DAEGU, South Korea, August 29, 2024 — Advances in wearable, mobile and Internet of Things technologies are driving demand for high-resolution displays. Efficient ultra-high-resolution displays can enhance the immersive experience of AR and VR applications and make using AR, VR and wearable technology more comfortable.
Researchers from the Daegu Gyeongbuk Institute of Science and Technology (DGIST), Ulsan Institute of Science and Technology (UNIST), and Institute of Basic Science (IBS) have developed a technique to create ultra-high definition screens for emerging display technologies. Using the technique, called dual-layer dry transfer printing, the researchers created highly efficient LEDs with quantum dots (QLEDs).
Conceptual diagram of dual-layer dry transfer printing technology. This technique offers high-resolution pixel patterning that can be used to create ultra-high resolution, highly efficient light-emitting devices for next-generation AR, VR, and wearable displays. Courtesy of DGIST, UNIST, IBS.
Quantum dots (QDs) have many advantages as emissive materials for displays, including high luminescence quantum yield, wide color range, and high color purity. However, the development of QD patterning processes for high-resolution pixels and efficient QLEDs is still in its early stages. Conventional dry transfer printing, in which QD ink is applied to a substrate, can be used to create ultra-high-resolution pixels. However, this method has not been used in practical display manufacturing due to its low luminous efficiency of less than 5%.
The dual-layer dry transfer printing technology allows the light-emitting layer and electron transport layer of the device to be transferred to the substrate simultaneously, which reduces the interfacial resistance within the device and facilitates the control of electron injection and leakage charge transport during the fabrication process. By minimizing the leakage current, the external quantum efficiency (EQE) of the QLED device was improved to 23.3%.
“By using a bilayer dry transfer technique that reduces the interface resistance and facilitates electron injection, we have fabricated a light-emitting device that simultaneously achieves ultra-high resolution and high efficiency,” said Professor Yang Ji-eun. “The bilayer thin-film light-emitting device fabricated using this technique exhibited a high EQE of up to 23.3%, which is comparable to the theoretical maximum efficiency of quantum dot light-emitting devices, and is a very significant result.”
Surface engineering of the viscoelastic stamp enabled the researchers to create RGB pixelated patterns at 2565 pixels per inch (PPI) and monochrome QD patterns at approximately 20,526 PPI using a dual-layer transfer printing technique.
Using quantum dot/zinc oxide (QD/ZnO) thin films, the researchers created ultra-high-resolution QD patterns with up to 25,526 PPI and achieved an area of 8 cm x 8 cm by repeated printing. The researchers demonstrated highly efficient wearable QLEDs fabricated using a bilayer dry transfer printing technique, confirming that devices can be mass-produced and commercialized using this technology.
The dual-layer dry transfer printing technique offers high-resolution pixel patterning capability, potentially supporting the development of full-color QD displays for next-generation display technologies by creating ultra-high resolution, highly efficient light-emitting devices that can produce bright light even at low currents.
“I am pleased that through this research, we have developed technology that will enable higher resolution screens for VR and AR,” said Professor Choi Moon-ki. “Through further research, we will strive to enable the widespread application of quantum dots with high color reproducibility and color purity to smart wearable devices.”
This research was published in Nature Photonics (www.doi.org/10.1038/s41566-024-01496-x).
