Enhancing the Performance and Stability of FAPbI₃ Perovskite X‐ray Detectors via Bi‐Doping

Perovskite materials have demonstrated significant potential in X‐ray detection due to their high atomic number and robust X‐ray absorption capacity, especially organic–inorganic hybrid perovskites. Among these, CH(NH₂)₂PbI₃ (FAPbI₃) stands out for its narrow bandgap and robust absorption properties. However, FAPbI₃ undergoes a rapid phase transition from a black octahedral perovskite phase to a yellow non‐perovskite phase under environmental conditions. This work addresses this issue by proposing the doping of Bi elements with mixed valence at the Pb site, verified through density functional theory simulations. The results indicate that Bi doping increases the formation of FA ionic vacancies, enhancing degradation energy and stabilizing the perovskite phase. FAPb_0.99Bi_0.01I₃ exhibits higher ion‐migration activation energy (0.75 eV), carrier mobility (6.88 × 10⁻³ cm² V⁻¹), and carrier lifetime compared to FAPbI₃. Additionally, Bi doping reduces FAPbI₃ perovskite crystal defects, inhibits ion migration, and increases resistivity. These improvements confirm the feasibility of B‐site non‐homovalent doping in perovskite X‐Ray detector applications.