Hybrid perovskite crystallization from binary solvent mixtures: interplay of evaporation rate and binding strength of solvents

In this work, we rationalize the chemical pathways and kinetics of the crystallization of methylammonium lead iodide hybrid perovskite. Our approach includes a combination of analysis of solvent coordination, the structure of intermediate solvate phases, and modeling evaporation rates of precursor solutions. The evolution of solution species via intermediate solvate phases and into perovskite thin films during drying was monitored by in situ grazing-incidence wide-angle X-ray scattering (GIWAXS). All studied precursor solutions exhibited the formation of intermediate solvate phases including a previously unreported GBL phase. In single-solvent solutions, crystallization kinetics are determined by the solvent evaporation rate and saturation concentration required for nucleation. In binary solvent mixtures, the evaporation rate of solutions is dominated by the most volatile solvent which leads to unequal evaporation of the components of the mixture. The structure of the intermediate phases in such systems strongly depends on the coordination strength and the availability of solvents upon nucleation. The combined approach described in this work allows predicting the kinetics and the chemical pathways of crystallization of hybrid perovskites in complex solvent mixtures. This insight is of great importance for future perovskite ink design.