Size dependent nonuniformity loss in thin film photovoltaics

We develop one- and two-dimensional PSPICE models of nonuniform thin-film photovoltaic (PV) cells and study the effects of lateral variations in device photovoltage on major integral PV parameters. These effects turn out to be size dependent with amplitude that decreases with cell series resistance. Fill factor is found to suffer the strongest nonuniformity loss most tightly correlated with efficiency; however, the effects of Voc and Jsc loss are significant as well. The observed size dependencies suggest a way of experimentally verifying the predicted effects, in particular, discriminating between them and the alternative 'field-dependent collection' explanation of the fill factor and efficiency loss. This discrimination is important, as leading to considerably different technological remedies.