A Cation‐Exchange Approach for the Fabrication of Efficient Methylammonium Tin Iodide Perovskite Solar Cells

Tin-based halide perovskite materials have been successfully employed in lead-free perovskite solar cells, but the overall power conversion efficiencies (PCEs) have been limited by the high carrier concentration from the facile oxidation of Sn²⁺ to Sn⁴⁺ . Now a chemical route is developed for fabrication of high-quality methylammonium tin iodide perovskite (MASnI₃ ) films: hydrazinium tin iodide (HASnI₃ ) perovskite film is first solution-deposited using presursors hydrazinium iodide (HAI) and tin iodide (SnI₂ ), and then transformed into MASnI₃ via a cation displacement approach. With the two-step process, a dense and uniform MASnI₃ film is obtained with large grain sizes and high crystallization. Detrimental oxidation is suppressed by the hydrazine released from the film during the transformation. With the MASnI₃ as light harvester, mesoporous perovskite solar cells were prepared, and a maximum power conversion efficiency (PCE) of 7.13 % is delivered with good reproducibility.