Suppressing Ion Migration in Heterostructure Single Crystals for Highly Sensitive Ultra‐Stable X‐Ray Detection

Abstract Heterostructure single crystals have emerged as a significant functional material system due to their unique properties and potential for novel optoelectronic device applications. Particularly, their distinctive structural characteristics offer promising prospects for suppressing ion migration, which is highly advantageous for X‐ray detection. Herein, by gradually modifying the cyclohexylmethylamine cation into the 4‐aminomethyltetrahydropyran cation, a layered heterostructure single crystal (PbCl 2 ) 2 (4‐Aminomethyltetrahydropyran) 2 PbCl 4 is successfully obtained. It comprises two distinct inorganic frameworks, namely a perovskite layer built from PbCl₆ octahedra and an intergrowth layer consisting of PbCl₂ units, wherein the organic components are firmly anchored to the intergrowth layer via Pb─O bonds, thereby enhancing the crystal stability and effectively suppressing ion migration, as evidenced by high ion migration activation energy (1.64 eV) and extremely low dark current drift (2.86 × 10 −18 A cm −1 V −1 s −1 ). X‐ray devices based on the ultra‐stable heterostructure single crystal demonstrate an extraordinary sensitivity of 8453.3 µC Gy −1 cm −2 (at 40 V), ultra‐low detection limit of 5.2 nGy s −1 and superior air stability (≈1 year). Such values make it one of the most outstanding candidates for high‐performance X‐ray detection. This work promotes the development of heterostructure single crystals optoelectronic applications.