Mitigation of Halide Segregation by Cation Composition Management in Wide Bandgap Perovskites

Light-induced phase segregation poses challenges for the application of mixed-halide hybrid perovskites in photovoltaics, causing voltage deficits. Here, we investigate the role of chemical composition in improving the photostability of wide bandgap mixed-halide perovskites. We partially substituted the formamidinium cation in the composition of (Cs_0.17FA_0.83)Pb(Br_0.2I_0.8)₃ with seven alternative cations to achieve a slight blue shift in the bandgap, typically achieved by increasing bromide content. Among alternative cations, dimethylammonium (DMA) and acetamidinium (Ac) induced greater blue shifts at 10% concentration without forming a new low-dimensional second phase. Photoluminescence studies, which analyzed the halide segregation induced by high-power laser irradiation of all new compositions, revealed reduced phase segregation for DMA and Ac compositions. Further adjustments, e.g., increased cesium content, effectively compensated for the lower bromide content in the bandgap while enhancing light stability. Among all compositions, Cs_0.25FA_0.65DMA_0.1Pb(Br_0.2I_0.8)₃ exhibited enhanced photostability. These findings highlight the potential of structural modifications to produce highly stable compositions with the desired bandgap, paving the way for the development of stable perovskite solar cells.