Wearables are exposed to whatever the wearer experiences throughout a day, and finding reliable light emitter displays that allow textiles to retain flexibility, breathability and comfort can be a challenge. But a team of researchers from the Korea Advanced Institute of Science and Technology (KAIST) believes that it has found a candidate for meeting the challenge. According to an article in Printed Electronics World, the team has developed a high-luminance organic LED (OLED) fiber that can be woven into textiles and knitted garments.
Fiber OLEDs that are used to create light-emitting thread have thus far had underwhelming optical performance—slower response times, lower luminance and shorter life spans—compared to OLEDs built on planar substrates. Also, some fiber-shaped applications incorporated steel wires using high-heat processes, which may not be a good workflow fit for heat-sensitive materials.
The KAIST team’s sought to create an OLED fiber with strong performance and a sustainable, low-temperature manufacturing process, starting with a fiber substrate made of polyethylene terephthalate (PET). Then they used a dip-coating method, depositing even layers of OLED components around the PET substrate.
The article reports that one layer used a cathode consisting of the conductive polymer PEDOT:PSS; a layer of polyethylenimine and zinc-oxide nanoparticles for the electron-injection layer; the light-emitting polymer Super Yellow from Merck as the emitting layer; a hole-injecting layer of molybdenum oxide; and an anode layer of aluminum.
For comparison, the team built up the same materials on glass to construct a planar OLED. Their experiments showed the fiber-based light-emitting device had exhibited “unprecedented” luminance values, “comparable to conventional glass-based OLEDs,” the scientists say.
The researchers found that the fibers emitted light even when bent and stretched, withstanding tensile strains up to 4.3 percent. The experiment created working OLED fibers ranging from 90 to 300 microns in diameter.
The team demonstrated that the fibers could be hand-woven into knitted garments, providing a positive outlook for low-cost, scalable, fiber-based wearable display solutions for the future.