The Effect of Methylammonium Iodide on the Supersaturation and Interfacial Energy of the Crystallization of Methylammonium Lead Triiodide Single Crystals

It is very important to study the crystallization of hybrid organic–inorganic perovskites because their thin films are usually prepared from solution. The investigation on the growth of perovskite films is however limited by their polycrystallinity. In this work, methylammonium lead triiodide single crystals grown from solutions with different methylammonium iodide (MAI):lead iodide (PbI₂) ratios were investigated. We observed a V‐shaped dependence of the crystallization onset temperature on the MAI:PbI₂ ratio. This is attributed to the MAI effects on the supersaturation of precursors and the interfacial energy of the crystal growth. At low MAI:PbI₂ ratio (<1.7), more MAI leads to the supersaturation of the precursors at lower temperature. At high MAI:PbI₂ ratio, the crystal growing plans change from (100)‐plane dominated to (001)‐plane dominated. The latter have higher interfacial energy than the former, leading to a higher crystallization onset temperature.