Researchers at Sandia National Laboratories have shrunk silicon solar cells down to the micro scale, opening new possibilities for improved efficiency.
Multi-crystalline silicon, currently the gold standard for solar-cell efficiency, is expensive and produces cells that are heavy and brittle. Sandia’s microscopic silicon solar cells use 100 times less material while operating with the same efficiency.
In addition to lower materials costs, the smaller scale of these cells means they could be incorporated into compact optical systems for cheaper light-tracking and concentration. Researchers might even suspend them in inks that could be printed onto plastic to make efficient, flexible silicon-solar modules.
“In microsystems, you’re looking for things that become cheaper, perform better, and gain new functionalities,” says Gregory Nielson, head scientist on the project.
So far, the Sandia researchers have assembled and tested a single micro solar cell as proof of principle. But they have begun testing functioning solar modules made from multiple tiny cells and are developing techniques for assembling them efficiently.
Sandia’s cells are between 0.25 and one millimeter in diameter. The main benefit of manufacturing such small cells would be lower materials costs, since the tiny cells can be made about 10 times thinner than conventional ones. Ordinarily, solar cells must be 100 micrometers thick to support their surface area–typically about 15 centimeters square.
Sandia makes its cells from silicon that has been processed using conventional chemical methods. Researchers carve the cells out of this silicon using a chemical etching technique that creates negligible waste. They treat the surface of the wafer to create the electrical properties necessary for a functioning cell, then top it with metal contacts. Researchers then etch the top 10 to 20 micrometers of the wafer surface using chemicals that only eat into a particular part of the crystal structure.
The resulting cells are about 20 micrometers thick but have the same efficiency as conventional cells, converting about 14.9 percent of sunlight into electrical energy. It’s also easier to make the cells in a hexagonal shape, which makes the most of the available area without wasting much silicon. “The materials savings are a big deal,” says Nielson.