Redox-Modulated Polyoxometalate-Incorporated Carbazole-Based Interface for High-Performance Perovskite Photodetectors

High-performance self-powered perovskite photodetectors demand hole transport layers (HTLs) concurrently possessing excellent energy level alignment, optimal wettability, and effective defect passivation. Although the widely used [2-(3,6-dimethoxy-9 H -carbazol-9-yl)ethyl]phosphonic acid (Me-4PACz) self-assembled monolayer (SAM) satisfies energy-level requirements, its hydrophobicity and limited defect passivation hinder concurrent optimization of film quality and interface defects, limiting device performance. Herein, we address this via a Sn 2+ -mediated interfacial chemical reconstruction of phosphomolybdic acid (PMA). Preforming a PMA:Sn composite and blending it with Me-4PACz yields a ternary HTL, Me-4PACz:(PMA:Sn). Sn 2+ reduces partial Mo(VI) to Mo(V) in PMA, enabling triple interface optimization: (i) tuning the PMA acidity to preserve the SAM transport characteristics, (ii) enhancing the interfacial polarity for the uniform perovskite film growth, and (iii) moderating Pb 2+ coordination to suppress detrimental PbI 2 formation. This results in high-quality, vertically oriented methylammonium lead triiodide (MAPbI 3 ) films. The corresponding photodetector achieves an ultralow dark current of 1.38 × 10 –10 A cm –2, a high detectivity of 5.76 × 10 13 Jones, a wide dynamic range of 143 dB, fast response of ∼5 μs, and stable operation. This work demonstrates redox-mediated polyoxometalate chemistry as a versatile strategy for rational SAM interface design in perovskite optoelectronics.