Abstract: A method of forming single crystal perovskite according to an exemplary embodiment of the present invention includes: forming a preliminary thin film by applying a perovskite precursor solution containing an additive on a substrate; exposing the preliminary thin film to a vacuum state by transferring the preliminary thin film to a vacuum chamber; and switching an internal pressure of the vacuum chamber to an atmospheric pressure, wherein the additive includes a substituted or unsubstituted C1 to C30 aliphatic ammonium salt, a substituted or unsubstituted C6 to C30 aromatic ammonium salt, a substituted or unsubstituted C1 to C30 aliphatic amine salt, a substituted or unsubstituted C6 to C30 aromatic amine salt, or a combination thereof.