Solid‐State Anion Exchange Enabled by Pluggable vdW Assembly for In Situ Halide Manipulation in Perovskite Monocrystalline Film

Abstract The fabrication of perovskite single crystal‐based optoelectronics with improved performance is largely hindered by limited processing techniques. Particularly, the local halide composition manipulation, which dominates the bandgap and thus the formation of heterostructures and emission of multiple‐wavelength light, is realized via prevalent liquid‐ or gas‐phase anion exchange with the utilization of lithography, while the monocrystalline nature is sacrificed due to polycrystalline transition in exchange with massive defects emerging, impeding carrier separation and transportation. Thus, a damage‐free and lithography‐free solid‐state anion exchange strategy, aiming at in situ halide manipulation in perovskite monocrystalline film, is developed. Typically, CsPbCl₃ working as medium to deliver halide is van der Waals (vdW) assembled to specific spots of CsPbBr_3, followed by the removal of CsPbCl₃ after anion exchange, with the halide composition in contact area modulated and monocrystalline nature of CsPbBr₃ preserved. CsPbBr₃‐CsPbBr_xCl_3‐x monocrystalline heterostructure has been achieved without lithography. Device based on the heterostructure shows apparent rectification behavior and improved photo‐response rate. Heterostructure arrays can also be constructed with customized medium crystal. Furthermore, the halide composition can be accurately tuned to enable full coverage of visible spectra. The solid‐state exchange enriches the toolbox for processing vulnerable perovskite and paves the way for the integration of monocrystalline perovskite optoelectronics.