Impact of local non-uniformities on thin-film PV

Individual shunts and "weak diodes" can have a significant effect, one much larger than implied by their physical area, on the performance of laboratory-sized (~ 1cm2) solar cells. For larger areas typical of thin-film modules, the sheet resistance of the transparent contact minimizes the impact of a single, small-area non-uniformity. If there are significant numbers of shunts or weak diodes throughout a module, however, its performance may also be reduced. In this case, the number, the magnitude, the nature, and the distribution of the non-uniformities combine to affect the degree of reduction. In particular, a concentration of most shunts or weak diodes in a small number of module cells will be less destructive than if they are distributed among a greater number of cells. In the case of non-uniform illumination, however, module performance is less degraded if the shadowing is spread relatively uniformly over all or most of the cells.