boosts efficiency of solar cells

In order for a solar cell to be as efficient as possible, the last thing it should be is reflective – after all, light should be getting absorbed by it, not being bounced off. With that in mind, a few years ago a group of Japanese scientists set out to create an antireflective film coating for use on solar cells. What they ended up creating utilizes the same principles that are at work in one of nature’s least reflective surfaces: moth’s eyes.

The moth-eye film was developed by Noboru Yamada, a scientist at Nagaoka University of Technology Japan, who collaborated with researchers at Mitsubishi Rayon Co. Ltd. and Tokyo Metropolitan University. Using anodic porous alumina molds, they were able to nanoimprint the microstructure of moth’s eyes into acrylic resin – this provided a high throughput, large-area/low-cost method of producing the film.

Based on the results of indoor and outdoor tests of crystalline silicon solar panels coated with the film, the team’s computer models indicated that use of the film could boost the annual efficiency of solar cells by five percent in Tokyo, and six percent in the “sun belt” city of Phoenix. “People may think this improvement is very small, but the efficiency of photovoltaics is just like fuel consumption rates of road vehicles,” said Yamada. “Every little bit helps.”

They are now working on improving the durability of the film, and optimizing it for use on different types of solar cells. They are also looking into using it to reduce glare on surfaces such as windows and computer screens, although in that area they may be facing some competition – Germany’s Fraunhofer Institute for Mechanics of Materials has already developed an anti-reflective coating for use on displays and eyeglasses, which was also inspired by moth’s eyes. In Franuhofer’s case, the coating is incorporated into the viewing surface during the molding process, instead of being added afterward in the form of a film.

The reasons that moths have anti-reflective eyes, incidentally, is to allow them to gather as much light as possible in the dark, and to avoid being seen by predators.

The moth-eye film research was recently published in the journal Energy Express.

Sourced & published by Henry Sapiecha

On Butterfly Wings

Inspire More Powerful Solar Cells

ScienceDaily (Feb. 5, 2009) — The discovery that butterfly wings have scales that act as tiny solar collectors has led scientists in China and Japan to design a more efficient solar cell that could be used for powering homes, businesses, and other applications in the future.

In the study, Di Zhang and colleagues note that scientists are searching for new materials to improve light-harvesting in so-called dye-sensitized solar cells, also known as Grätzel cells for inventor Michael Grätzel. These cells have the highest light-conversion efficiencies among all solar cells — as high as 10 percent.

The researchers turned to the microscopic solar scales on butterfly wings in their search for improvements. Using natural butterfly wings as a mold or template, they made copies of the solar collectors and transferred those light-harvesting structures to Grätzel cells. Laboratory tests showed that the butterfly wing solar collector absorbed light more efficiently than conventional dye-sensitized cells. The fabrication process is simpler and faster than other methods, and could be used to manufacture other commercially valuable devices, the researchers say.

Sourced and published by Henry Sapiecha 15th April 2010