Ligand stripping-induced asymmetric charge transport suppression for enhanced performance of blue quantum dot light-emitting diodes

Abstract

Surface ligand engineering plays a key role in optimizing the performance of colloidal quantum dot light-emitting diodes (QD-LEDs). While conventional ligand engineering strategies rely on ligand exchange processes that include both the removal of native ligands and the introduction of alternative passivating molecules, such approaches often introduce chemical complexity and overlapping effects. In this study, we demonstrate that selectively removing native oleic acid ligands, without introducing new ligands, can effectively enhance device efficiency and operational lifetime. Using trimethyloxonium tetrafluoroborate as a mild stripping agent, we tuned ligand density in ZnSeTe/ZnSe/ZnS blue quantum dots with controlled treatment concentrations. Thermogravimetric analysis confirmed progressive ligand removal, while photoluminescence (PL) quantum yield and time-resolved PL measurements revealed a concomitant increase in surface trap states. Despite the introduction of additional defects, the resulting QD-LEDs exhibited improved performance: the current efficiency increased from 9.0 to 14.4 cd A−1, and the operational lifetime LT50 (time to 50% luminance decay) extended from 17.9 to 61.5 h. Single-carrier measurements revealed that although both hole and electron transport decreased following ligand stripping, electron mobility was more strongly suppressed than hole mobility, resulting in improved charge balance. These findings suggest that surface defect formation, often considered detrimental, can instead be leveraged through careful ligand density control as a viable tool for enhancing QD-LED performance.