Intense and Stable Blue Light Emission From CsPbBr₃/Cs₄PbBr₆ Heterostructures Embedded in Transparent Nanoporous Films

Abstract Lead halide perovskite nanocrystals are attractive for light emitting devices both as electroluminescent and color‐converting materials since they combine intense and narrow emissions with good charge injection and transport properties. However, while most perovskite nanocrystals shine at green and red wavelengths, the observation of intense and stable blue emission still remains a challenging target. In this work, a method is reported to attain intense and enduring blue emission (470–480 nm), with a photoluminescence quantum yield (PLQY) of 40%, originating from very small CsPbBr₃ nanocrystals (diameter < 3 nm) formed by controllably exposing Cs₄PbBr₆ to humidity. This process is mediated by the void network of a mesoporous transparent scaffold in which the zero‐dimensional Cs₄PbBr₆ lattice is embedded, which allows the fine control over water adsorption and condensation that determines the optimization of the synthetic procedure and, eventually, the nanocrystal size. The approach provides a means to attain highly efficient transparent and stable blue light‐emitting films that complete the palette offered by perovskite nanocrystals for lighting and display applications.