Interfacial Charge Transfer Governs Bias-Polarity-Selective Electroluminescence in van der Waals Tunneling Heterostructures.

Inelastic electron tunneling (IET) provides an efficient route for electroluminescence (EL) in van der Waals (vdW) heterostructures, yet the microscopic origin of its bias-polarity dependence remains elusive due to structural asymmetry in prior devices. Here, we report a pronounced bias-polarity-selective EL in structurally symmetric graphene/hexagonal boron nitride (h-BN)/graphene tunneling junctions coupled to CrSBr; light emission is observed exclusively under positive bias and is fully quenched under negative bias. We demonstrate that strong interfacial charge transfer between CrSBr and the adjacent graphene electrode induces Fermi-level pinning and asymmetric band alignment, which enhances both the IET probability and energy transfer efficiency under positive bias while suppressing them under negative bias. The control device based on monolayer WSe2 exhibits nearly symmetric EL, confirming this mechanism. Our results establish interfacial charge transfer as a pivotal and tunable parameter governing IET-driven light emission and provide a general framework for engineering bias-polarity-selective optoelectronic functionalities in vdW heterostructures.