The role of gold oxidation state in the synthesis of Au-CsPbX heterostructure or lead-free CsAuAuX perovskite nanoparticles.

Here, we report that the oxidation state of gold plays a dominant role in determining the reaction products when gold halide salts are mixed with all-inorganic lead halide perovskite nanocrystals. When CsPbX nanocrystals react with Au(i) halide salts, Au nanoparticles are deposited on the surface of the perovskites through the reduction of Au ions by the surfactant ligand shell, to produce Au-CsPbX heterostructures. These heterostructures preserve comparably high photoluminescence quantum yield (PLQY) and show identical XRD diffractograms as the parent CsPbX nanocrystals. In contrast, the reaction of CsPbX nanocrystals with Au(iii) halide salts promotes complete cation exchange of Pb ions by Au ions in the nanocrystal perovskite lattice. The cation exchange products, CsAuAuBr or CsAuAuCl, show XRD patterns corresponding to a tetragonal mixed halide perovskite crystal structure and show no visible photoluminescence. This crucial dependence on the oxidation state of the Au ion informs synthetic strategies for producing and optimizing metal-perovskite heterostructures and lead-free perovskite nanoparticles.