Robust Fabrication of Hybrid Lead‐Free Perovskite Pellets for Stable X‐ray Detectors with Low Detection Limit

X-ray detectors are widely utilized in medical diagnostics and nondestructive product inspection. Halide perovskites are recently demonstrated as excellent candidates for direct X-ray detection. However, it is still challenging to obtain high quality perovskites with millimeter-thick over a large area for high performance, stable X-ray detectors. Here, methylammonium bismuth iodide (MA₃ Bi₂ I₉ ) polycrystalline pellets (PPs) are developed by a robust, cost effective, and scalable cold isostatic-pressing for fabricating X-ray detectors with low limit of detection (LoD) and superior operational stability. The MA₃ Bi₂ I₉ -PPs possess a high resistivity of 2.28 × 10¹¹ Ω cm and low dark carrier concentration of ≈10⁷ cm^-3 , and balanced mobility of ≈2 cm² V^-1 s^-1 for electrons and holes. These merits enable a sensitivity of 563 μC Gy_air ^-1 cm^-2 , a detection efficiency of 28.8%, and an LoD of 9.3 nGy_air s^-1 for MA₃ Bi₂ I₉ -PPs detectors, and the LoD is much lower than the dose rate required for X-ray diagnostics used currently (5.5 μGy_air s^-1 ). In addition, the MA₃ Bi₂ I₉ -PPs detectors work stably under high working bias field up to 2000 V cm^-1 after sensing an integrated dose >320 Gy_air with continuous X-ray radiation, demonstrating its competitive advantage in practical application. These findings provide an approach to explore a new generation of low LoD, stable and green X-ray detectors based on MA₃ Bi₂ I₉ -PPs.