Synthesis of Cu-Modified Nickel Oxide Nanocrystals and Their Applications as Hole-Injection layers for Quantum-Dot Light-Emitting Diodes.

Solution-processed NiOx thin films have been applied as hole-injection layers (HILs) in quantum-dot light-emitting diodes (QLEDs). The commonly used NiOx HILs are prepared by the precursor-based route, which requires high annealing temperatures of over 275 °C to in situ convert the precursors into oxide films. Such high processing temperatures of NiOx HILs hinder their applications in flexible devices. Herein, we report a low-temperature approach based on Cu-modified NiOx (NiOx -Cu) nanocrystals to prepare HILs. A simple post-synthetic surface-modification step, which anchors the copper agents onto the surfaces of oxide nanocrystals, is developed to improve the electrical conductivity of the low-temperature-processed (135 °C) oxide-nanocrystal thin films. In consequence, QLEDs based on the NiOx -Cu HILs exhibit an external quantum efficiency of 17.5 % and a T95 operational lifetime of ∼2,800 h at an initial brightness of 1,000 cd m-2 , meeting the commercialization requirements for display applications. The results shed light on the potential of using NiOx -Cu HILs for realizing high-performance flexible QLEDs.