Suppressing Ion Migration in MAPbI₃ Polycrystalline Wafer with BMIMBF₄ Ionic Liquid for X‐ray Detection and Imaging

Abstract 3D lead‐halide perovskite wafers, recognized for their superior photoelectronic properties and robust fabrication, are promising candidates for advanced X‐ray detectors. However, severe ion migration in 3D perovskite wafers leads to dark current baseline drift and long‐term operational instability, hindering their further development. Herein, 3D MAPbI 3 polycrystalline wafers with suppressed ion migration are prepared using the ionic liquid 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIMBF 4 ) and systematically investigated for X‐ray detection. The BMIMBF 4 ‐passivated MAPbI 3 wafers exhibit a low defect trap density ( n trap ) of 9.45 × 10 9 cm −3 , a high ion activation energy ( E a ) of 0.51 eV, a notable iodide ion migration energy barrier of 0.65 eV, and a decreased dark current drift ( I drift ) of 3.56 × 10 −4 nA cm −1 s −1 V −1 . The optimized MAPbI 3 wafer‐based detectors exhibit a high sensitivity of 12088.8 µC Gy air −1 cm −2 , a low detection limit (LoD) of 107.8 nGy air s −1 , and strong operational stability in X‐ray detection. Moreover, these detectors demonstrate outstanding X‐ray imaging capabilities, achieving a high spatial resolution of 5.17 lp mm −1 . Consequently, the utilization of ionic liquids with pseudo‐halide anions and polarized electron density distribution provides an innovative strategy for passivating 3D perovskite, advancing the field of powder‐pressed perovskite wafer X‐ray detection.