A Polymer‐Enabled Perovskite Homojunction for Simultaneous Stress Release, Defect Passivation, and Dark Current Suppression in Flat‐Panel X‐Ray Detection

Metal halide perovskites, in the form of large‐area, hundreds‐of‐micrometer thick polycrystalline films, hold great potential in revolutionizing current X‐ray imaging technologies. However, their monolithic integration with thin‐film transistor (TFT) backplanes is hindered by thermal expansion mismatch, excessive dark current, and buried‐interface defects. Herein, we introduce a multifunctional buried interlayer strategy that simultaneously surmount these obstacles. By engineering a polymer‐regulated perovskite interlayer, we create a mechanical buffer that effectively dissipates residual thermal stress, enabling delamination‐free growth of dense, 100‐µm‐thick films. Crucially, this architecture passivates interfacial defects and regulates the film growth, significantly suppressing defect‐mediated carrier trapping/detrapping and enabling fast, high‐fidelity response to millisecond‐scale X‐ray pulses used in practical clinically relevant conditions. Additionally, it constructs a perovskite homojunction that fortifies the hole injection barrier and enlarges the built‐in potential. The resulting detector exhibits a remarkable sensitivity‐to‐dark‐current ratio of 8.84 × 10 10 µC Gy air −1 A −1 and an ultralow limit of detection of 12 nGy air s −1 . We further validate this approach by demonstrating a high‐resolution flat‐panel detector via seamless TFT integration. This work establishes polymer‐enabled homojunction as a critical design paradigm for realizing stable, low‐noise, and scalable perovskite X‐ray detectors.