Interfacial Engineering for Controlled Crystal Mosaicity in Single‐Crystalline Perovskite Films

Abstract Organic–inorganic hybrid perovskites have attracted significant attention for optoelectronic applications due to their efficient photoconversion properties. However, grain boundaries and irregular crystal orientations in polycrystalline films remain issues. This study presents a method for producing crystalline‐orientation‐controlled perovskite single‐crystal films using retarded solvent evaporation. It is shown that single‐crystal films, grown via inverse temperature crystallization within a confined space, exhibit enhanced optoelectronic property. Using interfacial polymer layer, this method produces high‐quality perovskite single‐crystalline films with varying crystal orientations. Density functional theory calculations confirm favorable adsorption energies for (110) surfaces with methylammonium iodide and PbI₂ terminations on poly(3‐hexylthiophene), and stronger adsorption for (224) surfaces with I and methylammonium terminations on polystyrene, influenced by repulsive forces between the thiophene group and the perovskite surface. The correlation between charge transport characteristics and perovskite single‐crystalline properties highlights potential advancements in perovskite optoelectronics, improving device performance and reliability.