Chiral Dion‐Jacobson Silver/Antimony‐Based Double Perovskite Ferroelectrics Enable Ultralow Dose n ‐Type X‐Ray Detection

Emerging as viable substitutes for lead halide perovskites in optoelectronic applications, 2D hybrid double perovskites exhibit low environmental impact, enhanced stability, and compelling optoelectronic traits. This study details the first chiral 2D Ag/Sb‐based double perovskite ferroelectrics: ( R / S ‐3AMP) 2 AgSbBr 8 (where 3AMP = 3‐(aminomethyl)‐piperidine divalent cation), which exhibit a high Curie temperature of 440 K, an out‐of‐plane polarization of 3.8 µC cm −2 , and a strong second‐harmonic generation circular dichroism (SHG‐CD) response with an anisotropy factor up to 0.42. Moreover, the single‐crystal‐based X‐ray detector exhibits an ultralow dark current of 0.14 nA cm −2 , an ultralow detection limit of 3.78 nGy air s −1 , a high sensitivity of 1187.13 µC Gy air −1 cm −2 , and excellent operational stability with no observable baseline drift, outperforming state‐of‐the‐art perovskite single‐crystal detectors. The superior X‐ray detection performance is attributed to the synergistic effects of a suitable band gap, a unique 2D lattice, and a 1D electronic structure, as evidenced by density functional theory (DFT) calculations and crystal structure analysis. This study thus paves the way for next‐generation intelligent sensing technologies that integrate detection, perception, and information processing.