Multijunction metamorphic solar cell for space applications
View Patent ↗A multijunction solar cell assembly and its method of manufacture including first and second discrete semiconductor body subassemblies, each semiconductor body subassembly including first, second and third lattice matched subcells; a graded interlayer adjacent to the third solar subcell and functioning as a lateral conduction layer; and a fourth solar subcell adjacent to said graded interlayer being lattice mismatched with respect to the third solar subcell; wherein the average band gap of all four cells is greater than 1.44 eV.
1. A multijunction solar cell assembly including a terminal of first polarity and a terminal of second polarity comprising:
a first semiconductor body including a tandem vertical stack of at least a first upper solar subcell, a second solar subcell, and a bottom solar subcell, the first upper subcell having a top contact connected to the terminal of first polarity, and the bottom solar subcell having a top contact and a bottom contact;
a second semiconductor body disposed adjacent to the first semiconductor body and including a tandem vertical stack of at least a first upper, a second and a bottom solar subcells, the first upper subcell of the second semiconductor body having a top contact connected to the terminal of first polarity, and the bottom subcell of the second semiconductor body having a top contact and a bottom contact with its bottom contact connected to the terminal of second polarity;
wherein the first and second semiconductor body each comprises a first highly doped lateral conduction layer electrically connected to each other and disposed adjacent to and beneath the second solar subcell of each respective body;
and wherein the first and second semiconductor body each comprises a blocking p-n diode or insulating layer disposed adjacent to and beneath the first highly doped lateral conduction layer; and a second highly doped lateral conduction layer disposed adjacent to and beneath the respective blocking p-n diode or insulating layer,
an electrical connection between the first lateral conduction layer of the first and the second semiconductor body and the second lateral conduction layer of the first semiconductor body;
the bottom solar subcell of each respective body being disposed adjacent to and beneath the second highly doped lateral conduction layer, with the bottom subcell of the first semiconductor body being connected in a series electrical circuit with the bottom subcell of the second semiconductor body so that at least a four junction solar cell is formed by the assembly.
2. A multijunction solar cell assembly as defined in claim 1 , wherein the first lateral conduction layer in each of the first and second semiconductor bodies is compositionally graded to substantially lattice match the second solar subcell on one side and the bottom solar subcell on the other side, and is composed of any of the As, P, N, Sb based III-V compound semiconductors subject to the constraints of having the in-plane lattice parameter less than or equal to that of the second solar subcell and greater than or equal to that of the bottom solar cell.
3. A multijunction solar cell assembly as defined in claim 1 , further comprising a first electrical contact on the first lateral conduction layer, and a second electrical contact on the second lateral conduction layer, and wherein the electrical connection is a wire welded to the first electrical contact at one end, and the second electrical contact at the other end; and
an electrical connection between the bottom contact of the first bottom subcell, and the top contact of the second bottom subcell.
4. The multijunction solar cell assembly multijunction solar cell as defined in claim 2 , wherein bottom subcell of the first and second semiconductor bodies has a band gap in the range of approximately 0.67 eV, the second subcell of the first and second semiconductor bodies has a band gap in the range of approximately 1.3 to 1.5 eV and the upper first subcell of the first and second semiconductor bodies has a band gap in the range of 1.8 to 2.0 eV.
5. A multijunction solar cell assembly as defined in claim 1 , wherein the first and second semiconductor bodies include a tandem vertical stack of at least a first upper, a second and third solar subcells, and the first and second bottom subcells, so that at least a five junction solar cell is formed by the assembly, with the first upper, a second and third solar subcells being current matched, and the first and second bottom subcells being current mismatched from the first upper, a second and third solar subcells.
6. The multijunction solar cell assembly as defined in claim 5 , wherein the bottom subcell of the first and second semiconductor bodies has a band gap in the range of approximately 0.67 eV, the third subcell of the first and second semiconductor bodies has a band gap in the range of approximately 1.41 eV and 1.31 eV, the second subcell of the first and second semiconductor bodies has a band gap in the range of approximately 1.65 to 1.8 eV and the upper first subcell of the first and second semiconductor bodies has a band gap in the range of 2.0 to 2.20 eV.
7. A multijunction solar cell assembly as defined in claim 1 , wherein
the first lateral conduction layer in each semiconductor body is composed of In x Al y Ga 1-x-y As or In x Ga 1-x P with 0<x<1, 0<y<1, and x and y selected such that the band gap is in the range of 1.41 eV to 1.6 eV and may vary throughout its thickness, and is compositionally graded to substantially lattice match the second solar subcell on one side and the bottom solar subcell on the other side.
8. The multijunction solar cell assembly multijunction solar cell as defined in claim 1 , wherein:
the upper first subcell is composed of indium gallium aluminum phosphide (InGaAlP);
the second solar subcell includes an emitter layer composed of indium gallium phosphide (InGaP), indium aluminum gallium arsenide (InAlGaAs) or indium gallium arsenide phosphide (InGaAsP), and a base layer composed of indium aluminum gallium arsenide or indium gallium arsenide phosphide (InGaAsP);
the third solar subcell is composed of indium gallium arsenide;
the fourth subcell is composed of germanium or SiGeSn, GaSb, InGaAsN, InGaAsNSb, InGaAsNBi, InGaAsNSbBi, InGaSbN, InGaBiN, InGaSbBiN; and
the lateral conduction layer is composed of In x Al y Ga 1-x-y As or In x Ga 1-x P with 0<x<1, 0<y<1, and x and y selected such that the band gap is in the range of 1.41 eV to 1.6 eV and may vary throughout its thickness.
9. The multijunction solar cell assembly as defined in claim 1 , wherein
the upper first subcell has a band gap in the range of 2.0 to 2.20 eV and is composed of indium gallium aluminum phosphide (InGaAlP);
the second solar subcell has a band gap in the range of approximately 1.65 to 1.8 eV and includes an emitter layer composed of indium gallium phosphide (InGaP), indium aluminum gallium arsenide (InAlGaAs) or indium gallium arsenide phosphide (InGaAsP), and a base layer composed of indium aluminum gallium arsenide or indium gallium arsenide phosphide (InGaAsP);
the third solar subcell has a band gap in the range of approximately 1.3 to 1.41 eV and is composed of indium gallium arsenide; and
the fourth subcell is composed of germanium or SiGeSn, GaSb, InGaAsN, InGaAsNSb, InGaAsNBi, InGaAsNSbBi, InGaSbN, InGaBiN, InGaSbBiN; the upper first subcell is composed of indium gallium aluminum phosphide.
10. A multijunction solar cell assembly as defined in claim 1 , further comprising:
a distributed Bragg reflector (DBR) layer disposed above the bottom solar subcell and arranged so that light can enter and pass through the solar subcell disposed above the bottom subcell and at least a portion of which can be reflected back into the solar subcell located above the bottom subcell by the DBR layer, and the distributed Bragg reflector layer is composed of a plurality of alternating layers of lattice matched materials with discontinuities in their respective indices of refraction.
11. A multijunction solar cell assembly as defined in claim 9 , wherein the difference in refractive indices between alternating layers is maximized in order to minimize the number of periods required to achieve a given reflectivity, and the thickness and refractive index of each period determines the stop band and its limiting wavelength, and the DBR layer includes a first DBR layer composed of a plurality of p type Al x Ga 1-x (In)As layers, and a second DBR layer disposed over the first DBR layer and composed of a plurality of n or p type Al y Ga 1-y (In)As layers, where 0<x<1, 0<y<1, and y is greater than x, and the term (In) denotes an optional inclusion of up to 10% indium.
12. A multijunction solar cell as defined in claim 1 , further comprising:
a distributed Bragg reflector (DBR) layer adjacent to and between the third and the fourth solar subcells and arranged so that light can enter and pass through the third solar subcell and at least a portion of which can be reflected back into the third solar subcell by the DBR layer, and the distributed Bragg reflector layer is composed of a plurality of alternating layers of lattice matched materials with discontinuities in their respective indices of refraction.
13. A multijunction solar cell as defined in claim 1 , wherein the selection of the composition of the subcells and their band gaps maximizes the efficiency at high temperature (in the range of 40 to 100 degrees Centigrade) in deployment in space at a predetermined time after the initial deployment (referred to as the beginning of life or BOL), such predetermined time being referred to as the end-of-life (EOL), and the average band gap of all four cells (i.e., the sum of the four lowest direct or indirect band gaps of the materials of each subcell in the semiconductor body divided by 4) is greater than 1.44 eV.
14. A multijunction solar cell assembly as defined in claim 1 , wherein the first and second semiconductor bodies constitute a single semiconductor body that has been singulated to form to spatially separated bodies.
15. A multijunction solar cell as defined in claim 13 , wherein the bottom subcell is comprised of a direct or indirect band gap material such that the lowest direct band gap of the material is greater than 0.75 eV, and the average band gap of all four subcells in each of the semiconductor bodies (i.e., the sum of the four lowest direct or indirect band gaps of the materials of each subcell in the semiconductor body divided by 4) is greater than 1.44 eV.
16. A multijunction solar cell assembly as defined in claim 1 , further comprising a first alpha layer deposited over the first lateral conduction layer to a thickness of between 0.25 and 1.0 micron to prevent threading dislocations from propagating, either opposite to the direction of growth or in the direction of growth into the second subcell.
17. A multijunction solar cell assembly as defined in claim 16 , further comprising a second alpha layer deposited over the blocking p-n diode or insulating layer to a thickness of between 0.25 and 1.0 micron to prevent threading dislocations from propagating, either opposite to the direction of growth or in the direction of growth into the second subcell.
18. A multijunction solar cell as defined in claim 10 , further comprising a tunnel diode disposed over the first lateral conduction layer and below the distributed Bragg reflector (DBR) layer.