INVERTED METAMORPHIC MULTIJUNCTION SOLAR CELLS HAVING A PERMANENT SUPPORTING SUBSTRATE

1 . A solar cell comprising:

a semiconductor growth substrate;

a sequence of layers of semiconductor material forming a solar cell deposited over the growth substrate, including a first solar subcell deposited on said substrate having a first band gap; a second solar subcell deposited over said first subcell having a second band gap smaller than said first band gap;

a grading interlayer deposited over said second subcell composed of InGaAlAs and having a third band gap larger than said second band gap;

a third solar subcell deposited over the grading interlayer and 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;

a metal contact layer deposited over said sequence of layers;

providing a permanent support substrate with an adhesive surface;

the adhesive surface of a permanent supporting affixed to the substrate directly over the metal contact layer;

the supporting substrate being bonded to the metal contact layer by a thermocompressive technique.

2 . A solar cell as defined in claim 1 , further comprising a coating layer composed of a polymer, a polyimide composition, or an epoxy based photoresist material deposited over the metal layer by spinning-on, spraying, or brushing.

3 . A solar cell as defined in claim 2 , wherein the coating layer has a thickness of 20 to 25 microns.

4 . A solar cell as defined in claim 2 , wherein the coating layer is cured.

5 . A solar cell as defined in claim 4 , wherein the curing is performed by a soft bake, near UV exposure (350-400 nm), followed by post exposure bake at an annealing temperature of 205 degrees C. so that the coating layer is inert to subsequent chemical and thermal fabrication steps.

6 . A solar cell as defined in claim 1 , wherein the metal contact layer is preferably a sequence of metal layers Ti/Au/Ag/Au or Ti/Pd/Ag.

7 . A solar cell as defined in claim 1 , wherein the metal contact layer is specularly reflective over the wavelength range of incoming light.

8 . A solar cell as defined in claim 2 , further comprising depositing a bonding layer over the coating layer.

9 . A solar cell as defined in claim 1 , wherein the thermocompressive technique utilizes a press for directly applying pressure and heat.

10 . A solar cell as defined in claim 1 , wherein the permanent supporting substrate is a glass substrate and further comprising bonding an adhesive polyimide layer to the surface of the support substrate at a curing temperature above 350° C., prior to the supporting substrate being affixed to the metal contact layer.

11 . A solar cell as defined in claim 1 , wherein the semiconductor substrate is removed after the surrogate substrate has been attached by grinding, etching, or epitaxial lift-off.

12 . A solar cell as defined in claim 1 , further comprising following removal of the semiconductor growth substrate forming grid electrodes on the surface of the layers of semiconductor material to form a top or light-incident surface of the solar cell.

13 . A solar cell as defined in claim 12 , further comprising attaching a cover glass over the grid electrodes on the top surface of the solar cell.

14 . 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, including a first solar subcell deposited on said substrate having a first band gap;

a second solar subcell deposited over said first subcell having a second band gap smaller than said first band gap;

a grading interlayer deposited over said second subcell composed of InGaAlAs and having a third band gap larger than said second band gap;

a third solar subcell deposited over the grading interlayer and 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:

depositing a metal contact layer over said sequence of layers;

depositing a coating layer over the metal contact layer;

providing a permanent support substrate;

bonding an adhesive polymer layer to one surface of the permanent support substrate at a curing temperature above 350° C.;

affixing the cured adhesive surface of a permanent supporting substrate directly over said metal contact layer;

permanently bonding the supporting substrate to the metal contact layer by a thermocompressive technique; and

removing the growth substrate.

15 . A solar cell as defined in claim 14 , wherein the coating layer is composed of a polymer, a polyimide composition, or an epoxy based photoresist material over the metal layer by spinning-on, spraying, or brushing.

16 . A solar cell as defined in claim 14 , wherein the coating layer has a thickness of 20 to 25 microns.

17 . A solar cell as defined in claim 14 , further comprising curing the coating layer.

18 . A solar cell as defined in claim 17 , wherein the curing is performed by a soft bake, near UV exposure (350-400 nm), followed by post exposure bake at an annealing temperature of 205 degrees C. so that the coating layer is inert to subsequent chemical and thermal fabrication steps.

19 . A solar cell as defined in claim 14 , further comprising depositing a bonding layer over the coating layer.

20 . 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, including a first solar subcell deposited on said substrate having a first band gap;

a second solar subcell deposited over said first subcell having a second band gap smaller than said first band gap;

a grading interlayer deposited over said second subcell composed of InGaAlAs and having a third band gap larger than said second band gap;

a third solar subcell deposited over the grading interlayer and 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;

depositing a metal contact layer over said sequence of layers;

depositing a coating layer over the metal contact layer;

curing the coating layer by a soft bake by UV exposure (350-400 nm);

annealing the coating layer at an annealing temperature of 205 degrees C.;

depositing a bonding layer over the annealed coating layer;

providing a permanent support substrate;

bonding an adhesive polymer layer to one surface of the permanent support substrate at a curing temperature above 350° C.;

affixing the cured adhesive surface of a permanent supporting substrate directly over the bonding layer on said metal contact layer;

permanently bonding the supporting substrate to the metal contact layer by a thermocompressive technique; and

removing the growth substrate.