High-efficiency quantum-dot light-emitting diodes enabled by boosting the hole injection

Abstract

Solution-processed quantum-dot light-emitting diodes (QLEDs) are attractive for large-area display panels owing to their high color purity and low-cost fabrication, but the inferior carrier mobility of the organic polymer hole-transport layer (HTL) seriously worsens the injection and transfer of holes, thus suppressing improvement in their efficiency. Here, we devise a high-carrier-mobility HTL, which is achieved by doping poly(9-vinylcarbazole) (PVK) into poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(4,4′-(N-(4-butylphenyl)] (TFB). The hole mobility is increased from 1.08 × 10⁻³ to 2.09 × 10⁻³ cm² V⁻¹ s⁻¹ due to the increased π–π stacking intensity. The highest occupied molecular orbital energy level is also downshifted to achieve good energy matching between the HTL and QDs, thus accelerating the hole-transfer capability and balancing the electron injection within the QLED. In addition, the doped HTL film shows a non-planar structure, which reduces the total internal reflection in the device. Consequently, the QLEDs present a high external quantum efficiency of 22.7%, and a luminance efficiency of 35.8 lm W⁻¹.