Interface Matters: Enhanced Photoluminescence and Long Term Stability of Zero-Dimensional Cesium Lead Bromide Nanocrystals via Gas-Phase Aluminum Oxide Encapsulation.

Cesium lead halide perovskite nanocrystals (PNCs), while possessing facile chemical synthesis and high photoluminescence (PL) emission properties, are still challenged by issues of instability and degradation. Although atomic layer deposition (ALD) of metal oxides has been one of the common encapsulation approaches for longer-term stability, its application inevitably resulted in severe loss of emission efficiency, and at times partial loss of structural integrity of perovskites, creating a bottleneck in its practical viability. We demonstrate a non-destructive modified gas-phase technique with co-deposition of both precursors trimethylaluminum (TMA) and water, to dramatically enhance the PL emission in zero-dimensional (0D) Cs4PbBr6 PNCs via alumina encapsulation. XPS surface analysis of Cs4PbBr6 films reveals the alumina deposition to be accompanied by the elemental composition changes, particularly by the reduction of the excessive cesium content. Ab-initio DFT simulations further unfold that the presence of excess Cs on the surface of PNCs leads to decomposition of structural [PbBr6] octahedra in 0D perovskite lattice, which can be prevented in presence of added hydroxyl groups. Our study thus unveils the pivotal role of the PNC surface composition and treatment in the process of its interaction with metal oxide precursors to control the PL properties as well as the stability of PNCs, providing the unprecedented way to use conventional ALD technique for their successful integration into optoelectronic and photonic devices with improved properties.