Dual-junction GaAsP/SiGe on silicon tandem solar cells

GaAsP/SiGe dual-junction solar cells have been grown on silicon substrates which have the potential of achieving tandem efficiencies of 40%. This lattice-matched structure facilitates high performance from the III-V top cell while maintaining the cost advantages of silicon solar cells. The SiGe graded buffer allows for lattice matching of the top and bottom cell while providing a low dislocation interface between the silicon substrate and the device layers. Initial structures have reached an efficiency of 18.9%. Near term improvements to 25.0% under AM1.5G will be described.