Wafer level interconnection of inverted metamorphic multijunction solar cells

1. A multijunction solar cell array comprising a plurality of solar cells mounted on a carrier, each solar cell comprising:

a top contact;

an upper first solar subcell having a first band gap disposed over the top contact, wherein the first band gap is in the range of 1.8 to 2.1 eV;

a middle second solar subcell disposed over the upper first solar subcell having a second band gap smaller than the first band gap;

a graded interlayer composed of InGaAlAs disposed over the middle second solar subcell having a third band gap greater than the second band gap;

a lower third solar subcell disposed over the graded interlayer having a fourth band gap smaller than the second band gap such that the lower third solar subcell is lattice mismatched with respect to the middle second solar subcell;

a bottom metal contact layer disposed over the lower third solar subcell; and

a bond layer disposed over the bottom metal contact layer that mounts the solar cell to the carrier;

wherein the graded interlayer is compositionally graded to lattice match the middle second solar subcell on one side and the lower third solar subcell on the other side; and

wherein each pair of solar cells is electrically interconnected by a discrete conductor from the top contact of one solar cell to the bottom contact of the other solar cell for each pair of solar cells.

2. The array as defined in claim 1 , wherein the bond layer is an adhesive layer.

3. The array as defined in claim 1 , wherein the carrier is selected from the group of consisting of Ge, GaAs, and silicon.

4. The array as defined in claim 1 , wherein the carrier is electrically insulating and the solar cell structure is eutectically bonded to the carrier.

5. The array as defined in claim 1 , wherein the discrete conductor is selected from the group consisting of wire bonds and film traces.

6. The array as defined in claim 1 , wherein the solar cell structure further comprises layers forming a bypass diode.

7. The array as defined in claim 6 , wherein said plurality of discrete solar cells and said bypass diode are connected in parallel by welds, solder, or wire bonds.

8. The array as defined in claim 1 , wherein the upper first solar subcell is composed of InGa(Al)P.

9. The array as defined in claim 1 , wherein the middle second solar subcell is composed of a GaAs, GaInP, GaInAs, GaAsSb, or GaInAsN emitter region and a GaAs, GaInAs, GaAsSb, or GaInAsN base region.

10. The array as defined in claim 1 , wherein the middle second solar subcell has a band gap in the range of 1.2 to 1.8 eV.

11. The array as defined in claim 1 , wherein the lower third solar subcell is composed of an InGaAs base and emitter layer, or a InGaAs base layer and a InGaP emitter layer.

12. The array as defined in claim 1 , wherein the lower third solar subcell has a band gap in the range of 0.7 to 1.2 eV.

13. The array as defined in claim 1 , wherein the graded interlayer has approximately a 1.5 eV band gap throughout its thickness.

14. The array as defined in claim 1 , wherein the graded interlayer is composed of nine or more steps of layers of semiconductor material with monotonically changing lattice constant and constant band gap.

15. A multijunction solar cell array comprising a plurality of solar cells mounted on a carrier prepared by a method comprising:

providing a first semiconductor substrate;

depositing on the first semiconductor substrate a sequence of layers of semiconductor material forming a solar cell;

depositing a sequence of layers of semiconductor material forming a bypass diode on the first semiconductor substrate;

mounting a carrier on top of the sequence of layers;

forming a plurality of discrete solar cells from the sequence of layers; and

electrically interconnecting the solar cells.

16. A multijunction solar cell array comprising a plurality of solar cells mounted on a carrier prepared by a method comprising:

providing a first semiconductor substrate;

depositing on said first semiconductor substrate a sequence of layers of semiconductor material forming a solar cell;

mounting a carrier on top of the sequence of layers;

forming a plurality of discrete solar cells from said sequence of layers; and

electrically interconnecting said solar cells,

wherein the interconnecting step includes depositing a conductive layer between the discrete solar cells; and

wherein depositing said sequence of layers comprises:

forming an upper first solar subcell on said first substrate having a first band gap;

forming a middle second solar subcell over said upper first solar subcell having a second band gap smaller than said first band gap;

forming a graded interlayer having a third band gap greater than said second band gap over said middle second solar subcell; and

forming a lower third solar subcell over said graded interlayer having a fourth band gap smaller than said second band gap such that said lower third solar subcell is lattice mismatched with respect to said middle second solar subcell, wherein the fourth band gap is in the range of 0.7 to 1.2 eV.

17. The array as defined in claim 16 , wherein the graded interlayer is composed of InGaAlAs.

18. The array as defined in claim 16 , wherein the graded interlayer has approximately a 1.5 eV band gap throughout its thickness.

19. The array as defined in claim 16 , wherein the graded interlayer is composed of any of the As, N, Sb based III-V compound semiconductors subject to the constraints of having the in-plane lattice parameter greater or equal to that of said middle second solar subcell and less than or equal to that of said lower third solar subcell, and having a band gap energy greater than that of said middle second solar subcell.