Hydroxylamine Cation as B‐Site with Radius and Dipole Moment Modulation for Metal‐Free Halide Perovskite to Enhance X‐ray Detection Performance

Abstract Nowadays, metal‐free halide perovskites (MFHPs) with good structural tunability, biocompatibility, and light weight have been studied in the X‐ray field. Unlike the strong ionic bonds in metal halide perovskites, weak hydrogen bonds play a significant role in the stability and performance of MFHPs. However, as a critical component in the formation of hydrogen‐bond networks, the B‐site cation (NH 4 + ) exhibits spatial, geometric, and symmetry conflicts with the octahedral framework, constraining the viable material and structure compositions in MFHPs. In this study, the NH 3 OH + cation with larger radius and dipole moment is successfully incorporated into MFHPs to explore the functional mechanisms of B‐site design. Theoretical simulations and experiments reveal that the NH 3 OH + cation can regulate octahedral composition and structural dimensionality of MFHPs, thereby optimizing bandgap and carrier transport capacity. Importantly, hydroxyl groups in NH 3 OH + can increase hydrogen‐bond sites and strength, reinforcing the hydrogen‐bond networks to stabilize the lattice structure and inhibit ion migration, thereby optimizing the device stability. Finally, the designed DABCO‐NH 3 OHCl 3 detector exhibited exceptional stability and sensitivity (1460 µC Gy air −1 cm −2 at 200 V bias) under prolonged X‐ray irradiation, achieving ultralow dark current drift (1.86 × 10 −7 nA cm −1 V −1 s −1 ). Hence, the reported NH 3 OH + cation will offer design guidelines for future MFHPs optimization.