Efficient and Stable Blue- and Red-Emitting Perovskite Nanocrystals through Defect Engineering: PbX2 Purification

Current efforts to reduce the density of structural defects such as surface passivation, doping, and modified synthetic protocols have allowed us to grow high-quality perovskite nanocrystals (PNCs). However, the role of the purity of the precursors involved during the PNC synthesis to hinder the emergence of defects has not been widely explored. In this work, we analyzed the use of different crystallization processes of PbX2 (X = Cl- or I-) to purify the chemicals and produce highly luminescent and stable CsPbCl3-xBrx and CsPbI3 PNCs. The use of a hydrothermal (Hyd) process to improve the quality of the as-prepared PbCl2 provides blue-emitting PNCs with efficient ligand surface passivation, a maximum photoluminescence quantum yield (PLQY) of similar to 88%, and improved photocatalytic activity to oxidize benzyl alcohol, yielding 40%. Then, the hot recrystallization of PbI2 prior to Hyd treatment led to the formation of red-emissive PNCs with a PLQY of up to 100%, long-term stability around 4 months under ambient air, and a relative humidity of 50-60%. Thus, CsPbI3 light-emitting diodes were fabricated to provide a maximum external quantum efficiency of up to 13.6%. We claim that the improvement of the PbX2 crystallinity offers a suitable stoichiometry in the PNC structure, reducing nonradiative carrier traps and so maximizing the radiative recombination dynamics. This contribution gives an insight into how the manipulation of the PbX2 precursor is a profitable and potential alternative to synthesize PNCs with improved photophysical features by making use of defect engineering.