Self-Assembled Monolayer Enables Hole Injection Layer-Free Quantum-Dot Light-Emitting Diodes with Over 31% External Quantum Efficiency

PEDOT:PSS is widely employed as a hole injection layer (HIL) in quantum dot light-emitting diodes (QLEDs). However, its hygroscopicity and acidity can lead to electrode corrosion and compromise device stability. Here, high-performance HIL-free QLEDs are demonstrated, enabled by carbazole-based self-assembled monolayers (SAMs) functioning as an interfacial modification layer (IML) on ITO. The SAMs boost ITO work function for direct hole injection and use shallow low unoccupied molecular orbital level (LUMO) to curb leakage. Consequently, the QLED incorporating 2-(9H-carbazol-9-yl)ethyl phosphonic acid (2PACz) IML achieves high external quantum efficiency (EQE) of 31.33%, an excellent brightness of 430 900 cd m − 2 and a long T 95 operational lifetime of 5971 h at 1000 cd m −2 , all of which significantly outperforming the PEDOT:PSS device. To the best of the knowledge, these performances are the highest ever reported for HIL-free QLEDs. Furthermore, the 2PACz-based QLEDs can also sustain high EQE (≈20%) at extremely low current densities of 0.015 mA cm −2 (3.6 cd m − 2 ), which is very beneficial for displays to achieve high efficiency at low brightness. This work paves the way for stabler, high-performance QLEDs and faster commercialization.