Sequential Improvement from Cosolvents Ink Formulation to Vacuum Annealing for Ink-Jet Printed Quantum-Dot Light-Emitting Diodes

• Published in: Materials 2020-10, Vol.13 (21), p.4754
• Main Authors: Han, Young Joon, Kim, Do Yeob, An, Kunsik, Kang, Kyung-Tae, Ju, Byeong-Kwon, Cho, Kwan Hyun
• Format: Article
• Language: English
• Subjects: Annealing; Boiling points; Current efficiency; Efficiency; Emission analysis; Glass substrates; Hexanes; Inkjet printing; Light emitting diodes; Optimization; Quantum dots; Quantum efficiency; Reynolds number; Solvents; Surface tension; Vacuum annealing; Vapor pressure; Viscosity
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma13214754

Optimization of ink-jet printing conditions of quantum-dot (QD) ink by cosolvent process and improvement of quantum-dot light-emitting diodes (QLEDs) characteristics assisted by vacuum annealing were analyzed in this research. A cosolvent process of hexane and ortho-dichlorobenzene (oDCB) was optimized at the ratio of 1:2, and ink-jetting properties were analyzed using the Ohnesorge number based on the parameters of viscosity and surface tension. However, we found that these cosolvents systems cause an increase in the boiling point and a decrease in the vapor pressure, which influence the annealing characteristics of the QD emission layer (EML). Therefore, we investigated QLEDs' performance depending on the annealing condition for ink-jet printed QD EML prepared using cosolvents systems of hexane and oDCB. We enhanced the quality of QD EML and device performance of QLEDs by a vacuum annealing process, which was used to prevent exposure to moisture and oxygen and to promote effective evaporation of solvent in QD EML. As a result, the characteristics of QLEDs formed using ink-jet printed QD EML annealed under vacuum environment increased luminescence (L), current efficiency (CE), external quantum efficiency (EQE), and lifetime (LT ) by 30.51%, 33.7%, 21.70%, and 181.97%, respectively, compared to QLEDs annealed under air environment.