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

Abstract Solution‐processed NiO x thin films have been applied as hole‐injection layers (HILs) in quantum‐dot light‐emitting diodes (QLEDs). The commonly used NiO x 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 NiO x HILs hinder their applications in flexible devices. Herein, we report a low‐temperature approach based on Cu‐modified NiO x (NiO x ‐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 NiO x ‐Cu HILs exhibit an external quantum efficiency of 17.5 % and a T 95 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 NiO x ‐Cu HILs for realizing high‐performance flexible QLEDs.