Solution‐Processable Van Der Waals Heterojunctions on Silicon for Self‐Powered Photodetectors with High Responsivity and Detectivity

Abstract The high density of surface states on silicon has long impeded the development of high‐performance photodetectors, leading to excessive dark leakage currents that adversely affect responsivity and detectivity. Herein, an all‐solution‐processable method is presented for fabricating photodetectors through consecutive spray‐coating of a conductive metal‐organic framework (MOF, Cu 3 (HHTP) 2 ) and metallic Ti 3 C 2 MXene to form van der Waals dual junctions on a silicon substrate. The heterojunction configuration facilitates unidirectional electron‐hole separation within the Cu 3 (HHTP) 2 /Si interface with type I band alignment, while leveraging the potential barrier difference between the Cu 3 (HHTP) 2 /Si and Ti 3 C 2 /Cu 3 (HHTP) 2 Schottky junctions. The Ti 3 C 2 /Cu 3 (HHTP) 2 /Si photodetector demonstrates outstanding photoelectric performance, operating in a self‐powered mode with a high specific detectivity of 1.63 × 10 12 Jones and a large responsivity of 1.8 A W −1 under 365 nm illumination. It also exhibits an impressive on/off ratio exceeding 3.9 × 10 4 at an incident light power density of 330 µW cm −2 . Additionally, the photodetector maintains excellent responsivity across a broad wavelength range from 365 to 700 nm, spanning ultraviolet to visible light, and sets a new performance benchmark for MOF‐based photodetectors. This work introduces a straightforward, controllable approach for constructing high‐quality van der Waals junctions on semiconductor surfaces, enabling the fabrication of optoelectronic devices with enhanced performance.