Scientists, according to work published in the Nature Energy science journal, say they have developed a new type of ultra-thin photovoltaic device, coated on both sides with stretchable and waterproof films, which can continue to provide electricity from sunlight even after being soaked in water or being stretched and compressed. The scientists from the Japan-based research institute RIKEN and the University of Tokyo, according to an 18 September press release, have developed extremely thin and flexible organic photovoltaic cells (these convert sunlight into electricity), based on a material called PNTz4T, which they had developed in earlier work.
The ultra-thin device was then placed on to an acrylic-based elastomer (rubbery material composed of long chain-like molecules, or polymers) and the top side of the device was coated with an identical elastomer, giving it a coating on both sides to prevent water infiltration. The elastomer, while allowing light to enter, prevents water and air from leaking into the cells, making them more long lasting than previous experiments.
The researchers then subjected the device to a variety of tests. To test the resistance of the cells to water, they soaked the device in water for 2 hours, and found that the efficiency decreased by just 5.4%. And to test the durability, they subjected it to compression, and found that after compressing by nearly half for 20 cycles while placing drops of water on it, it still had 80% of the original efficiency.
In the press release, Kenjiro Fukuda, research scientist at the RIKEN Center for Emergent Matter Science, says, “We very much hope that these washable, lightweight and stretchable organic photovoltaics will open a new avenue for use as a long-term power source system for wearable sensors and other devices."
Researchers have been working on embedding solar cells in clothes for more than a decade. The reason is simple: Flexible solar cells, when integrated into clothing, can also provide power for portable electronic devices.
Netherlands-based fashion designer Pauline van Dongen, for one, launched a Solar Shirt in 2015, which was developed in collaboration with the Netherlands-based Holst Centre—an independent research and development (R&D) centre that develops technologies for wireless autonomous sensor technologies and flexible electronics. The Solar Shirt, work on which was on since 2014, incorporates 120 thin film solar cells that are combined into standardized functional modules using Holst Centre’s stretchable interconnect technology for integrating electronics into fabrics.
The modules can be mass-manufactured and incorporated into the fabric using familiar industrial “iron-on" techniques before the garment is stitched. In bright sunlight, it produces around 1 watt of electricity—enough to charge a typical phone in a few hours, according to van Dongen’s website.
The shirt, the website adds, generates enough power indoors to charge a phone. The shirt can also charge smartphones, MP3 players, cameras, GPS systems, and other USB-compatible hand-held or portable devices, according to a 16 March 2015 press release by Holst Centre.
In a paper published in Advanced Functional Materials in May, materials scientist Trisha Andrew at the University of Massachusetts Amherst and colleagues outlined how they have invented a way to apply breathable, pliable, metal-free electrodes to fabric, and off-the-shelf clothing, so it feels good to the touch and also transports enough electricity to power small electronics.
In their paper, Andrew and postdoctoral researcher Lu Shuai Zhang describe the method (vapour deposition) they use to coat fabrics with a conducting polymer—poly (3,4-ethylenedioxytiophene) also known as PEDOT—to make plain-woven, conducting fabrics that are resistant to stretching and wear and remain stable after washing and ironing.
“Our article describes the materials science needed to make these robust conductors," Andrew said in a 23 May press release. “We show them to be stable to washing, rubbing, human sweat and a lot of wear and tear," she added. Andrew and Zhang are working “on taking any garment you give us and turning it into a solar cell so that as you are walking around, the sunlight that hits your clothes can be stored in a battery or be plugged in to power a small electronic device".
Meanwhile, Andrew and Marianne Fairbanks, assistant professor of textiles and design at the University of Wisconsin in Madison, too, are developing a solar textile that could end up in clothing, curtains, car seats and tents.
Cutting Edge is a monthly column that explores the melding of science and technology.