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.