High-Performance Blue Quantum Dot Light-Emitting Diodes with Balanced Charge Injection

Abstract

The balance of hole–electron injection is always a vital factor for the luminance, efficiency and working lifetime of quantum-dot light-emitting diodes (QLEDs), especially blue QLEDs. However, currently most approaches proposed to solve this issue involve tedious optimization of device architecture or material composition. Here, high-performance blue QLEDs are reported based on CdZnS/ZnS quantum-dot (QDs) by utilizing ZnO nanoparticles (NPs) and Al:Al 2 O 3 as electron-transporting layer (ETL) and cathode materials, respectively. The effect of post-annealing temperature on the trap state density in ZnO NPs and the related mechanisms are investigated through optical and photoelectron spectroscopies. The method of controlling ZnO NPs annealing temperature leads to controllable electron-mobility of ETL, which ultimately optimizes the balance of charge injection. Together with partially oxidized Al cathode (Al:Al 2 O 3 ), high-performance blue QLEDs are fabricated with luminance and external quantum efficiency (EQE) up to 27 753 cd m −2 and 8.92%. As far as is known, the peak luminance achieved is the record of deep blue QLEDs. This simple method for regulating charge injection balance via annealing temperature requires no modification of device architecture, making it applicable for a variety of QLEDs structures.