Inorganic\nCsSnI<sub>3</sub> Perovskite Solar Cells\nwith an Efficiency above 13.6%

Due to the high Lewis acidity of Sn<sup>2+</sup>, it\nis a major\nchallenge to prepare high-quality CsSnI<sub>3</sub> films. To solve\nthis critical problem, here we propose a pseudohalide anion alloying\nprocess to regulate the crystallization of inorganic CsSnI<sub>3</sub> perovskite and achieve large grain sizes in the micron range. The\nintroduction of a pseudohalide anion changes the phase transition\npathways through the formation of intermediates, thereby slowing the\nrate of CsSnI<sub>3</sub> crystallization. The substitutional alloying\nof HCOO<sup>–</sup> in the CsSnI<sub>3</sub> crystal lattice\nfurther improves the oxidation resistance of Sn<sup>2+</sup> due to\nthe strong bonding between the HCOO<sup>–</sup> anions and\nSn<sup>2+</sup> cations. The fabricated CsSnI<sub>3</sub>-based planar\nperovskite solar cell with an inverted configuration and active area\nof 4.05 mm<sup>2</sup> exhibits certified power conversion efficiency\nof 13.68% at AM 1.5 solar irradiation (100 mW cm<sup>–2</sup>), which is among the best reported for CsSnI<sub>3</sub>-based inorganic\nperovskite cells.