Composite Hole Transport Layer Consisting of High-Mobility Polymer and Small Molecule With Deep-Lying HOMO Level for Efficient Quantum Dot Light-Emitting Diodes

Improving hole injection is a critical issue for further boosting the brightness and efficiency of quantum dot light-emitting diodes (QLEDs) with an organic-inorganic hybrid structure. In this work, a small molecule of 4,4’-bis-(carbazole-9-yl)biphenyl (CBP) with a deep-lying HOMO level was doped into high mobility polymer of poly(9,9-dioctylfluorene-co-N-(4-(3-methyl- propyl)) diphenylamine) (TFB) to construct an efficient composite TFB:CBP hole transport layer (HTL). Green QLEDs based on such solution-processed composite HTLs exhibited a maximum luminance of 90159 cd/m2, with a peak current efficiency of 21.6 cd/A and power efficiency of 12.3 lm/W. These values were over one-order of magnitude larger than those obtained in the CBP-only devices and also much larger than those in the TFB-only devices.