Semiconductor nanoparticles have been considered as building blocks of light-harvesting systems. Their role in capturing incident photons to induce separation of charges in quantum dot solar cells and photocatalyst systems is of particular interest. Lead-free halide double perovskites are emerging semiconductors for optoelectronic applications and offer a non-toxic alternative to traditional lead halide perovskites. Introduction of Au3+ ions to CsPbBr3 nanocrystals in low concentration results in CsPbBr3-Au heterostructures and in high concentration induces cation exchange which forms the non-fluorescent double perovskite Cs2Au2Br6. CsPbBr3-Au heterostructures enhance the quantum yield of photoinduced electron-transfer processes. When Au nanoparticles are deposited on the CsPbBr3 nanocrystal surface, they efficiently quench the photoluminescence of the semiconductor. Under steady-state photoirradiation of CsPbBr3–Au heterostructure, the photogenerated electrons from excited CsPbBr3 nanocrystals continue to charge the Au nanoparticles. The charging of gold nanoparticles further causes them to dismantle from the CsPbBr3 surface and aggregate into larger size gold nanoparticles. It still remains a major challenge in photocatalysis to design stable and tunable perovskite-metal heterostructure. As the concentration of Au(III) ions is increased, the perovskite lattice will be restructured with Au(III) and Au(I) producing double perovskites. The cation exchange process can be reversed in the presence of excess Pb2+ ions, reforming CsPbBr3 and restoring its fluorescence. Significant changes in the structural, optical, and excited-state properties allow us to track the reversibility of the cation exchange process. Similarly, under visible light irradiation, the Au ions within Cs2Au2Br6 become unstable, leading to the ejection of Au from the lattice. The expelled Au ions form separate and stable nanoparticles which aggregate upon further irradiation, rendering the light-induced Au expulsion irreversible. The “soft lattice” structure of halide perovskites not only allows the synthesis of Cs2Au2Br6 by introduction of Au(III) ions to CsPbBr3 suspension but also reverts to CsPbBr3 in the presence of Pb2+ ions. These provide insights into the dynamic nature of Au within the perovskite lattice under both chemical and light stimuli.

Dynamic nature of Au within the halide perovskite lattice

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