Wednesday, September 24, 2008
The most efficient solar cells ever produced, triple-junction solar cells, have become indispensable to modern life. But scientists and industrialists have long known they could be much better; they were looking to develop the next big idea. The next big idea has come in the form of the Inverted Metamorphic Multijunction (IMM) Solar Cell developed by scientists at the National Renewable Energy Laboratory (NREL), Golden, Colo., jointly with Emcore Corp., Albuquerque, N.M., and the Air Force Research Laboratories Space Vehicles Directorate, Kirtland Air Force Base, N.M. The IMM solar cell is a new class of multijunction solar cells that is the world-record holder for one-sun efficiency (40.8%). Two major innovations make this possible. The first is growing or depositing cell layers in an inverted sequence—from top to bottom—the reverse of the normal order. The second is using a transparent, compositionally graded transition layer to allow the growth of one subcell layer on another, even though that layer has a crystal structure with a different atomic spacing. These innovations combine for a tenfold reduction in weight compared to conventional solar cells in addition to high flexibility, which is revolutionizing the design of solar arrays used to power space vehicles.
NREL, www.nrel.gov