Cation substitution enables the complete conversion of 1D perovskites to 3D perovskites for photovoltaic application.

More versatile and effective strategies are needed to prepare high-quality perovskites and their precursors for promoting the efficiency of perovskite solar cells (PSCs). Herein, the strategy of amine (CH3NH2, MA) gas treatment is successfully exploited to synthesize high-quality MAI precursors and MAPbI3 perovskites. During MA gas treatment, ethylammonium (EA) cations in EAI are completely substituted with the MA cations from MA gas to generate pure MAI. Furthermore, cation substitution induced by MA gas treatment is further extended to convert 1D EAPbI3 perovskites to 3D MAPbI3 perovskites. Compared with traditional perovskites, 1D-to-3D perovskites show a much smoother surface and lower defect density. Consequently, the performance and stability of carbon-based PSCs without hole transport materials are considerably enhanced. Therefore, amine gas treatment has been proved to be a versatile and promising strategy for preparing high-quality perovskites and their precursors.