Two new solar technologies developed at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) have been recognized for excellence.
The Federal Laboratory Consortium for Technology awarded a national prize for the commercialization of federally funded research for new class of ultra-light, high-efficiency solar cells.
The TransferInverted Metamorphic Multijunction (IMM) Solar Cell, invented by Mark Wanlass of NREL’s Concentrating Photovoltaics (CPV) Group, received the 2009 Award for Excellence in Technology Transfer.
Since 2005, NREL and Wanlass have worked with Emcore Corp of
Albuquerque, N.M. to develop a commercial version of the IMM cell under
a Cooperative Research and Development Agreement (CRADA.)
Wanlass’s design established a solar cell efficiency of 37.9% under concentrated light equal to 10 suns in 2005. In 2008, a modified version of the IMM design set a new record of 40.8% efficiency under 326 suns at NREL.
NREL said the cell represents a new class of solar cells with clear advantages in performance, engineering design, operation and cost. For decades, conventional cells have featured wafers 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.
Commercialized versions of the IMM cell are aimed at the space satellite market and for use on Earth in concentrated photovoltaic arrays, which use lenses or mirrors to focus sunlight onto the solar cells.
Research and Development (R&D) Magazine also gave the technology an R&D 100 award, which showcases the 100 most significant new technologies commercialized worldwide.
Since 1969, NREL has won a total of 42 of the awards, which arekKnown as "the Oscars of Invention."
Hybrid CIGS
In addition to the award for IMM, NREL received an R&D 100 Award for 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. NREL said 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.
This simpler, combined approach could create enough of the flexible PV film to integrate it with windows, roofing, facades and other structural components, turning entire buildings and other into small, self-sustaining power plants.
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