Defect-programmed band alignment enables self-powered silicon photodiodes

Solution-processed oxide/Si heterojunctions are highly attractive for self-powered photodetection; however, their photovoltaic-mode performance remains sensitive to defect-controlled band alignment. Here, we demonstrate a stoichiometry-programmed route to self-powered silicon photodiodes by utilizing solution chemistry and oxygen-deficient annealing to tune the electronic energetics of vanadium oxide. VO_x films are dip-coated onto p -Si from either DI-water or H₂O₂ precursors and annealed in N₂ at 500 °C. While microscopy and XRD confirm both routes yield predominantly orthorhombic V₂O₅ with rod-like microstructures, XPS reveals distinct, route-dependent oxygen chemical states that persist post-annealing. Consequently, the water-derived, vacancy-rich junction exhibits robust diode rectification and strong broadband photoresponse, reaching ∼−750 μA at −5 V under 650 nm illumination. It achieves photosensitivity exceeding 10³ and maintains stable zero-bias photovoltaic operation. Conversely, the peroxide-derived junction displays transport-limited behavior and strongly suppressed sensitivity. Finally, a resistor-loaded photopixel demonstrates repeatable UV-to-visible voltage switching and microsecond-scale near-IR response (rise/fall ∼63/221 μs), validating defect-programmed band alignment for self-powered, silicon-compatible photodetectors.