High-efficiency InGaP/In0.01Ga0.99As tandem solar cells lattice-matched to Ge substrates

Conversion efficiency (AM1.5G) of more than 30% was achieved by adding a small quantity of Indium into a GaAs bottom cell in the conventional tandem solar cell on Ge substrate. It was found that the lattice-mismatch between GaAs and Ge caused misfit-dislocations in thick GaAs layers and reduced an open-circuit voltage (Voc) of the cell. An In0.49Ga0.51P/In0.01Ga0.99As tandem cell lattice-matched to Ge showed a great improvement in efficiency, which was attributed to an increase in the Voc of the bottom cell and increases in the photocurrents both in the top and bottom cells due to reductions in band-gap energy.