PEAI\nSurface Treatment for Low Ion Migration and High-Performance\nFAPbBr<sub>3</sub> Single-Crystal X‑ray Detectors

Organometal\nhalide perovskite single crystals (SCs) are the most\npromising candidates for the next generation of radiation detection\nmaterials. However, surface defects severely affect their detection\nperformance and limit further applications. Here, we identified the\nsurface defect types of FAPbBr<sub>3</sub> SCs and employed phenethylammonium\niodide (PEAI) solution to treat the crystal surface and to investigate\ntheir effects on ion migration, photoelectric performance, and X-ray\ndetection performance. Our experimental results demonstrated that\nthe surface defects, such as the metallic Pb and Br vacancies, can\nbe effectively passivated by both the PEAI and the two-dimensional\n(2D) PEA<sub>2</sub>PbI<sub>4</sub> layers. The PEAI layer can elongate\nthe carrier lifetime, lower the trap density, and suppress ion migration\nin FAPbBr<sub>3</sub> SCs. The 2D PEA<sub>2</sub>PbI<sub>4</sub> layer\ncan form a dense and full surface coverage, suppress ion migration,\nand lower the dark current of the SCs. The X-ray sensitivity of the\nPEAI-passivated FAPbBr<sub>3</sub> SC detectors is 227.93 μCGy<sub>air</sub><sup>–1</sup> cm<sup>–2</sup>, which is an\norder of magnitude higher than that of the pristine FAPbBr<sub>3</sub> SC detectors. This work demonstrates that surface treatment plays\na critical role in the crystal quality and the X-ray detection performance\nof SCs.