Multivariant ligands stabilize anionic solvent-oriented α-CsPbX₃ nanocrystals at room temperature

Cubic phase CsPbX₃ nanocrystals (NCs) are promising candidates for optoelectronic applications. However, their chemical stability heavily depends on the dynamic ionic surface. In this work, based on the interdependency of the ligands and the reaction solvent, a protocol is developed for high-quality α-CsPbX₃ under ambient conditions. Utilizing this method, the size and full width at half maximum of CsPbX₃ NCs can be simply tuned via changing the cationic ligands or reaction solvent, such as CH₃Cl, CH₂Cl₂, or toluene. One remarkable result is the synthesis of cubic CsPbI₃ NCs, for which large-scale syntheses have not been reported in the literature except for our method, due to significant phase transition at room temperature. Another result is that we have realized ultrasmall sized CsPbCl₃ NCs with emission at 385 nm for the first time. Furthermore, the elimination of reaction solvent (such as ODE, DMSO, DMF) in our protocol reduces the purification-induced surface ligand loss and the irreversible phase transition to a nonfluorescent phase. Our CsPbX₃ NCs show near-perfect photoluminescence quantum yield (PL QY) and long-term stability in the presence of moisture. Further characterization demonstrates that all the ligands, whether the initial paired X type or the degenerated hybrid L-X type, remain perfectly passivating on the defect sites throughout.