Tokyo, Japan--The eyes of moths are covered with a water-repellent antireflection (AR) coating that makes their eyes among the least reflective surfaces in nature, helping them to hide from predators at night. Mimicking the moth eye's microstructure, researchers in Japan have created a new AR film for solar cells and, especially important, have made it suitable for mass-production.
In a paper appearing in Energy Express, a new bi-monthly supplement to the OSA's Optics Express, the team describes how this film improves the performance of photovoltaic (PV) modules in laboratory and field experiments. They also calculate how the AR film would improve the yearly performance of solar cells deployed over large areas in either Tokyo, Japan or Phoenix, AZ.
The team looked at the effect of deploying this AR moth-eye film on solar cells in Phoenix and Tokyo because Phoenix is a "sunbelt" city, with high annual amount of direct sunlight, while Tokyo is well outside the sunbelt region with a high fraction of diffuse solar radiation.
They estimate that the films would improve the annual efficiency of solar cells by 6% in Phoenix and by 5% in Tokyo.
"People may think this improvement is very small, but the efficiency of photovoltaics is just like fuel consumption rates of road vehicles," says Noboru Yamada, a scientist at Nagaoka University of Technology Japan, who led the research with colleagues at Mitsubishi Rayon Co. Ltd. and Tokyo Metropolitan University. "Every little bit helps."
Yamada and his colleagues found the inspiration for this new technology a few years ago after they began looking for a broad-wavelength and omnidirectional AR structure in nature. The eyes of the moth were the best they found.
The difficulty in making the film, says Yamada, was designing a seamless, high-throughput roll-to-roll process for nanoimprinting the film. This was ultimately solved by Hideki Masuda, one of the authors on the Energy Express paper, and his colleagues at Mitsubishi Rayon Co.
The team is now working on improving the durability of the film and optimizing it for many different types of solar cells. They also believe the film could be applied as an AR coating for windows and computer displays.
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