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

The classic solvent system can't sufficiently separate one‐dimensional edge‐sharing SnI 2 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 Sn 2+ to modulate solvation behaviours on perovskite precursor and regulate crystallization kinetics. The large molecular volume of HMPA and stronger bind energy of SnI 2 ⋅ 2HMPA (−0.595 eV vs −0.118 eV for SnI 2 ⋅ 2DMSO) change the solvation structure of SnI 2 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.