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Posted: Nov 02, 2011

Solar power could get boost from new light absorption design

(Nanowerk News) 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.
trapezoid-shaped metal gratings on the nanoscale
Metal grating developed by Koray Aydin's research team.
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.
Source: By Sarah Ostman, Northwestern University
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