BiO(IO ₃ ) with Ultrahigh Effective Atomic Number and Density for Sensitive and Stable Hard X‐Ray Detection

Bismuth halide perovskites are promising materials for hard X-ray detection owing to their high effective atomic number (Z_eff) and excellent optoelectronic properties. However, the reported A-site cations or pseudohalides to address chemical stability issues inevitably reduce material Z_eff/density and aggravate electron localization. These changes significantly degrade X-ray absorption and charge transport, ultimately undermining detection performance. Herein, we chose the oxidized I⁵⁺ to replace I^-, and designed 2D BiO(IO₃). This substitution yields a significantly more compact crystal lattice while retaining two high-Z elements (Bi and I), affording the material an ultrahigh Z_eff (72.29) and density (7.399 g/cm³), which greatly enhances hard X-ray absorption. Concurrently, the small effective mass of the material facilitates efficient carrier transport, resulting in a high device sensitivity of 4563 µC Gy_air ^-1 cm^-2 for ∼25 keV X-ray photons. Furthermore, the formation of strong Bi-O and I-O bonds endows the material with excellent stability, leading to a high ion migration activation energy of 0.73 eV. Specifically, polycrystalline wafers with a thickness of 1 mm were successfully fabricated and showed no performance degradation after long time continuous aging test (160 kV X-ray, high voltage, temperature, etc.). This work provides a promising solution for developing high-performance hard X-ray detection materials.