Efficiency Enhancement and Hysteresis Mitigation by Manipulation of Grain Growth Conditions in Hybrid Evaporated-Spin-Coated Perovskite Solar Cells
Perovskite solar cells have become a game changer in the field of photovoltaics by reaching power conversion efficiencies beyond 23%. To achieve even higher efficiencies, it is necessary to increase the understanding of crystallization, grain formation, and layer ripening. In this study, by a systematic variation of methylammonium iodide (MAI) concentrations, we changed the stoichiometry and thereupon the crystal growth conditions in MAPbI3 perovskite solar cells, prepared by a two-step hybrid evaporation-spin-coating deposition method. Utilizing X-ray diffraction, scanning electron microscopy, atomic force microscopy, photoluminescence, and current-voltage (J-V) characterization, we found that a relatively lower concentration of MAI, or in other words higher content of remnant and unconverted PbI2, correlates with smaller and stronger interconnected grains, as well as with an improved optoelectronic performance of the solar cells and mitigation of hysteresis. The possible explanations are grain and interface passivation by the excess PbI2 and a positive contribution of the grain boundaries to current extraction.