MASCN Vapor‐Assisted Fabrication of Compact and Large‐Grain MAPbI₃ Polycrystalline Wafer for X‐Ray Detection and Imaging

Abstract Lead halide perovskite wafers, which have adjustable size and thickness, are promising for the tailored fabrication of X‐ray detectors. However, common voids and grain boundaries, acting as carrier traps in polycrystalline wafers, present a major challenge to achieving optimal optoelectronic properties. Herein, an innovative approach is adopted by introducing methylammonium thiocyanate (MASCN) vapor into the hot‐pressing environment of MAPbI 3 wafers, promoting perovskite grain merging and growth. The resulting compact wafers with larger crystal grains display an extended average carrier lifetime ( τ avg ) of 31.61 ns, a high ion activation energy ( E a ) of 0.47 eV, a reduced dark current drift ( I drift ) of 4.11 × 10 −4 nA cm −1 s −1 V −1 , and an improved mobility‐lifetime product ( µτ ) of 8.26 × 10 −4 cm 2 V −1 . These optimized MAPbI 3 wafer‐based detectors achieve a high sensitivity of 16611 µC Gy air −1 cm −2 , a low detection limit (LoD) of 47.5 nGy air s −1 , and robust operational stability in X‐ray detection. Furthermore, these detectors exhibit excellent X‐ray imaging capability, achieving a high spatial resolution of 5.64 lp mm −1 . Therefore, the deployment of volatile thiocyanate salt during hot pressing provides a novel strategy for engineering high‐quality polycrystalline perovskite wafers, propelling forward the field of X‐ray detection.