Enhanced Hole Injection in Quantum Dot Light-Emitting Diodes Using Sputtered Co-Doped NiO Layers

In this study, we fabricated high-performance green quantum dot light-emitting diodes (QLEDs) by introducing NiMgLiO thin films as optimized hole injection layer materials, deposited via radio frequency sputtering. The NiO matrix was co-doped with Mg and Li to modulate its electronic structure and enhance its charge transport properties. This co-doping approach substantially increased the Ni3+ ion concentration and deepened the valence band maximum, thereby reducing the hole injection barrier and improving the electrical conductivity of the NiO films. These modifications were associated with improved device performance, consistent with improved charge balance within the QLED. Consequently, the external quantum efficiency of the QLEDs increased from 6.83% to 9.02%, while the maximum luminance rose from 41711 to 57636 cd/m2. To the best of our knowledge, these values are the highest reported among sputtered NiO-based green QLEDs to date. Overall, this study demonstrates that co-doping with Mg and Li, in combination with a scalable sputtering process, offers a robust strategy for tuning the electrical and optical properties of oxide-based HILs, thereby advancing the development of high-efficiency, stable QLED technologies.