Long Live(d) CsPbBr3 Superlattices: Colloidal Atomic Layer Deposition for Structural Stability

Metal halide perovskite nanocrystals self-assemble under slow solvent evaporation leading to formation of superlattices that are interesting because of their collective photophysical properties, such as superfluorescence. These collective properties are, ostensibly, directly influenced by the stability of the perovskite nanocrystals and their dynamic surface chemistry, both factors that dictate the stability of the superlattice. In this work, we report on the formation of superlattices from aluminum oxide shelled CsPbBr3 perovskite nanocrystals where the oxide shell is grown by colloidal atomic layer deposition. We demonstrate that the structural stability of these superlattices is preserved over 25 days and that colloidal atomic layer deposition yields structural protection and an enhancement in photoluminescence quantum yields and radiative lifetimes as opposed to gas phase atomic layer deposition or excess capping group addition. Structural analyses found that shelling resulted in smaller nanocrystals that pack more tightly within the superlattice forming uniform supercrystals due to the aluminum oxide layers that cause increasingly hard cube behavior leading to a higher packing density than superlattices assembled from softer cubes without aluminum oxide. These effects are in addition to the increasingly static capping group chemistry initiated when oleic acid is used to terminate atomic layer deposition and is subsequently installed as a capping ligand directly on aluminum oxide. Together, these factors lead to fundamental observations that may influence future superlattice assembly design.