Ligands Optimization Governed by Solubility Principles for Pure Blue Emission in Mixed-Halide Perovskite LEDs

Mixed-chloride/bromide perovskite nanocrystals (PeNCs) possess unique advantages for pure blue emission but suffer from severe halogen segregation. While ligand exchange is a promising method to improve stability, there are limited studies on comparative evaluation of the ligand ion pair combinations. We conduct a comprehensive investigation of the ligand exchange process by combining different ion pairs. Surprisingly, changes of ligand ion combinations cause a deviation from pure blue emission of CsPbBrxCl3–x, even without intentional halogen alteration. This spectral shift is attributed to the halogen redistribution, which is dominated by the solubility principle in a nonpolar environment. With a detailed ligand-exchange study, we demonstrate pure-blue perovskite light-emitting diodes (PeLEDs) with an external quantum efficiency (EQE) of 7.45% and an operational half-lifetime (T50) of 61 min at an initial luminance of 100 cd m–2. Our findings provide a ligand selection guideline and promote mixed-halide, pure blue PeLEDs for practical applications.