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A Search for Degradation Mechanisms of CdTe/CdS Solar Cells

Published online by Cambridge University Press:  10 February 2011

P. V. Meyers ,
S. Asher  and
M. M Al-Jassim
P. V. Meyers
Affiliation:
Institute of Energy Conversion, University of Delaware, United States Department of Energy, University Center of Excellence for Photovoltaics Research and Education, Newark, DE 19716
S. Asher
Affiliation:
NREL, 1617 Cole Boulevard, Golden, CO 80401-3393
M. M Al-Jassim
Affiliation:
NREL, 1617 Cole Boulevard, Golden, CO 80401-3393
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Abstract

CdTe/CdS solar cells have demonstrated stability over thousands of hours of field testing, but have not yet established the same track record for reliability achieved by crystalline Si PV modules. In order to identify potential degradation mechanisms, this paper describes a series of experiments in which CdTe/CdS solar cells are subjected to combinations of temperature, voltage and illumination levels intended to stress the devices beyond levels which would be experienced in the field. During this process the devices display decreases in Voc and FF which are tentatively attributed to chemical changes at the low resistance contact to the CdTe and to changes in the electrical transport properties of the CdTe. Two thermally activated effects were observed depending upon stress bias. Reverse bias appears to degrade bulk CdTe electrical properties while forward bias strengthens a reverse diode which most likely is located at the back contact. Chemical analysis of the back contact region of the devices using XPS reveals strong oxide peaks in all stressed samples. Evidence of Cd diffusion into the Mo contacts is observed by SIMS and Auger. Mo diffusion into the CdTe is promoted by reverse bias stressing. Cu migration consistent with positively charged ions was indicated by SIMS.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 426: Symposium J – Thin Films for Photovoltaic and Related Device , 1996 , 317
Copyright
Copyright © Materials Research Society 1996

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