Elucidating the Key Role of a Lewis Base Solvent in the Formation of Perovskite Films Fabricated from the Lewis Adduct Approach

High-quality perovskite films can be fabricated from Lewis acid–base adducts through molecule exchange. Substantial work is needed to fully understand the formation mechanism of the perovskite films, which helps to further improve their quality. Here, we study the formation of CH 3 NH 3 PbI 3 perovskite films by introducing some dimethylacetamide into the PbI 2 / N, N -dimethylformamide solution. We reveal that there are three key processes during the formation of perovskite films through the Lewis acid–base adduct approach: molecule intercalation of solvent into the PbI 2 lattice, molecule exchange between the solvent and CH 3 NH 3 I, and dissolution–recrystallization of the perovskite grains during annealing. The Lewis base solvents play multiple functions in the above processes. The properties of the solvent, including Lewis basicity and boiling point, play key roles in forming smooth perovskite films with large grains. We also provide some rules for choosing Lewis base additives to prepare high-quality perovskite films through the Lewis adduct approach.