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

ABSTRACT 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 I 5+ to replace I − , and designed 2D BiO(IO 3 ). 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/cm 3 ), 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.