Dion‐Jacobson Type Lead‐Free Double Perovskite with Ultra‐Narrow Aromatic Interlayer Spacing for Highly Sensitive and Stable X‐ray Detection

Abstract The low‐toxic and environmentally friendly 2D lead‐free perovskite has made significant progress in the exploration of “green” X‐ray detectors. However, the gap in detection performance between them and their lead‐based analogues remains a matter of concern that cannot be ignored. To reduce this gap, shortening the interlayer spacing to accelerate the migration and collection of X‐ray carriers is a promising strategy. Herein, a Dion‐Jacobson (DJ) lead‐free double perovskite (4‐AP) 2 AgBiBr 8 ( 1 , 4‐AP = 4‐amidinopyridine) with an ultra‐narrow interlayer spacing of 3.0 Å, is constructed by utilizing π‐conjugated aromatic spacers. Strikingly, the subsequent enhanced carrier transport and increased crystal density lead to X‐ray detectors based on bulk single crystals of 1 with a high sensitivity of 1117.3 µC Gy −1 cm −2 , superior to the vast majority of similar double perovskites. In particular, the tight connection of the inorganic layers by the divalent cations enhances structural rigidity and stability, further endowing 1 detector with ultralow dark current drift (3.06 × 10 −8 nA cm −1 s −1 V −1 , 80 V), excellent multiple cycles switching X‐ray irradiation stability, as well as long‐term environmental stability (maintains over 94% photoresponse after 90 days). This work brings lead‐free double perovskites one step closer to realizing efficient practical green applications.