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

Abstract

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.

Hollow Cathode Gas Flow Sputtering of Nickel Oxide Thin Films for Hole‐Transport Layer Application in Perovskite Solar Cells

“…The narrowing of optical bandgap in Cu x Ni 1Àx O 1+δ films is consistent with previously reported literature. [84,85] The transmittance of NiO 1+δ films was found to be influenced by p(O 2 ), with films deposited at higher p(O 2 ) exhibiting greater transparency compared to those deposited at lower p(O 2 ) levels (Figure S5, Supporting Information). In NiO 1+δ , the Ni 3+ ions are known to be the color centers.…”

Flexible Substrate-Compatible and Efficiency-Improved Quantum-Dot Light-Emitting Diodes with Reduced Annealing Temperature of NiOx Hole-Injecting Layer

“…However, the vacuum-based processes, which involve costly and complex equipment, as well as the solution-based processes, which require high annealing temperatures (>275 °C) to induce decomposition and crystallization, present challenges in fabrication and hinder the production of flexible QLEDs. As an alternative, the pre-crystallized NiO x nanoparticles (NPs) can be utilized directly to form a uniform thin film at a relatively low annealing temperature (<150 °C) and are compatible with the flexible substrates [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. However, the electroluminescence performance of QLEDs utilizing NiO x NPs remains unsatisfactory in comparison to those based on PEDOT:PSS due to the inferior hole injection and transportation capability.…”