Abstract:

Significance As the window of human-machine interaction, demands on displays have become an important driving force for the development of the information society. The development of display technology ranges from the early three-dimensional bulky cathode ray tube display to flat-panel liquid crystal display, and now to the two-dimensional thin-film organic light-emitting diode display, and the displays are becoming flexible and lightweight by reducing the thickness of the device. With the rapid development of emerging fields such as wearable devices, smart interactions and the Internet of Things, displays are required to fit the irregular surface of the human body, match the human body in mechanical properties and remain stable under three-dimensional deformation. Additionally, future displays should be permeable for long-term comfort in the applications of human-machine interaction and health monitoring. Textile is an indispensable part of our daily life, and integrating displays into textile is an ideal way to realize new displays that is highly flexible, adaptive to complex deformation, and permeable.
Progress Light-emitting devices are the basic components of displays. Dynamic images in displays are realized by controlling light-emitting devices according to the driving program. Until now, three types of textile light-emitting device structures have been developed. They are textile-based planar light-emitting devices, light-emitting fibers, and warp-weft interwoven light-emitting devices.
Textile-based planar light-emitting devices are prepared by attaching flexible thin-film light-emitting devices to the textile substrate or depositing active materials layer by layer on the textile substrate to obtain light-emitting devices. Owing to the wide investigation on materials and fabrication of planar light-emitting devices, it is easy to achieve high luminance and efficiency in textile-based planar light-emitting devices for better display performance. However, the modulus of film materials is always higher than the modulus of textiles. The mismatch between the mechanical properties leads to reduced flexibility of the textile, and the devices can the easily peeled off from the textile or fade in performance during deformation.
The two-dimensional thin film light-emitting devices are converted into one-dimensional light-emitting fibers, which are the building blocks of textiles. Light-emitting fibers can be woven into textiles without sacrificing the inherent permeability and flexibility of textiles. Through the design of material and device structure, meter-length light-emitting fibers were realized based on AC electroluminescent material. Light-emitting fibers with good mechanical stability and flexibility can be woven into textile to display pre-designed weaving patterns. However, this is a significant limitation because simply based on pre-designed patterns, it is almost impossible for them to satisfy the display applications like computers and cell phones.
For real displays consisting of an array of pixels, the pixels are individually controlled in real time for dynamic change. A strategy is proposed to build micron-scale light-emitting devices at the warp and weft interwoven points. Composite warps that load luminescent materials and transparent conductive wefts were developed, and the textile pixels were formed by contacting two fibers during weaving. This method unifies the textile and the display device in function, structure, and fabrication method. High-resolution display in the textile was achieved by applying digital signals to warps and wefts.
Conclusion and Prospect In the past decade, many efforts are made to design materials, device structures, and fabricate methods for displaying textiles. High stability, flexibility, and permeability of displaying textiles are achieved by developing one-dimensional fiber devices, and pixel displays with high resolution and large-area integration are facilitated by developing warp-weft interwoven devices. However, the following problems remain to be solved to promote the practical application of displaying textile.
1) Luminescent materials are the basis for high display performance. Unique highly curved structures of fibers lead to new requirements for the composition, structure, film forming method and mechanical stability of light-emitting materials.
2) Full-color display is indispensable for human-machine interaction. In planar display, full color is realized by mixing the light emitting from three adjacent light-emitting devices in red, green, and blue. Fiber-shaped light-emitting devices are curved light sources. The space distribution of emitted light from fiber devices is different from that from planar devices, which demands new principles of color mixing.
3) Resolution is a key parameter for display quality. The resolution of displaying textiles is still far below that of the commercial displays. It is challenging to uniformly load the luminescent materials on superfine fiber and reveal the light-emitting mechanism of interwoven light-emitting devices in the size of tens of microns.
4) Systematic integration is the foundation of practical application. In order to integrate displaying textiles with other fiber devices such as battery fibers and sensing fibers, problems should be solved to connect fiber electrodes in high bonding strength and stable electrical conductivity under deformation. Matching of electrical parameters among textile devices should also be investigated for the reliable operation of the textile system.

Key words: light-emitting fiber, displaying textile, light-emitting material, display unit, flexible