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Article by Professor Kang’s Research Team from the Chemical and Biomolecular Engineering Department

Published in Prestigious Journal Nature Nanotechnology

 - Successfully developed a QD-based patterning technique for a large ultra-high-resolution area -

- One step closer to achieving future-oriented displays -



 (From left) Professor Kang Moon-sung and Researcher Kim Hyeok-jun of the Chemical and Biomolecular Engineering Department

 


On Friday, August 12, research findings revealed by a team led by Professor Kang Moon-sung of the Department of Chemical and Biomolecular Engineering (co-corresponding authors: Professor Bae Wan-ki of Sungkyunkwan University and Ph.D. Kang Chan-mo of the Electronics and Telecommunications Research Institute (ETRI)) were published online in Nature Nanotechnology (Impact Factor 40.523), one of the most prestigious journals in the field of nano science.


For their outstanding color gamut and high luminance efficiency, colloidal quantum dots (QDs) have gained attention as light-emissive materials for next-generation displays. However, in order to make QD-based displays, a patterning process that turns red, green, and blue QDs into pixels is required. Up to now, developing a technique that implements patterning without compromising the electrical and optical characteristics of QDs has remained one of the most challenging tasks for achieving next-generation QD-based displays.


Professor Kang’s research team worked out a method that enables non-destructive, ultra- high-resolution patterning of QDs – a technique that can be immediately applied to various solution-based processes. Of note, the team devised QD materials that employ photocrosslinkable ligands (PXLs), which are grafted onto the surface of QDs, thereby achieving the patterning process without the presence of chemical additives.


Photocrosslinkable ligands (PXLs) create covalent bonds with neighboring ligands in response to ultraviolet (UV) irradiation. Using a proper solvent, portions that were selectively not irradiated with UV ray can be removed to achieve patterned QD films with a simple process. With this technique, the research team was able to attain QD patterns that demonstrate a resolution of up to 15,000 pixels per inch (ppi) on a six-inch wafer. The resolution of 15,000 ppi is a level that far exceeds the threshold of 3,000 ppi required for AR- and VR-use displays. This means that the technology has laid the foundation for QDs to be applied to next-generation ultra-high-resolution displays.


Since the application of PXLs in no way undermines QD dispersions, the research team also confirmed that this technique could be instantly applied to all solution-based processes (photolithography and inkjet printing systems) to which QDs have been conventionally applied. In addition, the team revealed that the patterning process based on this technique did not compromise the optical or electrical transport properties of QD films. As a result, the team was able to achieve patterned QD LEDs.



▲ Schematic illustration of a dual-ligand QD structure and photocrosslink reaction




▲ Resulting RGB QD patterns

 


Professor Kang observed, “This research outcome is expected to make substantial contributions to the next-generation display industry, as this technique does not undermine the properties of materials and can be applied using equipment already deployed most commonly at display and semiconductor sites.”


This research was supported by the “Nano-Material Technology-Development Program” and “Individual Basic Research (Consolidator Research) Program” funded by the Ministry of Science and ICT (MSIT) and the National Research Foundation of Korea (NRF). This research was also supported by Samsung Display.


▶ Title of article: Direct Patterning of Colloidal Quantum Dots with an Adaptable Dual-Ligand Surface

▶ Link: https://www.nature.com/articles/s41565-022-01182-5


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