Hydroxylamine Cation as B-Site with Radius and Dipole Moment Modulation for Metal-Free Halide Perovskite to Enhance...

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 (NH₄ ⁺) exhibits spatial, geometric, and symmetry conflicts with the octahedral framework, constraining the viable material and structure compositions in MFHPs. In this study, the NH₃OH⁺ 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 NH₃OH⁺ cation can regulate octahedral composition and structural dimensionality of MFHPs, thereby optimizing bandgap and carrier transport capacity. Importantly, hydroxyl groups in NH₃OH⁺ 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-NH₃OHCl₃ 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 NH₃OH⁺ cation will offer design guidelines for future MFHPs optimization.