ULSAN — Researchers have developed an ultrahigh-resolution stretchable quantum-dot light-emitting diode (QLED) that stretches in every direction like skin while delivering the world's highest brightness for such a device, making it clearly visible outdoors. By overcoming the picture-quality loss that occurred when earlier displays were stretched, the technology is seen as a core platform that could speed the commercialization of next-generation wearable devices and electronic skin.
The National Research Foundation of Korea said on Sept. 14 that a team led by Professor Choi Moon-kee of UNIST, working with a team led by Professor Yang Ji-woong of DGIST and a team led by Kim Dae-hyeong, associate director of the Center for Nanoparticle Research at the Institute for Basic Science (IBS), had succeeded in developing a high-performance stretchable QLED. The findings were published in the online edition of Nature Nanotechnology, an international nanotechnology journal, dated Sept. 14.
Existing stretchable displays mostly relied on a design in which the light-emitting pixels stayed fixed while only the wiring stretched. With that approach, the effective light-emitting area shrank as the screen was expanded, causing picture quality to deteriorate sharply. Researchers later explored replacing the pixel material itself with stretchable substances, but the nature of flexible materials made fine patterning difficult and impeded charge transport, holding brightness to 15,000 nits or less.
The team solved the problem by devising a process called LIFT, which combines interfacial ligand exchange with intaglio transfer printing. The method precisely replaces the long insulating molecules on the surface of a quantum-dot emissive layer bonded with an elastic polymer with a shorter ligand, MPA. The process maximizes charge injection efficiency, improving device performance, while also strengthening adhesion to the intaglio mold to prevent the nanofilm from stretching or smearing.
Through this, the team produced ultrahigh-resolution fine patterns with a line width of about 700 nanometers and a resolution of roughly 16,000 pixels per inch. By precisely arranging red, green and blue emissive layers, the researchers also built a stable full-color pixel array.
The stretchable QLED maintained its light-emitting performance without mechanical damage even when stretched to as much as 1.65 times its original size. Its maximum brightness reached 53,300 nits, more than three times that of earlier stretchable light emitters and the highest level in the world.
The technology is expected to be used across next-generation soft electronics, including wearable healthcare devices, electronic skin, soft robots, free-form automotive displays and extended reality (XR) devices.
"We resolved both the drop in resolution and the limits on light-emitting performance, which had been the biggest challenges for stretchable displays, and secured core technology for commercialization," Choi said. "It will be used widely as a manufacturing platform for various next-generation soft devices, including wearables and electronic skin."
