Efficient, Cheap Solar Cells

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Some companies have already introduced products that pair a textured front with a mirrored back, and the technique has been demonstrated to work well in laboratories for years. But adding the reflective layer typically requires expensive processing and lithography. Rohatgi has developed proprietary materials that can be incorporated into the solar cells using screen printing. This, along with other advances that simplify the manufacturing process, allowed the company to produce highly efficient cells at a low cost.

Tonio Buonassisi, a professor of mechanical engineering at MIT, says that Suniva's new solar cell is "exciting" because "it's a demonstration that some of the high-efficiency technologies that have been worked on for years in the laboratory can be applicable in the marketplace." He says that Suniva's decision to use such technologies is a risk that most other solar-cell companies have been avoiding. Now that Suniva has developed a way to apply these techniques cheaply, he predicts that other solar-cell companies could be forced to do likewise to compete.

To be sure, significant work remains before the goal of 8 to 10 cents per kilowatt can be achieved. Suniva has demonstrated the crucial first step, which is to show that it can make solar cells that are more than 20 percent efficient using screen printing. The results have been confirmed by the National Renewable Energy Laboratory, in Golden, CO. But for those tests, Suniva used cells with 200-micrometer-thick silicon wafers, and reaching 8 cents a kilowatt will require 100-micrometer wafers. That this is technically possible has been established. The challenge lies in acquiring large amounts of such silicon, since wafers that thin aren't commercially available, Rohatgi says. What's more, factories will need to be retooled to handle 100-micrometer cells, which machines designed to handle thicker wafers could break.

The company's priority now is to scale up production of its highly efficient 200-micrometer cells, which could still lower the cost of solar power. Once it has established high-volume manufacturing, the next step is to introduce thinner wafers, bringing down the costs yet further.