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.