Local Shunting in Multicrystalline Silicon Solar Cells: Distributed Electrical Simulations and Experiments

In this paper, we analyze the effect of local shunts in photovoltaic (PV) solar cells by experimental characterization and distributed electrical simulations. To this purpose, we developed a quasi-3-D distributed electrical network that is based on two-diode circuit elementary units. It allows accounting for resistive losses associated to the transport through the emitter, the fingers and the busbars, and to local defects in the semiconductor. The electrical parameters of the equivalent circuit units are calibrated according to experiments performed on multicrystalline (mc-Si) silicon solar cells, including samples that feature local shunts due to localized defects, which lead to nonuniform distribution of electrical and optical properties. The distributed electrical simulations account for the degradation of fill factor and power conversion efficiency in case of local shunting. Moreover, by combining the proposed tool with a RC thermal network it is possible to estimate the temperature distribution in a shunted solar cell. Our analysis shows how a shunted cell that operates under hot-spot conditions is subject to significant local overheating, which possibly lead to permanent PV cell damages.