Solar cell that can be stretched by 50% without losing efficiency. Scientists from Japan's RIKEN laboratory have developed a new type of solar cell that can be stretched without losing its ability to convert light into electricity. This discovery could be a breakthrough in creating the next generation of wearable electronics. Current wearable devices such as smartwatches and medical monitors require periodic charging, which can be inconvenient for users. The development of flexible and stretchable solar cells could solve this problem, allowing devices to be charged by sunlight throughout the day. However, creating such cells is a challenge, as they must be flexible enough to stretch when the body moves, but still maintain their efficiency. A team of researchers led by Kenjiro Fukuda at the RIKEN Center for New Substances Research has developed a solution to this problem. “We are focused on creating thin, flexible devices, but such devices are not stretchable. Rather, they are like the plastic film used for food packaging - they can be stretched by 1% or 2%, but 10% is impossible because they tear easily,” Fukuda explains. Fukuda and his team developed a new approach by using stretchable materials for each functional layer in the device. However, this proved to be a challenge, as a balance had to be found between the stretchability of each layer and its performance. Finally, the researchers have created a high-performance flexible solar cell that exhibits exceptional stretchability. The cell's energy conversion efficiency drops by only 20% when the solar cell is stretched by 50% (i.e., stretched to 1.5 times its original, unstretched length). Moreover, it retains 95% of its original energy conversion efficiency after being stretched 100 times by 10%. The key to realizing this stretchability of the device lay in the inclusion of an organic compound called ION E in the electrode layer of the solar cell. This compound not only increases the stretchability of the electrode, but also enhances the adhesion between the electrode and the layers above and below it. Because of these two effects, the electrode can take up some of the strain of the active layer above it (which converts light into electrons), which improves the stretchability of the entire device. The researchers' long-term goal is to create a stretchable organic solar cell with a large area. However, in order to do so, the low conductivity of the polymer used to transmit the electricity generated must be addressed. The development of stretchable solar cells could have significant implications for the next generation of wearable electronics. This discovery could lead to devices that can be charged by sunlight throughout the day, making them more convenient and independent of power sources.