Terrestrial solar power system using III-V semiconductor solar cells
View Patent ↗A system for generating electrical power from solar radiation utilizing a thin film III-V compound multijunction semiconductor solar cell mounted on a support in a non-planar configuration.
1. A solar cell assembly comprising
a solar cell including a thin flexible film semiconductor body formed from III-V compound semiconductors including:
a first solar subcell having a first band gap,
a second solar subcell disposed over the first subcell and having a second band gap smaller than the first band gap,
a grading interlayer composed of InGaAlAs and disposed over the second subcell in said body and having a third band gap greater than the second band gap, and
a third solar subcell over said interlayer in the body and being lattice mismatched with respect to the second subcell and having a fourth band gap smaller than the third band gap; and
a non-planar support for mounting the solar cell, wherein the solar cell is shaped to conform to a non-planar surface of the non-planar support.
2. A solar cell assembly as defined in claim 1 , wherein said support is attached to a heat spreader.
3. A solar cell assembly as defined in claim 2 , wherein the heat spreader is a metal structure with cooling fins.
4. A solar cell assembly as defined in claim 1 , wherein said support is a portion of a solar concentrator that forms a Cassegrain reflector.
5. A solar cell assembly as defined in claim 1 , wherein the grading interlayer has a substantially constant band gap.
6. A solar cell assembly as defined in claim 5 wherein the constant band gap of the grading interlayer is 1.5 eV.
7. A solar cell assembly as defined in claim 1 , wherein the grading interlayer has a monotonically changing lattice constant.
8. A solar cell assembly as defined in claim 7 , wherein the grading interlayer is a compositionally step-graded InGaAlAs series of layers with monotonically changing lattice constant.
9. A solar cell assembly as defined in claim 1 wherein the first solar subcell includes an InGa(Al)P emitter region and an InGa(Al)P base region.
10. A solar cell assembly as defined in claim 1 wherein the second solar subcell includes an InGaP emitter layer.
11. A solar cell assembly as defined in claim 10 wherein the second solar subcell further includes an InGaAs base layer.
12. A solar cell assembly as defined in claim 11 wherein the InGaAs base layer is composed of In 0.015 GaAs.
13. A solar cell assembly as defined in claim 1 wherein the third solar subcell includes emitter and base layers composed of InGaAs.
14. A solar cell assembly as defined in claim 13 wherein the InGaAs base layers are composed of In 0.30 GaAs.
15. A solar cell assembly as defined in claim 1 further comprising:
a tunnel diode disposed over the second solar subcell, and a buffer layer disposed between the tunnel diode and the grading interlayer.
16. A solar cell assembly as defined in claim 15 wherein the buffer layer between the tunnel diode and the grading interlayer is composed of InGaAs.
17. A solar cell assembly as defined in claim 15 wherein the buffer layer has a thickness of about 1.0 micron.
18. A solar cell assembly as defined in claim 1 further including a metal contact layer over the third solar subcell.
19. A solar cell assembly as defined in claim 18 , wherein the metal contact layer includes a sequence of Ti/Au/Ag/Au layers.
20. A solar cell assembly as defined in claim 19 , wherein the grading interlayer is a compositionally step-graded InGaAlAs series of layers with monotonically changing lattice constant that achieves a transition in lattice constant from the second solar subcell to the third solar subcell.