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. The introduction of hexamethylphosphoramide (HMPA) changes the solvation structure of SnI2 from edge‐sharing cluster to monodisperse adduct and constructs a well‐dispersed Sn‐based precursor solution, which facilitates uniform distribution of nucleation sites and delays crystallization process, resulting in dense and uniform Sn‐based perovskite films over large area. Ultimately, HMPA‐incorporated device delivers a superior efficiency of 13.46 %.