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 their advantages of appropriate energy levels and the simple process at low temperatures. However, its high conductivity and abundant surface defects have become essential factors limiting the development of QLED. Here, we employed 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. The optimal doping content (3 wt.%) LZO (LZO3) QLED exhibits maximum external quantum efficiency (EQE), and current efficiency is approaching 16.4% and 24.1cd/A, respectively, which is1.3-fold greater than that of the device with ZnO ETL. It is the highest EQE value for the inverted red QLED adopting sol-gel ZnO as ETL reported so far. The Li-doping in sol-gel derived ZnO provides a feasible strategy for low-cost and high-performance inverted QLEDs