Engineering Water Stable Perovskite and Plasmonic‐Perovskite Nanocomposites: A Step toward Unleashing the True Potential of Perovskite Catalysis

Abstract Despite garnering so much research interest, the potential technological developments of perovskites are limited due to the instability of perovskites in polar solvents. Here, it is discovered that upon exposure to ethanol, the initial cubic cesium lead bromide nanocrystals (CsPbBr 3 NCs) undergo a phase transformation from the cubic phase to the orthorhombic phase. Further exposure of the orthorhombic phase to water leads to the formation of CsPbBr 3 perovskite nanoaggregates, which shows higher stability in water compared to pristine CsPbBr 3 NCs. A systematic investigation of the interfaces using various spectroscopic techniques demonstrating the self‐assembly process and phase transformation is presented. The increased stability of ethanol‐treated CsPbBr 3 NCs is attributed to the ethoxide ions adsorption on the CsPbBr 3 interface, owing to strong affinity of alkoxide ions to Pb 2+ . Effective surface passivation leads to enhanced charge‐carrier separation, a prerequisite to an effective photocatalyst. Ethoxide‐stabilized CsPbBr 3 in water is utilized to reduce Au 3+ to Au 0 to synthesize water‐stable Au‐CsPbBr 3 nanocomposites. The formation of hybrid plasmonic metal‐perovskites nanocomposite influences the perovskite's excited state charge carrier dynamics. This opens the possibilities of utilizing the synergistic effects of the light‐harvesting properties of plasmonic nanomaterials with the catalytic attributes of perovskite materials and controlling the interface properties by tuning plasmon–exciton coupling.