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Sumit Chaudhary, left, and Kanwar Singh Nalwa of Iowa State Univ. and the U.S. Department of Energy's Ames Laboratory have been working to improve the efficiency of polymer solar cells. Photo by Leah Hansen.
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Researchers from Iowa State Univ. and the Ames Laboratory have developed a
process capable of producing a thin and uniform light-absorbing layer on
textured substrates that improves the efficiency of polymer solar cells by
increasing light absorption.
"Our technology efficiently utilizes the light trapping scheme,"
said Sumit Chaudhary, an Iowa
State assistant professor
of electrical and computer engineering and an associate of the U.S. Department
of Energy's Ames Laboratory. "And so solar cell efficiency improved by 20%."
Details of the fabrication technology were recently published online by the
journal Advanced Materials.
Chaudhary said the key to improving the performance of solar cells made
from flexible, lightweight, and easy-to-manufacture polymers was to find a textured
substrate pattern that allowed deposition of a light-absorbing layer that's
uniformly thin—even as it goes up and down flat-topped ridges that are less
than a millionth of a meter high.
The result is a polymer solar cell that captures more light within those
ridges - including light that's reflected from one ridge to another, he said.
The cell is also able to maintain the good electrical transport properties of a
thin, uniform light-absorbing layer.
Tests indicated the research team's light-trapping cells increased power
conversion efficiency by 20% over flat solar cells made from polymers,
Chaudhary said. Tests also indicated that light captured at the red/near
infrared band edge increased by 100% over flat cells.
Researchers working with Chaudhary on the solar cell project are Kai-Ming
Ho, an Iowa State Distinguished Professor of Physics and Astronomy and an Ames
Laboratory faculty scientist; Joong-Mok Park, an assistant scientist with the
Ames Laboratory; and Kanwar Singh Nalwa, a graduate student in electrical and
computer engineering and a student associate of the Ames Laboratory. The
research was supported by the Iowa Power Fund, the Ames Laboratory and the
Department of Energy's Office of Basic Energy Sciences.
The idea of boosting the performance of polymer solar cells by using a
textured substrate is not a new one, Chaudhary said. The technology is commonly
used in traditional, silicon-based solar cells.
But previous attempts to use textured substrates in polymer solar cells
have failed because they require extra processing steps or technically
challenging coating technologies. Some attempts produced a light-absorbing
layer with air gaps or a too-thin layer over the ridges or a too-thick layer
over the valleys. The result was a loss of charges and short circuiting at the
valleys and ridges, resulting in poor solar cell performance.
But, get the substrate texture and the solution-based coating just right,
"and we're getting more power out," Nalwa said.
The Iowa State Univ. Research Foundation Inc. has filed a patent for
the substrate and coating technology and is working to license the technology
to solar cell manufacturers.
"This may be an old idea
we're using," Chaudhary said, "but it's never before been
successfully implemented in polymer solar cells."
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