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

Nickel oxide (NiOx) 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 NiOx thin film and nanoporous layer (NPL) have been utilized as the HIL for the fabrication of quantum dot light-emitting diodes (QLEDs). The obtained NiOx NPLs have sponge-like nanostructures that possess larger surface area to enhance carrier injection and to lower turn-on voltage, as compared with the NiOx thin film. The energy levels of NiOx were slightly downshifted by incorporating nanoporous structure. The amount of Ni2O3 species is higher than NiO in the NiOx NPL, confirming its good hole transport ability. The best QLED was achieved with 30 nm-thick NiOx NPL, revealing 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 NiOx NPL and ZnO NPs/PEIE is responsible for the improved device performance.