Low-light divergence in photovoltaic parameter fluctuations

We study statistics of the major photovoltaic (PV) parameters, such as open-circuit voltage, short-circuit current, etc., versus light intensity on a set of nominally identical thin-film CdTe/CdS solar cells. A crossover light intensity is found, below which the relative fluctuations of the PV parameters diverge inversely proportional to the square root of the light intensity. We propose a model in which the observed fluctuations are due to lateral nonuniformities in the device structure. The crossover is attributed to the lateral nonuniformity screening length exceeding the device size. From the practical standpoint, our study introduces a simple uniformity diagnostic technique.