Maximizing Next-Generation QLED Display Efficiency by Completely Eliminating 'Coffee Ring'

Research Team Led by Professor Kim Hyungsoo at KAIST

Schematic diagram of multi-array uniform quantum dot pattern fabrication technology. Image courtesy of KAIST.

[Asia Economy Reporter Kim Bong-su] Domestic researchers have developed a technology that can maximize the production efficiency of next-generation displays.

KAIST announced on the 2nd that a research team led by Professor Kim Hyung-soo of the Department of Mechanical Engineering has implemented a technology that can perfectly and uniformly pattern the coffee ring marks of quantum dots, the core material of display devices, from circular to polygonal shapes regardless of the pattern form.

Recently, quantum dots have been spotlighted as a core material for next-generation displays. Although there have been significant efforts to pattern them using inkjet printing technology, issues such as limited mass production capability, resolution constraints, and the coffee ring phenomenon occurring during the process have been pointed out as major problems that greatly reduce efficiency.

When a cup containing coffee is placed on a desk and then removed, the coffee stain left behind gradually concentrates at the edges over time, forming a ring-shaped mark. The coffee ring phenomenon refers to the inefficiency in display processing caused by the uneven evaporation rate on the droplet surface as the solvent droplet dries on a solid surface, making uniform surface treatment impossible during the display process.

Professor Kim, based on years of research controlling the coffee ring effect, recently announced a groundbreaking technology that completely eliminates coffee rings.

In addition to coffee ring marks, various pattern shapes have been proposed to improve display resolution; however, polygonal shapes generally tend to exhibit more severe coffee ring effects than circular ones. This study introduces a technology that can completely eliminate coffee rings regardless of the geometric shape of the quantum dot pattern. The research team successfully created a uniform pattern without any coffee ring at the scale of 100 micrometers (㎛) (one ten-thousandth of a meter) by appropriately adjusting the solvent components in which the quantum dots are dissolved and allowing the droplet to undergo a simple evaporation process without complex physical-chemical procedures.

A team official stated, "Quantum dot patterns for QLEDs can be sensitively affected by surrounding process factors. Using inkjet-based droplet ejection printing technology and the spontaneous Marangoni effect generated by the evaporation of droplet clusters, we prevented material damage and ensured pattern uniformity." They added that, in addition to experimental technology development, the study provides a fundamental explanation and control variables for the principles of Marangoni generation and the regulation of Marangoni mixed flow intensity based on theoretical models.

Professor Kim Hyung-soo said, "If the results of this study are applied to inkjet printing processes for actual display mass production, it will be possible to implement high-efficiency next-generation QLED displays with red, green, and blue quantum dot patterns without complex physical-chemical processes." He also mentioned that by expanding this coffee ring elimination technology to expensive materials used in printed electronics, it will be possible to effectively perform large-area printing and simplify the patterning process, thereby contributing to improved economic feasibility.

This research was conducted with support from the National Research Foundation of Korea through the Individual Basic Mid-career Research Program (NRF-2021R1A2C2007835) and in collaboration with Professor Jung Yeon-sik’s research team from the Department of Materials Science and Engineering at KAIST. It was published on the 7th of last month in the international academic journal Advanced Science.

This content was produced with the assistance of AI translation services.