Photoinduced Transformation of Cs 2 Au 2 Br 6 into CsPbBr 3 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. CsPbBr 3 nanocrystals undergo exchange of Pb 2+ with Au(I)/Au(III) to form double perovskite Cs 2 Au 2 Br 6 . When excited, a majority of the charge carriers undergo quick recombination in contrast to long-lived charge carries of excited CsPbBr 3 nanocrystals. This metal ion exchange process is reversible as one can regenerate CsPbBr 3 by adding excess PbBr 2 to the suspension. Interestingly, when subjected to visible light irradiation, Cs 2 Au 2 Br 6 nanocrystals eject reduced Au from the lattice as evidenced from the formation of larger gold nanoparticles. The presence of residual Pb 2+ ions in the suspension restores the original CsPbBr 3 composition. The results presented here provide insight into the dynamic nature of Au within the perovskite lattice under both chemical and light stimuli.