In this paper, we report on the conversion efficiency improvement in In0.50Ga0.50P/InxGa1-xAs tandem solar cells by employing metamorphic InGaAs bottom cell instead of lattice matched GaAs cell. In0.50Ga0.50P/In0.025Ga0.975As and In0.50Ga0.50P/GaAs double junction solar cells were grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) on GaAs substrates. High-resolution transmission electron microscopy (HR-TEM) measurement reveals the dislocation in the In0.025Ga0.975As layer which is caused by the lattice mismatch between In0.025Ga0.975As subcell and GaAs substrate. The increase of short circuit current density and decrease in open voltage circuit are attributed in bandgap decrease. Conversion efficiencies of these cells were measured to be 24.37% and 25.11% (AM1.5, 1 sun, 25oC) for the In0.50Ga0.50P/GaAs and In0.50Ga0.50P/In0.025Ga0.975As solar cells, respectively. These results prove the ability to fabricate high efficiency solar cell based on metamorphic approach with low dislocation densities.
