Patent ID: 8173891

Claim:
A monolithic, multi-bandgap, tandem, photovoltaic converter, comprising: a top subcell with a first bandgap grown epitaxially on a first graded layer that was grown epitaxially on a substrate with a starting lattice constant of the first graded layer being matched to the substrate and with a terminal lattice constant in the growth plane being smaller than the substrate lattice constant, wherein the first bandgap of the top subcell has a lattice constant that is smaller than the substrate lattice constant; a second graded layer grown epitaxially on the top subcell with a starting lattice constant of the second graded layer being matched to the lattice constant of the top subcell on which it is grown and a terminal lattice constant in the growth plane larger than the lattice constant of the top subcell on which it is grown, said second graded layer being transparent to radiation that can pass through the top subcell on which it is grown; and a bottom subcell grown epitaxially on the second graded layer with a second bandgap that is smaller than the first bandgap of the top subcell and a lattice constant that matches the terminal lattice constant in the growth plane of the second graded layer.