Surface-ligand-triggered synthetic control of defects in nanocrystals toward high-efficiency blue electroluminescence

Colloidal nanocrystals have emerged as promising building blocks for optoelectronic applications. Although substantial research has focused on the roles of surface ligands in controlling the crystal structure, morphology, dispersibility, and surface properties of nanocrystals, limited attention has been devoted to ligand-triggered internal defect regulation. Here, we exemplify that the defects of blue-emitting CsPb(Br_xCl_{1 - x})₃ nanocrystals can be extensively regulated with surface ligands, enabling outstanding optical and electroluminescence performance. The ionization reaction of the strong dodecylbenzenesulfonic acid (DBSA) ligand, combined with its interactions with the precursors, modulates the concentration of halide ions in the reactant and controls activity. The increased DBSA results in a significantly reduced chlorine content in the nanocrystals and thus suppresses the formation of internal chlorine-related defects, evidenced by thermal admittance spectroscopy and optical characterization. Immediate application of this understanding allows defect-less CsPb(Br_xCl_{1 - x})₃ nanocrystals with efficient radiative recombination to be synthesized by controlling the DBSA dosage, realizing blue light-emitting diodes with an external quantum efficiency of 24.5% and a brightness of over 1,000 cd m^-2 at 470 nm. This work provides new insights into the underlying mechanisms governing how ligands influence nanocrystal properties beyond those well-known functions, advancing nanocrystal synthesis from empirical exploration to rational design paradigms.