VOLTAGE ENHANCEMENT IN QUANTUM-WELL SOLAR-CELLS

It is known that quantum well solar cells (QWSCs) can enhance short ci rcuit current and power conversion efficiency in comparison with simil ar, conventional solar cells made from the quantum well (QW) barrier m aterial alone. In this article we report measurements of the dark-curr ent and open-circuit voltage (V-oc) of a number of quantum well cells in three different lattice-matched material systems, namely, Ala(0.35) Ga(0.65)As/GaAs, GaInP/GaAs, and InP/InGaAs. We also present the resul ts obtained from comparable control cells without wells formed either from the material of the barriers or the well material alone. Our resu lts clearly demonstrate in all three cases that, al fixed voltage, QWS C dark currents are systematically lower than would be expected from c ontrol cells with the same effective absorption edge. Measurements of V-oc in a white-light source show that the open-circuit voltages of th e QWSCs are higher than those of control cells formed from the well ma terial. Furthermore, this enhancement is more than is expected from th e shift in the absorption edge due to the effect of confinement in the wells. We discuss these results in the light of recent theoretical sp eculation about the upper limit to the efficiency of an ideal quantum well solar cell. We report on a 50 well QWSC with open-circuit voltage higher than the world record conventional cell formed from the well m aterial, namely, GaAs. (C) 1996 American? Institute of Physics.