TOKYO: Scientists have developed a new type of water-proof solar cell which can provide electricity even after being soaked in water or stretched and compressed.The finding could open the way for wearable solar cells, which will provide power to devices such as health monitors incorporated into clothing, researchers said.These could include sensors that record heartbeats and body temperature, for example, providing early warning of medical problems, they said.Researchers, including those from the University of Tokyo in Japan , developed extremely thin and flexible organic photovoltaic cells, coated on both sides with stretchable and waterproof films, based on a material called PNTz4T.They deposited the device in an inverse architecture onto a one-micrometre-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, finding first that it had a strong energy efficiency.To test its resistance to water, they soaked it in water for two hours, and found that the efficiency decreased by just 5.4 per cent.To test the durability of the solar cell, they subjected it to compression, and found that after compressing by nearly half for twenty cycles while placing drops of water on it, it still had 80 per cent of the original efficiency."We were very gratified to find that our device has great environmental stability while simultaneously having a good efficiency and mechanical robustness," researchers said."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," they added.The study was published in the journal Nature Energy.