World's Most Efficient Solar Cell

National Renewable Energy Laboratory, Spectrolab Set Record

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George Douglas, 303-275-4096
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Golden, Colo., Nov. 1, 1999 - A solar cell that can convert sunlight to electricity at a record-setting 32 percent efficiency has been developed by the U.S. Department of Energy's (DOE) National Renewable Energy Laboratory (NREL) and Spectrolab. The high efficiency makes the cells attractive for use in solar concentrator systems on Earth.

Spectrolab of Sylmar, Calif., "grew" the record-setting solar cell. After processing by NREL, the photovoltaic cell was measured this month at an efficiency of 32.3 percent at the laboratory's Solar Energy Research Facility. The efficiency of a solar cell is the percentage of sunlight it converts to electricity.

"This advance builds on the many successful photovoltaic projects funded by the Department of Energy," said Dan Reicher, DOE's Assistant Secretary for Energy Efficiency and Renewable Energy. "We are pleased that DOE support to industry is hastening the commercialization and everyday use of solar energy which will be an important contributor to Clean Energy for the 21st Century."

Similar high-efficiency solar cells - invented and developed over 10 years at NREL before being licensed and put into production by Spectrolab - had achieved close to 30 percent efficiency. This high rate of converting sunlight to electricity has made the gallium indium phosphide on gallium arsenide multi-junction design valuable for powering space satellites, the primary market for this type of solar cell.

The record-setting efficiency gained by adding an active germanium junction could help bring these high-powered solar cells down to Earth. "Multi-junction solar cells have made a major impact on the cost effectiveness and revenue-generating capabilities of high-power space satellites over the past five years and we expect them to have a similar impact on the terrestrial photovoltaics industry," said Dr. David Lillington of Spectrolab.

The high-efficiency cells are well suited for concentrator systems that use relatively inexpensive lenses or mirrors to focus sunlight on the photovoltaics, reducing cost by reducing the number of cells and the area needed to produce a required amount of electricity.

"This is a very encouraging result," said Dr. Jerry Olson, principal scientist in the High Efficiency and Concentrators Photovoltaics group at NREL. "The challenge now will be for industry and government to work together to get these cells into real-life power generating systems." Spectrolab grew the three-junction, gallium indium phosphide, gallium arsenide, germanium (GaInP/GaAs/Ge) cell using production equipment and a low-cost germanium substrate. Metallic contacts and an anti-reflection coating were added at NREL, resulting in a solar cell with just two terminals. The 32.3 percent efficiency was achieved using light concentrated to 47 times greater than sunlight, with the standard AM1.5 Direct spectrum. Spectrolab is a leading manufacturer of advanced solar cells and panels for space satellites and is a wholly owned subsidiary of Hughes Electronics. The National Renewable Energy Laboratory is the Department of Energy's premier laboratory for renewable energy and energy efficiency research, development and deployment.


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