In Situ Vapor‐Phase Halide Exchange of Patterned Perovskite Thin Films

Abstract Metal halide perovskites (MHPs) exhibit optoelectronic properties that are dependent on their ionic composition, and the feasible exploitation of these properties for device applications requires the ability to control the ionic composition integrated with the patterning process. Herein, the halide exchange process of MHP thin films directly combined with the patterning process via a vapor transport method is demonstrated. Specifically, the patterned arrays of CH ₃ NH ₃ PbBr ₃ (MAPbBr ₃ ) are obtained by stepwise conversion from polymer‐templated PbI ₂ thin films to CH ₃ NH ₃ PbI ₃ (MAPbI ₃ ), followed by halide exchange via precursor switching from CH ₃ NH ₃ I to CH ₃ NH ₃ Br. It is confirmed that the phase transformation from MAPbI ₃ patterns to MAPbBr ₃ shows time‐ and position‐dependences on the substrate during halide exchange following the solid‐solution model with Avrami kinetics. The photodetectors fabricated from the completely exchanged MAPbBr ₃ patterns display exceptional air stability and reversible detectivity from “apparent death” upon removing the adsorbed impurities, thereby suggesting the superior structural stability of perovskite patterns prepared through vapor‐phase halide exchange. The results demonstrate the potential of chemical vapor deposition patterning of MHP materials in multicomponent optoelectronic device systems.