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Photoconductive CdS: how does it Affect CdTe/CdS Solar Cell Performance?

Published online by Cambridge University Press:  01 February 2011

S. Hegedus ,
D. Ryan ,
K. Dobson ,
B. McCandless  and
D. Desai
S. Hegedus
Affiliation:
Institute of Energy Conversion, University of Delaware, Newark, DE 19716 USA
D. Ryan
Affiliation:
Institute of Energy Conversion, University of Delaware, Newark, DE 19716 USA
K. Dobson
Affiliation:
Institute of Energy Conversion, University of Delaware, Newark, DE 19716 USA
B. McCandless
Affiliation:
Institute of Energy Conversion, University of Delaware, Newark, DE 19716 USA
D. Desai
Affiliation:
Institute of Energy Conversion, University of Delaware, Newark, DE 19716 USA
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Abstract

Photoconductive CdS (PC-CdS) in CdS/CdTe solar cells from five different sources is investigated using spectral sensitization of apparent quantum efficiency (AQE) and J-V analysis. Red bias light significantly enhances the blue AQE, commonly leading to AQE>1 below 550 nm, and blue bias light enhances the red AQE, but to a much smaller extent. These enhancements are more pronounced with increasing forward bias, after stress and in devices with intentionally Cu-doped CdS. This behavior is observed to some degree in all devices with CdS, but is absent in cells without CdS. These effects are consistent with blue light, either ac monochromatic or dc bias, increasing the CdS conductivity. This causes an increase in the field and depletion width in the CdTe to maintain balanced space charge, leading to increased collection of carriers from the CdTe. The CdS conductivity modulation can also change the AQE due to a change in equivalent circuit resistance. Analysis of J-V data measured with white, blue, red or no light indicates little dependence of series resistance or diode quality factor on the illumination spectrum. Thus, the PC-CdS resistance has little effect on the solar cell J-V performance, but does influence AQE.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 763: Symposium B – Compound Semiconductor Photovoltaics , 2003 , B9.5
Copyright
Copyright © Materials Research Society 2003

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