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

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, Cu₃(HHTP)₂) and metallic Ti₃C₂ MXene to form van der Waals dual junctions on a silicon substrate. The heterojunction configuration facilitates unidirectional electron-hole separation within the Cu₃(HHTP)₂/Si interface with type I band alignment, while leveraging the potential barrier difference between the Cu₃(HHTP)₂/Si and Ti₃C₂/Cu₃(HHTP)₂ Schottky junctions. The Ti₃C₂/Cu₃(HHTP)₂/Si photodetector demonstrates outstanding photoelectric performance, operating in a self-powered mode with a high specific detectivity of 1.63 × 10¹² 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 × 10⁴ 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.