Universality of non-Ohmic shunt leakage in thin-film solar cells

Abstract

Universality of non-Ohmic shunt leakage in thin-film solar cells" We compare the dark current-voltage ͑IV͒ characteristics of three different thin-film solar cell types: hydrogenated amorphous silicon ͑a-Si:H͒ p-in cells, organic bulk heterojunction ͑BHJ͒ cells, and Cu͑In, Ga͒Se 2 ͑CIGS͒ cells. All three device types exhibit a significant shunt leakage current at low forward bias ͑V Ͻ ϳ 0.4͒ and reverse bias, which cannot be explained by the classical solar cell diode model. This parasitic shunt current exhibits non-Ohmic behavior, as opposed to the traditional constant shunt resistance model for photovoltaics. We show here that this shunt leakage ͑I sh ͒, across all three solar cell types considered, is characterized by the following common phenomenological features: ͑a͒ voltage symmetry about V =0, ͑b͒ nonlinear ͑power law͒ voltage dependence, and ͑c͒ extremely weak temperature dependence. Based on this analysis, we provide a simple method of subtracting this shunt current component from the measured data and discuss its implications on dark IV parameter extraction. We propose a space charge limited ͑SCL͒ current model for capturing all these features of the shunt leakage in a consistent framework and discuss possible physical origin of the parasitic paths responsible for this shunt current mechanism.

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