Inverted metamorphic multijunction solar cells having a permanent supporting substrate

1. A method of manufacturing a solar cell comprising:

providing a semiconductor growth substrate;

depositing on said growth substrate a sequence of layers of semiconductor material forming a solar cell, the sequence of layers comprising a top layer and a bottom layer identified according to a top of the solar cell being a light receiving surface;

applying a metal contact layer over said sequence of layers at the bottom layer, wherein the metal contact layer is reflective; and

affixing an adhesive polyimide surface of a permanent supporting substrate directly over said metal contact layer on the sequence of layers and permanently bonding it thereto with a thermocompressive technique.

2. A method as defined in claim 1 , further comprising:

removing the semiconductor growth substrate subsequent to affixing the adhesive polyimide surface of the permanent supporting substrate directly over said metal contact layer and permanently bonding it thereto; and

attaching a cover glass to a top surface of the solar cell,

wherein the semiconductor substrate is removed after the permanent supporting substrate has been attached by grinding, etching, or epitaxial lift-off.

3. A method as defined in claim 2 , further comprising forming grid electrodes on the top surface of the layers of semiconductor material to form the top surface of the solar cell prior to attachment of the glass cover.

4. A method as defined in claim 1 , wherein said step of depositing a sequence of layers of semiconductor material includes forming a first solar subcell on said substrate having a first band gap; forming a second solar subcell over said first subcell having a second band gap smaller than said first band gap; forming a grading interlayer over said second subcell having a third band gap larger than said second band gap; forming a third solar subcell having a fourth band gap smaller than said second band gap such that said third subcell is lattice mismatched with respect to said second subcell.

5. A method as defined in claim 1 , wherein said growth substrate is composed of GaAs.

6. A method as defined in claim 4 , wherein said first solar subcell is composed of an InGa(Al)P emitter region and an InGa(Al)P base region.

7. A method as defined in claim 4 , wherein said grading interlayer is composed of (In x Ga 1−x ) y Al 1−y As, wherein 0<x<1 and 0<y<1 with x and y selected such that the band gap of each interlayer remains constant throughout its thickness.

8. A method as defined in claim 4 , wherein said first subcell is composed of an GalnP, GaAs, GalnAs, GaAsSb, or GalnAsN emitter region and an GaAs, GalnAs, GaAsSb, or GalnAsN base region, and the second subcell is composed of an InGaP emitter layer and a GaAs or GalnAs base layer.

9. The method as defined in claim 4 , wherein the lower solar subcell is composed of an InGaAs base and emitter layer, or a InGaAs base layer and a InGaP emitter layer.

10. The method as defined as claim 4 , wherein the graded interlayer is compositionally graded to lattice match the middle subcell on one side and the lower subcell on the other side, and is composed of (In x Ga 1−x ) y Al 1−y As, wherein 0<x<1 and 0<y<1 with x and y selected such that the band gap of the interlayer remains constant throughout its thickness and greater than said second band gap.

11. The method as defined in claim 1 further comprising forming the adhesive polyimide surface on the permanent supporting substrate using spin coating, spraying or brushing.

12. The method as defined in claim 1 wherein the adhesive polyimide surface has a thickness of the adhesive polyimide surface is at least the thickness of the sequence of layers of the semiconductor material.

13. The method as defined in claim 1 wherein the adhesive polyimide surface has a thickness of at least about 12 microns.

14. The method as defined in claim 1 further comprising crosslinking the polyimide after affixing the adhesive polyimide surface to the metal contact layer.

15. The method as defined in claim 14 wherein the crosslinking comprises UV exposure and a hard bake at an anneal temperature.

16. The method as defined in claim 1 wherein the adhesive polyimide layer is cured at a temperature of at least about 350° C.

17. The method as defined in claim 1 wherein the permanent supporting substrate is a glass surrogate substrate.