Cation In Situ Exchange for Fabrication of CsSnI3 Perovskite Solar Cells

Inorganic CsSnI3 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 CsSnI3 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 CsSnI3 perovskite films with tin iodide (SnI2), cesium formate (CsFa), and dimethylammonium iodide (DMAI) as the precursors, where DMASnI3 first forms and then transforms into black CsSnI3 during the thermal annealing, followed by the removal of dimethylamine and formic acid. The prepared CsSnI3 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 SnI2 and CsI as precursors. Moreover, the target device exhibits improved stability in an N2 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.