Ecofriendly Solvent for Green QD-LED Fabrication

Quantum-dot light emitting diode (QDLED) displays have been attracted great attention because of their high potential as a future display technology. The color performance and theoretical quantum efficiency of QDLEDs far exceed those of OLEDs, and solution processability is also regarded as an important advantage for low-cost manufacturing capabilities. However, the use of toxic and environmentally hazardous organic solvents is the dark side of solution processable QDLEDs. Chlorobenzene, chloroform, 1-4 dioxane, and 1,2-dichlorobenzene are representative toxic solvents for the manufacture of QDLEDs, and these are mainly used as solvents in the hole transport layer (HTL). For example, chlorobenzene is known as a solvent with long-term toxic effects on human causing dizziness and neurasthenia, central nervous system disease and renal degeneration, and also affects aquatic life if it enters rivers and seas. Therefore, it is important to find an environmentally friendly solvent for (HTL), but to date, this has not been studied. In this presentation, we report a new methodology for finding solvents that are environmentally friendly, have good processability, and have solvent orthogonality with adjacent layers. Using the proposed methodology, which is designed based on Hansen solubility parameters (HSPs) and solvent selection guidelines (SSGs), an alternative green solvent for HTL was found and an all-solution processed eco-friendly QDLED device was fabricated. The HTL layer fabricated using the green solvent exhibits lower roughness and does not have interlayer mixing; as a result, the device shows superior electro-optical performance compared to the reference device using chlorobenzene solvent. Thus, the new solvent selection method can provide a green solution for future QDLED displays.