Potential performance of "Out-of-Sequence" multi-junction solar cells: III-V on virtual Ge substrates with active Si bottom sub-cell

We look at the design of a novel Out-of-Sequence (OoS) tandem where a GaInP/GaAs top junction is stacked on top of a very thin Ge active cell which in turn is stacked on top of an active bottom junction Si substrate. We have also investigated the conversion efficiency of an upright metamorphic Gallium Indium Phosphide (GaInP)/Gallium Arnside (GaAs)/Germanium (Ge)/Silicon (Si) tandem structure where Ge acts purely as a buffer layer between the Si and upper III-V layers. The impact of various Ge buffer layer thicknesses on the tandem efficiency and the performance of tandem stack structure using different optical generation schemes have been investigated. Finally, we determine under what conditions the Ge should be an active cell in the stack, rather than a simple parasitic absorber layer in the structure.