Patent ID: 8039736

Claim:
A structure comprising at least two photovoltaic cells in tandem for converting incident radiation from one wavelength to another comprising; a plurality of layers comprising a semiconductor layer operable as a photovoltaic cell; and a rare earth compound layer; wherein the incident radiation is incident on the first of the plurality of layers consisting of a semiconductor layer of composition Si (1-m) Ge m and a rare earth layer consisting of composition [RE1] x [J] y ; the second of the plurality of layers is in contact with the first of the plurality of layers and comprises a semiconductor layer consisting of composition Si (1-n) Ge n and a rare earth layer consisting of composition [RE2] u [J] v ; wherein u, v, x, y>0, and m, n, >0 and J is chosen from a group consisting of oxygen, nitrogen, phosphorous and combinations thereof and RE1 and RE2 are different rare earths.