Rapid growth of high quality perovskite crystal by solvent mixing

High quality polycrystalline CH3NH3PbI3 was prepared by dripping the gamma-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 mu m 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 mu m 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.