Enhanced charge injection in quantum dot light-emitting diodes enabled by discotic liquid crystals

Abstract

Recent progress in quantum dot light-emitting diodes (QLEDs) has substantially improved their external quantum efficiency (EQE), nearing the theoretical limit of 25–30% for primary-color devices. Nevertheless, this peak performance is confined to low current densities and luminance levels, with a significant efficiency roll-off observed at elevated currents. This phenomenon has been primarily attributed to imbalanced charge carrier injection under high-current operation. While charge imbalance mitigation strategies hold critical importance, research on novel hole transport layer (HTL) materials addressing this issue remains relatively underexplored. Herein, we propose a discotic liquid crystals (DLCs) material, 2,3,6,7,10,11-hexabutoxytriphenylene (HAT-4), as an innovative HTL candidate for QLEDs. The HAT-4 system demonstrates enhanced hole mobility coupled with favorable energy level alignment for efficient hole injection into QD layers. However, its implementation is hindered by suboptimal film morphology characterized by excessive crystallinity. To address this limitation, we strategically introduced poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(4,4′-(N-(4-butylphenyl))] (TFB) as a morphology-regulating agent. Notably, the optimized HAT-4/TFB (80:20 wt%) hybrid HTL enables remarkable device performance at 5 V, achieving 953 mA·cm−2 (2.2× enhancement vs. TFB control) and 380,000cd·m2 (2.1× improvement vs. TFB control), respectively. These breakthroughs substantiate the effectiveness of DLC-based hybrid HTLs in suppressing efficiency roll-off while achieving high brightness, thus providing a viable pathway toward high-performance QLED commercialization.