Three-Dimensional Design Leads to Better Solar Cells

Technology Review
Sept 17, 2011

A Santa Barbara, California, company called Solar3D plans to make silicon solar cells that are more efficient than conventional cells by borrowing the light-trapping concept behind optical-fiber technology. The company claims that its three-dimensional design will funnel light into silicon and keep it trapped—giving the material more time to convert it into electricity.

Silicon has a theoretical maximum light-to-electricity conversion efficiency of 29 percent, but panels on the market today are only 15 to 18 percent efficient. Solar3D does not have exact efficiency numbers for its design yet, but CEO Jim Nelson says, "We think it's going to approach silicon's theoretical efficiency. We won't get to 29 percent—nobody's going to get that high with silicon—but we're hoping to get as close as possible."

Solar3D's design will tackle two factors that bring down solar efficiency. First, 30 percent of the light hitting solar panels is reflected and lost. Second, many of the electrons created when light hits silicon are reabsorbed by the material before they reach the external circuit.

The new design has channels in its top light-collecting layer, which will be made of silicon dioxide or another similar material; these direct light downward, helping to eliminate reflection, Nelson says. The lower layer is an array of three-dimensional structures, each a few micrometers wide, which trap light by emulating the waveguides used in optical fibers. Optical fibers contain two cylindrical layers with different refractive indices that continuously reflect light back into the core. Nelson says this 3D structure will allow the light to bounce around until the photons have yielded as many electrons as possible. "We'll also put contacts very close to where that happens so that the electrons don't have to travel very far," he says.
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