Self-Assembled Monolayer-Functionalized NiO Hole Injection layer for Improved Charge Injection in Quantum Dot Light-Emitting Diodes

The development of quantum dot light-emitting diodes (QLEDs) represents a promising advancement in next-generation display technology. However, there are challenges, especially in achieving efficient hole injection, maintaining charge balance, and replacing low-stability organic materials such as PEDOT:PSS. To address these issues, in this study, self-assembled monolayers (SAMs) were employed to modify the surface properties of NiO, a hole injection material, within the structure of ITO/HIL/TFB/QDs/ZnMgO/Al QLEDs. Specifically, using Br-2PACz-based SAMs resulted in surface defect passivation, improved hole injection, reduced exciton quenching, and enhanced electrical characteristics. Notably, QLEDs based on (NiO+Br-2PACz) demonstrated a turn-on voltage of 2.4 V, a maximum external quantum efficiency (EQE) of 8.30%, a maximum luminance of 88,831 cd/m2, and a maximum current efficiency of 32.78 cd/A. Compared to NiO-based QLEDs, these results represent a reduction in turn-on voltage by approximately 1.5 V, a 1.99-fold increase in EQE, and a 3.63-fold increase in luminance, indicating significantly enhanced performance with notable improvements in turn-on voltage, EQE, and luminance. They also showed higher EQE and luminance than PEDOT:PSS-based QLEDs; this could be attributed to the downshifting of energy levels by Br-2PACz, which reduced the hole injection barrier, increased the conductivity, and improved charge balance. In particular, the reduction in exciton quenching and the increase in electrical conductivity contributed significantly to the overall performance enhancement of the (NiO+Br-2PACz)-based QLEDs. This paper proposes a simple method for inorganic hole injection layer functionalize and application.