Redox‐Engineered Keggin‐Type Polyoxometalate Hole‐Transport/Electron‐Blocking Layer for Self‐Powered Perovskite Photodetectors With Ultralow Dark Current

Perovskite photodetectors face a challenge in balancing high photocurrent and low dark current for practical self‐powered applications. Conventional hole‐transport layer poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) suffers from instability and inadequate electron‐blocking capability. Herein, we report a solution‐processable Sn(II)‐doped phosphomolybdic acid (PMA:Sn) as a multifunctional hole‐transport/electron‐blocking layer for p–i–n type methylammonium lead iodide (MAPbI 3 ) photodetectors. The incorporation of Sn(II) optimizes the redox characteristics of the Keggin‐type PMA, enhancing the hole conductivity and adjusting its highest occupied molecular orbitals (HOMO) level for improved energy alignment with the perovskite, while simultaneously elevating its lowest unoccupied molecular orbital (LUMO) level to effectively block electron leakage from the perovskite. The resulting photodetectors achieve an ultralow dark current density of 2.13 × 10 −9 A·cm −2 and a photocurrent density of 9.53 × 10 −3 A·cm −2 at 0 V bias, yielding a record on/off ratio of 4.47 × 10 6 . The specific detectivity exceeds 10 12 Jones across 320–785 nm, with a linear dynamic range of 130 dB. The performance is attributed to the synergistic effect of high hole conductivity, optimal energy alignment, and efficient charge extraction, as validated by transient measurements. This work demonstrates the potential of redox‐tailored polyoxometalates as stable and superior alternatives to organic transport layers in next‐generation optoelectronics.