Small molecule doped polymer hole transport layers for all solution processed inverted QLED with using green solvents

Quantum-dot light-emitting diodes (QLEDs) have significant potential for use in next-generation displays. However, they face some challenges, such as low device efficiency due to poor hole injection and the use of toxic solvents. In this study, we introduce a facile method to prepare an efficient hole transport layer (HTL) using a polymer-small molecule mixture for all-solution-processed inverted QLEDs. We used poly(9-vinylcarbazole) (PVK) and tris(4-carbazoyl-9-ylphenyl)amine (TCTA) mixture for the HTL. PVK has excellent solution processability but low hole mobility, whereas TCTA has higher hole mobility but is not suitable for solution processing. Considering both the HTL performance and environmental sustainability, an appropriate green solvent (anisole) for the HTL mixture was selected by utilizing the Hansen solubility parameters and the CHEM21 solvent selection guide. When 30 wt% TCTA was doped into PVK, the external quantum efficiency improved dramatically. The proposed method can open a new way to improve the performance of QLEDs by optimizing the electrical properties of each layer using a polymer-small molecule mixture.