Self-Assembled\nMonolayer-Functionalized NiO Hole Injection\nlayer for Improved Charge Injection in Quantum Dot Light-Emitting\nDiodes

The development of quantum dot light-emitting\ndiodes (QLEDs) represents\na promising advancement in next-generation display technology. However,\nthere are challenges, especially in achieving efficient hole injection,\nmaintaining charge balance, and replacing low-stability organic materials\nsuch as PEDOT:PSS. To address these issues, in this study, self-assembled\nmonolayers (SAMs) were employed to modify the surface properties of\nNiO, a hole injection material, within the structure of ITO/HIL/TFB/QDs/ZnMgO/Al\nQLEDs. Specifically, using Br-2PACz-based SAMs resulted in surface\ndefect passivation, improved hole injection, reduced exciton quenching,\nand enhanced electrical characteristics. Notably, QLEDs based on (NiO+Br-2PACz)\ndemonstrated a turn-on voltage of 2.4 V, a maximum external quantum\nefficiency (EQE) of 8.30%, a maximum luminance of 88,831 cd/m<sup>2</sup>, and a maximum current efficiency of 32.78 cd/A. Compared\nto NiO-based QLEDs, these results represent a reduction in turn-on\nvoltage by approximately 1.5 V, a 1.99-fold increase in EQE, and a\n3.63-fold increase in luminance, indicating significantly enhanced\nperformance with notable improvements in turn-on voltage, EQE, and\nluminance. They also showed higher EQE and luminance than PEDOT:PSS-based\nQLEDs; this could be attributed to the downshifting of energy levels\nby Br-2PACz, which reduced the hole injection barrier, increased the\nconductivity, and improved charge balance. In particular, the reduction\nin exciton quenching and the increase in electrical conductivity contributed\nsignificantly to the overall performance enhancement of the (NiO+Br-2PACz)-based\nQLEDs. This paper proposes a simple method for inorganic hole injection\nlayer functionalize and application.