FYI,

"NREL Solar Cell Sets World Efficiency Record at 40.8 Percent"
National Renewable Energy Laboratory
http://www.nrel.gov/news/press/2008/625.html

: Scientists at the U.S. Department of Energy's National Renewable
: Energy Laboratory (NREL) have set a world record in solar cell
: efficiency with a photovoltaic device that converts 40.8 percent of
: the light that hits it into electricity. This is the highest
: confirmed efficiency of any photovoltaic device to date.

: The inverted metamorphic triple-junction solar cell was designed,
: fabricated and independently measured at NREL. The 40.8 percent
: efficiency was measured under concentrated light of 326 suns. One
: sun is about the amount of light that typically hits Earth on a
: sunny day. The new cell is a natural candidate for the space
: satellite market and for terrestrial concentrated photovoltaic
: arrays, which use lenses or mirrors to focus sunlight onto the
: solar cells.

: The new solar cell differs significantly from the previous record
: holder – also based on a NREL design. Instead of using a germanium
: wafer as the bottom junction of the device, the new design uses
: compositions of gallium indium phosphide and gallium indium
: arsenide to split the solar spectrum into three equal parts that
: are absorbed by each of the cell's three junctions for higher
: potential efficiencies. This is accomplished by growing the solar
: cell on a gallium arsenide wafer, flipping it over, then removing
: the wafer. The resulting device is extremely thin and light and
: represents a new class of solar cells with advantages in
: performance, design, operation and cost.

: NREL's Mark Wanlass invented the original inverted cell, which
: recently won a R&D 100 award. His design was modified by a team led
: by John Geisz that further optimized the junction energies by
: making the middle junction metamorphic as well as the bottom
: junction. Metamorphic junctions are lattice mismatched – their
: atoms don't line up. The material properties of the mismatched
: semiconductors allows for greater potential conversion of sunlight.

: 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.

Mark Reiff