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

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 1; no. 4; pp. 152 - 1526
• Main Authors: Cheng, Chunyan, Liu, Aqiang, Ba, Guohang, Mukhin, Ivan S, Huang, Fei, Islamova, Regina M, Choy, Wallace C. H, Tian, Jianjun
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 20.10.2022
• Subjects: Carrier mobility; Efficiency; Energy levels; Hole mobility; Light emitting diodes; Molecular orbitals; Planar structures; Polyvinyl carbazole; Quantum dots; Quantum efficiency
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d2tc03138h

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 cm 2 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 . We devise a high-carrier-mobility hole-transport layer with less hole loss, obtained via doping poly(9-vinylcarbazole) into poly[(9,9-dioctylfluorenyl-2,7-diyl)- alt -(4,4′-( N -(4-butylphenyl)))], achieving high external quantum efficiency QLEDs (22.7%).