Reverse Stress Metastability of Shunt Current in CIGS Solar Cells

Abstract — Partial shading in thin film solar panels can result in reverse bias stress across shaded cells. Therefore, it is important to understand the effect of such reverse stress in commercially competitive PV technologies such as CIGS. In this paper, we systematically investigate the effect of moderate reverse bias on solution-processed CIGS solar cells. We subject the solar cells to varying degrees of reverse biases and continuously monitor the impact of the stress on dark current. We also explore the relaxation behavior of dark current following passive storage and the long term effect of the shadow stress on power output of the cell. We find that the reverse stress affects only the localized shunt current paths, without affecting the bulk device characteristics. The shunt current exhibits a metastable change with reverse stress, and can increase or decrease on application of reverse stress. We analyze this phenomenon in detail, and discuss the hypothesis that can explain its characteristic features. Index Terms — semiconductor device breakdown, photovoltaic cells, shunt, CIGS. I