Interstitial Copper Doping in Cs₃Bi₂Br₉: A Pathway to Enhanced Radiation Detection Performance

The modulation of double perovskites via a cation transmutation approach is a viable strategy to enhance their optoelectronic performance. Here, we explored the cation transmutation approach by substituting Ag with Cu in double halide perovskites and investigated the role of Cu in X-ray detection performance. We observe that Cu does not incorporate in a double halide perovskite structure (Cs₂CuBiBr₆ does not form), rather resulting in interstitial dopants in its pristine Cs₃Bi₂Br₉ structure. We demonstrate the impact of Cu dopants on X-ray and α-particle detection and find that Cu dopants lead to elevated sensitivity and reduced limit of detection along with prolonged stability under continuous X-ray exposure. It also exhibits remarkable performance under high-energy photon irradiation from a 6 MV clinical linear accelerator, suggesting potential cancer treatment applications. Interstitial Cu⁺ ions are expected to interact with negatively charged defects in Cs₃Bi₂Br₉, neutralizing them and promoting carrier delocalization, which enhances carrier transport. Our results shed light on the modulation of bismuth halide perovskites and show that these lead-free perovskite detectors are viable options for dosimetry in radiotherapy, medical imaging, and industrial applications, including in remote regions with limited resources and power restrictions.