Thin light-emitting fibers that can be woven into textiles could be made into glowing clothes and other wearable electronics, researchers at Fudan University in Shanghai say.
Organic light-emitting diodes (OLEDs) are increasingly finding use in smartphones screens and televisions, offering a bright source of light with a wide range of colors that can be applied to rigid, curved, and even flexible surfaces. However, incorporating OLEDs into fabrics is difficult because they depend on cathodes that need relatively low amounts of energy to withdraw electrons completely from their surfaces. Such "low work function" materials—including calcium or magnesium—are sensitive to air, making them a problem for use in anything that can see as much use as fabric.
Instead, Zhitao Zhang at Fudan University in Shanghai and his colleagues explored devices known as polymer light-emitting electrochemical cells (PLECs). Like OLEDs, PLECs are usually made up of two metal electrodes connected to an electroluminescent organic semiconductor, but PLECs also incorporate salts into the light-emitting layer. This not only presents advantages such as high electron-to-photon conversion efficiency and high power efficiency compared to OLEDs, but PLECs also do not require low work function cathodes.
Now the scientists have developed a roughly one-millimeter-thick fiber-shaped PLEC consisting of a thin steel wire coated with a layer of zinc oxide nanoparticles, an electroluminescent polymer and an outer highly transparent layer of carbon nanotubes. These fibers can be twisted together and woven into patterns in lightweight, flexible, wearable textiles. Zhang, along with Huisheng Peng and their colleagues, detailed their findings online 18 March in the journal Nature Photonics.
The fibers can emit blue or yellow light from their entire surface when a few volts or more are applied between the inner metal wire and the outer carbon nanotube layer, and other colors might be possible in the future. The zinc oxide nanoparticles and the electroluminescent polymer are manufactured from simple solution-based processes that the scientists suggest could be scaled up for practical applications. The fibers "can be woven into light-emitting clothes for the creation of smart fabrics," Zhang said.
One challenge PLECs face is that their performance degrades over time: The brightness of these fibers decreases by half after only four hours of operation. However, electronics researchers Enrique Ortí and Henk Bolink at the University of Valencia in Spain, who did not take part in this study, noted in a review in Nature Photonics that PLECs now exist that can last for several thousand hours, suggesting that PLECs might one day be usable in long-lasting glowing fibers.