The Effect of Grain Size on the Stability of Perovskite Solar Cells

Perovskite solar cells are photovoltaic devices in which the active layer is a hybrid organic-inorganic semiconductor in a perovskite crystalline structure. Although the power conversion efficiency of perovskite cells can be up to 22.4%, their long-term stability is still compromised. In this project we studied the stability of samples and cells based on the perovskite compounds methylammonium lead iodide (MAPbI₃) and cesium/ formamidinium lead halides Cs_0.2FA_0.8Pb(I_0.6Br_0.4)­₃, prepared using the spray deposition technique at different conditions resulting in different grain sizes. The main hypothesis tested was the direct correlation between the stability of the solar cells and the perovskite grain size. The cells were exposed to concentrated sunlight, and their stability was characterized using current-voltage measurements and absorption spectroscopy. It was found that as the number of spray passes increases, the average grain size of both compositions increases, and that there is a correlation between the grain size and absorption degradation rate in CsFAPbIBr but not in MAPI, which was found to be more stable. However, no correlation was found between the degradation rate of the cell performance and the grain sizes, which may indicate that the degradation is related to other cell layers.