Researchers  from the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) have reported the first solar cell that produces a photocurrent that has an external quantum efficiency greater than 100 percent when photoexcited with photons from the high energy region of the solar spectrum. The external quantum efficiency reached a peak value of 114 percent.

The newly reported work marks a promising step toward developing Next Generation Solar Cells for both solar  and solar fuels that will be competitive with, or perhaps less costly than, energy from fossil or nuclear fuels

Source: http://www.nrel.gov/news/press/2011/1667.html
A paper on the breakthrough appears in the Dec. 16 issue of Science Magazine.