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Coating kills reflections from PV cells, boosts efficiency 5%

Moths can see well at night partly because their eyes are covered with a water-repellent, antireflective coating that makes their eyes among the least reflective surfaces in nature. The coating also helps them hide from predators in the dark.

Researchers in Japan have now mimicked the microstructure of the moth eye coating in a new film, suitable for mass-production, that is designed to cover solar cells. The coating is said to cut down on the amount of light reflecting off the cells and will help PV cells capture more power from the sun.

Researchers from Nagaoka University of Technology, Mitsubishi Rayon Co. Ltd., and Tokyo Metropolitan University describe the work in Energy Express, a bi-monthly supplement to Optics Express, an open-access journal published by the Optical Society.

The team looked at the effect of deploying this antireflective moth-eye film on solar cells in Phoenix and Tokyo. They chose the two locales because each experiences a different kind of sunlight: Phoenix sees a lot of direct sunlight, while Tokyo experiences a great degree of diffuse solar radiation.The researchers figure the films would improve the annual efficiency of solar cells by 6% in Phoenix and by 5% in Tokyo.

The tricky part of making the film was in designing a seamless, high-throughput roll-to-roll process for nanoimprinting it. Mitsubishi Rayon Co. Ltd. ultimately came up with a high throughput nanoimprint technique using anodic porous alumina molds to deposit a moth-eye structure made of acrylic resin on a substrate. The researchers say large-area low-cost moth-eye films can be fabricated with a roll-to-roll process by using this method. The shape of the moth-eye structure is optimized for applications to c-Si PV cells so the reflection and absorption can be minimized and transmission is maximized over a spectrum range that matches that of c-Si PV cells

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.

The paper is here: 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.

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