Effects of Fluorinated Aromatic Spacer in Ag–Bi Double Perovskite for X-ray Detector

Silver–bismuth halide double perovskites have recently emerged as one of the most promising green candidates for X-ray detection. However, their sensitivity still leaves behind the lead-based counterparts owing to the poor intrinsic optoelectronic properties and challenging crystal growth. Therefore, we conducted the space cation engineering by introducing fluorinated aromatic spacers to silver–bismuth perovskites, and the large (FPEA)4AgBiBr8 (FPEA+ is 4-fluorophenethylammonium) single-crystals were synthesized for the first time. The p−π coupling, large dielectric constant, and strong interlayer binding were revealed by ab initio calculation in this system. These effects further lead to better crystal quality and electrical properties, which was confirmed by the experimental characterizations. Consequently, X-ray detector based on (FPEA)4AgBiBr8 single-crystal exhibits low dark current as well as noise level and a good sensitivity of 27 μC Gyair–1 cm–2. This work reveals the effects of fluorinated aromatic spacer in Ag–Bi double perovskite and offers an inspiring strategy for materials design.