Highly efficient inverted quantum dot light-emitting diodes employing sol-gel derived Li-doped ZnO as electron transport layer

Zinc oxide (ZnO) is widely used as an electron transport layer (ETL) in quantum dot light-emitting diodes (QLED) because of its advantages of appropriate energy level and the simple process at low temperature. However, its high conductivity and abundant surface defects have become essential factors limiting the development of QLED. Here, we employ sol-gel derived lithium (Li)-doped ZnO (LZO) film as an ETL for inverted red QLED to achieve low-cost and high-efficiency QLED. We show that the conduction band minimum, the density of oxygen defects and conductivity of ZnO can be tuned by Li-doping. Consequently, the red QLED with 3 wt% Li-doped ZnO ETL exhibit maximum external quantum efficiency (EQE) and current efficiency of 16.4% and 24.1 cd/A, respectively, which are about 1.3-fold greater than those of the device with ZnO ETL. The Li-doping in sol-gel derived ZnO provides a feasible strategy for low-cost and high-performance inverted QLEDs.