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Semiconductor design maximises solar light absorption

Posted: 03 Mar 2014 ?? ?Print Version ?Bookmark and Share

Keywords:solar? superabsorbing? North Carolina State University? design?

A team of researchers from North Carolina State University has fabricated a "superabsorbing" design that maximises the light absorption efficiency of thin film solar cells while minimising manufacturing costs.

The superabsorbing design could decrease the thickness of the semiconductor materials used in thin film solar cells by more than one order of magnitude without compromising the capability of solar light absorption.

"State-of-the-art thin film solar cells require an amorphous silicon layer that is about 100nm thick to capture the majority of the available solar energy," said Dr. Linyou Cao, an assistant professor of materials science and engineering at NC State University and senior author of a paper describing the work. "The structure we're proposing can absorb 90 per cent of available solar energy using only a 10nm thick layer of amorphous silicon."

The design also does the same superabsorbing effect when used with other materials, Cao added. The capacity of a 1?m thick cadmium telluride layer can be achieved with just a 50nm thick layer. Similarly, the design can also allow a 30nm thick layer of copper indium gallium selenide to fully absorb solar light.

Cao noted that the deposition of semiconductor materials stands as a major bottleneck for improving manufacturing productivity and lowering the cost of thin film solar cells. Since the cells would use less material and the thin films could be deposited more quickly, Cao is confident that "a decrease in the thickness of semiconductor materials by one order of magnitude would mean a substantial improvement in manufacturing productivity and reduction in cost."

This is a diagram of a superabsorbing design that may significantly improve the light absorption efficiency of thin film solar cells and drive down manufacturing costs.

Figure 1: This is a diagram of a superabsorbing design that may significantly improve the light absorption efficiency of thin film solar cells and drive down manufacturing costs.

In cross-section, the design looks like a rectangular onion. The light-absorbing semiconductor material coats a rectangular core. The semiconductor, in turn, is coated by three layers of anti-reflective coating that do not absorb light.

To develop the design, the researchers began by examining the maximum light absorption efficiency of semiconductor materials using light-trapping techniques. They found that maximising solar absorption requires a design in which the light-trapping efficiency for solar light is equal to the intrinsic absorption efficiency of the semiconductor materials.

The design employs onion-like structures to match their light-trapping efficiency with the absorption efficiency of the semiconductor materials in thin film solar cells.

"We first theoretically predicted the maximum solar light absorption efficiency in given semiconductor materials, and then proposed a design that could be readily fabricated to achieve the predicted maximum. We developed a new model to do this work, because we felt that existing models were not able to find the upper limit for the solar absorption of real semiconductor materials," Cao said. "And if this works the way we think it will, it would fundamentally solve light-absorption efficiency problems for thin film solar cells."

- Jean-Pierre Joosting
??EE Times Europe

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