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

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 x 10(-3) to 2.09 x 10(-3) cm(2) V-1 s(-1) due to the increased pi-pi 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.