InGaP/GaAs/Ge multi-junction solar cell efficiency improvements using epitaxial germanium

Triple junction InGaP/GaAs/Ge solar cells are highly current mismatched due to the excess current generating capability of the germanium subcell. This severe current mismatch invites new approaches for increasing performance beyond that of current triple junctions. Presented here are two approaches for improving the efficiency of Ill-V multi-junctions beyond that of current triple junction technology. Both of these approaches involve the use of thin epitaxial germanium and do not require the development of new /spl sim/1 eV photovoltaic materials. The theoretical AM0 efficiency is over 30%. Modeling suggests the potential for over 1.5% absolute efficiency gain with respect to current InGaP/GaAs/Ge triple junction solar cells.