The National Renewable Energy Laboratory (NREL) has 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 quantum efficiency of a solar cell is a very important measure for solar cells as it gives information on the current that a given cell will produce when illuminated by a particular wavelength.
If the quantum efficiency is integrated (summed) over the whole solar electromagnetic spectrum, one can evaluate the current that a cell will produce when exposed to the solar spectrum.
The ratio between this current and the highest possible current gives the electrical efficiency of the solar cell.
With solar cells, one often measures the external quantum efficiency, which is the current obtained outside the device per incoming photon.
None of the solar cells to date exhibit external quantum efficiencies above 100 percent at any wavelength in the solar spectrum.
The external quantum efficiency reached at NREL a peak value of 114 percent.