Preceding studies applied InGaAs/GaAs/GaAsP quantum structures to solar cells, aiming to adjust the bandgap of sub-cells for multi junction solar cells. As research of solar cells containing quantum structures progressed, it was found that Wire-on-Well (WoW) nanostructure solar cells are superior to conventional planar superlattice (PSL) solar cells in terms of the photo-generated carrier collection efficiency. However, many physical properties of this unique nanostructure, WoW, still remain unknown. Further fundamental studies are needed to put WoW solar cells into practical use. In order to achieve high energy conversion efficiency, the gap between the realized open circuit voltage and its theoretical upper limit must be small. Our study evaluated the device characteristics of WoW solar cells more completely not only by I-V characteristics but also by electroluminescence (EL) measurements which enables us to compare the gap of open circuit voltage among the GaAs cells with WoW, PSL, and without superlattice. We revealed that Wire on Well nanostructure would improve the energy conversion efficiency of multi junction solar cells.