 

C tu 

0 

3 

U 

C 

0 

0 

Y 

c 

25 

2( 

15 

1c 1 I I I I 

5 10 15 20 25 30 

Tlrne'l2 (min112) 

5 

470 
MODULE AND ARRAY TECHNOLOGY 

R.G. Ross, Jr., and L.D. Runkle, Chairmen 

A status review of JPL-Clemson University cell reliability research 

activities was presented by J.W. Lathrop of Clemson. 

results from Arrhenius-modeled combined temperature-humidity tests on 

encapsulated and unencapsulated cell types and failure-analysis data that 

further delineated the Schottky barrier formation mechanism observed earlier 

in p-on-n cells. 

Included were recent 

Supporting the technology objectives of refining the understanding of the 

physics of module thermal interaction with natural environments, L.C. Wen of 

JPL sumnarized thermal characterization studies conducted on Southwest 

Residential Experiment Station (SW RES) arrays. Results included correlations 

useful in refining NOCT determinations. 

C.C. Gonzalez of JPL presented comparisons of annual array energy spectra 

for different tracking modes to assess the advantage of a given mode for any 

defined cell spectral response. 

L.J. Reiter of JPL presented a sumary of PV systems performance models. 

This study, performed for the Program Analysis and Integration Center, reviews 

a comprehensive set of PV systems performance models and differentiates between 

their wide range of purposes, approaches, and capabilities. Tables that allow 

a potential model user to cross-reference the models and a detailed set of 

characteristics are included. 

set of models and their limitations were discussed. 

tial users to match their requirements with an appropriate model. 

Recent extensions of the capabilities of this 

The study assists potenThe preliminary results of a study to examine what the National Photovoltaics Program could do to enhance the process of establishing voluntary 

consensus standards for measuring the performance of PV modules were discussed 

by G.A. Praver of JPL. Among the points raised, the study suggests that the 

prejudices regarding the selection of direct normal, global or some other 

spectrum as a standard for measurement must be promptly resolved, that this 

and other technical impediments to consensus be addressed by national laboratory task forces to facilitate resolution, and that funding be provided to 

support the costs of the voluntary consensus standard activity for both the 

international interactions and the national work. 

M.G. Thomas of the Sandia National Laboratories provided highlights from 

the Systems PIM held recently at SNLA. 

the remaining issues for large system power conditioning subsystem and residential system development. 

He followed this by a discussion of 

E.C. Kern, Jr., . the Massachusetts Institute of Technology described 

the cost experience of the various RES experiments between 1980 and 1983, and 

projected the costs for retrofit systems for the Northeast RES in 1984. These 

projections were made for exotic materials such as a-Si, GaAs, and GaAsSi as 

well as for single-crystal silicon. The single-crystal silicon costs were 

described in some detail and result in system costs consistent with the trends 

developed by actual experience. 

471 

TRANSPARENT CONDUCTING POLYMERS 

JET PROPULSION LABORATORY 

Amitava Gupta 

Technical Approach 

0 4lODELING AND FEASIBILITY DEMONSTRATION 

0 SYNT:iETIC APPROACHES 

0 CHARACTERIZATION 

0 EPJVIRONMENTAC STABILITY ASSESSMENT 

S!’d ITCH lPlC CHA RACTERI STlC S 

Modeling and Feasibility Demonstration 

0 RIODELING OF OPTICAL ABSORPTION PROPERTIES RECENTLY INITIATED 

0 :,\ODELING Gi- CHARGE CONDUCllON IN PROGRESS 

TCFS ARE \:,lTHlN A FACTOR OF TEN TO IT0 IN ITS PERFORillANCE AS 

4 TRANSPARENT CONDUCTIVE COATING 

0 RECENT RESULTS INDICATE [HAT CONDUCTIVITY AND OPTICAL ABSORPTION 

hlAY ARISE OUT OF DIFFERENT KlOLECULAR STRUCTURAL FEATURES 

0 TRUE TCPS ,!\AY BE FORhlED BY LOW LEVEL DOPING OF CERTAIN 

OPTlRl IZED POLY AIERIC STRUCTURES 

Synthetic Approaches 

0 PLAShIA POLYh\ERIZATION 

ELECTROCHERllCAL POLYAIERIZATION 

0 CHE?\IICAL POLYhlERlZATlON 
MODULE AND ARRAY TECHNOLOGY 

Novel Polymerization Procedure Developed at Caltech 

A NOVEL METALLACY CLOBUTANE CATALYST HAS BEEN 

DEVELOPED WHICH CAN CREATE PURE, UNCROSSLINKED 

POCY MERS f ROM HINDERED QLEf INS 

Example 

SOLUBLE, UNCROSSLINKED 

OEPOSIT AS THIN FILM 

OXIDANT 

is POLYACEWLENE 2-li T UCTURf 

474 
MODULE AND ARRAY TECHNOLOGY 

Characterization 

MAIN CHARACTERIZATION TECHNIQUES WHICH WILL BE 

USED ARE 

ESR AND PHOTO-ESR AS A FUNCTION 

OF DOPING LEVEL 

0 CONDUCTIVITY AND ABSORBANCE MEASUREMENTS 

0 ELEC TROCHEM IC AL C HA RAC TE RIZ AT ION, INCLU D ING 

PHOTOCAPACITANCE SPECTROSCOPY 

Environmental Stability 

RADIATION STABILITY OF CERTAIN TCPS e.g. POLYAZULENE REPORTED 

TO BE EXCELLENT 

STABILITY OF NEUTRAL JONCONDUCTING) 'ORM LIMITED BY RXN WITH 

07, WHILE STABILITY Of' OXIDIZED FORM IS LIMITED BY RXN WITH H20 

0 STABILITY OF THESE FORMS CORRELATE WITH REDOX POTENTIALS 

Polypyrrole Oxidation by 12: Electrical and 

Optical Properties of 4500-Angstrom-Thick Film 

[DATA FROM PFLUGER, ET. AL., J. CHEM. PHY., 78, 3213 (1983)] 

IN THIS REGION 

OPTICAL ABSORPTION 

AND flECTRlCAL 

CONDUCTIVITY ARE 

MCOUPLED 

/- 

2 

I I I I I 

? 4 b 8 10 0 L1.9.7 .S .I 

475 

WAMENGTH ( p m 1 
MODULE AND ARRAY TECHNOLOGY 

Long-Term Stability of Polaroid TCP Coatings 

in Ambient Laboratory Atmosphere 

01 I I 1 1 J 

0 25 50 75 100 125 

DAYS 

Specular Transmittance of Polaroid TCP on Glass 

(UNCORRECTED FOR REFLECTION LOSSES) 

100'' I ' 1 ' I ' 1 ' I ' 

- 

COATING THICKNESS = 1500 i 

0.3 0.4 0.5 0.6 0.7 0.6 0.9 

WAVELENGTH ( pm 1 

476 


ANALYSIS OF OPTICAL AND ELECTRICAL PERFORMANCE 

OF A TCP-COATED SOLAR CELL 

JET PROPULSION LABORATORY 

R.E. Daniel 

Introduction 

Purpose: 

To analyze the effect of the optical and electrical properties of a 

transparent conducting polymer ITCP) on a solar cell 

Questions to be answered: 

What affect does the transmission, reflection and absorption of 

the TCP have on the operating characteristics of the solar cell? 

What TCP film thickness and conductivity is necessary to 

conduct the generated photocurrent with a tolerable series 

resistance? 

479 
MODULE AND ARRAY TECHNOLOGY 

Analytical Procedure 

Optical: 

Calculate the expected short-circuit current density (Jsc) in a 

solar cell with a TCP coating 

Calculate the amount of light transmitted (TR) through the TCP 

*ThenJsc = 2QE(A) -Slh) -TRlA)dh 

to the solar cell across the spectrum 

where: QE( X ) = normalized collection efficiency 

C. A 1 = incident light flux (AM1-51 

TR( A) = transmitted light 

Simple case: nonabsorbing film 

arid TR + R = ? 

= (, Nj-1 + Nj 

With absorption N = N - iK 

where N = complex index of refraction 

N = real component of IF? 

K = imaginery component of IR - extinction coefficient 

Electrical: 

Calculate the power lost in the TCP film due to the TCP sheet 

resistivity ( Q~cp) 

For a TCP on a single crystal cell, consider a unit cell where 

the spacing between the grid lines (SI is held constant: 

JMP* S*P 

12 PI = Psi PTLP 

Psi + PTLP 

where p = 

For a TCP on an amorphous silicon solar cell, consider a 

series-connected cell configuration where the spacing between 

interconnected cells (W) is varied 

I = length of the cel! PI = JMP2w31 PTLP 

3 

Calculated values of the power lost are then compared with those of 

sn arbitrarily good lossless cell 

480 
MODULE AND ARRAY TECHNOLOGY 

Assumed Cell Characteristics 

Single-crystal: 

Lossless cell 

VI\II~ (Voltage max. power) = 0.45 volts 

JMP Current density max. power) = 35 mA/cm2 

Analyzed cell 

VMP = 0.45 

JMP varies 

Psi = 40 5212 

Amorphous: 

Lossless cell 

VMP = 0.85 

JMP = 21 

Analyzed cell 

VMP = 0.7 

JMP varies 

Psi infinite 

More Assumptions 

Only sheet resistance power loss considered 

No contact resistance problem 

Power loss through TCP film is negligible 

Film thickness is uniform 

Resistivity is linear with film thickness 

VMP change with attenuated light not considered 

No environmental consideration 

4C1 
MODULE AND ARRAY TECHNOLOGY 

Short-Circuit Current Density Generated vs TCP Thickness 

.. - 

482 
MODULE AND ARRAY 

I 

TECHNOLOGY 

20 

I 

- 

25 I I I I I I 1 

N1 - 1.5 

0 0.1 0.2 0.3 0.4 

N1 - 1.5 

0.1 0.2 0.3 0.4 

483 
MODULE AND ARRAY TECHNOLOGY 

25 

ZE 

15 N 

E 

E 

u v) 

u 

d 

- 

7 

10 

5 

c I I I I I I - A 

I 

- 

0.1 02 0.3 

484 
MODULE AND ARRAY TECHNOLOGY 

TCP Sheet Resistivity vs Conductivity 

10' 

1 o! 

0 10' 

c: 

c 

10 

i0 

iC 

0 01 01 1 10 100 

a, IR. cmJ-1 

485 
MODULE AND ARRAY TECHNOLOGY 

Fractional Power Lost in a TCP Due to Sheet Resistance 

I .V 

0.8 

0.6 

Q 

0.4 

0.2 

0 

p PCdER LOST 

POWER GENERATED 

JmP - 0.015 Alcm’ 

VmP - 0.7 V 

w - 0.5 cm 

I I I I I I 

10 20 30 40 50 60 

0, Rlo 

Ratio of Power Out to a Baseline Cell 

vs Current Density at Maximum Power 

486 
MODULE AND ARRAY TECHNOLOGY 

Summary 

Single-crystal 

Lateral conductivity dominated by the cell 

Optical characteristics useful for modeling candidate materials 

no value until PTLP -Psi 

Amorphous 

All current must be carried by the TCP 

Power loss in the sheet can be controlled by the geometry 

Optical response complicated by the transmissibility of a - Si; 

of the cell 

however, trends are indicated 

487 

N85 15294 

PERFORMANCE LOSS WITH SHORTED CELLS 

JET PROPULSION LABORATORY 

C.C. Gonzalez 

Objectives, Current Task 

a Detcrmine the power loss due to shorted cells for a given 

source-circuit series-parallel configuration after n years .=,XI 

a coqstant yearly failure rate 

Determine the optimum series-parallel configuration(si 

minimizing power loss 

Determine the cost-effective failure level 

L.ong-Range Objective 

Determine cost-effective circuit design 

Effect of Shorted Cells on Source-Circuit Maximum Power 

1.b CURVE OF 

NORMAL CELL STRING 

1.V CURVE OF 

CELL STRING WITH 

I 

SHORTED CELLIS) 

SYORlEO CELLS LEA0 TO :'CLTAGE 

MISMATCH AND MAX-POWER LOSS 

MAX-POWER LOSS INCREASES WITH 

INCREASE IN CROSS-TIES AND WITH 

INCREASE IN PARALI El STRINGS 

I 

489 
MODULE AND ARRAY TECHNOLOGY 

. *- I 

DETERMINE OPTIM?IM 

Approach 

7 

DETERMINE COSTI 

SERIES - PARALLEL 

CONFIGURATIONS 

I ASSUME A CELL I FAILURE RATE k 1 

EFFECTIVE - 

FAILURE LEVEL 

L--1----J I I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

Source-Circii;t Definition 

SOURCE CIRCUIT: 

3 PAAAll cL STRINGS 

6 SERIEL dLOCKS 

2 CELLS PER SUBSTRING 

1 OlOUE PER SERIES BLOCK 

493 
MODULE AND ARRAY TECHNOLOGY 

Problem 

Given a source circuit with: 

N total series cells 

NB series blocks 

NS substrings per series block 

NC cells per substring 

Dstermine t+e average number of series 

blocks with a given configuration of failed 

cells and substrings 

Definition of Source Circuit With Example Parameters 

PC 

e 

N - 12 

%SOURCE CIRCUIT: NE- 6 

3 PARALLEL STRINGS NS- 3 

6 SERIES BLOCKS NC- 2 

2 CELLS PER SUBSTRING 

491 
MODULE AND ARRAY TECHNOLOGY 

Statistical Analysis Solution Using Binomial Distribution 

If p = probability of a cell failure, the probability of obtaining x 

failures in n cells is: 

The probability of obtaining y1 substrings with xi failed cells, 

y2 substrings with x2 failed cells, y3 substrings with x3 

failed cells, etc., out of NS total substrings is: 

E: vdue of p(y 7, x 1 ;...I is the probability of obtaining a 

series block with a $veri substring and cell failure 

configuration: 

-.. p(y1, xq ;...I - NB is the number of series blocks with that 

configuration 

The following steps are performed after obtaining the above 

values: 

The I-V curves of each series-block configuration 

(including those without failures) are added 

source circuit with no failures 

The max-power is compared with that -)n identical 

492 
MODULE AND ARRAY TECHNOLOGY 

Array Power Loss: Four Parallel Strings 

I 1 I I1 Ilil I I Ii111,I 

0 CCOl fl t?91 0.0 1 0. 

t / /// 

I 

I 

Array Power Loss: Eight Parallel Strings 

CELL FAILURE OENSliV 

403 
MODULE AND ARRAY TECHNOLOGY 

Array Power Loss: 16 Parallel Strings 

1 

CELL FAILURE DENSTY 

Conclusions 

Power loss due to shorted cells increases with increased use 

of !.-. . k!ir.g and c:tcss-ties 

Yearly failure rate greater than 1 I1 0,000 leads to power 

losses in excess of the allocation for cell failures 

494 
INVESTIGATION OF ACCELERATED STRESS FACTORS 

AND FAILURE!DEGRADATION MECHANISMS 

CLEMSON UNIVERSITY 

J.W. Lathrop 

COMMERCIAL CELL TESTING 

SCHOTTKY BARRIER FORMATION 

NEW TEST DEVELOPMENT 

NEW ANALYTICAL FACILITY 

Clemson Accelerated Test Schedule 

for Unencapsulated Cells 

B-1 

B-T 

B-1 

I-144 

I-H 

CUMULATIVE CYCLES 

0 

. 

10 20 SO 40 50 60 

1 

lHERMAL CYCLE 

THERMAL StlOCK 

49 5 
MODULE AND ARRAY TECHNOLOGY 

N -- Average 

0 -- Abme average (- degradation) 

P -- Well below average 

Q -- Well above average (- degradation) 

R -- Above average (fracture) 

V -- Average 

W -- Below average 

X -- Above average (loss of grid metal) 

Y -- Above average (+ degradation) 

Z -- Above average (fracture) 

N _-- Below Average 

0 -- Above average C- degradation) 

P -- Not tested 

GI -- Above avernge (- degradation) 

R -- Not tested 

V -- Average 

W -- Average 

X -- Above average (loss of grid metal) 

Y -- Above average (4 degradation) 

Z -- Below average (threshold effect) 

496 
MODULE AND ARRAY TECHNOLOGY 

N -- Above average (back metal) 

0 -- Average 

P -- Below average 

Q -- Above average (grid metal) 

R -- Not tested 

V -- Above average (fracture) 

W -- Above average (fracture) 

X -- Well above average (grid metal) 

Y -- Above average (lead loss) 

Z -- Not. tested 

Equivalent Gircuit of a Degraded Solar Cell 

497 
MODULE AND ARRAY TECHNOLOGY 

c 

I-V Characteristics of a Degraded Solar Cell 

X=28 C 

e-7 c 

498 
MODULE AND ARRAY TECHNOLOGY 

T (OC> 

Io (Amp) 

Is (Amp) 

nl 

n2 

R1 <ohm> 

R2 (ohm) 

I 

BO 

60 

40 

20 

0 

-20 

-40 

Equivalent Circuit Parameters 

28. 0 

1.714E-5 

0.465 

1.927 

2,270 

0,023 

0.776 

21. 4 

0.984E-5 

0.332 

1, 926 

2m 165 

0. 025 

0.961 

7m 0 

Om 101E-5 

0.162 

1.800 

2.000 

Om 027 

0.2 0.4 

1.600 

\ 

499 
MODULE AND ARRAY TECHNOLOGY 

Atomic and Molecular Species at 

Unencapsulated Cell Surface 

AMBIENT 1 

MOLECULE 

02' 8 

MOLECULE 

HZ 8 

st BONOS 

Percentage Decrease in Pm for 85/85 Test Q-Cells 

Stress Time in Hours 

250 500 1000 

UNENCAP 7 8 11 

G/EVA/F 23 41 56 

G/EMA/T 26 38 54 

G/EVA/T 24 36 48 

T/EVA/S 1 0 6 

2000 

16 

53 

53 

so 

6 

500 
MODULE AND ARRAY TECHNOLOGY 

Atomic and Molecular Species at 

Encapsulated Cell Surface 

Encapsulated Cells 140 Days Outdoors 

XP (C/EVA/T> 

XP (G/EMA/T> 

XP (G/EVA/G) 

X (G/EVA/T) 

X G/EMA/l) 

X (G/EVA/G> 

Pm 

5 

2 

5 

4 

3 

6 

I sc 

4 

5 

5 

4 

4 

5 

BONDS 

50 1 
MODULE AND ARRAY 1ECHNOLOGY 

.I Unencapsulated Cells - 

N 

0 

P 

Q 

w 

X 

Y 

z 

Pm 

18 

5 

6 

4 

4 

60 

14 

18 

I sc 

9 

2 

2 

2 

2 

34 

4 

2 

14u uays uutaoors 

Inspection 

Grid 

Grid 

Grid 

Grid 

Grid 

Leads 

Leads 

.severe) 

(moderate) 

(slight) 

(slight) 

(severe) 

85/85 ard 93OC/85% RH Testing 

85/85 93/85 ACCEL Ea/ (eV) 

G/EVA 3. 5 4. 2 1D 2 0. 26 

G/EVA/T 2. 1 3. 1 ID 5 0. 57 

Measured % decrease in Prn 

Calculated acceleration fac.tor 

Calculated activation energy 

502 
w N85 15296 

THERMAL CHARACTERIZATION OF PHOTOVOLTAIC 

MOLULES IN NATURAL ENVIRONMENTS 

Jet Propulsion Laboratory 

L. Wen 

Background 

Past activities at JPL 

NOCT 

Wind effect 

Unglazed PV / T collector study 

Residential PV thermal 

Currert concerns 

Data scatter in NOCT determination 

Marginal accuracy in detailed transient 

thermal simul,.tion 

Representative Cell Temperature Profiles 

0.00 o 23 0.40 o 60 0.80 1.00 1.x i 40 1.60 i.ao 2.00 2.20 2.40 2.60 2 80 3.00 

I I 1 I I 40.00 

39 00 

54.03 

c' 

zz w 37.00 m ' w 3600 

m 

3500 a 

a 

> 

0 

w 

c 2 3400 w L1.

E 3300 

4 

4 w 

3200 

31 00 

I I i I ' 3C.00 

000 020 940 060 085 l.O@ 120 140 1.60 180 2.00 a.20 240 2.60 2 80 300 

ELAPSED TES; TIME, h 

503 
MODIJLE AND ARRAY TECHROLOGY 

Experimental Uncertainties 

Cell temperature measurements 

Measurements of major environmental parameters 

Solar irradiance 

Ambient temperature 

Wind conditions 

Estimate of secondary environmental factors 

Ground reflection 

* Ground emission of IR radiation 

Sky radiation 

Study Objectives 

To refine understanding of the physics of module thermal 

interaction with natural environments 

To develop specific recommendations relative to NOCT 

test procedure and evaluation methodology 

To provide refined algorithms for predicting PV array 

operating temperatures 

Study Approach 

Representative module 

NOCT type testing 

Minimize experimental error 

Thermocouple calibration 

Irradiance measurement calibration 

Redundancy 

Additional instrumentation 

Ground reflection 

Ground IR 

0 Hygrometer for sky radiation 

Reference plates 

Validate resultant correlations by comparing 

transient simulation with test data 

504 
MODULE AND ARRAY TECHNOLOGY 

Sky Radiation, ‘??at Day 

I 

1 2 3 

! 

2oOL--- 

TIYE Of 011. h 

505 
MODULE AND ARRAY TECHNOLOGY 

Direct (Front) and Reflected (Back Surface) 

Solar Irradiation 

_. . __ IXGC - CHANNEL NUYMR - 3 

CHINWtl WYMR - 29 llo50 - 

506 
MODULE AND ARRAY TECHNOLOGY 

Sky Radiation, Cloudy Day 

36 1 

I 

I 

25 

~ YLASUAfD DATA 

I z4 - ANALVTICAL RESULTS 

om 335 I983 

-+ 

i 22 - 

507 
MODULE AND ARRAY TECHNOLOGY 

Absorbed Solar Energy 

- 

TOTAL SOUR - 900 1 

C 11!111I 

8 9 10 11 12 13 14 15 

TIME. h 

5 08 
MODULE AND ARRAY TECHNOLOGY 

ABSORBED 

Thermal Radiaton Balance 

MODULE 

IR EMISSION , fl 1000 t 

N 

E 

5 

X' 

3 

Y 

c 

Y 

4 

X 

700 

I 

NET IA LOSS 

400 1 

L. 

ABSOABED 1 

I 

3V AAOlATlON 200 t 

8 9 15 !1 12 13 14 15 

TIME, h 

509 
MODULE AND ARRAY TECHNOLOGY 

Resultant 

1000 

, I , , , 

Heat Loss 

i b 

FUEE 

CJNVt CTlON 

LOSS 

T 1 

NET IL - LOSS ‘7 

a 9 10 11 12 13 14 15 

TIME. h 

510 
MODULE AND ARRAY TECHNOLOGY 

Instantaneous Heat Balance 

500 

400 

300 

200 

100 

0 

~ io0 

zoo 

300 

~ 400 

I I -500 - 

8 9 10 11 12 13 14 15 

TIME, h 

51 1 
MODULE AND ARRAY TEC~~PJOLOGY 

52 

Computed KOCT Values 

52 - - 

I 

20 IL-r-----, d 15 

8 0 10 11 12 13 14 

TIME, h 

512 
MODULE AND ARRAY TECHhC'LOGY 

Comparison of Transient Temperature and Simulation 

_- 48r-- MEASURED GITA I ---__ I 

ANALVIIC9L SIMLiLAItON 

5 

Summary 

Experimental error budget can be reduced with periodic calibrations 

Ground reflection was measured a! % 10%- 1 2% of direct irradiance 

Ground IR reaches a plateau around 11 a.m. and is a major factor 

in a.m./p.m. NOCT discrepancy 

Algorithms for clear-day sky radiation can be confirmed 

Conclusions 

Improved understanding of module thermal charactorization 

Accurate ( %l°C uncertainty) transient predictten can be expected 

Establislicd useful correlations to refine NOCT testing and evaluation 

513 

ANNUAL ENERGY SPECTRUM FOR TRACKING ARRAYS 

JET PROPULSION LABORATORY 

C.C. Gonzalez 

Objective 

To compare array energy spectra for different tracking modes, 

to assess the advantage of a given mode for any defined cell 

spectral response 

Approach 

Use computer code and hour-by-hour SOLMET irradiance &?a tc obtain 

hourly integrated irradiance for array tracking mode 

Use solar radiation spectral analysis computer cod6 to estimate amount 

of hourly irradiance in given wavelength intervals 

Do an annual and monthly integration of irradiance In each wavelength 

interval; result is independent of anv particular cell spectral response 

In addition: Do an annual and monthly integration of the convolution of 

a given cell spectral resDonse and the hourly solar energy spectral 

distribution 

Tracking Modes Considered 

Fixed tilt at angle oi ts?itude, facing south 

Tilt angle and array direction can be varied 

Single-axis tracker, north-south horizontal ?racking axis 

Tracking-axis tilt angle can be varied 

Two-axis tracker 

515 
MODULE AND ARRAY TECHNOLOGY 

Currec ;t Status 

W 

V 

2 

0 

c 

4 

u 0.75 - 

4 

a = 

c u U'

0.50 - 

E c 

U 

U 

0 

W c 

P 

5- 

W 

c 

W 

5 

a 

0 

Compute: code for annual and seasonal integration sf 

irradiance is complete 

c 

t... 

c2.t 

Q.25-- 

Computer code %r convoluting cell spectral response 

witb solar radiat'm spectrum is under development 

Comparison of Integrated Spectral irradiance 

for Different Tracking Modes: FresnD, Summer 

- 1 .oo 7- - FIXED AXIS 

r 

..... S!NGLE.AXIS TRACKER 

***a TWO.AXIS TRACKER 

300 400 500 

-I600 I Boa 900 1000 1100 1200 

WAVE LENGTH, nm 

516 
MODULE AND ARRAY TECHNOLOGY 

Comparison of Integr; led Spectral Irradiance 

for Different Tracking Modes: Fresno, Annual 

1 OG 

- FIXE0 AXIS 

300 400 500 

+.... SINGLE.AXIS TRACKER 

b. TWO.AXIS TRACKER 

600 700 800 900 1000 1100 1200 

WAVE LENGTH, nm 

Comparison of Integrated Spectral Irradiance 

for Different Tracking Modes: Albuquerque, Annual 

ALBUQUERQUE, ANNUAL 

Y 

0 

2 

5 

a 

9 

a 

0.75 

2 

U 

c 

u W 

0.50 

E! 

z 

c 

U 

nz 

0.25 W 

tW 

z 

5 

a 

0 

- FIXE0 AXIS ! ***** SINGLE.AXIS TRACKER TYRCU 

300 400 500 600 700 600 900 1000 1100 il00 

WAVE LENGTH, nm 

517 
MODULE AND ARRAY TECHNOLCGY 

075 1 i 

0.50 - 

- ...... 0.25 - 

0 

Comparison of integrated Spectral irradiance 

for Different Tracking Modes: Miami, Annual 

- 

**' 

w 

V 

z 

0 

s 

a 

a 

oc 

A 

U 

m IV 

W k 

v) 

s 

I4 

(7 W 

c 

a 

L 

4 

W > 

I- 

- 

Ly 

U 

1 .oo '7 

- FIXED AXIS 

e.*.* SINGLE-AXIS TRACKE9 

I 

I 

I 600 

WAVE LENGTH, nm 

Future Work 

Completion and checkout of computer code for convoluting 

cell spectral response with the solar radiation spectrum 

Comparison of results obtained with other than crystalline 

silicon solar cells 

Conclusions 

Tracking array accumulates more integrated irradiance in the 

spectral region in which crystalline silicon cells are most 

sensitive 

Effect greatest for summer in Fresno: 1.5% more for 

Effect least in Miami: 0.8% more for wavelengths 

wavelengths greater than 500 nm 

greater ?hsn 500 nm 

518 
N85 15298 .: 7 

SUMMARY OF PHOTOVOLTAIC PERFORMANCE 

MODELS (JPL PUBLICATION 84-8) 

JET PROPULSION LABORATORY 

J.H. Smith 

L.J. Reiter 

There are a number of computer models which are usually placed in the 

category of photovoltaic systems performance models. These cover a range of 

approaches and capabilities from aggregate, "first-order" models to far more 

detailed analyses of PV systems. 

complete set of models which fit our criteria; review each one in detail to 

determine its purpose, approach, and capabilities; and present this 

information in an easily referenceable format. This work was performed for 

the Project Analysis and Integration Center at JPL and has resulted in a 

report entit led, "Summary of Photovoltaic Systems Performance tlodels" (JPL 

Pub. 84-8, D@E/ET-20356-11). 

The objective of this study was to find the 

Study Motivation and Scope 

To identify, summarize and distinguish between the various PV 

system performance models 

To provide users in the PV community with an in-depth reference 

document for selection of appropriate PV system models 

economic models were not included 

Focus was on performance models of flat-plate systzms; purely 

Model descriptions were reviewed by the model authors to ensure 

completness and accuracy 

51 9 
MODULE AND ARRAY TECHNOLOGY 

Approach 

Identify a comprehensive set of models 

Identify a set of topics to br 'be basis for describing the approaches 

and capabilities of the models 

Perform a detailed assessment of each model's purpose, approach, 

Tabulate information in a convenieat format 

and capabilities 

Identify recent extensions in PV performance modeling 

Note: No numerical comparisons of model results were made 

Model Selection 

A complete set of available photovoltaic systems performance 

models that: 

Have been used by the PV community in general for PV system 

Have been used as a tool for policy analysis by the national 

Have been used as a system design tool and in performance 

Have available documentation 

assessment 

laboratories 

analysis as reported in the literature 

520 
MODULE AND ARRAY TECHNOLOGY 

Models Included in the Study 

Model 

Engineering and Reliability 

Lifetime Cost and 

Performance 

Photovoltaic Performance 

Model 

Photovoltaic Transient 

Analysis Program 

Solar Cell Modtl, Version 2 

Solar Reliability 

Solar Energy System 

Analysis Program 

Transient Simularion 

ProgramlASU version 

Transient Simulat;on 

ProgramlMlT version 

_I 

PhOtOVOIt8iC F-CHART 

Name 

E&R 

LCP 

PV F-CHART 

- 

PVPM 

PV-TAP 

SOLCEL-li 

SOLREL 

SOLSYS 

TRNSYSIASU 

TRNSYSIMIT 

Originator 

Jet Propulsion Laboratory IFSA) 

Jet Propulsion laboratory IFSA, PV 

PA&I Center) 

Univ. of Wisconsin Solar Energy lab 

Electric Power Research Institute 

BDM Corp., Sandia Labs 

Sandia Labs 

Battelle Columbus Labs, Sandia Labs 

Sandia Labs 

Univ. of Wisconsin Solar Energy Lab, 

Arizona State Univ., Sandia Labs 

Univ. of Wisconsin Solar Energy Lab, 

MIT Lincoln Lab 

The following topics served as a general framework against which each 

model was compared. 

characteristics. The models were examined to determine which characteristics 

they either addressed analytically (i.e., contain an analytical model of it), 

treated externally (e.g., the element is input by the user), or do not address. 

Under each topic were a number of more detailed 

Performance Modeling Characteristics 

Cell level 

Module level 

Array orientation and geometry 

Array level 

PCU siibsystern 

Plant level 

Operations and maintenance 

Site-specific 

521 
MODULE AND ARRAY TECHNOLOGY 

The following is one of the nine tables of this type in the study report. 

It is included here to illustrate the format which was used. The manner in 

which each of the ten models addresses the characteristic is displayed and is 

easy to cross-reference. Thus, the reader can approach these tables to 

determine the capabilities of a certain model or to find a model which most 

appropriately addresses the particular characteristics of interest. 

522 
MODULE AND ARRAY TECHNOLOGY 

analytic model for I 

either isotropic or 

anisotropic diffuse 

cmponent 

Site-Specific Characteristics 

~ ~ 

analytic model usine 

mdified Liu and 

Jordan (1960) 

approach 

input file for direct 

norul iniolaticn or 

analytic model uiing 

Ddified Liu and 1 Jordan (1960) approocl ~~ 

user input to electrical netuort equivalmt of photocurrent 

alert amerator for 

ielected time scale 

analytic model of uier input network 

direct inlolation ai required to chiracnonlinear voltale terire behevior of 

controlled current diffuie component 

generator 

Total Global Direct lb~l 

Solar hdietion I Solar bdiation I &-;ric Method of 

Calculation 

Ground 

kflecitivitv ~~ 

input file of hourly 

ilobal inaolation 

fur a year 

analytic model of 

direct (adified LiuJordan. 1960) or uier 

input file of hourly 

alobal insolation 

iser input sinrle 

mlue 

iotropic-mdi tied 

iu-Jordm (1960) 

niiatropic--l(lucher, 

979 

analytic model of 

direct inroletion 

(hei. et el., 1976) 

or uier input file 

of hourly data 

iotropic--bel et 

I., 1976 

ninotrnpic-Klucher , 

979 

iacr inwt: 12 values 

:I p-r lath) 

analytic wdel for 

either iiotropic or 

anisotropic diffuse 

component 

analytic rndel for 

isotropic diffuac 

colwnent 

uier input file of 

hourly alobel insolation for a year 

analytic model of 12 

.+erase profilei (1 

per onth) calibrated 

by site specific input. tZc* mites in 

prosram 1 

~~ ~~ 

tier input: I2 

wnthly valuri (1 per 

wnth) 

sotropic--trhs. et 

I.. 1982 

hourly input file for 

total alobal insolicion for period of 

in teres t 

analvtic model for 

isotropic diffuse 

component 

.sotrooic-%odi f ied 

.iu-Jordan, 1960 

NlA 

iser input variable 

roltare element 

quired to reprelent diffuie 

input files for total 

#lobal hourly iniolation for a year 

input filei for direci 

norul hourly insoletion or analytic 

mdel uiina modified 

Liu md Jordan (1960) 

approoch (bots. et a1 

1976) 

anelvtic model for 

isotropic diftuie 

component 

motropic--bes et 

11.. 1976 

user input iinrle 

value 

W /A N IA N /A N IA n 

input file for total 

global hourly insolecion for a year 

analytic adal for 

isotropic diffuse 

component 

iiotrooic-wdif ied 

Liu-Jordan (1960) 

a value of .5 is 

included in the code 

input file for direct 

nom1 hourlr insolation or analytic model 

uiina modified LiuJordm (1960) rthod 

(her et a1. 1976) 

user inputi insolation for ielected 

tiricale (SOll(t1 

and RIY) 

user inputi total inroletion for selected 

tiricale (SOIJIET and 

my) 

isotropic-- 

3 malyric options: 

- Liu & Jordan, 1960 

- Duller, 1977, or 

- kern, et 01.. 1976 

uier input 

uier input iinele 

value 

analytic modeli for 

iiotropic diffuie or 

user input of meaiurcd total (which 

includei diffuae) 

for selected timeicilc 

isotropic-- 

3 analytic optionm: 

- Liu 1 Jordan. 1960 

- kea, et al., 1976 

- Bualer. 1977 or 

user input 

user input iinrle 

value 

for a year for selected time523 
Three General Categories of Models 

First Order 

PV F-CHART 

PVPM 

Detailed 

Flat-Plate Only 

E&R 

LCP 

TRNSYSlMlT 

Flat-Plate and Concentrator 

SOLCELL-II 

SOLSYS 

TRNSYSlASU 

Recent Extensions 

Modeling of anisotropic atmosphere for diffuse 

solar radiation 

Fresnel refraction of the encapsulant material 

Using variable time scales, especially as it applies 

Effects of insolation spectral distribution on 

to utility interaction 

power output 

Model Limitations 

Specialized 

PV-TAP 

SOLREL 

LCP and E&R 

LCP and E&R 

TRNSYS 

E&R 

Lack of high-quality data in some categories 

Shadowing assumptions 

Power quality not addressed 

Validation is limited 

524 
MODULE AND ARRAY TECHNOLOGY 

Conclusions 

There are various models, with different capabilities, approaches, 

and purposes 

Neither the simplicity nor complexity of a model implies a more 

useful tool; the key is to find the appropriate model for a given task 

There are limitations to the PV program's current modeling capability 

Data 

Shadowing 

Power quality 

Validation 

This report serves to assist in the choice of an appropriate PV 

performance model for a user's requirements 

525 

STANDARDS: AN OVERVIEW 

JET PROPULSION LABORATORY 

G.A. Praver 

Purpose of Study 

WHAT SHOULD THE NATIONAL PHOTOVOLTAI cs 

PROGRAM DO TO ENHANCE THE PROCESS OF ESTABLISHING VOLUNTARY CONSENSUS STANDARDS 

FOR MEASURING AND RATING THE PERFORMANCE 

OF PV MODULES? 

Map of Possible PV Cell and Module Standards 

527 
MODULE AND ARRAY TECHNOLOGY 

Study Approach 

0 lDENTlFY A SET OF KEY 1NDIVIDUALS REPRESENTING A 

CROSS SECTION OF VIEWS ABOUT THE STANDARD PROCESS. 

0 CONDUCT A SERIES OF INTERVIEWS WITH KEY INDIVIDUALS, 

0 SYNTHESiZE THE INTERVIEW RESULTS INTO A RECOMENDED 

PLAN OF ACTION FOR THE NATIONAL PV PROGRAM, 

Key Entities 

o GOVERNMENT LABORATOR~ES 

JPL 

SNLA 

SERI 

o PV MANUFACTURERS 

SOLAVOLT 

PHOTO WATT 

ARC0 SOLAR 

o PV USERS 

BOM 

ROGERS 8 COMPANY 

ACUREX 

o OTHERS 

DSET 

ASU 
MODULE AND ARRAY TECHNOLOGY 

Interview Topics 

o WHY DO WE NEED STANDARDS? 

o WHAT ARE THE TECHNOLOGICAL PROBLEMS THAT ARE IMPEDING THE IJEVELOPMENT AND ADOPTION OF W STANDARDS? 

o ARE THERE SOLUTIONS TO THESE PROBLEMS? 

o ARE THERE ECONOMIC LIMITATIONS TO OBTAINING THE SOLUTIONS? 

0 h0 SHOULD SOLVE THE TECHKICAL PROBLEMS? 

o WHAT IS AN APPROPRIATE REFERENCE SPECTRUM? 

0 

J 

0 

IS ASTM ATTEMPTING TO URITE TOO MANY DETAILED STANDARDS? 

ARE THE PROPER PEOPLE INVOLVED IN PREPARING STANDARDS? 

WHAT IS THE GREATEST IMPEDIMENT TO GETTING STANDARDS WRITTEN? 

o YHAT IS A POSSIBLE ROLE OF GOVERNMENT IN FURTHERING THIS EFFORT? 

Preliminary Synthesis 

o THE PROCESS OF ESTABLISHING VOLUNTAW CONSENSUS STANDARDS 

FOR MEASURING AND RATING THE PERFORMANCE OF Pv MODULES 

NEED ENHANCING, 

c THE NATIONAL W PROGRAM SHOULD FUND TRAVEL TO CONSENSUS 

STANDARD MEETINGS SUCH AS :EEE, ASTf’!. IEC, 

o THE NATIONAL W PROGRAM SHOULD SPONSOR SMALL RESEARCH TASKS 

TO RESOLVE SPECIFIC TECHNICAL PROBLEMS WHICH ARE IMPEDING 

PARTICULAR STANDARDS 

o 

o 

FUNDING SHOULD FLOW THROUGH NATIONAL LABORATORIES 

DIRECTION SHOULD COME FROM CONSENSUS STANDARDS COMMITTEES 

0 SOME EXAMPLF RESEARCH TASKS ARE, I I 

529 
MODULE AND ARRAY TECHNOLOGY 

Preliminary Con sensus 

COMPARE DIRECT NORI I~~. GLOPAL AND MATHEMATICAL SPECTRA UNDER 

ACTUAL TEST CONDITION: TO ESTABLISH A BASE OF TESTING EXPERIENCE 

FOR VARIOUS CELL TECHNOLOGIES, 

SEEK A SIMPLE METHOD TO QUANTIFY FFFECTS OF SPECTRAL MISMATCH 

ON REFERENCE CELL HEASUREHENTS, How MUCH MISMATCH IS SIGNIFICANT? 

HOW ACCURATELY CAN SPECTRAL RESPONSE 8E MEASURED? 

UNDERSTAND WIDE VARIATIONS IN ROUND ROBIN TEST RESULTS AND 

PROMULGATE EXPERIMENTAL PROCEDURES TO REDUCE THESE ERRORS, 

IMPROVE UNDERSTANDING OF RELATIONSHIPS BETWEEN PEA ’. HOCL -E 

PERFORMANCE AND TIME-AVERAGED PERFORMANCE. 

530 
RESIDENTIAL ARRAY DEVELOPMENT 

MASSACHUSElTS INSTITUTE OF TECHNOLOGY 

E.C. Kern, Jr. 

Overview 

Residential System Cost Estimates in 

1979 

Costs incurred at the NE RES and SW RES 

during 1980 - 1981 

Costs incurred at the SE RES in 1983 

Detailed costiq for Retrofit Systems 

(20 stpare meter arrays) at the NE RES 

System Cost Estimates in 1979 IC. H. Cox. 1111 

System Wle Pover Instl 

System System Cost cost m. Ratls.6 

Name Location Cost Labor 

(S/wp) (VWP) (b/Wp) O/WF) 

EW-LO Design $1.18 $0.70 $0.19 $0.29 

NEW-HI 9esign $3.04 $1.06 $1.36 $0.60 

RETRO-HI Design $3.30 s1.a $1.36 $0.06 

RETRO-LO bign $1.44 $0.70 $0.19 $0.55 

Northeast Residential Experimerit Station - 1980 

System 

Name 

System 

Location 

system 

cost 

Fbdule 

cost 

$14.65 

$11.32 

$20.65 

$32.43 

$12.35 

Power Instl 

cod. nat1s.a 

Cost Labor 

(VW) (L/W) 

$2.56 $1.48 

$3.14 $2.65 

$1.83 $0.49 

$0.73 x.72 

$0.47 $1.47 

.---------------- 

'31 

MODULE AND ARRAY TECHNOLOGY 

Pu Array kterialsr khmical 

PY kray ktsriais: Electrical 

2- 

2- 

3- 

3a 

s109.26 

f25.a 

u6.W 

120.16 

SlS.a7 

110.00 

m.m 

M6.a 

533 
MODULE AND ARRAY TECHNOLOGY 

Pavar Cmitiaur 

po*l.r Caditiwr Raterids 

Imtrllrtion 

Oixmwuct 

PV Array: Labor 

pnaf Assy. 

1nrt.U 

uire 

Ncter(1) Prica as qmtd to MIT for witin sufficient to built three systems 2 kilomatts m. 

534 
MODULE AND ARRAY TECHNOLOGY 

Wtowoltaic Wles ARa) 1')53 Laminates 45 ea 

Pu Array hterials: -mica1 

hl Array ktrriaist Electrical 

Cmim Box Hoffman box BnlOd (AbOBnLU) 1 ea 

op5T switches 

FuFuse holders 

Diofhs (.6 rrp. OOO volt) 

Grand ref mistors, 1 PbhA, .2S U 

Varistors. OOO volt. OC rrp 

RiscellrmuJ uirinq 

PUC condrit 1/2" dim (3 #e &res) 

Array l~rtim Box (Hoffman 6x6~4) 

Conduit clm. L-ann. box ent:y 

ca.&J.it 

1 ea 

lea 

1 ea 

le8 

1 ea 

lea 

1 ea 

60 ft 

1 ea 

15 ea 

s0.m 

m.m 

s0.m 

s0.105 

$4 .?a 

u2.m 

$9.880 

%,.220 

14.160 

$0.820 

m.fM 

$1.900 

s2.000 

Lo.130 

$22.500 

$1 .om 

5209.92 

99.10 

$6.50 

$6.30 

$6.50 

S2e.M 

$22.76 

w.m 

s0.m 

$0.00 

$9.88 

w .n 

$4.16 

m.82 

$0.05 

$1 -90 

V.80 

92.50 

s15.00 

u.m 

$0.1002 

m.0047 

m.mx 

m.msz 

samx 

st~.rni7 

m.oosi 

$0.0167 

So.m# 

$0.oooo 

L0.0M0 

$0.0022 

SO.Wtl 

$0.oooa 

$.moa 

$0.0010 

SO.Ot!G 

mmo 

w.m 

sa.- 

535 
MODULE AND ARRAY TECHNOLOGY 

Povcr Canditiomr 

Power Cmitioncr Raterials 

Installation 

Discumect 

PY Array: Labor 

Panel Assy. 

Raof Prep 

Install 

X Ewip 

PCS: Labor 

Install 

Wire 

nDduln uatt(p*) 63.10 

Labor Rate ($/tu) 

Factory $7.50 

Field si s .m 

System A: cmr. Standoff 

10 we Rorx 9 ft 

Clmit breaker (20 arg RED) 1 ea 

~ag bolts, fraering lea 

Outdoor boa u/erkr lea 

Place panels in position. wire. secu 8 hr 

bt cOnainer boa, cdit, dixom 6 hr 

Uire combiners to RS lhr 

Systsr 8: RIT/rn Standoff 

mt (res to -11 1 hr 

Install EO cir brkr, wire iXS to n 1 hr 

m.m w.mm 

m.m m.mm 

ul.m m.oam 

s1s.m si2o.m ~0.0619 

s1s.m s6o.w o.mm 

s1s.m si5.m 10.0~7 

s0.m u1.oopD 

1195.00 $0.1M15 

kter(1) Prices to MT for the purchase of gwntities sufficient to hiid three systems at tw kilcu8tts ~iece, 

- with 5 excaQtim of the ptiw far lminates, hat ct~amels, cdge protectors/inteKmnetr mc~ silicon 

adhesives vhich are estimates llpd. by the wthor uithout consultation with the HIpplicr. 

536 
MODULE AND ARRAY TECHNOLOGY 

System 

Name 

-- fill Retrcfit System Oesiqns (1984L 

System 

Location 

System 

cost 

lrbdule 

Cost 

Power Instl 

Cd. Rat1s.a 

Cost Labor 

WP) (J/lrlP) .---- -----_--I- 

$4.47 W.74 

51.93 $0.32 

$1.20 $0.13 

$1.93 s0.m 

51.79 $0.19 

Note:(l) Nominal $1 per wtt &le cost asslmed for S%,20$, and 30% arrays 

(2) Two kilowatt PRI used for der one kilowatt array in the 5% array 

(3) Each array fixed with an area of 180 square feet 

Conclusions 

0 Lowest cost arrays to date are the direct munt GE 

shingles (their degradation, however, dictates against 

-1 

0 For new construction situations, integral momts have 

proven to be the loblest cost. 

Buildin9 black panels appear ta offer siqificant 

ahrantages for both retrofit and new construction 

situations. 

e Installation materials and labor casts for X-Si are 

potentially 0.32 $/Wp; A-Si (SS) 0.71 $/Wp; GaAs 

(m) 0.19 S/Wp; CaAsSi (30%) 0.13 $/Up 

s37