Monodisperse Adducts-Induced Homogeneous Nucleation Towards High-Quality Tin-Based Perovskite Film

The classic solvent system can't sufficiently separate one-dimensional edge-sharing SnI₂ crystals in solution, which severely restricts the fabrication of high-quality tin-based perovskite film. Herein, a strong Lewis base (hexamethylphosphoramide, HMPA) has been introduced to coordinate Sn²⁺ to modulate solvation behaviours on perovskite precursor and regulate crystallization kinetics. The large molecular volume of HMPA and stronger bind energy of SnI₂  ⋅ 2HMPA (-0.595 eV vs -0.118 eV for SnI₂  ⋅ 2DMSO) change the solvation structure of SnI₂ from edge-sharing cluster to monodisperse adduct, which contributes to uniform nucleation sites and prolongs crystal growth process. Delightfully, a fully-covered perovskite film is formed on the large-area substrate and tin-based perovskite solar cells processed with HMPA exhibit an excellent efficiency of 13.46 %. This research provides novel insights and directions for the solution preparation of smooth and uniform large-area tin-based perovskite film.