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Solar Cells Suck It Up
Environment News Service

6:54 a.m. April 25, 2001 PDT

A longstanding efficiency record for electricity produced by solar cells made from cadmium telluride has been broken by researchers at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL).

The NREL team created cells that convert 16.4 percent of the available sunlight that strikes them into electricity. The previous record was 15.8 percent for a cadmium telluride cell -- a record that has stood since 1992

In recent months, the rising cost of fuels and the California power crisis have triggered a greater surge in the installation of solar electric systems for homes and businesses. The expanding solar industry will be able to use these more efficient solar cells to help meet that demand.

Cadmium telluride represents one of the most promising technologies for so-called thin film solar cells, says NREL research manager John Benner. In the thin film manufacturing process, layers of differing electricity-producing materials are applied sequentially to a glass, plastic or steel backing.

Many experts believe thin film cells are the wave of the future, because thin films use materials that are less expensive than the materials used in earlier, conventional solar panels.

Of the several materials that can be used for thin film panels, cadmium telluride yields higher wattage per square foot, at a lower price per watt of capacity.

Increasing efficiency and lowering costs have been the two most important goals during the more than 20 years the National Renewable Energy Laboratory has been conducting research on improving photovoltaic systems.

The record-setting cadmium telluride (CdTe) process is different from previous cells and benefits from new understanding of the operation of solar cells, says Benner. The cell utilizes new materials that interact chemically with the cadmium telluride to improve adhesion, light collection and electronic properties.

"This technology offers the prospect of getting a better product to customers," said Benner. "Our industry partners can use this technology in expanding capacity to meet the rapidly mounting demand for photovoltaics." In 2000, the solar photovoltaic industry increased production by 29 percent in the United States and 39 percent worldwide.

The record-setting cadmium telluride solar cell is still only about half as efficient as a solar cell that can convert sunlight to electricity at 32 percent efficiency, developed in 1999 by NREL and Spectrolab of Sylmar, California. The Boeing Company acquired Spectrolab in October 2000.

The record-setting Spectrolab gallium indium phosphide on gallium arsenide multi-junction design is valuable for powering space satellites, the primary market for this type of solar cell. On Earth it is attractive for use in solar concentrator systems.

The NREL team that produced the new cadmium telluride solar cell works within the National Center for Photovoltaics in collaboration with the National CdTe Team that also includes scientists from universities and industry.

The Department of Energy established the National Center for Photovoltaics at NREL in 1996 to provide for coordinated research and development to improve the cost effectiveness, performance and reliability of solar-electric technologies. Sandia National Laboratories also participates in the center.

Earlier this month, NREL announced $6 million in awards to 11 universities and five companies for technology research into non-conventional, photovoltaic technologies for creating electricity from sunlight.

Some of the new concepts will explore entirely new methods, materials and processes for turning sunlight into electricity. Two contracts, for instance, explore solar cells based on new plastic materials.

The awards will support fundamental and exploratory research into increasing the amount of electricity produced by photovoltaic cells, reducing the cost of electricity produced, and ensuring performance over longer periods of time.