Properties of GaAs/InGaAs quantum well solar cells under low concentration ratios

Multi-quantum well (MQW) GaAs/In_0.19Ga_0.81As solar cells have been measured under low concentration levels (1~4 suns). An efficiency of 22% has been obtained at a ratio of 4 suns as opposed to 18% under 1 sun AM1.5 conditions. We explain the results in terms of an enhancement in minority-carrier lifetime under concentration. Even when the concentration ratio is low, the high-injection regime can be achieved since the carrier concentration in the intrinsic layer is very low. The existence of a high concentration of defects in the base layer has been observed by the DLTS analysis. Enhancement of the minority-carrier lifetime under concentration is thought to be due to recombination probability saturation of recombination centers with high-injection of minority carriers