Multi-junction solar cells

1. A structure comprising:

a first photovoltaic sub-cell including a first semiconductor material having a first lattice constant and a first bandgap energy;

a second photovoltaic sub-cell including a second semiconductor material having a second lattice constant different from the first lattice constant and a second bandgap energy lower than the first bandgap energy;

a defect-trapping layer disposed between the first and second photovoltaic sub-cells, the defect-trapping layer including a crystalline material, the crystalline material having a third bandgap energy higher than the second bandgap energy; and

a non-crystalline material having at least one opening, the crystalline material and the second photovoltaic sub-cell being wholly disposed in the at least one opening, the crystalline material comprising defects terminating at the non-crystalline material.

2. The structure of claim 1 wherein the second semiconductor material comprises a III-V compound, and the second photovoltaic sub-cell comprises a photovoltaic junction defined by the III-V compound.

3. The structure of claim 1 wherein the first photovoltaic sub-cell comprises a photovoltaic junction defined in a substrate, the second photovoltaic sub-cell being above the substrate.

4. The structure of claim 1 wherein the second photovoltaic sub-cell comprises a first III-V compound, the first photovoltaic sub-cell comprises silicon.

5. The structure of claim 3 wherein the substrate comprises silicon.

6. A multi-junction solar cell device comprising:

a first solar sub-cell comprising a first non-Si photovoltaic junction, the first solar sub-cell comprising a first defect in a first crystalline material, the first defect terminating at a first dielectric sidewall of a first dielectric material, the first solar sub-cell having an uppermost surface and a lowermost surface, the uppermost surface of the first solar sub-cell being opposite the lowermost surface of the first solar sub-cell;

a second solar sub-cell disposed below the first solar sub-cell and comprising a Si photovoltaic junction, the second solar sub-cell having an uppermost surface and a lowermost surface, the uppermost surface of the second solar sub-cell being opposite the lowermost surface of the second solar sub-cell, the lowermost surface of the first solar sub-cell being proximate the uppermost surface of the second solar sub-cell; and

a third solar sub-cell disposed below the second solar sub-cell and comprising a second non-Si photovoltaic junction, the third solar sub-cell comprising a second defect in a second crystalline material, the second defect terminating at a second dielectric sidewall of a second dielectric material, the third solar sub-cell having an uppermost surface and a lowermost surface, the uppermost surface of the third solar sub-cell being opposite the lowermost surface of the third solar sub-cell, the uppermost surface of the third solar sub-cell being proximate the lowermost surface of the second solar sub-cell,

wherein at least one of (i) a distance of the uppermost surface of the first solar sub-cell from the uppermost surface of the second solar sub-cell is equal to or less than a distance of an uppermost surface of the first dielectric material from the uppermost surface of the second solar sub-cell, and (ii) a distance of the lowermost surface of the third solar sub-cell from the lowermost surface of the second solar sub-cell is equal to or less than a distance of a lowermost surface of the second dielectric material from the lowermost surface of the second solar sub-cell.

7. A multi-junction solar cell device comprising:

a first solar sub-cell having a first energy bandgap;

a first dielectric layer having at least one first opening, the first solar sub-cell being wholly disposed in the at least one first opening;

a second solar sub-cell formed below the first solar sub-cell and having a second energy bandgap greater than the first energy bandgap and approximately equal to 1.1 eV;

a third solar sub-cell formed below the second solar sub-cell and having a third energy bandgap greater than the second energy bandgap; and

a second dielectric layer having at least one second opening, the third solar sub-cell being wholly disposed in the at least one second opening.

8. The multi-junction solar cell device of claim 7 , wherein the first energy bandgap is less than 1.1 eV and the third energy bandgap is greater than 1.1 eV.

9. The multi-junction solar cell device of claim 8 wherein the first energy bandgap is less than about 0.8 eV.

10. The multi-junction solar cell device of claim 7 wherein the second bandgap is selected from a range of about 1.0 eV to about 1.2 eV.

11. The multi-junction solar cell device of claim 7 wherein the third energy bandgap is greater than about 1.6 eV.