Covalent Self-Assembled Monolayer Passivation Enables Ultrahigh-Sensitivity and Ultrastable MAPbI 3 Single-Crystal X-Ray Detectors via Interfacial Dipole Engineering

Abstract

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 Gyair-1 cm-2 and a limit of detection (LOD) down to 2.64 nGyair·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.