Rigid Bis‐Amidinium Anchoring Engineering Enables Synergistic Defect Suppression and Ion Stabilization for High‐Performance Flexible Perovskite X‐Ray Detectors and TFT‐Array Imaging

Flexible direct‐conversion X‐ray detectors based on halide perovskites hold great promise for mechanically compliant and array‐integrated imaging, yet their performance is limited by grain‐boundary defects and electrical instability in polycrystalline thick films. Here, we introduce 1,4‐benzenedicarboximidamide dihydrochloride (p‐BDAm) as an additive for regulating polycrystalline methylammonium lead iodide (MAPbI 3 ) detector layers. Spectroscopic measurements and density functional theory (DFT) calculations support multisite interactions between the bis‐amidinium framework and Pb–I‐containing species as a plausible contribution to the p‐BDAm‐mediated regulation of the local grain‐boundary environment and crystallization behavior. Overall, p‐BDAm incorporation suppresses nonradiative recombination, increases the resistivity and mobility–lifetime product, raises the apparent activation energy extracted from temperature‐dependent conductivity from 0.17 to 0.49 eV, and substantially improves dark‐current stability. The optimized flexible perovskite composite membrane detector achieves a sensitivity of 2165.5 µC Gy air −1 cm −2 at 10 V and an estimated detection limit of 15.0 nGy air s −1 . Moreover, the p‐BDAm‐regulated MAPbI 3 layer is compatible with thin‐film transistor (TFT)‐array integration, enabling parallel X‐ray imaging. A representative TFT image was obtained at an X‐ray dose rate of 12.3 µGy air s −1 with an exposure time of 0.5 s. These results demonstrate a transferable molecular‐regulation strategy for stabilizing polycrystalline perovskite X‐ray detectors across flexible and array‐integrated architectures.