Organo-Metal Halide Perovskites Films and Methods of Making the Same

An aspect of the present disclosure is a method that includes applying a solution that includes a first solvent, a halogen ­containing precursor, and a metal halide to a substrate to form a coating of the solution on the substrate, contacting the coating with a second solvent to form a first plurality of organo-metal halide perovskite crystals on the substrate, and thermally treating the first plurality of organo-metal halide perovskite crystals, such that at least a portion of the first plurality of organo-metal halide perovskite crystals is con­verted to a second plurality of organo-metal halide perovskite crystals on the substrate. The halogen-containing pre­cursor and the metal halide are present in the solution at a molar ratio of the halogen-containing precursor to the metal halide between about 1.01: 1.0 and about 2.0: 1.0, and a property of the second plurality of organo-metal halide perovskite crystals is improved relative to a property of the first plurality of organo-metal halide perovskite crystals.