A Type-II Bismuth Iodide Ferroelectric for Sensitive X-ray Detection and Single-Pixel Imaging

Bismuth iodides have emerged as a promising class of novel semiconductors for direct X-ray detection due to their nontoxicity and strong X-ray absorption. However, translating the electrical response of Bi-based detectors into spatially resolved X-ray images remains challenging. Here, we report a one-dimensional (1D) hybrid bismuth iodide (S-MeOMBA)BiI4·0.75H2O, which crystallizes in the chiral polar space group P21 with infinite edge-sharing [Bi2I8]2- chains. Piezoresponse force microscopy confirms its intrinsic ferroelectricity via well-defined rectangular hysteretic phase loops, suggesting the existence of spontaneous polarization that can facilitate photogenerated charge separation. Density functional theory calculations unveil a direct bandgap with type-II band alignment between the organic cations and inorganic chains, further boosting charge transport properties. As a direct consequence, the X-ray detectors based on single crystals of (S-MeOMBA)BiI4·0.75H2O achieve high performance with a low detection limit of 352 nGyair s-1, substantially below the benchmark required for medical diagnostics. Strikingly, by integrating the detectors into a single-pixel point-scanning system, we successfully convert the dose-dependent electrical signal into images that clearly reproduce the contour and local structural features of a metallic key. These results establish (S-MeOMBA)BiI4·0.75H2O as a promising eco-friendly semiconductor for direct X-ray detection and imaging.