Defect‐Functionalization‐Mediated Tunneling Drives Nonlinear Photoemission in Perovskites

The deliberate functionalization of defects represents a largely unexplored frontier in advanced optoelectronics. Within Einstein's photoelectric framework, we elucidate how deep‐level defects in CsPbBr 3 films act as functional mediators to govern carrier transport, interfacial electron escape, and quantum efficiency multiplication via a defect‐mediated tunneling process. First, in solid‐state photonics, it overcomes strong exciton binding in an Au/CsPbBr3/Au transistor, yielding a >70‐fold photoconductive gain at sub‐nA dark current and a spectral response extension of >0.88 eV. Second, in vacuum electronics, electron beam bombardment creates localized electropositive centers, forming a defect‐functionalized activation layer that induces pronounced band bending and shifts interface dominance from luminescence to photoemission, offering a robust alternative to chemical methods. Thirdly, we demonstrate transient quantum efficiency multiplication that reaches 16.8% under 266 nm pulsed excitation and achieves a 34 dB gain at 355 nm, functionally establishing a photoemissive comparator. By transforming the conventional role of defects from detrimental to functional, this work represents “defect‐functionalized optoelectronics” as an alternative design route for advanced nonlinear device function.