Tandem GaAsP/SiGe on Si solar cells.

GaAsP/SiGe dual-junction solar cells have been epitaxially grown on silicon substrates which have the potential of achieving 1-sun tandem efficiencies of 40%. With the addition of light trapping this lattice-matched two-terminal structure can be current-matched and 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. This two-terminal dual-junction structure design is presented and demonstrates a 10.4% relative improvement in J SC and a 1.7% absolute improvement in efficiency over previous best devices. These initial structures have reached an efficiency of 18.9% under 1-sun. The devices suffer from high series resistance and exhibit reduced fill factors. A near term pathway to efficiencies approaching 25% is described. [ABSTRACT FROM AUTHOR]