Cu-Atom-Doped CsPbBr₃ Nanocrystals for Enhanced Photocatalytic CO₂ Reduction Reaction

Photocatalytic CO₂ reduction (CO₂RR) is particularly attractive due to its ability to directly harvest solar energy, representing a promising and sustainable route toward carbon neutrality. All-inorganic halide perovskite nanocrystals, such as CsPbBr₃, have emerged as highly promising photocatalysts owing to their exceptional electronic and optical properties. In this work, Cu-atom-doped CsPbBr₃ perovskite nanocrystals (Cu-CsPbBr₃ PNCs) were successfully developed, and the role of the Cu single atom in CsPbBr₃ PNCs for modulating their photocatalytic CO₂RR was elucidated. Comprehensive structural characterizations, including X-ray diffraction (XRD), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and X-ray absorption spectroscopy (XAS), collectively confirm that the Cu element is atomically distributed as single atoms uniformly within the nanocrystal lattice rather than undergoing phase segregation into clusters or long-range-ordered Cu phases. A slight red shift of the Cu K-edge XANES under illumination was found, indicating a partial reduction of Cu²⁺ in Cu-CsPbBr₃ PNCs. The results represented the occurrence of photoexcited electron transfer from CsPbBr₃ to the doped Cu sites during the CO₂RR. Moreover, photocatalytic CO₂RR revealed that an optimal Cu-doping concentration in Cu-CsPbBr₃ PNCs achieves a significantly enhanced CO production rate of 2.80 μmol g^-1 h^-1, outperforming pristine CsPbBr₃ (1.47 μmol g^-1 h^-1). Time-resolved photoluminescence (TRPL) measurements show a substantial decrease in carrier lifetime from 3.17 ns (pristine CsPbBr₃ PNCs) to 0.72 ns (optimal Cu-CsPbBr₃ PNCs), evidencing efficient electron trapping by single Cu single atoms. Transient absorption (TA) spectra further reveal modified hot-carrier dynamics and pronounced carrier-trapping behavior. Overall, the enhanced photocatalytic activity of Cu-CsPbBr₃ PNCs toward CO₂ reduction is attributed to efficient nonradiative charge transfer from photoexcited CsPbBr₃ PNCs to the dopant Cu atoms. This design strategy opens a general avenue for the development of metal-atom-doped perovskite-based photocatalysts with improved efficiency for the CO₂ reduction reaction.