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Impact of Nonuniformities on Thin Cu(In,Ga)Se2 Solar Cell Performance

Published online by Cambridge University Press:  01 February 2011

Ana Kanevce  and
James R. Sites
Ana Kanevce
Affiliation:
[email protected], Colorado State University, Physics, Physics Department, Colorado State University, Fort Collins, CO, 80523, United States, (970) 491-6072, (970) 491-7947
James R. Sites
Affiliation:
[email protected], Colorado State University, Physics Department, Fort Collins, CO, 80523, United States
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Abstract

Solar-cell performance degradation due to physical nonuniformities becomes more significant as the thickness of polycrystalline absorbers is reduced. “Voltage” nonuniformities such as those due to band-gap fluctuations, variations in the back-contact proximity, and areas where the absorber is completely depleted can have very significant impact on cell performance. Similarly local shunts can seriously degrade the efficiency. “Current” nonuniformities such as optical defects have generally much less impact. The analysis presented is based on Cu(In,Ga)Se2 cells, but the qualitative results should be applicable to thin-absorber devices in general. For lateral nonuniformity studies, the solar cell is simulated by a two dimensional network of parallel diodes separated by resistors. The nonuniformities are approximated by small regions of reduced photovoltage, often referred to as “weak diodes”, and by isolated shunt resistors. The weak-diode approach allows investigation of device performance as a function of the weak-diode voltage deficit, the ratio of weak-to strong-diode area, and the weak diodes' spatial distribution. Increased TCO resistance can isolate weak diodes, thus limiting the voltage loss due to nonuniformities, but increasing fill-factor losses.

Keywords

photovoltaicsimulationelectrical properties
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1012: Symposium Y – Thin-Film Compound Semiconductor Photovoltaics-2007 , 2007 , 1012-Y08-02
Copyright
Copyright © Materials Research Society 2007

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