Highly Efficient Blue Light‐Emitting Diodes with Low Efficiency Roll‐Off Based on Large‐Size and Gradient Alloy Quantum Dots

Abstract Quantum dot light‐emitting diodes (QD‐LEDs) exhibit significant advancements in new‐generation display and lighting applications that require high efficiency, high brightness, and high resolution, such as automotive heads‐up displays (HUD) and augmented reality (AR)/virtual reality (VR). However, state‐of‐the‐art blue QD‐LEDs have yet to meet these requirements due to defect‐induced nonradiative recombination and unbalanced carrier injection. Herein, a novel blue quantum dots (QDs), which feature a large‐size (≈10.5 nm) CdSe@ZnSe gradient alloy core and an ultra‐thin ZnS outermost shell, have been demonstrated through reversely adding seed crystal with composition regulating. The as‐synthesized QDs possess near‐unity quantum yield, shallower hole injection barrier, and excellent photo‐chemical stability. By employing CdSe@ZnSe/ZnS QDs as the emitting layers (EML), blue QD‐LEDs with electroluminescence (EL) peak at 475 nm exhibit a record‐high external quantum efficiency (EQE) of 24.3% and low efficiency roll‐off, sustaining over 90% of the maximum EQE within the luminance of 2,220–22,910 cd m −2 . Key to success is the suppression of defect‐related nonradiative recombination, reduced leakage current, and improves charge injection balance through QD structural engineering. This work indicates a significant potential of newly developed large‐size and gradient alloy QDs in promoting the commercialization of QD‐LEDs.