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Proceedings Paper

Accelerated stress testing and diagnostic analysis of degradation in CdTe solar cells
Author(s): David S. Albin
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Paper Abstract

Solar cell module reliability is inextricably linked to cell-level reliability. This is particularly so with thin-film technologies. In CdTe, reliability issues historically associate with back contact stability and the use of Cu as an extrinsic dopant. Using a simple approach by which identical cells are heated under open-circuit bias and 1-sun illumination, degradation activation energies of 0.63 and 2.94 eV in laboratory-scale CdS/CdTe devices were identified in the accelerated stress temperature range of 60 to 120 °C. At lower stress temperatures, cell performance changes were linearly correlated with changes in both fill factor (FF) and short-circuit current (Jsc). At higher stress temperatures, changes in efficiency were correlated with changes in FF and open-circuit voltage (Voc). The measured activation energy of 0.63 is associated with Cu-diffusion. During the early stage of stress testing, which may provide additional back contact annealing, improvements in FF were due to Cu-diffusion. Decreased performance observed at longer stress times (decreased FF and Voc), according to a two-diode Pspice model, were due to both increased space-charge recombination (near the junction) and decreased recombination in the bulk. Kirkendall void formation (S-outdiffusion) at the CdS/CdTe interface is given as responsible for the 2.9 eV degradation mechanism.

Paper Details

Date Published: 10 September 2008
PDF: 10 pages
Proc. SPIE 7048, Reliability of Photovoltaic Cells, Modules, Components, and Systems, 70480N (10 September 2008); doi: 10.1117/12.795360
Show Author Affiliations
David S. Albin, National Renewable Energy Lab. (United States)

Published in SPIE Proceedings Vol. 7048:
Reliability of Photovoltaic Cells, Modules, Components, and Systems
Neelkanth G. Dhere, Editor(s)

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