Thermodynamic efficiency limits for semiconductor solar cells with carrier multiplication

Our recent quantum efficiency measurements showed that more than one electron/hole pair per absorbed photon can be created in a solar cell. Thermodynamic consideration of carrier multiplication leads to new efficiency limits for photovoltaic energy conversion. An efficiency of 43% is theoretically possible for cells which are illuminated by the sun's unconcentrated black body radiation. For sun light of full concentration, the new limit is 85%. These ideal values are thermodynamically possible with a single semiconductor which makes optimum use of carrier multiplication and shows radiative recombination only. The theoretical description of the thermodynamics of radiative recombination in a cell with carrier multiplication leads us also to a novel mathematical description of the saturation current density.