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NREL Solar Research Gains Two R&D 100 Awards

July 17, 2008

An ultra-light, highly efficient solar cell and use of ink-jet printing to manufacture thin-film photovoltaics—both developed at the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory—have been named among this year’s most significant innovations by Research & Development (R&D) Magazine.

Known as "the Oscars of Invention," the R&D 100 Award showcases the most significant new technologies commercialized worldwide. NREL has won a total of 42 of the awards, which the magazine has been presenting annually since 1969.

The new Inverted Metamorphic Multi-Junction solar cell was developed at NREL and is being commercialized by Emcore Corp. of Albuquerque, N.M., in partnership with the Air Force Research Laboratories Space Vehicles Directorate at Kirtland Air Force Base in Albuquerque. The cell already had set a pair of world records for solar conversion efficiency when it was nominated for the R&D 100 award, and recently it set a third world record with a solar conversion rate that exceeded 40%.

The thin-film photovoltaic (PV) manufacturing process combines NREL's precursor inks with a rapid reactive bonding technique being commercialized by HelioVolt Corp. of Austin, Texas.  The combination eliminates complex manufacturing methods and could create enough of the flexible film to turn entire buildings and other structures into small, self-sustaining power plants. Xcel Energy also supported the work.

“These two technologies represent a new wave of breakthroughs in development of solar cells that will have a significant impact on the penetration of solar energy in the marketplace,” said Dan Arvizu, NREL Director. 

 “This is yet the latest example of how the Department of Energy and our National Laboratories are continuing to demonstrate world-class leadership in innovation, as we enhance our energy security, national security and economic competiveness," Energy Secretary Samuel W. Bodman said. "On behalf of the Department, I would like to congratulate all of our employees who have earned R&D 100 awards and in particular this year's winners.”

Both R&D 100 awards recognize research at NREL's National Center for Photovoltaics.

The Inverted Metamorphic Multi-Junction Solar Cell represents a new class of solar cells with clear advantages in performance, engineering design, operation and cost.  It employs an entirely new way of constructing solar cells. For decades, conventional cells have featured multi-layer structures of semiconducting materials with similar crystalline structure. Their performance and cost effectiveness is constrained by growing the cells in an upright configuration. Meanwhile, the cells are rigid, heavy and thick with a bottom layer made of germanium.

In the new method, the cell is grown upside down. These layers use high-energy materials with extremely high quality crystals, especially in the upper layers of the cell where most of the power is produced. Not all of the layers follow the lattice pattern of even atomic spacing. Instead, the cell includes a full range of atomic spacing, which allows for greater absorption and use of sunlight.  The thick, rigid germanium layer is removed, reducing the cell's cost and 94% of its weight. By turning the conventional approach to cells on its head, the result is an ultra-light and flexible cell that also converts solar energy with record efficiency.

The new cell is a natural candidate for use for powering spacecraft and on-board instruments, perhaps by being incorporated into the satellite's very skin or unfurling a solar array like an awning.  This would eliminate the need for conventional wing-shaped solar arrays with heavy metal frames and balky mechanical controls.  Those same qualities also will open new commercial uses for solar power on Earth, especially in the solar concentrator market.

NREL's second R&D 100 award spotlights a new technology for manufacturing Hybrid CIGS, or thin film PV employing layers of copper indium gallium diselenide.  Thin films may not achieve the outer limits of solar conversion efficiency enjoyed by crystalline silicon cells but their advantage is that they can be manufactured quickly and in large volumes using inks that cost a fraction of the cost of silicon.

NREL developed a method in which the hybrid CIGS cells are manufactured in layers by using ink-jet and ultrasonic technology to precisely apply metal-organic inks in separate layers directly into common building materials such as metal and glass. This will allow solar panels to be integrated into the building architecture to turn entire buildings into clean energy power plants

NREL's partner, HelioVolt, has developed a proprietary processing system that quickly bonds the film layers under heat and pressure forming large-grain CIGS crystals. The process takes seconds to complete at substantially lower temperatures, whereas other solar cell manufacturing requires hours at temperatures 500-700 degrees Celsius higher as well as vacuum processing, evaporation and other capital intensive steps.

NREL is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for DOE by Midwest Research Institute and Battelle. More on NREL's photovoltaics research can be found at


—George Douglas