Suppressing Degradation in QLEDs via Doping ZnO Electron Transport Layer by Halides

Recent findings show that electron transport layers (ETLs) significantly influence the electroluminescence (EL) lifetime of quantum-dot light-emitting diodes (QLEDs). In this work, it is found that using halide dopants in the ZnO ETL significantly enhances device EL lifetime. Electrical, photoluminescence, and photoelectron spectroscopy measurements on QLEDs and specially designed devices are used for elucidating the root causes of the lifetime enhancement. Results show that charge transfer occurs at the ZnO/QDs interface in QLEDs, producing positively charged states in ZnO, subsequently leading to luminance loss, a mechanism that contributes to EL loss. Furthermore, XPS studies show that electrical stress of QLEDs leads to an increase in the concentration of ZnO species with higher oxidative states and that a correlation between the magnitude of EL loss and the concentration of these species exists. The use of halide dopants is found to reduce this interfacial charge transfer and the formation of the ZnO species with higher oxidative states, possibly due to the dopants role in acting as hole scavengers that trap and efficiently neutralize holes in ZnO. The findings underscore the significant role that managing positive charges in ZnO plays in EL lifetime and provide an effective strategy for achieving highly stable QLED.