Efficient Red Quantum Dot Light-Emitting Diodes Realized by PEDOT:PSS-Free Ternary Blended Hole-Transport Layers with a Lowered Energy Barrier and Suppressed Leakage

Quantum-dot light-emitting diodes (QLEDs) have recently approached over 20% external quantum efficiency (EQE); however, maintaining sustained carrier balance remains challenging due to inefficient hole injection caused by the deep valence band of quantum dots. Inspired by bulk-heterojunction (BHJ) hole-transport layers (HTLs) that simultaneously enhance hole mobility and suppress electron leakage, we herein introduce a ternary polymer blended HTL composed of PTAA, TFB, and Poly-TPD. A staircase of nearly degenerate HOMO levels (∼5.20, ∼5.31, and ∼5.46 eV) funnels holes from ITO to QDs while simultaneously raising an energy barrier that blocks electron leakage. Furthermore, the omission of the PEDOT:PSS layer instantly boosts the transmittance of the PTAA:Poly-TPD:TFB film. Consequently, red QLEDs fabricated with this ternary blended HTL achieved a peak EQE of 26.01%, a maximum luminance of 378,700 cd/m2. The operational lifetime of the QLEDs with the ternary blended HTL was extended by 2.22 times compared to that of conventional control devices. Our work elucidates the critical role of HTL engineering in minimizing exciton quenching and provides a generalizable design strategy for high-efficiency electroluminescent devices.