(a) Schematic illustrations of solution process to fabricate 2D PbI₂ nanosheets, vapor-phase conversion process to transfer PbI₂ to 2D MAPbI₃ perovskite nanosheets, and the crystal structure of single unit cell thick 2D MAPbI₃ perovskite. (b) Atomic force microscope (AFM) topography images of 2D MAPbI₃ nanosheets. (c) Schematic image of a transistor device based on 2D perovskite. (d) I–V curves of the 2D perovskite-based device under different light intensities.^[145] (e) High-magnification SEM images of 2D ultrathin CsPbBr₃ nanosheets. (f) AFM image and height profile of monolayer and bilayer CsPbBr₃ nanosheets with a thickness of 1.6 nm and 3.3 ± 0.2 nm, respectively. (g) I–V curves of the PD in the dark and under 442 nm light ( 0.35 mW · cm − 2 ).^[143] (h) Schematic diagrams of different layer-structured perovskite materials and the perovskite-based PD. (i) Ultraviolet–visible (UV–vis) absorption spectra for layer-structured perovskite materials. (j) Wavelength-dependent photocurrent of the devices with a bias of 30 V.^[154]