Clay DeHart

National Renewable Energy Laboratory

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Bobby To

National Renewable Energy Laboratory

R. Noufi

National Renewable Energy Laboratory

Ingrid Repins

National Renewable Energy Laboratory

T. A. Gessert

National Renewable Energy Laboratory

Darius Kuciauskas

National Renewable Energy Laboratory

Lorelle M. Mansfield

National Renewable Energy Laboratory

F. J. Pern

National Renewable Energy Laboratory

Carolyn Beall

National Renewable Energy Laboratory

Steve Johnston

National Renewable Energy Laboratory

Jian V. Li

United States Air Force Research Laboratory

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National Renewable Energy Laboratory

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Colorado School of Mines

Office of Scientific and Technical Information

National Technical Information Service

Colorado State University

Chinese Academy of Sciences

University of Toledo

Massachusetts Institute of Technology

University of Delaware

National Research Council Canada

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Reflection optimization for alternative thin-film photovoltaics

2012 IEEE 38th Photovoltaic Specialists Conference (PVSC) PART 2 (2013)

Jonathan Mann Jian Li Ingrid Repins K. Ramanathan Stephen Glynn

The recent improvements in efficiencies for kesterite (copper zinc tin selenide, CZTS) devices warrant an investigation into how the kesterite device stack can best be capped to minimize losses due to reflection. Additionally, ongoing efforts to replace the cadmium sulfide (CdS) layer in copper indium gallium selenide (CIGS)-based devices, most notably with zinc sulfide (ZnS), need to be accompanied by a similar investigation into how to best finish a CIGS/ZnS stack to minimize reflection losses. An optical analysis of how CZTS/CdS and CIGS/ZnS devices reflect light has been performed for the purpose of optimizing the transparent conducting oxide and antireflection layers for each stack. This research addresses what is similar and what is different between the alternative stacks and the routine CIGS/CdS stack and how to best reduce the reflection losses for each situation.

Kesterite

Cadmium sulfide

Reflection

Indium tin oxide

10.1109/pvsc-vol2.2013.6656758

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High-efficiency polycrystalline CdTe thin-film solar cells with an oxygenated amorphous cds (a-CdS:O) window layer

X. Wu R. G. Dhere Y. Yan I.J. Romero Y. Zhang

In the conventional CdS/CdTe device structure, the poly-CdS window layer has a bandgap of /spl sim/2.4 eV, which causes absorption in the short-wavelength region. Higher short-circuit current densities (J/sub sc/) can be achieved by reducing the CdS thickness, but this can adversely impact device open-circuit voltage (V/sub oc/) and fill factor (FF). Also, poly-CdS film has about 10% lattice mismatch related to the CdTe film, which limits the improvement of device V/sub oc/ and FF. In this paper, we report a novel window material: oxygenated amorphous CdS film (a-CdS:O) prepared at room temperature by rf sputtering. The a-CdS:O film has a higher optical bandgap (2.5-3.1 eV) than the poly-CdS film and an amorphous structure. The preliminary device results have demonstrated that J/sub sc/ of the CdTe device can be greatly improved while maintaining higher V/sub oc/ and FF. We have fabricated a CdTe cell demonstrating an NREL-confirmed J/sub sc/ of 25.85 mA/cm/sup 2/ and a total-area efficiency of 15.4%.

Cadmium telluride photovoltaics

Open-circuit voltage

10.1109/pvsc.2002.1190619

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Analysis of the Junction Properties of CdS/CdTe Devices in Substrate and Superstrate Configurations

World Conference on Photovoltaic Energy Conversion (2011)

R. G. Dhere Joel N. Duenow Clay DeHart J. V. Li Darius Kuciauskas

The best efficiency of CdS/CdTe devices fabricated in the substrate configuration reported to date is about 8%, which is about half the 17.3% reported for the conventional superstrate configuration. The performance of substrate devices is affected by lower open-circuit voltage (Voc), about 700 mV, and low fill factor (FF), which indicates that these devices are primarily limited by non-ideal junction properties and possibly by the ohmic contact to CdTe. In our study of the junction properties of superstrate devices, we show that lower-Voc devices ( 800 mV, the junction is between an n-type, Te-rich CdSTe alloy with a bandgap of 1.45 eV and p-type CdTe with a bandgap of 1.5 eV. Because the crystal structure of both the Te-rich alloy and the CdTe is cubic zinc blende, and the lattice mismatch between the two is minimal, the device in this case can be considered a quasi-homojunction. These higher-Voc devices are therefore affected less by the highmore » charged defect density at the hetero-interface, which lies outside of the depletion region. We present analysis of the junction properties of our recent and improved substrate-configuration devices with Voc well in excess of 800 mV, FF approaching 60%, and efficiencies around 10%. We also compare devices fabricated in both the substrate and superstrate configurations and with comparable Voc in the range of 700 to more than 800 mV. Photoluminescence (PL) and temperature-dependent PL, current density-voltage and quantum efficiency analysis, and modulated reflectance measurements are used to study device properties.« less

Homojunction

Cadmium telluride photovoltaics

Ohmic contact

Wide-bandgap semiconductor

Quantum Efficiency

10.4229/26theupvsec2011-3do.9.2

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Kesterite Successes, Ongoing Work, and Challenges: A Perspective From Vacuum Deposition

IEEE Journal of Photovoltaics (2012)

Ingrid Repins M.J. Romero Jian V. Li Su‐Huai Wei Darius Kuciauskas

Recent years have seen dramatic improvements in the performance of kesterite devices. The existence of devices of comparable performance, made by a number of different techniques, provides some new perspective on what characteristics are likely fundamental to the material. Here, we review progress in kesterite device fabrication, aspects of the film characteristics that have yet to be understood, and challenges in device development that remain for kesterites to contribute significantly to photovoltaic manufacturing. Performance goals, as well as characteristics of midgap defect density, free carrier density, surfaces, grain boundaries, grain-to-grain uniformity, and bandgap alloying are discussed.

Kesterite

Vacuum deposition

10.1109/jphotov.2012.2215842

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Citations (86)

All-laser scribing for thin-film CuInGaSe<inf>2</inf> solar cells

F. J. Pern Lorelle M. Mansfield Stephen Glynn Bobby To Clay DeHart

This paper describes the results from collaborative efforts in establishing an all-laser scribing technological capability for fabricating monolithically integrated CuInGaSe ₂ (CIGS) mini-modules. The scribing parameters required for each of the three scribing steps (P1, P2, P3) were determined and optimized by using three specific samples fabricated at NREL. A fiber laser system using a single wavelength at 1064 nm was employed for the scribing, which allowed fine control of programmable pulse shape and pulse train. In general, the three scribe lines were clean and smooth. For the first time, two mini-modules, with an effective area of ~7-cm × 7-cm having 10 cell strips in series connection, were fabricated by the "all-laser-scribing" technology. Small-beam localized quantum efficiency (QE) analysis showed large non-uniformity across the cell arrays. Performance-degrading factors were investigated by photoluminescence (PL) and electroluminescence (EL) analysis. By increasing the ZnO:Al (AZO) thickness and re-scribing with P3, the two reworked mini-modules showed substantial improvements in efficiency (best at 8.3%) with a decrease in series resistance and an increase in shunt resistance and fill factor.

10.1109/pvsc.2010.5614717

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Accelerated development of CuSbS 2 thin film photovoltaic device prototypes : Accelerated development of CuSbS 2 thin film photovoltaic device prototypes

Adam W. Welch Lauryn L. Baranowski Paweł Zawadzki Clay DeHart Steve Johnston

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Accelerated development of CuSbS2 thin film photovoltaic device prototypes

arXiv (Cornell University) (2015)

Adam W. Welch Lauryn L. Baranowski Paweł Zawadzki Clay DeHart Steve Johnston

Development of alternative thin film photovoltaic technologies is an important research topic due to the potential for low-cost, large-scale fabrication of high-efficiency solar cells. Despite the large number of promising alternative absorbers and corresponding contacts, the rate of progress is limited by complications that arise during solar cell fabrication. One potential solution to this problem is the high-throughput combinatorial method, which has been extensively used for research and development of individual absorber and contact materials. Here, we demonstrate an accelerated approach to development of thin film photovoltaic device prototypes based on the novel CuSbS2 absorber, using the device architecture employed for CuInxGa(1-x)Se2 (CIGS). The newly developed three-stage, self-regulated CuSbS2 growth process enables the study of PV device performance trends as a function of phase purity, crystallographic orientation, layer thickness of the absorber, and numerous back contacts. This exploration results in initial CuSbS2 device prototypes with ~1% conversion efficiency; currently limited by low short-circuit current due to poor collection of photoexcited electrons, and a small open-circuit voltage due to a cliff-type conduction band offset at the CuSbS2/CdS interface (suggested by first-principles calculations). Overall, these results illustrate the potential of combinatorial methods to accelerate the development of thin film photovoltaic devices with novel absorbers.

Open-circuit voltage

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Oxygen incorporation during fabrication of substrate CdTe photovoltaic devices

Joel N. Duenow R. G. Dhere Darius Kuciauskas Jian V. Li Joel Pankow

Recently, CdTe photovoltaic (PV) devices fabricated in the nonstandard substrate configuration have attracted increasing interest because of their potential compatibility with flexible substrates such as metal foils and polymer films. This compatibility could lead to the suitability of CdTe for roll-to-roll processing and building-integrated PV. Currently, however, the efficiencies of substrate CdTe devices reported in the literature are significantly lower (~6%-8%) than those of high-performance superstrate devices (~17%) because of significantly lower open-circuit voltage (V _oc ) and fill factor (FF). In our recent device development efforts, we have found that processing parameters required to fabricate high-efficiency substrate CdTe PV devices differ from those necessary for traditional superstrate CdTe devices. Here, we investigate how oxygen incorporation in the CdTe deposition, CdCl ₂ heat treatment, CdS deposition, and post-deposition heat treatment affect device characteristics through their effects on the junction. By adjusting whether oxygen is incorporated during these processing steps, we have achieved V _oc values greater than 860 mV and efficiencies greater than 10%.

Cadmium telluride photovoltaics

10.1109/pvsc.2012.6318264

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Differences between CuGa/In and Cu/Ga/In films for selenization

Christopher P. Muzzillo Lorelle M. Mansfield Clay DeHart Karen Bowers R. C. Reedy

CuGa/In and Cu/Ga/In metal precursor films were deposited by co-evaporation and selenized in situ. Differences were studied by XRF, GIXRD, SEM, EPMA, and SIMS for precursors, partially selenized, and completely selenized films. Solar cells were fabricated from completely selenized absorber films, and were characterized by JV and QE measurements. More intermixing of Cu and Ga was exhibited by CuGa/In, relative to Cu/Ga/In precursors. This caused a lower Ga/(Ga+In) composition near the surface, which led to higher current, lower voltage, and worse photovoltaic performance for CuGa/In. The difference in relative selenization kinetics of Ga and In were not responsible for the evolution of the contrasting Ga/(Ga+In) profiles.

10.1109/pvsc.2015.7356374

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Rapid fabrication of Cu(In,Ga)Se<inf>2</inf> thin films by the two-step selenization process

2012 IEEE 38th Photovoltaic Specialists Conference (PVSC) PART 2 (2013)

Shogo Ishizuka Lorelle M. Mansfield Clay DeHart Marty Scott Bobby To

Two-step processes currently used for the industrial Cu(In,Ga)Se 2 (CIGS) module production require a long process time of several hours for the CIGS absorber formation. In this paper, we are studying the reaction pathway to rapid selenization of stacked metal precursors in elemental Se vapor. The objective is to understand the reaction kinetics to find the best precursor structure and the optimal selenization conditions to form high-quality CIGS films with proper Ga depth profiles. In addition to stacked metal precursors, the effect of the use of Se-containing precursors was also examined. As expected, the stacking order of themetal precursors influences the properties of the resultingCIGS absorbers. The Cu amount deposited for the precursor formation critically affected the final film and cell properties, as well.We also found that the formation of CIGS films with large grain sizes and flat Ga depth profiles was possible even for [Cu]/([In] + [Ga]) < 1 conditions with the use of particular precursor structures and selenization conditions. The results suggest that the selenization reaction pathway can be dictated with the precursor structure, and further improvements are expected by controlling reaction kinetics with precursor structure modification.

10.1109/pvsc-vol2.2013.6656749

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