Progress in High-Performance 

PV: Polycrystalline Thin-Film 

Tandem Cells 

 

August 2004 • NREL/CP-520-35174 

Martha Symko-Davies

Prepared for the 19th European PV Solar Energy 

Conference and Exhibition 

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June 7–11, 2004 

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PROGRESS IN HIGH-PERFORMANCE PV: POLYCRYSTALLINE 

THIN-FILM TANDEM CELLS 

Martha Symko-Davies 

NREL, 1617 Cole Boulevard, Golden, CO 80401-3393, USA, TEL: 303-384-6528, FAX: 303-384-6490, e-mail: 

Martha_Symko_Davies@nrel.gov

Abstract: The High-Performance Photovoltaic (HiPerf PV) Project was initiated by the U.S. Department of Energy 

to substantially increase the viability of PV for cost-competitive applications. The goal is that PV will contribute 

significantly to the U.S. and world energy supply and environmental enhancement in the 21st century. The HiPerf 

PV Project aims at exploring the ultimate performance limits of existing PV technologies, approximately doubling 

their sunlight-to-electricity conversion efficiencies during its course, to accelerate and enhance their impact in the 

marketplace. To accomplish this, the National Center for Photovoltaics (NCPV) directs in-house and subcontracted 

research in high-performance polycrystalline thin-film and multijunction concentrator devices. This paper will 

describe progress of the subcontractor and in-house R&D on critical pathways for a PV technology having a high 

potential to reach cost-competitiveness goals: 25%-efficient, low-cost polycrystalline thin-film tandems for largearea, flat-plate modules. 

Keywords: Polycrystalline – 1: Thin-film – 2: High-Efficiency – 3 

1. INTODUCTION 

The HiPerf PV Project aims at exploring the ultimate 

performance limits of existing PV technologies, 

approximately doubling their sunlight-to-electricity 

conversion efficiencies during its course, to accelerate 

and enhance their impact in the marketplace. Along with 

other criteria for success (module manufacturing cost and 

reliability, which are central to other components of the 

DOE National PV Program), module sunlight-toelectricity conversion efficiency is a key parameter 

driving the economics of PV-generated electricity. 

Simply put, raising sunlight-to-electricity conversion 

efficiency reduces cost per unit of electrical output. The 

HiPerf PV Project directs Federal resources toward some 

of the most critical barriers to the widespread use of 

photovoltaics for energy-significant applications. This 

addresses one of the highest-priority goals for applied 

research in the U.S. Photovoltaics Industry Roadmap [1]: 

“developing high-efficiency, low-cost materials and 

devices.” 

This paper will describe progress on exploring 

critical pathways for a PV technology having a high 

potential to reach cost-competitiveness goals: low-cost 

polycrystalline thin-film tandems for large-area, flat-plate 

modules (Figure 1). 

Figure 1: Tandem schematic 

(monolithic structure) 

The concept was introduced to increase efficiency, but its 

potential for reducing cost also became apparent many 

years ago [2]. This technology has the potential to reach 

the installed system cost goal of about $1/Wp with 

continued progress in efficiency, reliability, and 

manufacturing cost. 

2.0 APPROACH 

2.1 Project Description 

The NCPV at the National Renewable Energy 

Laboratory (NREL) directs in-house and subcontracted 

research in high- performance polycrystalline thin-film 

and multi-junction concentrator devices. During the 

project period and pushing the research toward 

established goals extensive collaboration should produce 

significant contributions to the entire PV industry. A 

roadmap of the High Performance PV Project approach is 

shown for approximately the next decade (Figure 2). 

I 

E xploring and A ccelerating

Ulti mate Path w ays, P hase I B 

Identifying C ritical Path w ays, 

P hase I A 

I mple m entation, P hase II 

C o m m ercial P rototype 

P roducts, P hase III 

2001 2003 2006 2009 

Figure 2: Roadmap of the High Performance PV Project 

The first phase of the project is critical because it 

provides a means to identify, explore, and accelerate the 

most promising paths for implementation, followed by 

commercial prototype products. These latter efforts 

constitute the second and third phases of this planned 

research program. The first of a two-part phase, 

“Identifying Critical Pathways,” investigated a wide 

range of complex issues in both the polycrystalline thinfilm tandems and III-V multi-junction concentrators. 

These investigations provided initial modeling and 

baseline experiments for several advanced concepts to 

clarify some of the challenges and identify critical paths 

for the longer-term development and application of highn-type (top cell) 

p-type (top cell) 

p+ (interconnect) 

n+ (interconnect) 

n-type (bottom cell) 

p-type (bottom cell) 

1 
performance PV technologies. The current Phase IB, 

“High Performance PV—Exploring and Accelerating 

Ultimate Pathways,” is a continuation of Phase I and 

addresses exploring and accelerating ultimate pathways 

to reach the project’s long-term goals. It is thought that 

several promising approaches will be explored in each 

category during this phase, which will lead to Phase II, 

“Implementation of Pathways.” Seven companies and 

universities were competitively selected and have 

received awards for the HiPerf PV Phase IB (see 

Table I). 

Table I: Phase IB, “Exploring and Accelerating Ultimate 

Pathways” Subcontractor Awards 

Subcontractor Title 

Georgia Institute 

of Technology 

Thin-Film Si Bottom Cells 

for Tandem Device 

Structures 

University of 

Delaware (IEC) 

High-Performance PVPolycrystalline Thin-Film tandem 

Cells 

University of 

Toledo 

Sputtered II-VI Alloys and 

Structures for Tandem PV 

University of 

Florida 

Identification of Critical 

Paths in the Manufacturing 

of Low-Cost HighEfficiency CGS/CIS TwoJunction Tandem Cells 

University of 

Oregon 

Identifying the Electronic 

Properties Relevant to Improving 

the Performance of High Bandgap Copper Based I-III-VI2 

chalcopyrite thin film PV devices 

Oregon State Novel Materials Development for 

Polycrystalline Thin-Film Solar 

Cells 

Light Spin 

Technologies 

Novel Polycrystalline Thin-Film 

Solar Cells 

3.0 PROJECT GOALS AND R&D FOCUS 

3.1 Goals 

To address HiPerf PV R&D long-term goals of 

bringing polycrystalline thin-film tandem cells 

(combining high-band gap and low-band gap singlejunctions) and modules toward 25% and 20% 

efficiencies, the project investigates a wide range of 

complex issues and provides initial modeling and 

baseline experiments of several advanced concepts. 

Recent work by Coutts et al. [3] modeling state-of-the-art 

thin-film devices has provided critical guidance for the 

project. A near-term milestone chart of the R&D thinfilm polycrystalline tandems is shown by year and will 

be described here (see Table II). Throughout the projects 

term, there will be opportunities to reach established 

program goals by both disruptive technology advances 

and/or multiple incremental improvements. 

Table II: Near-term Milestones, High-Performance PV 

Project, Polycrystalline Thin-Film Tandems 

Date 

2002 10%-Efficient, 1.5 <Egap<1.8 eV Cell 

(Completed) 

2003 

Compare Device Design in Terms of 

Monolithic/Mechanical Structure 

(Completed) 

2004 Assess Research on Exploring Pathways 

2005 12%-Efficient Polycrystalline 

Thin-Film Tandem 

2006 15%-Efficient PolycrystallineThin-Film 

Tandem 

Milestone 

3.2 R&D Focus 

The wide-bandgap top cell material of the tandem is 

critical; it is anticipated that two-thirds of the tandem cell 

efficiency originates here. Therefore, R&D is focused on 

a top cell, which is integrated with the bottom cell via an 

interconnect junction. Transmission through the top cell 

is a challenge, requiring an optical band-gap (Eg) in the 

range of 1.5<Eg<1.8 eV, and minimal sub-bandgap 

absorption. High-bandgap alloys based on I-III-VI2 and 

II-VI compounds and other novel materials for the top 

cell are being investigated. Low-bandgap CIS and its 

alloys, thin Si, and other novel approaches are being 

considered for the bottom cell. 

Integration of the thin-film interconnect with the top 

cell optically, electrically, and with an eye toward 

process compatibility is being investigated; this includes 

the role of defects and how they affect the transport 

properties of this junction, as well as diffusion of 

impurities into the bulk. Transparent conducting oxide’s 

(TCO) are able to form a one-sided p/n+ interconnect 

(shorting/tunneling junction) between the TCO and a 

non-degenerate p-type absorber [4], playing a strong role 

in the tandem cell. 

The design in terms of a monolithic or mechanical 

stack is primarily determined by the choice of the highbandgap top cell material. There are pros and cons to 

both approaches. For example, with the monolithic 

approach, only one thick TCO, one grid, and one antireflection coating (ARC) would be needed. However, 

current-matching and temperature-stability issues arise, 

as well as the necessity of a close thickness tolerance 

with the tunnel junction. Whereas the mechanical stack 

design may appear at first glance much simpler than the 

monolithic design, other issues are involved. For 

example, more materials (ARCs, TCOs, and glass) would 

be needed for the overall structure. Regardless of the 

designs, both structures are being pursued during the 

project. 

4.0 PROGRESS IN HIGH-BANDGAP MATERIALS 

Several high-bandgap top cell materials have been 

identified under the project, but they still need further 

exploration (see Table III). The table lists several 

materials that have been highly successful in terms of the 

operating parameters for the tandem structure. Several of 

the materials listed are described below. 

2 
The Polycrystalline Thin Film PV Group at NREL 

has demonstrated that a surface-modified CGS cell 

exhibits the following NREL-confirmed device operating 

parameters: Voc = 0.823 volts, Jsc = 18.61 mA/cm2

, fill 

factor = 66.8%, and total-area-efficiency = 10.2%. CGS 

is a candidate top cell absorber material for thin film 

tandem devices. Its bandgap is ideal at 1.68 eV. This 

particular device had a bandgap of 1.64 eV. Improving 

CGS device efficiency has proven to be a challenge over 

the past several years. The recent understanding of the 

differences in structural and electronic properties 

between CuIn(Ga)Se2 and CGS thin films and devices 

has led to varying the growth process in a way that is 

likely to make the CGS surface region similar to that of 

CI(G)S and to minimize defects in the material. 

This change led to a gain in the current density of about 

3.7 mA/cm2 versus the previous record cell. 

The University of Delaware, Institute of Energy 

Conversion (IEC) is investigating Cu(InGa)(SeS)2 films 

and Cd1-xZnxTe films of varying compositions and on 

specific substrates for the top cell of the tandem [5]. 

Recently Cu(InGa)(SeS)2 films were deposited as part of 

a set of experiments in which the relative concentrations 

of sulfur to selenium and gallium to indium were varied 

to give a fixed bandgap of 1.5 eV. The highest cell 

efficiencies in these experiments were achieved using 

absorber layers that contained no sulfur and with a 

relative gallium composition ratio of Ga/(In+Ga) = 0.75 

± 0.03. This corresponds to an optical bandgap of 1.5 ± 

0.03 eV. Solar cells were fabricated at IEC using the 

structure glass/ Mo/Cu(InGa)(SeS)2/CdS/ZnO/ITO with 

Ni-Al collection grids and total area, defined by 

mechanical scribes, of 0.47 – 0.51 cm2

. Current-voltage 

measurements were completed at NREL on devices from 

two different depositions. The best cell from one run had 

Table III: High-Bandgap structures and their operating 

parameters (NREL verified) 

efficiency = 10.9 % with VOC = 0.826 V, JSC = 20.4 

mA/cm2

, and fill factor = 64.5 %. From the other run, 

the best cell had efficiency = 10.9 % with VOC = 0.836 V, 

JSC = 20.4 mA/cm2

, and fill factor = 64. 

The Polycrystalline Thin Film PV Group at NREL 

modified CdS/CdTe devices to assist in early 

identification of limitations to high optical transparency 

of high-performance top cells [6]. Initial attempts have 

produced devices demonstrating ~9 % efficiency. First 

Solar material was used, and the devices were contacted 

with ZnTe:Cu/Ti. A project goal is to identify issues 

limiting Near-Infrared (NIR) optical transmission of the 

top device, spectrophotometry studies were initiated on 

similar transparent devices (i.e., incorporating ITO + 

metal grid contacts), as well as spectroscopic 

ellipsometry studies of component layers. Preliminary 

results from these studies have shown that the 9% 

efficiency cell can be maintained for cells with NIR 

transparency of ~25%. Although this result establishes a 

good initial baseline, it also indicates that NIR 

transmission must be improved considerably for highefficiency two-junction operation. Numerical modeling 

studies have shown that much of this NIR absorption can 

be ascribed to the specific type of TCO incorporated into 

the First Solar starting materials used in these studies. 

Recently, University of South Florida demonstrated 

an 80% transparent CdSe device (Figure 3). The CdSe 

was deposited on a transparent conductor and a ZnSe/Cu 

contact was added. The highest efficiency reported was 

17 mA/cm2

. This is believed to be a record for a thin-film 

solid-state CdSe device. The challenge for these materials 

will be to develop p-type window layer contacts with the 

requisite optical and electronic properties to qualify for 

use in transparent, high-bandgap II-VI devices. 

50% 

transmission 

Glass/CdSnO4/ZnSnO4 .776 24 68.21 12.7

/CdS/CdTe/CuTe (1.5 eV) 

NREL 

Glass/Mo/Cu(InGa)Se2/ .826 20.4 64.5 10.9

CdS / ZnO/ITO (1.5 eV) 

University of 

Delaware (IEC) 

Glass/Mo/CGS/CdS/ZnO .905 14.8 70.9 9.53

(1.68 eV) 

NREL 

First Solar CSS 

CdTe, 25% 

transmission 

Glass/SnO2/CdS/CdTe/Zn .785 17.5 64.9 8.93

Te:Cu 

(1.5 eV) 

NREL 

60%-70% 

transmission 

Glass/SnO2/CGS/CdS/ZnO .864 15.36 51.25 6.8

(1.68 eV) 

NREL 

.53 

66.8 

Fill 

Factor 

(%) 

14 

18.61 

Jsc(mA/ 

cm2) 

1.9 

10.2 

Efficiency 

(%) 

.250 

.823 

Voc 

(V) 

80% 

transmission 

University of Glass/TC/CdSe (1.7eV) 

South Florida 

Surface 

modified CGS 

Glass/Mo/CGS/CdS/ZnO 

(1.64 eV) 

NREL 

High Band-Gap Top Cell comments

Structure (eV) 

Organization 

50% 

transmission 

Glass/CdSnO4/ZnSnO4 .776 24 68.21 12.7

/CdS/CdTe/CuTe (1.5 eV) 

NREL 

Glass/Mo/Cu(InGa)Se2/ .826 20.4 64.5 10.9

CdS / ZnO/ITO (1.5 eV) 

University of 

Delaware (IEC) 

Glass/Mo/CGS/CdS/ZnO .905 14.8 70.9 9.53

(1.68 eV) 

NREL 

First Solar CSS 

CdTe, 25% 

transmission 

Glass/SnO2/CdS/CdTe/Zn .785 17.5 64.9 8.93

Te:Cu 

(1.5 eV) 

NREL 

60%-70% 

transmission 

Glass/SnO2/CGS/CdS/ZnO .864 15.36 51.25 6.8

(1.68 eV) 

NREL 

.53 

66.8 

Fill 

Factor 

(%) 

14 

18.61 

Jsc(mA/ 

cm2) 

1.9 

10.2 

Efficiency 

(%) 

.250 

.823 

Voc 

(V) 

80% 

transmission 

University of 

South Florida 

Surface 

modified CGS 

Glass/Mo/CGS/CdS/ZnO 

(1.64 eV) 

NREL 

High Band-Gap Top Cell comments

Structure (eV) 

Organization 

*Not NREL verified 

3 
0 

10 

20 

30 

40 

50 

60 

70 

80 

90 

100 

600 700 800 900 

Wavelength(nm) 

% Transmission 

Figure 3: University of South Florida device 

transparency for 2-micron glass/TC/CdSe 

5.0 PROGRESS IN TANDEM SOLAR CELLS 

Several polycrystalline thin-film tandem structures 

have been developed and demonstrated under the HiPerf 

project, but they still need further exploration (Table IV). 

The table lists several structures, both mechanical and 

monolithic designs, in terms of the operating parameters. 

Several of these novel devices will be described below. 

The NREL High-Performance Polycrystalline ThinFilm Tandem Group demonstrated a prototype monolithic 

tandem using Si and CdS/CuGaSe2 (CGS) as the bottom 

and top cell absorbers, respectively [6]. Figure 4 shows a 

schematic of the device. The bottom cell is an NRELgrown, crystalline Si cell, with a diffused Al back contact 

and a p/n+ junction. The CGS top cell was grown by 

elemental evaporation following the NREL-patented 3-

stage process. The interconnect junction consists of an n+ 

indium tin oxide layer on n+ c-Si, which had been shown 

earlier to produce a reasonably good transparent back 

contact to CGS[7]. The non-official measurement shows 

excellent voltage addition of about 1.3 V, a short circuit 

Table IV: Tandem structures and their parameters 

(NREL verified) 

current of 9 ma/cm2, and a fill factor of 43%, with an 

overall efficiency of about 5.1%. Witness CGS cells 

grown on Mo showed Voc of about 730 mV, despite the 

non-ideal Cu/Ga ratio of ~0.99. 

ZnO 

CdS 

CuGaSe2 

ITO 

n+ Si 

p Si 

Al 

Figure 4: Schematic of CGS, c-Si tandem 

Quantum efficiency results reveal that the top cell is still 

far from ideal. 

The NREL High-Performance Polycrystalline ThinFilm Tandem Group demonstrated a prototype 

mechanical stack tandem using CGS and CIS for the top 

cell absorber and bottom cell, respectively [7]. The CGS 

top cell was grown by elemental evaporationfollowing 

the NREL-patented 3-stage process. The transmission 

data are shown to be 70%-80% for SnO2 /CGS/CdS/ZnO 

device (Figure 5). This was a mechanical stack with an 

official NREL measurement of 9.7% efficiency and a 

Voc of 1.29 V with an AR coating. 

University of Toledo (UT) under a High-Performance 

PV subcontract, “Polycrystalline Thin-Film Tandem. 

Photovoltaic Cells,” demonstrated a two-terminal CdTeHgCdTe cell (Figure 6). The tandem cell was fabricated 

in the superstrate structure starting with a sputterdeposited top cell [SnO2:F/CdS/CdTe (1.8-2.0 μm)] with 

UT's standard processing and CdCl2 treatment condition 

P-type ZnTe:N and n-type ZnO: Al layers were used to 

Organization Tandem Structure Voc 

(V) 

Jsc 

(mA/cm 

2) 

Fill 

Factor 

(%) 

Effici 

ency 

(%) 

Comments 

NREL Top cell: glass/ SnO2//CGS/CdS/ZnO 

Bottom cell: glass/Mo/CIS/CdS/ZnO 

Mechanical stack 

.864 

.456 

1.29 

15.36 

12.46 

51.25 

69.17 

6.8 

3.9 

9.7 

4-terminal 

device 

University of 

Delaware 

(IEC)* 

NREL 

University of 

Toledo 

Monolithic structure: 

ZnO/ITO/CdS/Cu(InGa)Se2 

/ZnO/CdS/CIS/Mo/glass 

Monolithic structure: 

ZnO/CdS/CGS/ITO/n+Si/pSi/ Al 

Monolithic structure: 

SnO2:F/CdS/CdTe/ZnTe:N/ZnO:Al/CdS 

/HgCdTe 

.688 

1.32 

.960 

10.4 

9 

2 

52.8 

43 

62 

3.8 

5.1 

1.2 

*Not NREL verified 

4 
CdTe 

SnO 2 :F 

CdS 

ZnTe 

HgCdTe 

ZnO 

CdS 

Cu/Au 

glass 

2:F 

CdS 

2 

CdTe 

SnO 2 :F 

CdS 

ZnTe 

HgCdTe 

ZnO 

CdS 

Cu/Au 

glass 

2 :F 

CdS 

2

% Transmission 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

400 500 600 700 800 900 1000 1100 1200 1300 1400 

Wavelength (nm) 

CIS 

% T 

% A 

% R 

0.96 eV 

Figure 5: Transmission for SnO2/CGS/CdS/ZnO Device 

form a recombination junction [8,9]. The bottom cell, 

CdS/HgCdTe (1.2-1.5μm), was also sputter-deposited 

with a bandgap of HgCdTe of about 1.0-1.15 eV. A 

second CdCl2 treatment was given before finishing the 

cells with UT's standard evaporated Cu/Au back contact. 

glass 

SnO 2:F 

CdS 

CdTe 

ZnTe 

ZnO 

CdS 

HgCdTe 

Cu/Au 

Figure 6: Schematic of the University of Toledo 

SnO2:Fe/CdS/CdTe/ZnTe:N/ZnO:Al/CdS/HgCdTe 

Device 

Researchers from UT believe that better deposition 

control and the optimization of post-deposition treatment 

of HgCdTe films will lead to better cell performance for 

both single-junction HgCdTe cells and tandem cells. The 

cell area was 0.06 cm2

. The I-V measurement shows Voc 

of 960mV, and Jsc of 1.92 mA/cm2 and efficiency of 

1.2%. The QE characterization shows that the 

photocurrent was limited by the HgCdTe cell current due 

to the bandgap being too large. This is an excellent first 

demonstration of a two-terminal CdTe-HgCdTe. 

Georgia Institute of Technology, under a High 

Performance PV subcontract, is investigating the 

compatibility of c-Si-based bottom cells with CGS top 

cell materials. As a component of a thin-film tandem solar 

cell, the Si bottom cell is an excellent candidate for 

surviving the fabrication of the top cell. This will be 

demonstrated by fabricating monolithic tandem structures. 

To date, it has been found that the junction quality of the 

Si bottom cell remains intact after CIGS deposition. 

Cu(InGa)Se2

 reduces the long wavelength QE response 

of the Si cell, which is likely due to sub-bandgap 

absorption in the Cu(InGa)Se2

 film. 

6.0 CONCLUSIONS 

Phase IB, “Exploring and Accelerating Ultimate 

Pathways,” of the HiPerf PV Project is underway with inhouse and subcontracted research efforts in highperformance polycrystalline thin-film tandems. 

Our investigations have led to several wide-bandgap 

materials that are now world-record efficiencies. These 

high-bandgap materials are beginning to meet 

requirements in terms of Voc, Jsc and transmission for 

polycrystalline thin-film tandems. 

Both monolithic and mechanical tandems have been 

developed under the project, they are listed in Table IV. 

These devices used high band-gap alloys based on I-IIIVI2 and II-VI compounds. The developments under the 

High-Performance PV Project reported here are progress 

towards achieving long-term DOE-goals [1]. The project 

is focused to assure that tandem thin-film polycrystalline 

modules reach efficiency levels consistent with costcompetitive goals. 

7.0 ACKNOWLEDGEMENTS 

This work is supported under DOE Contract No. DEAC36-99GO10337 with NREL. Many people have 

contributed to the development and implementation of 

the High Performance PV project and to the R&D efforts 

carried out in this program. 

The author thanks the NREL High Performance 

Polycrystalline Thin-Film Tandem Group: Rommel 

Noufi, Tim Coutts, Anna Duda, David Young, Tim 

Gessert, Scott Ward, Miguel Contreras, Xianzhu Wu, 

Dave Albin, Tracy Berniard, Ramesh Dhere, Kannan 

Ramanathan, Fallah Hasoon, Jehad Abushami, Dean 

Levi, Sally Asher, Manuel Romero, Yanfa Yan. The 

author also thanks William Shafarman (IEC), Al 

Compaan (University of Toledo), and Don Morel 

(University of South Florida). 

8.0 REFERENCES 

[1] U.S. Photovoltaic Industry Roadmap, Chicago 

Illinois, Facilitated by the NCPV for the U.S. PV 

Industry, Prepared by Energetics, Incorporated 

(Columbia, Maryland), May, 2001, 32 pp., URL: 

www.nrel.gov/ncpv/pdfs/30150/pdf 

[2] E.D. Jackson, Rand Conf, Use of Solar Energy, p. 

122. Tuscon, Arizona (1955). 

[3] T. J. Coutts, S. Ward, D. Young, K. Emery, T. 

Gessert, and R. Noufi, Progress in Photovoltaics 

Research and Applications, 2003; 11-359-375. 

[4] D. L. Young, M. Contreras, M. Romero, S. Asher, C. 

Perkins, T. Gessert,J. Keane, T. Coutts, R. Noufi, 

International PVSEC-14, Bangkok, Thailand, 2004. 

5 
[5] M. Gossla and W. Shafarman, “Five source PVD for 

the deposition of Cu(In1-xGax)(Se1-ySy)2 absorber 

layers,” submitting to Thin Solid Films, 2004. 

[6] T. Gessert, T. Coutts, A. Duda, R. Dhere, S. Johnston, 

and D. Levi, NREL National Center for Photovoltaics 

and Solar Program Review Meeting, Denver, Colorado, 

2003. 

[7] David L. Young, James Keane, Anna Duda, Jehad A. 

M. AbuShama, Craig L. Perkins, Manuel Romero and 

Rommel Noufi, “Improved performance in 

ZnO/CdS/CuGaSe2 thin-film solar cells,” Progress in 

PV: Research and Applications, 2003; 11: 535-541. 

[8] S.H. Lee, A. Gupta, and A.D. Compaan, 

"Polycrystalline sputtered Cd(Zn,Mn)Te films for top 

cells in PV tandem structures," phys. stat. sol. (c), to be 

published (2004). 

[9] S.L. Wang, S.H. Lee, A. Gupta, and A.D. Compaan, 

"RF sputtered HgCdTe films for tandem cell 

applications," phys. stat. sol. (c), to be published (2004). 

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5c. PROGRAM ELEMENT NUMBER 

6. AUTHOR(S) 

M. Symko-Davies 

5d. PROJECT NUMBER 

NREL/CP-520-35174 

5e. TASK NUMBER 

PVP30100 

5f. WORK UNIT NUMBER 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 

8. PERFORMING ORGANIZATION 

REPORT NUMBER 

NREL/CP-520-35174 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S) 

NREL 

11. SPONSORING/MONITORING 

AGENCY REPORT NUMBER 

12. DISTRIBUTION AVAILABILITY STATEMENT 

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

13. SUPPLEMENTARY NOTES 

14. ABSTRACT (Maximum 200 Words) 

The High-Performance Photovoltaic (HiPerf PV) Project was initiated by the U.S. Department of Energy to 

substantially increase the viability of PV for cost-competitive applications. The goal is that PV will contribute 

significantly to the U.S. and world energy supply and environmental enhancement in the 21st century. The HiPerf PV 

Project aims at exploring the ultimate performance limits of existing PV technologies, approximately doubling their 

sunlight-to-electricity conversion efficiencies during its course, to accelerate and enhance their impact in the 

marketplace. To accomplish this, the National Center for Photovoltaics (NCPV) directs in-house and subcontracted 

research in high-performance polycrystalline thin-film and multijunction concentrator devices. This paper will 

describe progress of the subcontractor and in-house R&D on critical pathways for a PV technology having a high 

potential to reach cost-competitiveness goals: 25%-efficient, low-cost polycrystalline thin-film tandems for large-area, 

flat-plate modules. 

15. SUBJECT TERMS 

PV; polycrystalline; thin-film; high-efficiency 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION 

OF ABSTRACT 

UL 

18. NUMBER 

OF PAGES 

19a. NAME OF RESPONSIBLE PERSON 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified 

c. THIS PAGE 

Unclassified 19b. TELEPONE NUMBER (Include area code) 

Standard Form 298 (Rev. 8/98) Prescribed by ANSI Std. Z39.18 

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