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

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.