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Tiny Solar Cell Could Make a Big Difference

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The U.S. Department of Energy’s National Renewable Energy Laboratory recently validated greater than 41 percent efficiency at a concentration of 1,000 suns for tiny cells made by Semprius — one of the highest efficiencies recorded at this concentration.

Semprius’ triple-junction cells are made of gallium arsenide. Low-cost lenses concentrate the sun light onto the tiny cells 1,100 times. Their tiny size means they occupy only one-one thousandth of the entire solar module area, reducing the module cost. In addition, the use of a large number of small cells helps to distribute unwanted heat over the cell’s structure, so there’s no need for expensive thermal management hardware such as heat fins.

Semprius engineers use the company’s patented micro-transfer printing process to allow the micro-cells to be transferred from the growth substrate to a wafer. In a massive parallel process, thousands of cells are transferred simultaneously. This allows the original substrate to be used again and again, dramatically cutting costs. It also provides a way to handle very small cells.

This low-cost approach, which Semprius executives say can cut manufacturing expense by 50 percent, caught the eye of energy giant Siemens, which this year took a 16 percent stake in Semprius, as part of a $20 million investment from venture capitalists.

NREL scientist Keith Emery examines a Semprius solar module at the laboratory’s Outdoor Test Facility. NREL helped Semprius characterize and test its tiny solar cells, which are the diameter of a dot made by a ballpoint pen (600 microns wide).
Credit: Dennis Schroeder

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