Impacts of Grain-Scale Disorder on Polycrystalline Solar Cells

As polycrystalline photovoltaic device efficiencies continue to rise, performance loss mechanisms must be further scrutinized. Conventional mechanisms, including recombination and poor carrier collection are important, but losses can also occur solely due to nonuniformity in optoelectronic properties, such as spatially varying band gap, doping, and lifetimes. The disorder effects act in parallel to the conventional mechanisms. Herein, a simulation approach is developed based on the finite element method that can predict the behavior of a solar cell with any spatial distribution of parameters that vary on a grain-to-grain basis. Open circuit voltage (Voc) loss calculations are found to be in accordance with analytical predictions that disorder-induced losses are directly proportional to the square of the standard deviation of the spatial distribution. This approach also enables model inputs based on spatially mapped characterization data instead of assuming a probability distribution. It can be extended to allow coupling of the electronic physics with thermal physics and time dependence.