Chemical transformation of typically "nonlayered" phases into two-dimensional structures remains a formidable task. Among the thickness tunable CsPbX3 (X = Br, Br/I, I) nanosheets (NSs), CsPbBr1.5I1.5 NSs with a thickness of ∼4.9 nm have structural stability superior to ∼6.8 nm CsPbI3 NSs and better hole mobility than ∼3.7 nm CsPbBr3 NSs. Moving beyond the much-explored CsPbBr3 photodetectors, we demonstrate a sharp improvement of the photodetection of CsPbBr1.5I1.5 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 × 1011 Jones at 1.5 V, due to the increase in carrier mobility up to 7.9 × 10-4 cm2 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.
Keywords: carrier mobility; lead-halide perovskite; nanosheet; photodetector; responsivity.