Interfacial Layer to Utilize Charge Transfer Complex for Enhancing Hole Injection Properties in Quantum Dot Light-Emitting Diodes

Abstract

Quantum dot light-emitting diodes (QD-LEDs) have struggled with charge imbalance due to inefficient hole injection. Traditional strategies focus on enhancing the hole transport layer (HTL) and reducing the injection barrier at the HTL-QD interface. Although these approaches improve hole injection at specific interfaces, they fail to ensure efficient hole injection across all interfaces in QD-LEDs. Therefore, engineering the hole injection layer (HIL) is required to comprehensively address these challenges. Optimized HIL designs align the energy levels of the anode/HIL and the HTL, enable efficient hole injection, and suppress leakage current-thereby improving both performance and stability of QD-LEDs. These findings highlight the importance of comprehensive HIL engineering. In this study, a multilayered HIL structure composed of a poly(9-vinylcarbazole) (PVK): phosphomolybdic acid (PMA) layer coupled with MoO3 is proposed. The PVK:PMA layer forms charge-transfer complexes (CTCs), enhancing hole injection into the HTL, while MoO3 scavenges excess electrons, thereby reducing non-radiative recombination. Additionally, the high ionization potential (IP) of PVK:PMA alleviates the hole injection barrier that may arise from the MoO3 and the organic HTL. This HIL structure doubles the power efficiency and extends the device lifetime by six times compared with conventional designs, demonstrating its potential for high-efficiency, stable QD-LEDs.