Image: Northwestern University
Solar power may be on the rise, but solar cells are only as
efficient as the amount of sunlight they collect. Under the direction of a new
McCormick professor, Northwestern
have developed a new material that absorbs a wide range of wavelengths and
could lead to more efficient and less expensive solar technology.
A paper describing the findings, “Broadband polarization-independent resonant light absorption
using ultrathin plasmonic super absorbers,” was published in Nature
“The solar spectrum is not like a laser—it’s very broadband,
starting with UV and going up to near-infrared,” says Koray Aydin, assistant
professor of electrical engineering and computer science and the paper’s lead
author. “To capture this light most efficiently, a solar cell needs to have a
broadband response. This design allows us to achieve that.”
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,
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 says.
If applied to semiconducting materials, the technology could
lead to thinner, lower-cost, and more efficient solar cells, he says.