Improved Charge Balance in Quantum Dot Light-Emitting Diodes with Sputtered Li-doped NiO and a Dual-function Self-Assembled Monolayer

Achieving high-performance quantum dot light-emitting diodes (QLEDs), which are promising candidates for next-generation displays, requires balanced charge injection in terms of electrons and holes while minimizing nonradiative recombination. In this study, to improve charge balance in QLEDs, we enhanced the electrical conductivity of the hole injection layer by depositing NiO:Li thin films via radio frequency sputtering under varying oxygen partial pressures. Furthermore, a self-assembled monolayer (SAM) made of 4-trifluoromethyl benzoic acid was introduced on the NiO:Li films to reduce the hole injection barrier and facilitate efficient hole transport. This SAM was also applied on top of the quantum dot layer to act as an electron blocking layer by increasing the electron injection barrier, thereby suppressing excessive electron injection. The optimized QLEDs exhibited a maximum external quantum efficiency of 9.41% and a peak luminance of 50,199 cd/m2. These findings demonstrate a viable strategy to enhance QLED performance via the synergistic modulation of charge injection and recombination dynamics.