Epitaxial Growth of Lattice‐Matched BaWO₄/CH₃NH₃PbX₃ (X = Cl, Br, I) Hetero‐Micro/Nanostructure with Suppressed Halide Ion Migration

Abstract Intrinsic instability of lead halide perovskites has always been a key obstacle to manifest their excellent optoelectronic applications. Here, a solvent‐free thermally driven heteroepitaxial growth strategy is proposed to assemble BaWO 4 /MAPbX 3 (MA = CH 3 NH 3 + ; X = Cl − , Br − , or I − ) micro‐nanostructure. Tetragonal BaWO 4 matrix restrains the halogen ion migration in epitaxial MAPbX 3 thanks to their perfect lattice matching degrees, also imparting the integration of exceptional durability to light, heat, polarity solvents, and capabilities to fine‐tune the luminescent colors. Furthermore, MABr‐triggered surface nucleation of MAPbBr 3 and its removal by H 2 O appear with switchable and reversible color changes, demonstrating great potential in advanced anticounterfeiting. The general approach in engineering heteroepitaxy of MAPbX 3 heterostructure opens up a new idea toward improved stability by the lattice matching principle.