Suppressed Defects and Improved Stability of All‐Inorganic CsSnI ₃ Films by Solid Additive‐Assisted Chemical Vapor Deposition Process

All-inorganic Sn-based halide perovskite CsSnI₃ is a promising candidate for perovskite solar cells (PSCs) owing to its narrower bandgap (≈1.3 eV) and lower toxicity as compared with traditional organic-inorganic hybrid Pb-based counterparts. However, CsSnI₃ rapidly degrades in ambient air and simultaneously generates intrinsic defect states, thus seriously impairing the optoelectronic property of the film, as well as the corresponding device performance. Herein, a solid additive-assisted chemical vapor deposition (SACVD) method is reported to prepare CsSnI₃ films with high quality. Combining with theoretical calculations, Fourier transform infrared spectroscopy, temperature-dependent photoluminescence, and scanning Kelvin probe techniques prove that the lone electron pairs in the solid additive form coordination interactions with Sn²⁺, resulting in the suppression of Sn²⁺ oxidizing to Sn⁴⁺ and thus reducing defect density. This work not only provides a new strategy to prepare eco-friendly and stability-improved tin halide perovskite thin films for PSCs, but also reveals the underlying physical properties of CsSnI₃ film upon solid state modification (i.e., without any organic solvent).