Historically, solar panels have been made out of glass or plastic—materials that are hard and can be destroyed fairly easily. Researchers first turned to textiles in 2001 in an effort to create a solar component that is pliable, breathable and flexible. Since then, solar fabrics have been incorporated into stadium covers, carports and even wearable art, but Andrew and Fairbanks claim that their fabric is superior to other groups’ in breathability, strength and density. Not only have they figured out how to utilize their process on any type of fabric, but because this is a collaboration between scientist and designer, they also have the ability to broaden the scope of solar textiles within a more commercial, consumer-friendly market.
“The biggest problem is that textiles, from an engineering and chemistry concern, are that they're incredibly rough,” says Andrew. “They're a three dimensional substrate; they're not flat.”
Their solar cell consists of one layer of fabric that has four coats of different polymers. The first coat is Poly(3,4-ethylenedioxythiophene), or “PEDOT”, which Andrew and her post-doc research assistant, Lushuai Zhang, discovered worked incredibly well to increase a fabric’s conductivity. The other three coats are various semiconducting dyes, such as blue dye copper phthalocyanine, that act as the photoactive layers or light absorbers for the cell. Andrew and Fairbanks have achieved repeated success with the first two coats but are still working out the kinks for coats three and four.
Fabrics, as opposed to smooth and shiny glass or plastic, are porous, which makes evenly coating them with specific polymers a bit tricky. If you consider how a piece of fabric is created, it’s made up of multiple fibers twisted together. Each fiber will have a different level of roughness, which, from a chemistry standpoint, includes multiple light scales (nanometer, micrometer, etc.).
“In order to actually put the electronically conductive polymer over that surface, you have to traverse all of these different light scales,” says Andrew. “And that’s hard.”
To get around this issue, Andrew decided to try Chemical Vapor Deposition (CVD), a technique typically reserved for inorganic experiments that use hard substrates like metals or plastics. By taking advantage of the mass transport properties, or the general physical laws governing the movement of mass from one point to another, Andrew can uniformly coat any arbitrary substance, including fabric, because the nanomaterials used don’t care about the surface of the substrate. Even better, she applies the PEDOT within a vacuum.
The next step was determining which fabrics would work best.
“I brought over silk, wool, nylon—all of these different substrates,” says Fairbanks, noting that the materials were standard samples from Jo-Ann Fabrics. To test the fabrics, they coated each one with PEDOT and other semiconductor materials, then hooked them up to electrode clips and wires. They applied voltage and measured the output current for each swatch.
“Some of them would warm up and take the energy and translate it into heat; some of them dispensed the heat, yet conducted much more easily,” says Fairbanks.
“The conductivity of the PEDOT was completely determined by the underlying textiles,” adds Andrew. “If we had a porous textile, we got conductivity higher than the copper. If we had a very fuzzy textile, like fuzzy cotton jersey or wool felt, or very tightly woven textiles, then the conductivity of the PEDOT was really bad.”
Based upon their initial experiments, Andrew proposed a glove prototype to take advantage of the various properties of each fabric. Essentially, their design used specific textiles to conduct electricity to warm different parts of the glove. The prototype is made out of pineapple fiber, which is very conductive and absorbs the heat, and cotton, which acts as a brake to keep the heat contained between the layers. This is the first item the duo has created that they hope to actually market.
“What’s really fascinating about this collaboration,” says Fairbanks, “is that we didn’t come together to create this glove, specifically. It was just one of these other side outputs of the original research.”
Through the process of research and development, Andrew and Fairbanks have experimented beyond their initial solar textile idea, which is still a work in progress, to another solar innovation that involves coating each individual fiber with PEDOT and weaving the pieces together to form the working circuit. This completely original fabric works like a triboelectric device, translating mechanical motion into power. The duo has constructed 10-by-10-inch swatches of different weave patterns, with the most efficient generating about 400 milliwatts of power, by simply waving it around like a little flag.
“If you actually made a standard curtain for a house, something 4-by-4-feet, then that is more than enough power to charge your smartphone,” says Andrew, noting that the material would only need a breeze coming through the window to generate that level of power.
Andrew and Fairbanks are working with several companies within a variety of industries that are interested in incorporating these ideas into future products. Andrew, for example, has an Air Force grant aimed at producing solar tents for soldier use and has outdoor gear in development with Patagonia.
“I get really excited, because textiles are portable and lightweight,” says Fairbanks. “They could be deployed in the wilderness for a hunter or in the field for medical or military applications in a way that big clunky solar panels never could be.”
Fairbanks sees boundless potential. The solar textile, she says, could be used for hundreds of future applications, including umbrellas, awnings and refugee shelters, while the triboelectric fabric could be used in housewares or athletic gear, such as running shirts and tennis shoes—anything that requires motion since that’s how it generates power.
“I’m excited to get it 100 percent functioning and out into the world,” says Fairbanks.
