New upper efficiency limits for semiconductor solar cells

Abstract

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