Molecular Doping of Flexible Lead-Free Perovskite-Polymer Thick Membranes for High-Performance X-Ray Detection

X-ray detectors have broad applications in medicine and industry. Although flexible lead-free perovskite films are competitive because of their lightweight and low toxicity, they are less efficient due to low charge transport. Herein, we report low-toxicity, flexible X-ray detectors based on p-type doped MA₃ Bi₂ I₉ (MA=methylammonium) perovskite-filled membranes (PFMs). Strong coordination between dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) and MA₃ Bi₂ I₉ and the establishment of charge-transfer complex (CPX) improved the conductivity by four times. The flexible X-ray detector achieved a high sensitivity of 2065 μC Gy_air ^-1  cm^-2 and an ultra-low detection limit of 2.71 nGy_air  s^-1 , which is among the highest values in all environmentally friendly flexible X-ray detectors. Importantly, the PFMs retained excellent charge transport under mechanical stress. All of those make flexible MA₃ Bi₂ I₉ membranes more competitive as next-generation X-ray detection.