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, 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.

2. A method as defined in claim 1 , 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.

3. A method as defined in claim 1 , wherein the coating layer has a thickness of 20 to 25 microns.

4. A method as defined in claim 1 , further comprising curing the coating layer.

5. A method 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 method as defined in claim 1 , further comprising depositing a bonding layer over the coating layer.

7. A method as defined in claim 1 , wherein the metal contact layer is comprises a sequence of metal layers Ti/Au/Ag/Au or Ti/Pd/Ag.

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

9. A method as defined in claim 1 , wherein the grading interlayer is composed of In Ga Al As.

10. A method as defined in claim 1 , wherein the curing temperature is above 350° C.

11. A method as defined in claim 1 , wherein the step of permanently bonding the permanent supporting substrate to the metal contact layer is performed by a thermocompressive technique.

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

13. A method as defined in claim 1 , wherein the permanent supporting substrate is a glass substrate.

14. A method as defined in claim 1 , wherein the semiconductor growth substrate is removed by at least one of grinding, etching, or epitaxial lift-off.

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

16. A method as defined in claim 5 , further comprising attaching a cover glass over the grid electrodes.