New method could yield cheaper, thinner solar cells

New method could yield cheaper, thinner solar cells
Researchers from North Carolina State University in the US have found a way to create much slimmer thin film solar cells without sacrificing the cells' ability to absorb solar energy. The breakthrough, they believe, could significantly decrease manufacturing costs for the technology.

According to Dr Linyou Cao, an assistant professor of materials science at NC State, the efficiency is owed to a 'nanoscale sandwich' design with an ultra thin 'active' layer. "We created a solar cell with an active layer of amorphous silicon that is only 70nm thick," she explained. "This is a significant improvement, because typical thin film solar cells currently on the market that also use amorphous silicon have active layers between 300 and 500nm thick."

Dr Cao continued: "The 'active' layer in thin-film solar cells is the layer of material that actually absorbs solar energy for conversion into electricity or chemical fuel. The active layer (blue line) is sandwiched between layers of dielectric material. 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."

The new technique relies largely on conventional manufacturing processes, but is said to result in a very different finished product. First, the researchers created a pattern on the substrate using standard lithography techniques. The pattern outlines structures made of transparent, dielectric material measuring between 200 and 300nm. The researchers then coated the substrate and the nanostructures with an extremely thin layer of active material, such as amorphous silicon. This active layer was then coated with another layer of dielectric material.

According to Cao, using dielectric nanostructures beneath the active layer created a thin film with elevated surfaces evenly spaced all along the film.

"One key aspect of this technique is the design of the 'nanoscale sandwich,' with the active materials in the middle of two dielectric layers," she said. "The nanostructures act as very efficient optical antennas, focusing the solar energy into the active material. This focusing means we can use a thinner active layer without sacrificing performance. In the conventional thin film design, using a thinner active layer would impair the solar cell's efficiency."

Laura Hopperton

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