Cation In Situ Exchange for Fabrication of CsSnI3 Perovskite Solar Cells

Abstract Inorganic CsSnI 3 perovskite solar cells (PSCs) have attracted increasing research interest owing to their excellent optoelectronic properties and thermal stability. However, it is a great challenge to fabricate high‐quality CsSnI 3 films with low defect density due to the quick crystallization growth rate and high content of Sn (II)‐related defects. Here, a cation in situ exchange strategy is employed for the fabrication of CsSnI 3 perovskite films with tin iodide (SnI 2 ), cesium formate (CsFa), and dimethylammonium iodide (DMAI) as the precursors, where DMASnI 3 first forms and then transforms into black CsSnI 3 during the thermal annealing, followed by the removal of dimethylamine and formic acid. The prepared CsSnI 3 film exhibits high coverage and improved crystallinity with low defects, and the resultant PSC achieves a power conversion efficiency (PCE) of 12.62%, greater than the value (6.82%) for the traditional device with SnI 2 and CsI as precursors. Moreover, the target device exhibits improved stability in an N 2 environment, maintaining over 85% of its initial power conversion efficiency after 30 days. This cation exchange strategy paves the way to the realization of Sn‐based halide perovskite solar cells with high performance and stability.