A highly responsive hybrid photodetector based on all-inorganic 2D heterojunction consisting of Cs2Pb(SCN)2Br2 and MoS2

Abstract

2D perovskites recently receive significant research attention due to their unique semiconducting properties and superior stability than 3D counterparts (ABX3). In this study, a rare 2D Cs2Pb(SCN)2Br2 is prepared by partially substituting X-site halide anion with an asymmetric pseudo-halide anion, SCN-. Such 2D Cs2Pb(SCN)2X2 possess not only an all-inorganic structure but also a much smaller spacing between perovskite sheets among the reported 2D perovskites comprising large A-site organic cations. This stable 2D Cs2Pb(SCN)2Br2 is integrated with MoS2 to constitute an all-inorganic 2D heterojunction, and this all-inorganic 2D heterojunction is shown to greatly improve the performance of MoS2-based photodetector, wherein 2D Cs2Pb(SCN)2Br2 serves as light absorbing layer with regard to its intense light-harvesting property and MoS2 functions as the transport layer with regard to its remarkable electrical properties. That is, Cs2Pb(SCN)2Br2 serves as a photo-gating layer to modulate the conductive behavior of MoS2. It reveals a type-II energy band alignment formed between Cs2Pb(SCN)2Br2 and MoS2 enables efficient charge transfer from Cs2Pb(SCN)2Br2 to MoS2. Besides, Cs2Pb(SCN)2Br2 seems to passivate the surface defects on MoS2 to facilitate interfacial charge transfer. As a result, the hybrid photodetector exhibits an impressively high responsivity of 1.22 × 105 A W−1 with response time shortened to ms, among the best values reported for perovskite/MoS2 hybrid photodetectors. This encouraging result paves a new avenue for all-inorganic 2D perovskite-based optoelectronic devices.