Light-enhanced reverse breakdown in Cu(In,Ga)Se2 solar cells

Abstract

Partial shading of solar modules can subject shaded cells to significant reverse bias, often large enough to force them into electrical breakdown, possibly resulting in irreversible damage. Therefore, better understanding of reverse current–voltage characteristics might lead to improvements in the design of solar modules. The focus of this study is the breakdown behavior of Cu(In,Ga)Se2 (CIGS) cells in darkness and under illumination. Two series of CIGS cells were investigated, with CdS and Zn–Sn–O buffer layers of varying thickness. Electrical breakdown was found to be highly dependent on the buffer layer. Under blue illumination a remarkable decrease in breakdown voltage was observed for both buffer types. Metastable defects in the buffer/CIGS interface region are tentatively proposed as the source of this effect and tunnelling is suggested as the main mechanism responsible for breakdowns.