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Title:
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Identifying parasitic current pathways in CIGS solar cells by modelling dark J-V response
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Author(s):
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Williams, B.L.; Smit, S.; Kniknie, B.J.; Bakker, N.J.; Keuning, W.; Kessels, W.M.M.; Schropp, R.E.I.; Creatore, M.
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Published by:
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Publication date:
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ECN
Solar Energy
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9-1-2015
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ECN report number:
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Document type:
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ECN-W--15-003
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Article (scientific)
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Number of pages:
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10
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Published in: Progress in Photovoltaics: Research and Applications (John Wiley & Sons Ltd.), , 2015, Vol.online, p.-.
Abstract:
The non-uniform presence of shunting defects is a signi?cant cause of poor reproducibility across large-area solar cells, or from batch-to-batch for small area cells, but the most commonly used value for shunt parameterisation (the shunt resistance) fails to identify the cause for shunting. Here, the use of equivalent circuit models to describe dark current–voltage characteristics of ZnO:Al/i-ZnO/CdS/CIGS/Mo devices in order to understand shunting behaviour is evaluated. Simple models, with a single shunt pathway, were tested but failed to ?t experimental data, whereas a more sophisticated model developed here, which includes three shunting pathways, yielded excellent agreement throughout the temperature range of 183–323 K. The temperature dependence of ?tting parameters is consistent with known physical models. Activation energies and contact barriers are determined from the model, and extracted diode factors are unique across the voltage range. A case study is presented whereby the model is used to diagnose poor reproducibility for CIGS devices (ef?ciency ~3–14% across a 100 cm2 plate). It’s shown that lower ef?ciencies correlated with greater prevalence of Ohmic and non-Ohmic shunt currents, which may form due to pinholes in absorber and buffer layers respectively, whereas the quality of the main junction was constant for all cells (diode factor ~1.5–2). Electron microscopy con?rmed the presence of ZnO:Al/i-ZnO/Mo and ZnO:Al/CIGS/Mo regions, supporting the multi-shunt pathway scheme disclosed by modelling. While the model is tested with CIGS cells here, this general model is a powerful diagnostic tool for process
development for any type of thin-?lm device.
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