Ultrahigh Photoluminescence Quenching (>90%) and Negative Photoresponse in Vertically Stacked Graphene/WSe ₂ van der Waals Heterojunctions

The interface effect plays a crucial role in determining the performance of van der Waals heterojunctions. Here, we fabricated graphene/WSe 2 heterojunctions and investigated how graphene proximity dramatically alters their optical, electrical, and photoelectrical properties. It was found that graphene proximity induces ultrahigh photoluminescence quenching exceeding 90%, accompanied by substantial effective hole depletion in the WSe 2 layer due to strong interfacial charge transfer. Photo illumination can further enhance charge transfer and charge accumulation at the interface. Electrical characterization shows that gate voltage effectively modulates interfacial charge transfer and thus the tunneling behavior. Notably, a transition from positive to negative photoresponse emerges when the effective tunneling barrier width is reduced below ∼1 nm, highlighting a tunneling-controlled photoresponse mechanism governed by the competition between interfacial charge transfer and bias-induced electric fields. These results provide comprehensive insights into interlayer charge transfer, exciton dynamics, and tunable photoelectrical properties in graphene/WSe 2 heterostructures, paving the way for next-generation optoelectronic devices based on 2D vdW materials.