Covalent self-assembled monolayer passivation enables ultrahigh-sensitivity and ultrastable MAPbI₃ single-crystal...

Metal halide perovskite MAPbI₃ single crystals are ideal candidates for next-generation direct-conversion X-ray detectors, but their practical applications are severely limited by high dark current, severe non-radiative recombination, and poor environmental stability caused by intrinsic surface defects. In this work, we performed covalent passivation on the surface of MAPbI₃ single crystals using a 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFTS) self-assembled monolayer (SAM), and systematically revealed its interfacial bonding mechanism, electronic structure regulation effect, and X-ray detection performance. The results show that PFTS can saturate the undercoordinated Pb²⁺ sites on the surface through Si-O-Pb covalent bonding, reducing the trap state density by more than 55%. The oriented interfacial dipole effect of PFTS can increase the Schottky barrier between Au and perovskite, significantly suppressing the dark current. The final device achieves an ultra-high sensitivity of (5.11 ± 0.13) × 10⁴ µC Gy_air^-1 cm^-2 and a limit of detection (LOD) down to 2.64 nGy_air s^-1, along with significantly optimized environmental stability and response speed. This work provides an efficient strategy for the interface design of high-performance perovskite X-ray detectors.