Utilization of Nanoporous Nickel Oxide as the Hole Injection Layer for Quantum Dot Light-Emitting Diodes

[Image: see text] Nickel oxide (NiO(x)) has been extensively investigated as the hole injection layer (HIL) for many optoelectronic devices because of its excellent hole mobility, high environmental stability, and low-cost fabrication. In this research, a NiO(x) thin film and nanoporous layers (NPLs) have been utilized as the HIL for the fabrication of quantum dot light-emitting diodes (QLEDs). The obtained NiO(x) NPLs have spongelike nanostructures that possess a larger surface area to enhance carrier injection and to lower the turn-on voltage as compared with the NiO(x) thin film. The energy levels of NiO(x) were slightly downshifted by incorporating the nanoporous structure. The amount of Ni(2)O(3) species is higher than that of NiO in the NiO(x) NPL, confirming its good hole transport ability. The best QLED was achieved with a 30 nm thick NiO(x) NPL, exhibiting a maximum brightness of 68 646 cd m(–2), a current efficiency of 7.60 cd A(–1), and a low turn-on voltage of 3.4 V. More balanced carrier transport from the NiO(x) NPL and ZnO NPs/polyethylenimine ethoxylated (PEIE) is responsible for the improved device performance.