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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, researchers 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 Tuesday in the journal Nature Communications.
"The solar spectrum is not like a laser – it's very broadband, starting with
UV and going up to near-infrared," said 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, Aydin said.
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.
Aydin comes to McCormick from the California Institute of Technology, where
this research was conducted in the group of Professor Harry Atwater and
supported by the DOE Light-Material Interactions Energy Frontier Research
Center (EFRC). While at Caltech, Aydin served as a research scientist in
applied physics and materials science and as the assistant director of the
DOE Light-Material Interactions EFRC. Previously Aydin received his BS and
PhD in physics from Bilkent University in Ankara, Turkey.
He said he was drawn to Northwestern because of its collaborative work
environment and its proximity to unmatched facilities, such as Argonne
National Laboratory.
"When I came to interview in the electrical engineering department at
McCormick, I interviewed with not just that department's faculty, but also
met with members of the materials science department," Aydin said. "That
showed me how much the school values collaboration and interdisciplinary
interactions."
This fall, Aydin is teaching an undergraduate course, EECS 223, Fundamentals
of Solid State Engineering, and is looking forward to involve undergraduate
students in active research.
For more information visit www.northwestern.edu.
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