Rapid growth of high quality perovskite crystal by solvent mixing

Abstract

High quality polycrystalline CH₃NH₃PbI₃ was prepared by dripping the γ-butyrolactone (GBL) solution of CH₃NH₃PbI₃ into toluene, dimethylformamide (DMF) and dimethylsilicone oil. In toluene, a compact CH₃NH₃PbI₃ thin film was observed but with grain size smaller than 1 μm because of the rapid extraction of GBL. As CH₃NH₃PbI₃ is soluble in DMF, the crystallization in DMF is understood by interdiffusion induced local and temporal supersaturated droplets, which allow for growth of irregular, separated single crystals with size of more than 0.1 mm. In dimethylsilicone oil, compact, yolk-like polycrystalline CH₃NH₃PbI₃ was observed. Unlike the round grains observed in toluene, it is composed of single crystal grains with clear angular surfaces. The average crystal size is tens of μm and can be modulated by the solvent temperature. We suggest that the poor miscibility between GBL and dimethylsilicone oil, and the poor solubility of CH₃NH₃I, PbI₂ and CH₃NH₃PbI₃ in the dimethylsilicone oil, allow slow extraction of GBL while keeping the stoichiometry of CH₃NH₃PbI₃. The results offer a feasible and high-yielding method for growing uniform CH₃NH₃PbI₃ crystals in a few seconds.