Voltage performance of quantum well solar cells in the Alx Ga1-xAs/GaAs and the GaAs/InyGa1-yAs material systems

The open circuit voltage V_oc and reference voltage V _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_xGa_1-xAs/GaAs and GaAs/In_yGa_1-y As material systems. For both combinations, QW solar cells show a better voltage performance in V_oc and V_ref than one would expect from a single bandgap solar cell with the same effective absorption bandgap E_a. For the AlGaAs/GaAs cells, V _oc is related to structural parameters of the QW cells such as the well width L_W and the Al fraction x. For the strained GaAs/InGaAs cells a relationship is found between V_ref and the barrier width L_B, which is a dominant parameter in determining strain relaxation and defect formation at a fixed In fraction