Alta Devices Breaks Solar-Cell Record

Technology Review
June 21, 2011

A startup that has been working in stealth mode for several years says it has achieved a record solar-cell efficiency of 28.2 percent, nearing the theoretical maximum of 33.5 percent. The mark is roughly 2 percentage points higher than a record set last year—a major advance in an industry that typically measures improvements in tenths of a percent. Alta Devices, founded in 2007 and based in Santa Clara, California, says its innovative techniques lend themselves to large-scale manufacturing.

Improving efficiency is essential if solar power is to be competitive with fossil fuels. Increasing the power output of individual solar cells reduces the number of cells needed per installation and also cuts the cost of things such as installation, wiring, and electronics for connecting the panels to the grid.

Alta Devices researchers worked with gallium arsenide to improve inherent properties that make it "almost an ideal solar-cell material," says Harry Atwater, a professor of applied physics at Caltech and cofounder of the company. When a solar cell absorbs sunlight, some of the energy in the sunlight generates electrons that are quickly extracted from the cell to make electricity. If the electrons are not extracted fast enough, they decay, releasing their energy as either heat or light. Losing the energy as heat reduces both the voltage and the amount of current the cell can make, reducing power output. But if the electron instead produces light, the light can be reabsorbed by the solar cell to generate another electron, providing another chance for the energy in sunlight to become electricity.
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