A new generation of solar cells
Scientists from RIKEN and the University of Tokyo have developed a new type of ultra-thin photovoltaic device which can continue to provide electricity from sunlight even after being soaked in water or being stretched and compressed. They achieved this by coating both sides with stretchable and waterproof films.
The paper, published in Nature Energy, could open the door to wearable solar cells, which will provide power to devices such as health monitors incorporated into clothing.
One of the biggest challenges of the Internet Of Things (IoT) is to provide power to a myriad of devices, including devices that can be worn on the body. These could include sensors that record heartbeats and body temperature, providing early warning of medical problems.
Previous attempts have been made to create photovoltaics that could be incorporated into textiles, but they lacked at least one of the important properties — long-term stability in both air and water, energy efficiency, and robustness including resistance to deformation — that are key to successful devices.
For the present work, researchers developed ultra-thin and flexible organic photovoltaic cells, based on a material called PNTz4T, which they had developed in previous work. They deposited the device in an inverse architecture, which they had previously developed, onto a 1-um-thick parylene film. The ultra-thin device was then placed onto acrylic-based elastomer 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, prevented 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, realizing that it had a strong energy efficiency of 7.9 percent, producing a current of 7.86 milliwatts per square centimeter. They then soaked it in water for two hours, and found that the efficiency decreased by just 5.4 percent. As for the durability test, it still had 80 percent of the original efficiency.
Kenjiro Fukuda of the RIKEN Center for Emergent Matter Science said “We were very gratified to find that our device has great environmental stability while simultaneously having a good efficiency and mechanical robustness. 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.”