Multijunction solar cell assembly for space applications
A multijunction solar cell assembly and its method of manufacture including first and second discrete and different semiconductor body subassemblies which are electrically interconnected to form a five junction solar cell, each semiconductor body subassembly including first, second, third and fourth lattice matched subcells; wherein the average band gap of all four cells in each subassembly is greater than 1.44 eV.
1. A solar cell module 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, a second and a bottom solar subcells; and
a second semiconductor body disposed adjacent and parallel to the first semiconductor body and including a tandem vertical stack of at least a first upper, a second and a bottom solar subcells substantially identical to that of the first semiconductor body, the first upper subcell of the first and second semiconductor bodies having a top contact connected to the terminal of first polarity, the third bottom subcell of the second semiconductor body having a bottom contact connected to the terminal of second polarity;
wherein the third subcell of the first semiconductor body is connected in a series electrical circuit with the third subcell of the second semiconductor body so that the interconnection of subcells of the first and second semiconductor bodies forms at least a four junction solar cell; and
wherein the sequence of layers in the first and the second semiconductor bodies are different.
2. A module as defined in claim 1 , wherein the upper first subcell of the first and second semiconductor bodies is composed of indium gallium phosphide (InGaP); the second solar subcell of the first and second semiconductor bodies disposed adjacent to and lattice matched to said upper first subcell, the second solar subcell composed of aluminum gallium arsenide (AlGaAs) or indium gallium arsenide phosphide (InGaAsP), and the third subcell is the bottom subcell of each of the semiconductor bodies and is lattice matched to said second subcell and is composed of germanium (Ge).
3. A module as defined in claim 1 , wherein the upper first subcell of the first semiconductor body is composed of aluminium indium gallium phosphide (AlInGaP); the second solar subcell of the first semiconductor body is disposed adjacent to and lattice matched to said upper first subcell, and is composed of aluminum gallium arsenide (AlGaAs); the third subcell is disposed adjacent to and lattice matched to said second subcell and is composed of gallium arsenide (GaAs), and the bottom subcell of the first and second semiconductor body is lattice matched to said second subcell and is composed of germanium (Ge).
4. A module as defined in claim 1 , wherein the first semiconductor body further comprises a first highly doped lateral conduction layer disposed adjacent to and beneath the second solar subcell.
5. A module as defined in claim 1 , wherein the second semiconductor body further comprises a second highly doped lateral conduction layer disposed adjacent to and beneath the second solar subcell, and a blocking p-n diode or insulating layer disposed adjacent to and beneath the second highly doped lateral conduction layer, and a third highly doped lateral conduction layer disposed adjacent to and beneath the blocking p-n diode or insulating layer.
6. A module as defined in claim 1 , wherein the short circuit density (J sc ) of each of the bottom subcells is at least twice that of the first and second subcells.
7. A module as defined in claim 1 , wherein the short circuit current density (J sc ) of the first and second subcells are each approximately 17 mA/cm 2 , and the short circuit current density (J sc ) of each of the bottom subcells is approximately 34 mA/cm 2 .
8. A module as defined in claim 3 , wherein the short circuit current density (J sc ) of the first, second and third middle subcells are each approximately 11 mA/cm 2 .
9. A module as defined in claim 8 , wherein the short circuit current density (J sc ) of each of the bottom subcells is approximately 22.6 mA/cm 2 .
10. A module as defined in claim 3 , wherein at least the base of at least one of the first, second or third solar subcells has a graded doping.
11. A module as defined in claim 1 , further comprising a third middle solar subcell composed of gallium arsenide (GaAs) disposed adjacent to and beneath the second solar subcell, and above the bottom solar subcell.
12. A module as defined in claim 1 , further comprising a first conductive interconnect extending between the contact layer of the first upper subcell of the first semiconductor body to the contact layer of the first upper subcell of the second semiconductor body.
13. A module as defined in claim 11 , further comprising a second conductive interconnect extending between the bottom contact layer of the third subcell of the first semiconductor body to the bottom contact layer of the third subcell of the second semiconductor body.
14. A module as defined in claim 13 , further comprising a third conductive interconnect extending between the bottom contact layer of the bottom subcell of the first semiconductor body to the top contact layer of the bottom subcell of the second semiconductor body.
15. A module as defined in claim 1 , further comprising a third semiconductor body disposed adjacent to the second semiconductor body and including a tandem vertical stack of at least a first upper, a second, third and a fourth bottom solar subcells, the first upper subcell having a top contact connected to the terminal of first polarity, the fourth bottom subcell having a bottom contact connected to the terminal of a second polarity;
wherein the top contact of the first upper subcells of the first, second and third semiconductor bodies are connected, and the fourth subcell of the first semiconductor body is connected in a series electrical circuit with the fourth subcell of the second semiconductor body, which in turn is connected in a series electrical circuit with the fourth subcell of the third semiconductor body.
16. A multijunction solar cell assembly as defined in claim 1 , wherein the respective selection of the composition, band gaps, open circuit voltage, and short circuit current of each of the subcells maximizes the efficiency of the assembly (i) 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), wherein such predetermined time is in the range of one to twenty-five years; or (ii) at low temperature (in the range of −150 to −100 degrees Centigrade), and low solar radiation intensity less than 0.1 suns, 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), wherein such predetermined time is in the range of one to twenty-five years.
17. A multijunction solar cell assembly as defined in claim 1 , wherein one or more of the subcells have a base region having a gradation in doping that increases exponentially from a value in the range of 1×10 15 to 1×10 18 free carriers per cubic centimeter adjacent the p-n junction to a value in the range of 1×10 16 to 4×10 18 free carriers per cubic centimeter adjacent to the adjoining layer at the rear of the base, and an emitter region having a gradation in doping that decreases from a value in the range of approximately 5×10 18 to 1×10 17 free carriers per cubic centimeter in the region immediately adjacent the adjoining layer to a value in the range of 5×10 15 to 1×10 18 free carriers per cubic centimeter in the region adjacent to the p-n junction.