Minimum performance criteria for quantum well based junctions in multi-junction solar cells

A systematic survey of the opportunities for incorporating quantum well structures into multi-junction space cells is presented. The quantum well solar cell provides a means for extending the absorption edge of a conventional p/n cell, but normally at the cost of a reduction in the open circuit voltage. However, in a current limited multi-junction solar cell, an increased efficiency can result from trading the sub-cell voltage for a higher overall device current. The suitability of a strain-balanced MQW junction as a higher current replacement for the GaAs junction is discussed, as well as an approach for attaining a high-quality 1 eV junction, suitable for a highly efficient 4-junction solar cell. The minimum performance that must be attained from the MQW junction is outlined and offered as a roadmap for the successful incorporation of quantum wells into the next generation of space solar cells.