Green Design

Composite Metamaterial for Solar Tech

A Northwestern University research team has developed a new material that absorbs a wide range of wavelengths and could lead to more efficient and less expensive solar technology. The researchers used two unconventional materials – metal and silicon oxide – to create thin but complex, trapezoid-shaped metal gratings on the nanoscale that can trap a wider range of visible light.

The use of these materials is unusual because on their own, they do not absorb light; however, they worked together on the nanoscale to achieve very high absorption rates, said Koray Aydin, assistant professor of electrical engineering and computer science at Northwestern's McCormick School of Engineering.

The uniquely shaped grating captured a wide range of wavelengths due to the local optical resonances, causing light to spend more time inside the material until it gets absorbed. This composite metamaterial was also able to collect light from many different angles – a useful quality when dealing with sunlight, which hits solar cells at different angles as sun moves from east to west throughout the day.

This research is not directly applicable to solar cell technology because metal and silicon oxide cannot convert light to electricity; in fact, the photons are converted to heat and might allow novel ways to control the heat flow at the nanoscale. However, the innovative trapezoid shape could be replicated in semiconducting materials that could be used in solar cells, Aydin said. If applied to semiconducting materials, the technology could lead to thinner, lower-cost, and more efficient solar cells, he said.

(Northwestern University)