Tungsten trioxide is the core material in a new type of reflective screen — sometimes described as “electronic paper” — that offers optimal color display and uses ambient light to keep energy consumption to a minimum. The new technology could be used in displays for smart devices. Traditional digital screens use a backlight to illuminate the text or images displayed upon them, which limits the ability of the material they are displaying to be seen in bright sunshine. Reflective screens use ambient light, mimicking the way our eyes respond to natural paper. The researchers, from Chalmers University, previously developed an ultrathin, flexible material that reproduced all the colors an LED screen can display, and that required only a tenth of the energy that a standard tablet consumes. In previous studies, the researchers also used polymers. However, in their earlier design, the colors on the reflective screen did not display with optimal quality. In the new study, the researchers used a porous and nanostructured material containing tungsten trioxide, gold, and platinum to achieve the display. The technology in the reflective screens is based on the material’s ability to regulate how light is absorbed and reflected. The researchers inverted the design in such a way that the colors appeared much more accurately on the screen. Specifically, they placed the component that makes the material electrically conductive underneath the pixelated nanostructure that reproduces the colors, instead of above it as was previously the case. The material that covers the surface conducts electronic signals throughout the screen and can be patterned to create high-resolution images. In the new design, one looks directly at the pixelated surfaces, therefore seeing the colors much more clearly. In addition to minimal energy consumption, reflective screens have other advantages; they are much less tiring for the eyes compared to looking at a regular screen, for example. Certain rare metals such as gold and platinum are required to make reflective screens, but because the final product is so thin, the amounts needed are very small. Further, the researchers hope that it will eventually be possible to significantly reduce the quantities needed for production. Research leader Andreas Dahlin, professor in the Department of Chemistry and Chemical Engineering at Chalmers, said, “Our main goal when developing these reflective screens, or ‘electronic paper’ as it is sometimes termed, is to find sustainable, energy-saving solutions. Courtesy of Chalmers University. “In this case, energy consumption is almost zero because we simply use the ambient light of the surroundings,” he said. Reflective screens are already available in some tablets, but they only display black and white well, which limits their use. “A large industrial player with the right technical competence could, in principle, start developing a product with the new technology within a couple of months,” Dahlin said. He envisions further applications for the technology. In addition to smartphones and tablets, it could also be useful for outdoor advertising, offering energy and resource savings compared with both printed posters and moving digital screens. The research was published in Nano Letters (www.doi.org/10.1021/acs.nanolett.1c00904).