A sliver of solar slashes the cost of green energy

An ultra thin solar cell could significantly cut the cost of solar power, according to a German project.

The cell, designed by researchers at the Hahn Meitner Institute in Berlin, uses cheaper semiconductor materials than conventional solar cells, and is up to 50 times more efficient, according to a paper published in the latest issue of Semiconductor Science & Technology.

Solar cells are usually built as sandwiches, with a surface that absorbs solar radiation – the absorber – back by a substrate layer. The trick, German physicist Rolf Koenenkamp told edie, is to find a design that can combine a cheap absorber with a cheap substrate.

Typical cells that use planar substrates require expensive absorbing materials, so the German team devised an alternative substrate that could be used with cheaper absorbers, while also redesigning the shape of the absorber. The result was a cell with a layer of light-sensitive cadmium telluride (CdTe) placed on top of a layer of porous titanium dioxide.

The secret, says Koenenkamp, now at Portland State University in Oregon, is in the structure. The trend in solar technology is towards thin film absorbers, but the German design is thinner still. “Extremely thin,” says a delighted Koenenkamp.

The key is the porous substrate, which ensures that when sunlight hits the cell. Light is caught inside the pores and scattered back into the cadmium telluride layer, making the device more efficient by a factor of 50 compared with an equivalent cell made with non-porous material.

“The new structure allows the use of cheaper and lower quality materials,” says Koenenkamp, whose group has also tested ‘rough’ zinc oxide and zinc telluride in a similar cell.

CdTe is already commercially available and is used in some solar cells. The goal for Koenenkamp is to come up with a cheap, undeveloped absorber that has previously been rejected for its poor performance in a conventional cell. “We want to show how well it could work in our cell,” says Koenenkamp, adding that the German design could theoretically be applied to all kinds of cells, including silicon and compound solar cells.




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