Exciton dynamics and photoresponse of a CVD-grown WS2/thermally evaporated CsSnBr3 heterostructure

Abstract

Transition metal dichalcogenide (TMDC)/metal halide perovskite photodetectors provide a promising new route for the realization of high-performance photodetectors owing to their unique optoelectronic features. However, previous studies mostly focused on vertically stacked TMDC/perovskite heterostructures and only on relatively thick perovskites (over 100 nm), whereby a large imbalance between the thicknesses of the perovskite and TMDC monolayer exists, which hinders further exploration of interface interactions from a possible coupling between the two components. Moreover, normally toxic Pb-based, not benign Sn-based, ones are widely reported. In this study, chemical vapor deposition (CVD)-grown WS₂/thermally evaporated CsSnBr₃ photodetectors with a planar structure were fabricated and their photoresponse, as well as their photophysical properties and morphology and structure characteristics, were investigated. A robust WS₂ triangular domain with an edge length around 120 μm was generated on Si/SiO₂via tuning the CVD process whereby an apparent selective deposition of CsSnBr₃ with a preferential (200) orientation on WS₂ could be achieved. A superior photoresponse compared to the isolated monolayer WS₂ and CsSnBr₃ films was demonstrated, which could be ascribed to the facilitation of the separation of the photogenerated electron–hole pairs due to the formation of a type-II band alignment at the WS₂/CsSnBr₃ junction. Exciton dynamics analysis confirmed such carriers were transferring across the interface, especially an excessive receipt of holes in the monolayer WS₂. The thickness of CsSnBr₃ had a critical influence on the photoresponse, whereby 50 nm CsSnBr₃ realized the optimal balance between the light absorbance and built-in potential effect. Our study provides a simple way to obtain TMDC/Sn-based metal halide perovskite photodetectors.