Electronic displays for integration with clothing and textiles are a rapidly developing field in the realm of wearable electronics. However, flexible LEDs designed to form part of an elastic or deformable coating for clothing or apparel – even displays specifically designed to be directly bio-compatible – still rely on a hard substrate on which to layer the appropriate electroluminescent material. Now researchers at the Korea Advanced Institute of Science and Technology (KAIST) have created a fiber-like LED that can be directly knitted or woven to form part of the fabric itself.
"Our research will become a core technology in developing light emitting diodes on fibers, which are fundamental elements of fabrics," said Professor Choi, head of the research team at the School of Electrical Engineering at KAIST. "We hope we can lower the barrier of wearable displays entering the market."
To produce their LED strands, the scientists start with a fiber of polyethylene terephthalate, which they then dip several times into a solution of PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) and then dry at 130° C (266° F) for 30 minutes to ready it for layering with organic materials. Once dried, the dipped fiber is then re-dipped in a bath of super-yellow (poly-(p-phenylenevinylene) polymer organic LED (OLED)) solution, dried again in an oven, and finally coated with a Lithium Fluoride/Aluminum (LiF/Al) compound.
This process, the researchers claim, is a much more efficient way of applying LED materials to small cylindrical structures than any heat-treating method. By carefully adjusting the extraction rate of the fiber from the solution, the researchers say they can control the deposition thickness to within hundreds of thousandths of a nanometer.
The researchers believe their method of producing LED fibers could be an accelerator for the commercialization of wearable displays because inexpensive, automated high-volume production of fibers using such textile manufacturing methods as roll-to-roll processing could be employed. In this way, LED fibers could be mass-produced as easily as nylon or polyethylene fiber is produced today.
"This technology will eventually allow the production of wearable displays to be as easy as making clothes," said Seon-Il Kwon, a member of the KAIST Electrical Engineering team.
The results of this work were recently published in the journal Advanced Electronic Materials