Identification, characterization, and implications of shadow degradation in thin film solar cells

We describe a comprehensive study of intrinsic reliability issue arising from partial shadowing of photovoltaic panels (e.g., a leaf fallen on it, a nearby tree casting a shadow, etc.). This can cause the shaded cells to be reverse biased, causing dark current degradation. In this paper, (1) we calculate the statistical distribution of reverse bias stress arising from various shading configurations, (2) identify the components of dark current, and provide a scheme to isolate them, (3) characterize the effect of reverse stress on the dark current of a-Si:H p-i-n cells, and (4) finally, combine these features of degradation process with shadowing statistics, to project ‘shadow-degradation’ (SD) over the operating lifetime of solar cells. Our results establish shadow degradation as an important intrinsic reliability concern for thin film solar cell.