Inverted metamorphic multijunction solar cells having a permanent supporting substrate
The present disclosure provides a method of manufacturing a solar cell that includes providing a semiconductor growth substrate; depositing on said growth substrate a sequence of layers of semiconductor material forming a solar cell; applying a metal contact layer over said sequence of layers; affixing the adhesive polyimide surface of a permanent supporting substrate directly over said metal contact layer and permanently bonding it thereto by a thermocompressive technique; and removing the semiconductor growth 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;
affixing an 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;
removing the growth substrate.
2. A method as defined in claim 1 , further comprising depositing a coating layer composed of a polymer, a polyimide composition, or an epoxy based photoresist material over the metal contact layer by spinning-on, spraying, or brushing.
3. A method as defined in claim 2 , wherein the coating layer has a thickness of 20 to 25 microns.
4. A method as defined in claim 2 , 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 , wherein the metal contact layer comprises a sequence of metal layers Ti/Au/Ag/Au or Ti/Pd/Ag.
7. A method as defined in claim 1 , wherein the metal contact layer is specularly reflective over the wavelength range of incoming light.
8. A method as defined in claim 2 , further comprising depositing a bonding layer over the coating layer.
9. A method as defined in claim 1 , wherein the thermocompressive technique utilizes a press for directly applying pressure and heat.
10. A method as defined in claim 1 , wherein the permanent supporting substrate is a glass substrate, the method further comprising bonding an adhesive polyimide layer to a 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 method as defined in claim 1 , wherein the semiconductor substrate is removed, after the surrogate substrate has been attached, by at least one of grinding, etching, or epitaxial lift-off.
12. A method as defined in claim 1 , further comprising following removal of the semiconductor growth substrate forming grid electrodes on a surface of the layers of semiconductor material to form a top or light-incident surface of the solar cell.
13. A method as defined in claim 12 , further comprising attaching a cover glass over the grid electrodes.