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Fabricated rolls of moth-eye film; the rolls appear green due to the color of the protection film. Image courtesy Nagaoka University of Technology.
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The
eyes of moths, which allow them to see well at night, are also covered
with a water-repellent, antireflective coating that makes their eyes
among the least reflective surfaces in nature and helps them hide from
predators in the dark. Mimicking the moth eye's microstructure, a team
of researchers in Japan has created a new film, suitable for
mass-production, for covering solar cells that can cut down on the
amount of reflected light and help capture more power from the sun.
In a paper appearing in Energy Express, a bi-monthly supplement to Optics Express, the open-access journal published by the Optical Society (OSA),
the team describes how this film improves the performance of
photovoltaic modules in laboratory and field experiments, and they
calculate how the anti-reflection film would improve the yearly
performance of solar cells deployed over large areas in either Tokyo,
Japan or Phoenix, Ariz.
"Surface
reflections are an essential loss for any type of photovoltaic module,
and ultimately low reflections are desired," 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.
The
team chose to look at the effect of deploying this antireflective
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 percent in Phoenix and by 5 percent 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 Yamada. "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 antireflective 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. Ltd.
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 anti-reflection coating to windows and
computer displays.
Paper: "Characterization of antireflection moth-eye film on crystalline silicon photovoltaic module," Noboru Yamada, Toshikazu Ijiro, Eiko Okamoto, Kentaro Hayashi, and Hideki Masuda, Optics Express, Vol. 19, Issue S2, pp. A118-A125.
SOURCE: Optical Society of America
