NASA Technical Memorandum 102103 

Indium Phosphide Solar Cell Research in 

the United States-Comparison With 

Nonphotovoltaic Sources 

I. Weinberg, C.K. Swartz, 

and R.E. Hart, Jr. 

Lewis Research Center 

Cleveland, Ohio 

. 

Prepared for the 

European Space Power Conference 

sponsored by the European Space Agency 

Madrid, Spain, October 2-6, 1989 

(NA SA-TM-10 21 03) I NDIU H PHOSPHIDE SOL AB N a 9- 27 a 68 

CELL BESEARCH IN THE US: COHPABISOH YITH 

NONPHOTOVOLTAIC SO CJElCES [HA SA. Levi S Besearch Center) 13 p CSCL loa Unclas 

G3/31 0225956 
INDIUM PHOSPHIDE SOLAR CELL RESEARCH IN THE UNITED STATES - 

COMPARISON WITH NONPHOTOVOLTAIC SOURCES 

I. Weinberg, C.K. Swartz, and R.E. Hart, Jr. 

National Aeronautics and Space Administration 

Lewis Research Center 

Cleveland, Ohio 44135 

SUMMARY 

Highlights of the InP solar cell research program are presented. Homojunction cells with AM0 efficiencies approaching 19 percent were demonstrated 

while 17 percent has been achieved for ITO/InP cells. The superior radiation 

resistance of these latter two cell configurations over both Si and GaAs have 

been demonstrated. InP cells on board the LIPS 111 satellite show no degrada- 

:ion after more than a year in orbit. Computer modelling calculations have 

been d:rected toward radiation damage predictions and the specification of concentrator cell parameters. Computed array specific powers, for a specific 

orbit, are used to compare the performance of an InP solar cell array to solar 

dynamic and nuclear systems. 

Q, 

m ‘9 

d I 

d 

INTRODUCTION 

Though still in an early developmental stage, indium phosphide solar 

cells are prime candidates for use in the space radiation environment. 

is apparent from their greatly increased radiation resistance when compared to 

gallium arsenide and silicon (refs. 1 and 2). It has also been shown that 

radiation damage in InP can be reduced by exposure to light at room temperature (ref. 3). In addition, air mass zero efficiencies of over 21 percent are 

predicted by computer modelling calculations (ref. 4). These results have 

served as motivation for the NASA Lewis Research Center to initiate and continue a program of InP solar cell research directed toward their use in space. 

This research effort has, involved, beside NASA Lewis and the Naval Research 

Laboratory, efforts at several universities and industrial laboratories in the 

United States. At the same time, a continuing major effort is underway in 

Japan. Additional ongoing research in the United Kingdom has been focused 

mainly on the development of ITO/InP solar cells. 

highlights in the U.S. program. Results emanating from other countries are 

included where appropriate. 

This 

The current paper summarizes 

BACKGROUND 

Considering silicon solar cells, a long period of R&D directed toward 

their use in space, was followed by an intensive program directed toward their 

use in the terrestrial environment. Exactly the opposite has occurred for InP. 

Prior to 1984, published research on InP solar cells was concerned with terrestrial applications. Much of the early work considered multicomponent structures such as ITO/InP, Cds/InP (refs. 5 and 7) and simplified structures such 

as MIS Schottky barrier cells (ref. 8). Reports of the first reasonably good 

monolithic cell appeared in 1980 (ref. 9). A summary of some early results is 

shown in table I for measurements reported at other than air mass zero. 
The first reported radiation damage data on InP appeared in 1984 when 

Yamaquchi and his coworkers in Japan reported on the comparative radiation 

resistance of InP, GaAs and Si under 1 MeV electron irradiation (ref. 2). This 

was followed, in the United States by the observed superior radiation resistance of InP over GaAs and Si under 10 Mev proton irradiation (ref. 1). It can 

be noted from table I, that a wide disparity of reporting methodology existed 

in the terrestrial effort. Measurements in this early program were reported 

at air masses varying between 1 and 2 and, in some cases, in terms of active, 

rather than total cell area. Since it is standard practice in the space solar 

cell community to report total area efficiencies at air mass zero, we shall 

I adhere to this procedure in the remainder of this paper. 

CELL PERFORMANCE 

Progress in achieving high efficiency, dating from 1984, is shown in figure 1. The first cells were prepared by a closed tube diffusion process 

(refs. 2 and 11). The highest efficiency (18.8 percent) was achieved by a combination of both OMCVD and ion-implantation (ref. 12). The geometry and dopant 

concentration of this cell are shown in figure 2. In addition to the aforementioned process, cells in the U.S. have been processed by open tube diffusion 

and LPE (refs. 13 and 15). All of the cells depicted in figure 1 were small 

with areas varying between 0.25 and 0.31 cm2. These sizes represent economic 

limitations imposed by the high InP wafer cost. Larger area (2 and 4 cm2) 

cells have been produced in Japan using a closed tube diffusion process 

(ref. 16). These latter cells have been produced in relatively large quantities arid are intended to power a small piggy back lunar orbiter on board the 

Japanese MUSES A satellite, scheduled for launch in 1990 (ref. 17). The highest efFiciency achieved for these large area cells is 16.6 percent. This 

represents the best efficiency achieved using a diffusion process (ref. 16). 

In addition to monolithic InP, cells processed by sputtering n-indium tin 

oxide onto p-type InP (ITO/InP> are of interest because they represent a simpler, relatively inexpensive processing alternative. The best ITO/InP cells, 

processed at SERI by DC magnetron sputtering, have achieved AM0 efficiencies 

of 17 percent (ref. 18). Parameters of the best cells produced by different 

techniques are shown in table 11. Of the various processes listed, OMCVD is 

the most flexible and has produced the best, albeit small area, cells. 

EFFECTS OF RADIATION 

Experimental Data 

Both n/p homojunction and ITO/InP cells are included in small experimental 

modules, presently in space, on board the LIPS I11 satellite (refs. 19 and 20). 

The homojunction cell module was supplied by NASA Lewis. The ITO/InP module 

contains cells processed by Newcastle Upon Tyne Polytechnic and is under the 

aegis of RAE Harnwell. The status of the NASA Lewis module will be discussed 

at this conference (ref. 20). In summation, after more than a year in orbit, 

have no information on the ITO/InP module. Since the latter cells represent a 

simplified processing alternative, and reasonable high efficiencies have been 

achieved, it is necessary to determine their comparative performance in a laboratory environment. Hence, we have irradiated ITO/InP cells, obtained from 

I no degradation was observed in the homojunction cells. On the other hand, we I 

2 
t 

~ 

SERI, with 10 MeV protons and compared their performance to n/p InP and GaAs 

homo\jbnction cells including large area n/p cells similar to those on board 

the MLSES A satellite. Preirradiation parameters for these cells are shown in 

table I11 while figure 3 shows normalized efficiency as a function of fluence. 

It is seen that the ITO/InP cells exhibit radiation resistance, under 10 MeV 

proton irradiations, which is comparable to that of the InP homojunction cells. 

It is noted that the larger InP cell outperforms the remaining cells at low 

fluences but falls off at the higher fluences. With regard to the behavior at 

high fluence; it is noted that the junction depth of the larger InP cell lies 

between 0.2 and 0.3 pm (ref. 16) while the junction depth of the smaller area 

cell is well under 0.1 pm (ref. 13). Dependence of radiation resistance on 

junction depth has previously been noted for GaAs where a decrease in junction 

depth accompanied increased radiation resistance (ref. 21). In the absence of 

similar data for InP, it is speculated that the fall off at high fluence may 

be due to the cell's relatively deep junction depth. On the other hand, the 

increased radiation resistance, observed at lower fluence, may be due to 

improved sabstrate quality. Additional research is required to assess the 

di ty of these speculations. 

Modelling of Radiation Damage 

Comparison of InP and GaAs cells, under laboratory conditions, have 

oyed cells with widely differing BOL characteristics. For example; the 

GaAs cell of figure 3 has a base dopant concentration which is an order of 

magn'ltude greater than that of the InP cells. Previous comparisons under 1 MeV 

electron irradiations, shown in figure 4, have used p/n GaAs cells with an 

AlGaAs window and compared them to n/p InP cells with no window and with widely 

differing base dopant concentrations (ref. 22). In order to compare these 

cells on an equal basis, a calculation was performed using a previously published computer model (ref. 23). Parameters used in the comparison are shown 

in table IV. The model predicts an AM0 efficiency of 20.4 percent for InP and 

21.5 percent for GaAs. However by reducing the emitter width to 300 A, grid 

shadowing to 4 percent and use of an optimized 2 layer AR coating, the optimum 

efficiency is 21.5 percent for InP and 22.5 percent for GaAs. 

Because of carrier removal effects, lifetime rather than diffusion length 

damage coefficients were employed using, 1/, = l/rg + K-t +, where K, is the 

lifetime damage coefficient. The plot used to obtain K, for InP is shown in 

figure 5, a similar plot being used for GaAs. From these data, it was found 

that, for a p-base concentration of 5xl016/cm3, K, = 1.3~10-6 and 3.1~10-5 cm2/ 

sec For InP and GaAs respectively. The calculated performance for these cells 

under. 7 MeV electron irradiation, is shown in figure 6 where it is seen that 

the InP cell outperforms the GaAs cell. 

Estlmated Performance in Space 

A comparison of the estimated performance, of PV arrays and nuclear and 

solar dynamic systems, in a 30" circular orbit, is shown in figure 7. Array 

specific powers were obtained for a distribution of altitudes with a 5 yr stay 

at each altitude. The calculations were performed using silicon 1 MeV electron 

equivalent data (ref. 24). This is admittedly a rough approximation for GaAs 

an3 InP. However, it is felt that the use of silicon data tends to overestimate the degradation of the III-V solar cells. Specific powers were calculated 

3 
using published data for the JPL/TRW Advanced Photovoltaic Solar Array (APSA) 

(ref. 25). 

spec fic power of approximately 132 W/kg using 2.2 mil, 13.5 percent silicon 

solar cells , a 2 mil cover glass and a 10 percent weight add-on for contingencies Our calculations were performed using the same cell thickness with the 

substitution of a 10 mil cover glass. The BOL efficiencies used, at 28 "C for 

the flat plate cells, were 18, 19 and 15 percent for InP, GaAs and Si respective;y. These values were felt to be reasonably close to the values achievable 

in productton. 

lens concentrator array at 100 "C and lOOX assuming a BOL efficiency of 22 percent at this concentration and temperature (refs. 26 and 29). The considerable 

effect of battery storage was included by assuming 100 W-Hr/kg for the battery 

and a nominal eclipse period of 112 hr. 

appears achievable using sodium-sulphur batteries. Specific powers for the 

nuclear (SP-100) and solar dynamic systems were obtained from previously pubiished data, assuming no degradation while in orbit (ref. 27). It was also 

assumed. based on annealing data, that the InP conceqtrator cells would not 

degrade at lOOX and 100°C (refs. 3 and 28). The results indicate that the InP 

flat plate and concentrator salar cell arrays could outperform the solardynamic system and that the concentrator system performs as well as the nuclear 

system. These results are tentative, pending the acquisition of 1 MeV electron 

damage equivalents for InP and GaAs and confirmation of the assumed annealing 

I behaviar or' the Inp concentrator rells. It is also noted that the APSA array 

is an advanced system whose ultimate goal is to achieve a specific power of 

300 Cllkg (ref. 25). 

The 5.3 kW wing developed under the APSA program achieves a BOL 

An additional specific power was calculated for InP in a Fresnel 

The battery specific energy used 

I PREDICTED BEHAVIOR UNDER CONCENTRATION 

The high cost of InP wafers makes concentrators, with their greatly 

decreased cell slze, an attractive alternative. Since Inf concentrator cells 

are not readily available, we used the model of reference 23 to compute the 

expected performance of these cells under varying concentration and temperature. The calculations were performed using cell geometries suitable for the 

cassegranian and SLATS concentrators. The geometry of a circular cell for the 

Cassegranian concentrator and a rectangular cell for the SLATS concentrator are 

shown in figures 8 and 9. Cell parameters are shown in table V. Some calculated results are shown in figures 10 and 11. At 80" and lOOX, the circular cell 

,fficiency is 21.1 percent while the rectangular cell efficiency, at 80 "C and 

ZOX, is 20.6 percent. It is noted that a more comprehensive computer model is 

under development, using a multilayer AR coating and is expected to add at 

least 1 percent to these efficiencies. Furthermore, the addition of a prismatic cell cover is expected to also add efficiencies between 1 and 2 percent 

(ref. 26). 

CONCLUSION 

Although progress in developing InP cells for use in space has been satisfactory, several avenues of research merit increased attention. Additional 

effort needs to be directed toward producing large area high efficiency 

devices. Since cells 8 cm2 in area are commonplace for both Si and GaAs, this 

size is a desirable goal for InP. However a more significant contribution lies 

in reoucing cell cost. At present the wafer accounts for over 90 percent of 

the cell cost. One effort, now underway, aims toward the processing of solar 

cells using a few microns of InP epitaxially deposited on cheaper substrates 

I 4 
? 

I 

such as Si. In this case one needs to overcome problems caused by lattice misfit and thermal expansion differences. Additional research is directed toward 

the use of techniques such as the CLEFT process. This latter method incorporate!; the use of reuseable substrates. In addition to the preceding there 

exists a need for high efficiency concentrator cells. In our opinion, succC?Ssful ccmpletion of these efforts is required in order to realize the full potential cf InP solar cells for use in space. 

REFERENCES 

1. Weinberg, I.; Swartz, C.K.; and Hart, R.E.: Potential for Use of InP 

Solar Cells in the Space Radiation Environment. Eighteenth IEEE 

Photovoltaic Specialists Conference - 1985, IEEE, 1985, pp. 1722-1724. 

2. Yamaguchi, M., et al.: Electron Irradiation Damage in Radiation-Resistant 

InP Solar Cells. Jpn. J. Appl. Phys., vol. 23, no. 3, Mar. 1984, 

pp. 302-307. 

3. Ando, K.; and Yamaguchi, M.: Radiation Resistance of InP Solar Cells Under 

Light Illumination. Appl. Phys. Lett., vol. 47, no. 8, Oct. 15, 1985, 

pp. 846-848. 

4, Coradia, C.; Geier, J.V.; and Weinberg, I.: Theory of the InP Shallow 

Homojunction Solar Cell. Solar Cells, vol. 25, no. 3, 1988, pp. 235-253 

5. Sree Harsha, K.S., et al.: n-Indium Tin Oxide/p-Indium Phosphide Solar 

Cells. Appl. Phys. Lett., vol. 30, no. 12, June 15, 1977, pp. 645-646. 

6. Eachmann, K.J., et al.: Solar Cell Characteristics and Interfacial 

Chemistry of Indium-Tin-OxideIIndium Phosphide and Indium-Tin-Oxide/ 

Gallium Arsenide Junctions. J. Appl. Phys., vol. 50, no. 5, May 1979, 

pp. 3441-3446. 

7. Bettini, M.; Bachmann, K.J.; and Shay, J.L.: CdSIInP and CdSIGaAs 

Heterojunctions by Chemical Vapor Deposition of CdS. J. Appl. Phys., 

vol. 49, no. 2, Feb. 1978, pp. 865-870. 

8. Kamimura, K.; Suzuki, T.; and Kunioka, A.: Metal-Insulator Semiconductor 

Schottky-Barrier Solar Cells Fabricated on InP. Appl. Phys. Lett., 

VOI. 38, no. 4, Feb. 15, 1981, pp. 259-261. 

9. Turner, G.W.; Fan, J.C.C.; and Hsieh, J.J.: High-Efficiency InP 

Homojunction Solar Cells. Appl. Phys. Lett., vol. 37, no. 4, Aug. 15, 

1980, pp. 400-402. 

10. Coutts, T.J.; and Naseem, S.: High Efficiency Indium Tin Oxide/Indium 

Phosphide Solar Cells. Appl. Phys. Lett., vol. 46, no. 2, Jan. 15, 1985, 

pp. 164-166. 

11. Yamamoto, A.; Yamaguchi, M.; and Uemura, C.: High Conversion Efficiency 

and High Radiation Resistant InP Homojunction Solar Cells. Appl. Phys. 

Lett., vol. 44, no. 6, Mar. 15, 1984, pp. 611-613. 

5 
12. Keavney, C.J.; and Spitrer, Y.B.: Indlum Phosphlde Solar Cells Made by 

Ian Implantation. Appl. Phys. Lett., vol. 52, no. '7. Apr. 25, 1988, 

pp. 1439-1440. 

13. Parat, K.K., et al.: Solar Cells in Bulk InP, Made by an Open Tube 

Diffusion Process. Solid State Electron., vol. 30, no. 3, 1987, 

3~. 283-287. 

14. Chol, K.Y.; and Shen, C.C.: p/n InP Homojunction Solar Cells With a 

Modified Contacting Scheme by Liquid Phase Epitaxy. J. Appl. Phys., 

vol. 63, no. 4, Feb. 15, 1988, pp. 1198-1202. 

15. Weinberg, I., et al.: Comparative Radiation-Resistance, TemperatureDependence and Performance of Diffused Junction Indium-Phosphide Solar 

Cells. Solar Cells, vol. 22, no. 2, 1987, pp. 113-124. 

16. 

17. 

18. 

19. 

20. 

21. 

I 

I 

'7 _. 

I 23. 

I 

I 24. 

~ I

25. 

Okasaki, H., et al.: Production of Indium Phosphide Solar Cells for Space 

Power Generation. Twentieth IEEE Photovoltaic Specialists Conference - 

1988, VO~. 2, IEEE, 1988, pp. 886-892. 

Nagatomo, M.: Private Communication. Institute of Space and Astronautical 

S:ience, Tokyo, Japan, 1988. 

Coutts, T.J.. et al.: Proceedings of the 4th International Science ,and 

EJglneering Conference, Sydwy, Australia, Feb. 14-17, 1988, to be 

paJb1 i shed. 

6-inker, D.J.; Hart, R.E.; and Weinberg, I.: InP Homojunction Solar Cell 

Performance on the LIPS I11 Flight Experiment. Twentieth IEEE Photovoltaic Specialists Conference - 1988, vol. 2, IEEE, 1988, pp. 819-823. 

Brinker, D.J.: On-Orbit Results of the LIPS III/InP Homojunction Solar 

Cell Experiment. NASA TM-102131, 1989, (Also This Conference). 

Loo, R.; Kamath, G.S.; and Knechtli, R.C.: Radiation Damage in GaAs Solar 

Cells. Fourteenth IEEE Photovoltaic Specialists Conference - 1980, IEEE, 

Weinberg, I., et a].: Radiation and Temperature Effects in Gallium 

Arsenide, Indium Phosphide, and Silicon Solar Cells. Nineteenth IEEE 

Photovoltaic Specialists Conference - 1986, IEEE, 1986, pp. 548-557. 

1980, pp. 1090-1097. 

Goradia, C.; Geier, J.V.: and Weinberg, I.: Experimental and Theoretical 

Comparison of 1 MeV Electron-Induced Radiation Damage in InP and GaAs 

Space Solar Cells. Technical Digest, 3rd International Photovoltaic 

Science and Engineering Conference, Japan Society of Applied Physics, 

pp. 207-210, 1987. 

Tada, H.Y., et al.: Solar Cell Radiation Handbook, 3rd Edition, 

JPL-PUB-82-69, NASA CR-169662, 1982. 

Kurland, R.M.; and Stella, P.: Advanced Photovoltaic Solar Array 

Development. Space Photovoltaic Research and Technology - 1988, NASA 

CP-3030, 1988, pp. 128-144. 

b 
26. O'Neill, M.J 

ConcentrdtotPr 1 sma t I c Ce 

Conference - 

-- Cell type 

n/p homojunction 

ITO/InP (n/p) 

n-CdS/p-InP 

n+/p/p+ 

MIS 

; and Pi szczi r , M. F. : An Advanced Space Photovol tai c 

Array Using Fresnel Lenses, Gal 1 ium Arsenide C;11 s, and 

1 Covers. Twentieth IEEE Photovoltaic Specialists 

1988, VO~. 2, IEEE, 1988, pp. 1007-1012. 

- Source Air mass Efficiency.a Ja FF, 

percent ";s' mAf~2 percent 

- 

Ibaraki ECL 1.5 b18.6 833 27.7 81 

Ref. 10 1 15.8 768 26.9 76.7 

1.5 b16.2 

Ref. 7 2 ; c15 780 18.7 73.5 

Ref. 9 1 15 780 26.5 71.5 

Ref. 8 2 14.5 739 17.8 79 - 

27. Brandhorst, H.W., Jr.; Juhasz, A.J.; and Jones, B.I.: Alternative Power 

Generation Concepts for Space. Proceedings of the Fifth European 

Symposium on Photovoltaic Generators in Space, W.R. Burke, ed., 

€SA-SP-267, European Space Agency, 1986, pp. 13-19. 

Cell Growth Are?, Efficiency, J V FF, !2e f e rence 

type method cm percent m~?Er;12 %' percent 

"+PP+ OMCVD 0.25 18.8 35.7 873 82.9 12 

and 

ion-implant 

"+P C1 osed 4 16.6 33.7 828 81.6 16 

tube 

di ffusi on 

28. Yamaguchi, M., et a1 .: Injection-Enhanced Annealing of InP Solar-Cell 

Radiation Damage. J. Appl. Phys., vol. 58, no. 1, July 1, 1985, 

pp. 568-574. 

1 ITO/InP DC 0.72 17 28 

magnetron j sputtering 

29. Goradia, C., et al.: Predicted Performance of Near-Optimally Designed 

IndiuFn Phosphide Space Solar Cells at High Intensities and Temperatures. 

Twentieth IEEE Photovoltaic Specialists Conference -. 1988, ,101. 1, IEEE, 

1988, pp. 695-701. 

813 83 18 

TABLE 111. - PREIRRADIATION AM0 PARAMETERS OF CELLS IN FIGURE 3 

n/p InP 2 16.4 32.9 825 83 

n/p InP 0.25 13.6 27.6 826 81.8 1 

ITO/InP 0.717 13.2 32.6 761 78 

n/p GaAS 4 16.6 29 960 81.8 1 

7 
InP Gabs 

' Junction area,T 1 .oo 1 .oo 

Total illuminated area, cm2 0.94 0.94 

Grid coverage, percent 6.00 6.00 

Specific contact resistance, *cm* 1 .oX10--3 1 .oX10-3 

Front surface recombination velocity. cm/sec 1 .0x105 3.0~10~ 

n+ emitter width, A 40 0 400 

n+ emitter doping, cm-3 6.0~10 6.0~10 

p base width, pm 1.50 1.50 

p base doping, cm-3 5.0~10 5.0~1 0l6 

p+ BSFIbuffer layer widt'l. pm 250 250 

p+ BSF/buffer layer dopiqg, cm-3 5.OX10 5.OX1018 

- 

TABLE V. - GEOMETQICAL AND PATERIAL PARAMETERS OF NEAR-OPTIMUM CELI- DESIGN 

[The following parameters are identical for both rectangular and circular 

cells. I 

~~ ~ ~ ~ ~~ ~~ ~~ ~ ~ 

Base 

Width, We, pll ......................... 1.5 

Effective lifetime, T~, ns .................. 17.8 

OOpi "g, Nzb, Cm-3 ....................... 5x1Ol6 

Diffusion length, Lnx, pm ................... 12.75 

BSF region 

Width,WBs~,pm ........................ 250 

Doping, Wz, BSF, cm-3 ..................... 5~10'~ 

Effective lifetime, T,,, BSF. ns ................ 0.18 

Diffusion length, L, BSF, pm ................ 7.06 

- 

~ ~~~~~ ~ ~~ ~~ ~~ ~~ ~ ~~ ~ ~~ ~~ ~~~ ~~~ ~~ ~ 

Emitter 

Width, WE, pll (A) ....................... 0.04 (400) 

Doping, WdE, cm-3 ....................... 2x1018 

Effective lifetime, rpE, ns .................. 1.26 

Diffusion length, Lp~, pm .................. 0.42 

a 
2o r 

12 

1984 1985 1986 1987 

YEAR 

FIGURE 1. - InP - PROGRESS IN ACHIEVING HIGH-EFFICIENCY. 

,-AR COAT ZnS/MgF2 

I Ge:Au-Ag 

Zn : 5~10~~/d I p+ I SUBSTRATE 

1 IGURE 2. - N+PP+ InP CELL STRUCTURE - WVD. 

1.0 

>- .9 

w 

u, 

U L 

.8 W 

W N 

n 

- .7 f 0 

z .6 

.5 

11 

J 

5 101' 1012 10~3 

10 MEV PROTON FLUENCE. CH-2 

FIGURE 3. - NORMALIZED EFFICIENCY VERSUS PROTON 

FLUENCE. ITO/InP. n/p InP. AND n/p G1AS. 

4r RPI CELLS KK-88A AND KK-88B - IflP / 

- KK-88A 

w3 c ----- KK-88B 

/'- KT = 1.3xd CM~/SEC 

1 MeV ELECTRON FLUENCC x 10-13/CM2 

FIGURE 5. - GRAPHICAL PLOTS U;ED TO OBTAIN LIFETIME 

DAMAGE COEFFICIENTS FOR InP. 

1.0 

> .9 x 

Y 

U 

LL W 

0 

.8 

kl - .7 3 

s 

.6 

.5 

1 

r InP. ILLUMINATED InP. DARK -1 / 

1 MEV ELECTRON FLUENCE. CM-~ 

FIGURE 4. - NORMALIZED EFFICIENCIES OF InP, GAAS AND SI 

AFTER 1 MEV ELECTRON IRRADIATION. 

3 ;:;I --- 

g 20 

1012 10~3 10~~ 1015 1016 

1-MEv ELECTRON FLUENCE. e-/cM * 

FIGURE 6. - PERFORMANCE PARAMETERS VERSUS 1 MEV 

e- FLUENCE: THEORETICAL VARIATION FOR InP AND 

GaAs . 

9 
ORGINAL PAGE 

BLACK AtYO WHITE PHOTOGRAPH 

9- r IIP-Pv 

0 

400 600 1OOO 2000 4OOO 10000 20 000 

ALTITUDE, NM 

FIGURE 7. - SPECIFIC POWER AFTER 5 YEARS IN ORBIT. 

5nn 

FIGURE 8. - CIRCULAR CELL FOR CASSEGRAINIAN CONCENTRATOR 

loo Awl. 80 oc. 

FIGURE 9. - RECTANGULAR CELL FOR SLATS CONCENTRATOR 20 Am). 

a0 oc. 

10 
23 

80 OC 100 oc 

I 

22 

H 

i 

20 

CONCENTRATION 

- 

23 r 

300 320 340 360 380 

CELL TEMPERATURE, K 

FIGURE 11. - EFFICIENCY VERSUS WERATURE AT VARIOUS AM0 

CmEWTRATlMS - RECTA)(GULAR ELLS. 

11 
Report Documentation Page 

NASA TM- 102 103 

4. Title and Subtitle 

S~kwe Adnwwff.~lm 

1. Report No. 1 2. Government Accession No. I 3. Recipient’s Catalog No. 

5. Report Date 

9 Performing Organrzation Name and Address 

National Aeronautics and Space Administration 

Lewis Research Center 

Cleveland. Ohio 44135-3191 

’ 12 Sponsoring Agency Name and Address 

I 

I 

I Indium Phosphide Solar Cell Research in the United States- 

, Comparison With Nonphotovoltaic Sources 

11. Contract or Grant No. 

13. Type of Report and Period Covered 

Technical Memorandum 

6. Performing Organization Code 

17. Key Words (Suggested by Author@)) 

Solar cells 

Indium phosphide 

Radiation damage 

I 

8. Performing Organization Report No. I 7. Author(s’ 

18. Distribution Statement 

Unclassified - Unlimited 

Subject Category 3 1 

1 I. Weinberg, C.K. Swam. and R.E. Hart, Jr. 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 

Unclassified Unclassified 

E-4869 

10. Work Unit No. 

21. No of pages 22. Price’ 

12 A03 

I National Aeronautics and Space Administration 

Washington. D.C. 20546-0001 , 1 14. Sponsoring Agency Code 

, I 

’ 15 Supplementary Notes 

Prepared for the European Space Power Conference sponsored by the European Space Agency, Madrid, Spain, 

October 2-6. 1989. 

16. Abstract 

Highlights of the InP solar cell research program are presented. Homojunction cells with AM0 efficiencies 

approaching 19% were demonstrated while 17% has been achieved for ITO/InP cells. The superior radiation 

resistance of these latter two cell configurations over both Si and GaAs have been demonstrated. InP cells on 

board the LIPS I11 satellite show no degradation after more than a year in orbit. Computer modelling calculations 

have been directed toward radiation damage predictions and the specification of concentrator cell parameters. 

Computed array specific powers, for a specific orbit, are used to compare the performance of an InP solar cell 

array to solar dynamic and nuclear systems. 

~~ 

‘For sale by the National Technical Information Service, Springfield. Virginia 221 61 NASA Fm 1616 OCT