Kirigami, the ancient Japanese art of paper cutting, could help create flexible solar cells that track the sun to generate more electricity than stationary panels. With help from an art professor, researchers at the University of Michigan recently created such cells using a GaAs thin film applied to Kapton, a science-grade plastic. A CO2 laser was used to perforate the material. The perforations cause the solar cells to tilt when the substrate is stretched. The angle of tilt can be controlled to within ±1°, allowing the cell surface to stay perpendicular to the sun's rays throughout the day. Solar cells capture up to 40 percent more energy when they can track the sun across the sky, but conventional, motorized trackers are too heavy and bulky for pitched rooftops and vehicle surfaces. Kirigami solar cells, on the other hand, would be about the same size and weight as conventional cells installed on rooftops today. "The beauty of our design is, from the standpoint of the person who's putting this panel up, nothing would really change," said Max Shtein, an associate professor of materials science and engineering. "But inside, it would be doing something remarkable on a tiny scale: the solar cell would split into tiny segments that would follow the position of the sun in unison." The design with the best solar-tracking promise was impossible to make at the university because the solar cells would be very long and narrow. Scaling up to a feasible width, the cells became too long to fit into the chambers used to make the prototypes on campus, so the team is looking into other options. The optimized design is effective because it stretches easily, allowing a lot of tilt without losing much width. According to the team's simulations of solar power generation during the summer solstice in Arizona, it is almost as good as a conventional single-axis sun-tracking solar panel, offering a 36 percent improvement over a stationary panel. The university is pursuing a patent on the technology and is seeking commercialization partners. Funding came from the National Science Foundation and NanoFlex Power Corp. The research was published in Nature Communications (doi: 10.1038/ncomms9092).
Photosensitizers