Voltage performance of quantum well solar cells in the Al/sub x/Ga/sub 1-x/As/GaAs and the GaAs/In/sub y/Ga/sub 1-y/As material systems

The open circuit voltage V/sub oc/ and reference voltage V/sub ref/ defined as a measure of the dark current quality, have been studied for a large number of quantum well (QW) solar cells and homogenous control cells. Samples were grown in the Al/sub x/Ga/sub 1-x/As/GaAs and GaAs/In/sub y/Ga/sub 1-y/As material systems. For both combinations, QW solar cells show a better voltage performance in V/sub oc/ and V/sub ref/ than one would expect from a single bandgap solar cell with the same effective absorption bandgap E/sub a/. For the AlGaAs/GaAs cells, V/sub oc/ is related to structural parameters of the QW cells such as the well width L/sub W/ and the Al fraction x. For the strained GaAs/InGaAs cells a relationship is found between V/sub ref/ and the barrier width L/sub B/, which is a dominant parameter in determining strain relaxation and defect formation at a fixed In fraction.