THERMODYNAMIC EFFICIENCY LIMITS FOR SEMICONDUCTOR SOLAR-CELLS WITH CARRIER MULTIPLICATION

Our recent quantum efficiency measurements showed that more than one e lectron/hole pair per absorbed photon can be created in a solar cell. Thermodynamic consideration of carrier multiplication leads to new eff iciency 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 concentr ation, the new limit is 85%. These ideal values are thermodynamically possible with a single semiconductor which makes optimum use of carrie r multiplication and shows radiative recombination only. The theoretic al description of the thermodynamics of radiative recombination in a c ell with carrier multiplication leads us also to a novel mathematical description of the saturation current density.