Photodetectors with High Responsivity by Thickness Tunable Mixed Halide Perovskite Nanosheets

Chemical transformation of typically “nonlayered” phases into two-dimensional structures remains a formidable task. Among the thickness tunable CsPbX 3 ( X = Br, Br/I, I) nanosheets (NSs), CsPbBr 1.5 I 1.5 NSs with a thickness of ∼4.9 nm have structural stability superior to ∼6.8 nm CsPbI 3 NSs and better hole mobility than ∼3.7 nm CsPbBr 3 NSs. Moving beyond the much-explored CsPbBr 3 photodetectors, we demonstrate a sharp improvement of the photodetection of CsPbBr 1.5 I 1.5 NS devices by thickening the NSs to ∼6.1 nm through combining 8-carbon and 18-carbon ligand surfactants. Thereby, the responsivity increases up to one of the highest values of 3313 A W –1 at 1.5 V (and 3946 A W –1 at 2 V) with detectivity of 1.6 × 10 11 Jones at 1.5 V, due to the increase in carrier mobility up to 7.9 × 10 –4 cm 2 V –1 s –1 . The better device performance of the NSs than 8.6–13.9 nm nanocubes (NCs) is due to their planarity which facilitates in-plane mobilization of the charge carriers.