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Quantum Efficiency Measurements to Deduce Non-Ideal Solar-Cell Features

Published online by Cambridge University Press:  01 February 2011

Timothy J. Nagle ,
Alan R. Davies  and
James R. Sites
Timothy J. Nagle
Affiliation:
tjnagle@lamar.colostate.edu, Colorado State University, Physics, 1875 Campus Delivery, Fort Collins, CO, 80523-1875, United States, 970-491-1105, 970-491-7947
Alan R. Davies
Affiliation:
daviesar@lamar.colostate.edu, Colorado State University, Department of Physics, Fort Collins, CO, 80523, United States
James R. Sites
Affiliation:
sites@lamar.colostate.edu, Colorado State University, Department of Physics, Fort Collins, CO, 80523, United States
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Abstract

Appropriate interpretation of quantum-efficiency (QE) measurements made on non-ideal solar cells often reveal subtle features of the photodiodes. QE measurements on CIGS and CdTe thin-film solar cells with CdS buffer layers demonstrate some of these features, and in each case we identify the electrical processes responsible. One well-known complication in cells with CdS buffer layers is “photodoping”, where blue light exposure increases the n-type CdS carrier density. The resulting modification of the p-n junction alters the carrier collection for all wavelengths and can lead to misinterpretation of results. The use of a white, DC-bias light during QE measurements generally solves this problem, but it has not been clear what bias light level is sufficient for accurate results. Measurements with varying intensities of DC-bias light show that complications due to CdS photoconductivity are generally mitigated near 0.05 sun intensity. Other factors which can cause misinterpretation of QE measurements include the presence of secondary barriers, and photoconductivity in the absorber layer. Numerical simulations of band profiles under various light-bias conditions are consistent with the experimental data. The analysis is used to suggest a standard set of measurement conditions for reliable QE analysis.

Keywords

photovoltaicthin filmII-VI
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1012: Symposium Y – Thin-Film Compound Semiconductor Photovoltaics-2007 , 2007 , 1012-Y12-03
Copyright
Copyright © Materials Research Society 2007

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