Defect Mitigation in Cesium–Copper–Iodide Perovskite Nanocrystals for High-Performance Lead-Free Nanocomposite X-ray Detectors

Lead-free perovskites nanocrystals (PNCs) have attracted significant attention as promising candidates for X-ray detection due to their high X-ray stopping power, remarkable radioluminescence light yield and favorable biocompatibility. However, the bulk and surface defects in the PNCs, formed during the purification or device fabrication process, may remarkably affect the charge transport properties and stability of the detectors. In this study, we discovered that the Cs₃Cu₂I₅ PNCs are quite sensitive to the thermal annealing temperature, and a high temperature larger than 100 °C can trigger the decomposition of the PNCs and therefore the generation of bulk defects within them. By optimizing the annealing process, we are able to achieve the efficient solvent evaporation while maintaining the structure integrity of the PNCs. Additionally, a NaI assisted in situ surface passivation strategy was proposed to repair the surface defects caused by ligand detachment during the PNC purification process, further reducing the nonradiative recombination and suppressing the ion-migration effect. The resultant Cs₃Cu₂I₅ PNC-organic bulk heterojunction nanocomposite X-ray detectors achieve a remarkable sensitivity of over 4000 μC·Gy_air^–1·cm^–2 and a low detection limit of 30 nGy_air·s^–1, alongside enhanced response speed and irradiation stability, positioning them among the best-performing lead-free perovskite film-based X-ray detectors reported to date.