ZnO nanoparticles (NPs) are widely used as the electron transport layer (ETL) in quantum dot light-emitting diodes (QLEDs) owing to their suitable electrical properties. However, because of the well-aligned conduction band levels, electrons in QDs can be spontaneously transferred to adjacent ZnO NPs, leading to severe exciton dissociation, which reduces the proportion of radiative recombination and deteriorates the device efficiency. In this work, Al-doped ZnO NPs are thoroughly investigated as a replacement of ZnO for QLEDs. The energy band structures of Al-doped ZnO are modified by adjusting the concentration of Al dopants. With the increasing Al content, the work function and the conduction band edge of ZnO are gradually raised, and thus the charge transfer at the interface of QDs/ETL is effectively suppressed. Consequently, the green QLEDs with 10% Al-doped ZnO NPs exhibit maximum current efficiency and external quantum efficiency of 59.7 cd/A and 14.1%, which are about 1.8-fold higher than 33.3 cd/A and 7.9% of the devices with undoped ZnO NPs. Our work suggests that Al-doped ZnO NPs can serve as a good electron transport/injection material in QLEDs and other optoelectronic devices.
Keywords: Al-doped ZnO nanoparticles; QLEDs; charge transfer; electron transport layer; metal oxide.