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Solar Cells Slimmed with Nanosandwich

RALEIGH, N.C., June 28, 2012 — A new technique to fabricate slimmer thin-film solar cells without compromising their ability to absorb solar energy could reduce production costs for the technology.

North Carolina State University researchers fabricated the solar cells utilizing a “nanoscale sandwich” design that involves an ultrathin “active” layer of amorphous silicon only 70 nm thick. Typical thin-film solar cells that also use amorphous silicon have active layers between 300 and 500 nm thick.

“The technique we’ve developed is very important because it can be generally applied to many other solar cell materials, such as cadmium telluride, copper indium gallium selenide and organic materials,” said Dr. Linyou Cao, an assistant professor of materials science and engineering.

In solar cells, energy is absorbed by the active layer for conversion into chemical fuel or electricity. This new technique relies on traditional production processes but results in a totally different end product.

Researchers from North Carolina State University have found a way to create much slimmer thin-film solar cells without sacrificing the cells’ ability to absorb solar energy. The active layer can be as little as 70 nm thick. (Image: Dr. Linyou Cao, North Carolina State University)

To create the cells, the scientists used a standard lithography technique to form a pattern on the substrate, outlining structures composed of transparent dielectric material with dimensions of 200 to 300 nm. Next, an ultrathin amorphous silicon active layer is coated over the substrate and the nanostructures, and this active layer is coated with another dielectric material layer.

“One key aspect of this technique is the design of the ‘nanoscale sandwich,’ with the active materials in the middle of two dielectric layers,” Cao said.

The dielectric nanostructures below the active layer form a thin film featuring elevated, uniformly spaced surfaces resembling crenellations over a medieval castle.

“The nanostructures act as very efficient optical antennas, focusing the solar energy into the active material,” he said. “This focusing means we can use a thinner active layer without sacrificing performance."

The research, supported in part by the US Department of Energy, was published online by Nano Letters.

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