Articles such as clothes, watches, shoes, and accessories are essential to people around the world. However, going beyond the basic roles and purposes of these items, the concept of “wearability” is rapidly evolving to include computing power and the ability to connect to the internet. In other words, information, communication, and technology (ICT) are beginning to be integrated into wearables. Because wearable electronics can provide a more comfortable and convenient life for wearers, research on and the development of wearables have emerged as major interests both academically and industrially. In particular, a wearable information display for intuitive communication between wearers and wearable devices has attracted a great deal of attention, and it can create additional value in the fashion, military, automobile, and architecture industries while also making functional wearable devices available to all.
Wearable displays have begun to change from rigid and stiff to flexible and pliable to enable more ergonomic designs. It is crucial to preserve the intrinsic flexibility of clothes when adding electronic functions to fabrics and fibers. In this condition, organic light-emitting diodes (OLEDs) are a promising candidate for wearable displays. OLEDs have superb merits, such as thinness, flexibility, light weight, and even transparency. However, it is difficult to integrate operable OLEDs into textiles due to their typically extremely rough surfaces and wavy shapes.
A research team led by Prof. Kyung Cheol Choi of the School of Electrical Engineering at the Korea Advanced Institute of Science and Technology (KAIST), in collaboration with KOLON Glotech, Inc., a Korean outdoor clothing company, succeeded in developing clothing-based light-emitting devices using OLEDs. The KAIST team demonstrated two types of devices, reliable fabric-based OLEDs and high-luminance fiber-based polymer light-emitting diodes (PLEDs). The fabric-based OLEDs, encapsulated by flexible and transparent multilayer barrier films, were designed for long-term reliability, with measured operational lifetimes exceeding 1,000 hours under the conditions of 30°C and 90% relative humidity. The team successfully operated the OLEDs on rough fabrics through the thermal lamination of thin planarization sheets, later verifying the stable operation of these devices by means of cyclic bending tests. The fiber-based PLEDs were realized using a simple dip-coating method to coat polymer layers concentrically onto fibers. First, the research team dip-coated a conducting polymer, PEDOT:PSS, several times, with the layers then functioning as planarization layers as well as electrodes. The resulting device showed high luminance exceeding 1,000 cd/m2, a level sufficiently high for everyday applications.
Photo: Textile-based Wearable Electronics and Fashion Displays (credit: KAIST)
Professor Choi said, “Our research will become a core technology in the development of light-emitting diodes on textiles, which are fundamental elements of fabrics. Hopefully, we can lower the barrier of wearable displays to enter the market.” A researcher on the team also added, “This technology will accelerate the commercialization of fiber-based wearable displays because it offers low-cost mass production using roll-to-roll processing, a type of technology applied to create electronic devices on a roll of flexible plastic or metal foil.”
The result of the fabric-based OLEDs was reported in Advanced Electronic Materials (vol 2, no 11, 2016, DOI: 10.1002/aelm.201600220) on the front cover under the title “Reliable Actual Fabric-Based Organic Light-Emitting Diodes: Toward a Wearable Display,” and the research result of the fiber-based PLEDs was also published in Advanced Electronic Materials (vol 1, no 9, 2015, DOI: 10.1002/aelm.201500103) as an inside front cover article under the title “High Luminance Fiber-Based Polymer Light-Emitting Devices by a Dip-coating Method.”
 W. Kim, S. Kwon, S.-M. Lee, J. Y. Kim, Y. Han, E. Kim, K. C. Choi, S. H. Kang, and B. C. Park, Adv. Electron. Mater., 2016, DOI: 10.1002/aelm.201600220
 S. Kwon, W. Kim, H. Kim, S. Choi, B. C. Park, S. H. Kang, and K. C. Choi, Adv. Electron. Mater., 2015, 1, DOI: 10.1002/aelm.201500103
Source: Korea Advanced Institute of Science and Technology (KAIST)