Dynamic Control of Band Alignment and Built-In Potential in High Performance Self-Powered InSe/SnS₂ Van der Waals Photodetectors via Gas Molecular Physisorption

Molecular physisorption provides a versatile strategy to dynamically tailor the optoelectronic properties of van der Waals (vdW) heterostructures, enabling extended carrier lifetimes, broadened spectral response, and erasable memory effects in self-powered photodetectors. Here, we report how NO₂ physisorption precisely modulates band alignment and built-in potentials in self-powered InSe/SnS₂ heterojunction photodetectors. Using electrostatic gating, we identify three distinct regimes: (I) a robust p–n configuration (V_g ≤ –50 V), where adsorption induces a collective electron-withdrawing effect, enabling efficient p-i-n-like behavior with near-ideal charge separation; (II) an intermediate p–n regime (–50 V < V_g < –30 V), where competing electron withdrawal and recombination effects allow dynamic tuning the electronic structure and optoelectronic properties, and (III) an illumination-sensitive n–n⁺ mode (V_g ≥ –30 V), where NO₂ molecules act as recombination centers, suppressing the built-in potential. This dual control via gating and molecular adsorption provides unprecedented manipulation of charge separation and transport, opening avenues for next-generation multifunctional optoelectronic devices.