Quantum dot light-emitting diodes with high efficiency at high brightness via shell engineering.

Quantum dot light-emitting diodes (QD-LEDs) have made great development in the performance. However, the efficiency droop at high brightness limits their applications in daylight displays and outdoor lightings. Herein, we systematically regulate the shell structure and composition, and the results indicate that CdSe-based QDs with ZnSe interlayer and thinner ZnSeS outermost layer as emitting layers (EML) enable high-performance QD-LEDs. Accordingly, the devices exhibit peak external quantum efficiency (EQE) of 22.9% with corresponding brightness of 67,840 cd/m, and this efficiency can be still maintained > 90% of the maximum value even at 100,000 cd/m, which satisfies the requirements for high-brightness display and lighting applications. This strong performance is mainly attributed to the ZnSe/ZnSeS graded shell that smooths the injection barrier between QD EML and the adjacent hole transport layers (HTL), and then improves the hole injection and charge injection balance, in particular at the high luminance and/or at high current density.