Origin of the anisotropic-strain-driven photoresponse enhancement in inorganic halide-based self-powered flexible photodetectors

Abstract

Strain engineering has been recognized as a critical strategy in modulating the optoelectronic properties of perovskite halide materials. Here, we demonstrate a self-powered, flexible photodetector based on CsPbBr₃ thin films with controllable compressive or tensile strain of up to ±0.81%, which was produced <i>in situ via</i> a sequential two-step deposition on bent polymer substrates. The best photoresponsivity of ∼121.5 mA W^-1 with a photocurrent of 5.15 μA was achieved at zero bias under a power intensity of 0.47 mW cm^-2 for the maximum tensile strain of +0.81%, which corresponds to a ∼100.2% increase relative to that of the unstrained case. The <i>in situ</i> tensile strain adjusted the band alignments, making them favorable for enhanced charge transport and thus a higher photoresponse. The structural origin of this superlative balanced photodetection performance was systematically revealed to be associated with the distortion of coupled PbBr₆ octahedra and the atomic displacement within the octahedron.