Advances in Bragg stack quantum well solar cells

Strain-balanced quantum well solar cells (SB-QWSC) extend the photon absorption edge beyond that of bulk GaAs by incorporation of quantum wells in the i-region of a p-i-n device. The addition of a distributed Bragg reflector (DBR) can substantially increase the photocurrent with little or no detriment to the dark-current. Experimental results are presented that show improvements of DBR cell efficiencies over SB-QWSC's without DBR's. In addition, at high dark-current levels appropriate to high concentration, we observe that the dark-currents of the SB-QWSC's exhibit ideal diode behaviour. We present evidence that the ideality n=1 dark-current is reduced in the DBR cells and discuss the possible efficiency improvements if the dark-current is radiatively dominant.