Active rare earth tandem solar cell

1. A solid state device comprising at least two solar cells in tandem for converting incident radiation into electrical energy comprising;

a first solar cell of first composition;

a second solar cell of second composition; and

a third region of third composition separating the first solar cell from the second solar cell;

wherein the first composition is different from the second composition and the third region consists of a first and second rare-earth and at least one element chosen from a group consisting of oxygen, nitrogen and phosphorous such that a portion of the incident radiation passing through the first solar cell is converted into radiation of a different wavelength by the third region for subsequent passage through the second solar cell; wherein said first and second compositions comprise elements substantially from Group IV.

2. A solid state device of claim 1 wherein said composition of said third region consists of compounds described by [RE 2 ] w [RE 3 ] x [J 1 ] y [J 2 ] z wherein [RE] is chosen from a rare earth; [J 1 ] and [J 2 ] are chosen from a group consisting of Oxygen (O), Nitrogen (N), and Phosphorus (P), and 0≦z≦5, and 0<w, x, y≦5.

3. A solid state device of claim 2 wherein said third region comprises,

a first portion of fourth composition adjacent said first solar cell;

a second portion of fifth composition; and

a third portion of sixth composition separated from the first portion by the second portion and adjacent said second solar cell wherein the fifth composition is different from the fourth and sixth compositions.

4. A solid state device of claim 3 wherein said second portion comprises a first surface adjacent said first portion and a second surface adjacent said third portion and said fifth composition varies between the first surface and the second surface.

5. A solid state device of claim 3 wherein said second portion comprises a first surface adjacent said first portion and a second surface adjacent said third portion and comprises a superlattice with a structure comprising two layers of different composition which repeat at least once.

6. A solid state device of claim 3 wherein said first portion is in a first state of stress and said third portion is in a second state of stress different than the first state of stress.

7. The solid state device of claim 1 wherein the first solar cell is of composition X (1−m) Y m and the second solar cell is of composition X (1−n) Y n wherein n is different from m, and X and Y are chosen from a Group IV semiconductor such that 0≦n, m≦1.

8. The device of claim 7 wherein the third region consists of a composition described by [RE 1 ] v [RE 3 ] x [J 1 ] y [J 2 ] z and [RE] is chosen from a rare earth; [J 1 ] and [J 2 ] are chosen from a group consisting of oxygen (O), nitrogen (N), and phosphorus (P) and wherein 0≦z≦5 and 0<v, x, y≦5 for a least a portion of the rare earth layer.

9. A solid state device comprising at least two photovoltaic cells in tandem; for converting incident radiation to electrical energy comprising,

first semiconductor layer operable as a photovoltaic cell;

second semiconductor layer operable as a photovoltaic cell; the first semiconductor layer and the second semiconductor layer being arranged in tandem; and

a rare earth layer comprising first and second regions of first and second rare earth compositions separating the first semiconductor layer from the second semiconductor layer;

wherein the first rare earth consists of a composition described by [RE 1 ] v [RE 2 ] w [RE 3 ] x [J 1 ] y [J 2 ] z and the second rare earth consists of a composition is described by [RE 1 ] a [RE 2 ] b [RE 3 ] c [J 1 ] d [J 2 ] e wherein [RE] is chosen from a rare earth; [J 1 ] and [J 2 ] are chosen from a group consisting of oxygen (O), nitrogen (N), and phosphorus (P), and 0≦a, b, e, v, w, z≦5, and 0<c, d, x, y≦5 such that the first rare earth composition is different than the second rare earth composition wherein a portion of the incident radiation passing through the first semiconductor layer is converted into radiation of a different wavelength by the rare earth layer for subsequent passage through the second semiconductor layer.

10. The device of claim 9 wherein the first and second semiconductor materials are chosen substantially from a group consisting of Group IV elements.

11. The device of claim 9 wherein said rare earth layer comprises a superlattice of a structure that repeats at least once.

12. A solid state device for converting incident radiation to electricity comprising,

first semiconductor layer operable as a photovoltaic cell;

second semiconductor layer operable as a photovoltaic cell in tandem with the first semiconductor layer;

a first rare earth layer consisting of a first rare earth composition separating the first semiconductor layer from the second semiconductor layer; and

a second rare earth layer consisting of a second rare earth composition separated from the first rare earth layer by the second semiconductor layer; wherein

the first rare earth composition is described by [RE 1 ] v [RE 2 ] w [RE 3 ] x [J 1 ] y [J 2 ] z and the second rare earth composition is described by [RE 1 ] a [RE 2 ] b [RE 3 ] c [J 1 ] d [J 2 ] e wherein [RE] is chosen from a rare earth; [J 1 ] and [J 2 ] are chosen from a group consisting of oxygen (O), nitrogen (N), and phosphorus (P), and 0≦a, b, e, v, w, z≦5, and 0<c, d, x, y≦5 such that the first rare earth composition is different from the second rare earth composition and at least one of the first or second rare earth layers is operable as a wavelength conversion layer such that a portion of the incident radiation passing through the first semiconductor layer is converted into radiation of a different wavelength by the one or more wavelength conversion layers for subsequent passage through the second semiconductor layer.

13. The device of claim 12 wherein the first and second semiconductor materials are chosen substantially from a group consisting of Group IV elements.

14. The device of claim 12 wherein the second rare earth layer comprises a first region and a second region such that the composition of the first region is different from the composition of the second region.

15. The device of claim 14 wherein at least one of said first and second regions comprises a Group IV element.