Photoinduced Transformation of Cs₂Au₂Br₆ into CsPbBr₃ Nanocrystals

Lead-free halide double perovskites offer an environmentally friendly alternative to lead halide perovskites for designing optoelectronic solar cell devices. One simple approach to synthesize such double halide perovskites is through metal ion exchange. CsPbBr₃ nanocrystals undergo exchange of Pb²⁺ with Au(I)/Au(III) to form double perovskite Cs₂Au₂Br₆. When excited, a majority of the charge carriers undergo quick recombination in contrast to long-lived charge carries of excited CsPbBr₃ nanocrystals. This metal ion exchange process is reversible as one can regenerate CsPbBr₃ by adding excess PbBr₂ to the suspension. Interestingly, when subjected to visible light irradiation, Cs₂Au₂Br₆ nanocrystals eject reduced Au from the lattice as evidenced from the formation of larger gold nanoparticles. The presence of residual Pb²⁺ ions in the suspension restores the original CsPbBr₃ composition. The results presented here provide insight into the dynamic nature of Au within the perovskite lattice under both chemical and light stimuli.