Solution Processing of Methylammonium Lead Iodide Perovskite from γ‑Butyrolactone: Crystallization Mediated by Solvation Equilibrium

The chemical origin of solvents typically used for preparation of hybrid lead halide perovskitesdimethyl sulfoxide (DMSO), dimethylformamide (DMF), and γ-butyrolactone (GBL)strongly influences the process of perovskite crystallization because of the formation of intermediate adducts with different structures and morphology. The composition and crystal structures of the adducts depend on the coordination and binding ability of the solvents and the ratio of the precursors. New adducts of perovskite and GBL with either an unusual cluster structure, (MA)<sub>8</sub>(GBL)<sub><i>x</i></sub>[Pb<sub>18</sub>I<sub>44</sub>], or an adduct, (MA)<sub>2</sub>(GBL)<sub>2</sub>Pb<sub>3</sub>I<sub>8</sub>, similar to those observed for DMF and DMSO are described for the first time. Complex equilibriums between chemical species existing in perovskite solutions are revealed by Raman spectroscopy. As a result, new features of the perovskite crystallization through intermediate adduct phases are discussed, and effective perovskite deposition pathways are suggested.