U.S. Navy Lab, partners developing solar cell to capture more than half the sun’s power

Schematic diagram of a multi-junction (MJ) solar cell formed from materials lattice-matched to InP and achieving the bandgaps for maximum efficiency. (Courtesy of US Navy Lab).

The U.S. Naval Research Laboratory, the Imperial College London and MicroLink Devices, Inc. of Niles, Ill., are developing a super solar photovoltaic (PV) cell that could convert more than half the sun’s light into electricity. The trio have proposed a triple-junction solar cell they said has the potential to break the 50 percent conversion efficiency barrier and could go much, much higher. In the world of solar, that would far surpass the 44 percent efficiency reached by Solar Junction and the National Renewable Energy Laboratory, which currently holds the record for PV cells.

The team is exploring novel semiconductor materials and applying band structure engineering with strain-balanced quantum wells, and have produced a design for a multi-junction PV cell that can achieve direct band gaps from 0.7 to 1.8 electron volts, meaning the device can respond to a wider range of light. The layers can be grown and lattice-matched to InP (Indium phosphide) semiconductors. “Having all lattice-matched materials with this wide range of band gaps is the key to breaking the current world record," said Robert Walters, Ph.D., NRL research physicist.

"It is well known that materials lattice-matched to InP can achieve band gaps of about 1.4 electron volts and below, but no ternary alloy semiconductors exist with a higher direct band-gap," Walters said. "At present, the world record triple-junction solar cell efficiency is 44 percent under concentration and it is generally accepted that a major technology breakthrough will be required for the efficiency of these cells to increase much further."

That’s where the new research comes in. "This research has produced a novel, realistically achievable, lattice-matched, multi-junction solar cell design with the potential to break the 50 percent power conversion efficiency mark under concentrated illumination," Walters said. The high-efficiency PV cell design uses quaternary alloys of InAlAsSb (Indium, Aluminum, Arsenic and Antimony) as the high-band gap material layer for the device, which can achieve a band-gap as high as 1.8 electron volts.

The research team was recently awarded a U.S. Department of Energy Advanced Research Projects Agency-Energy (ARPA-E) award to execute a three-year program to develop the new solar technology, according to the lab.

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