Monolithic metamorphic multi-junction solar cell
A monolithic multi-junction solar cell comprising a first III-V subcell and a second III-V subcell and a third III-V subcell and a fourth Ge subcell, wherein the subcells are stacked on top of one another in the specified order, and the first subcell forms the top subcell and a metamorphic buffer is formed between the third subcell and the fourth subcell and all subcells each have an n-doped emitter layer and a p-doped base layer and the emitter doping in the second subcell is lower than the base doping.
1. A monolithic metamorphic multi-junction solar cell comprising:
a first III-V subcell;
a second III-V subcell;
a third III-V subcell;
a fourth Ge subcell, the first, second, third and fourth subcells being stacked on top of one another in the specified order, and the first subcell forms a top subcell, the first, second, third, and fourth subcells each have an n-doped emitter layer and a p-doped base layer;
a metamorphic buffer formed between the third subcell and the fourth subcell;
wherein no semiconductor bond is formed between the first, second, third and fourth subcells,
wherein a thickness of the emitter layer of the second subcell is less than a thickness of the base layer,
wherein, in the second subcell, an emitter doping of the emitter layer in a region at an interface between the emitter layer and the base layer is lower than a base doping of the base layer in a region at the interface between the emitter layer and the base layer, and
wherein the second subcell is formed as a hetero cell.
2. The monolithic metamorphic multi-junction solar cell according to claim 1 , wherein the emitter doping in the second subcell is lower than the base doping at least by a factor of 3.
3. The monolithic metamorphic multi-junction solar cell according to claim 1 , wherein the base layer in the second subcell comprises InGaAsP or consists of InGaAsP.
4. The monolithic metamorphic multi-junction solar cell according to claim 3 , wherein the thickness of the base layer in the second subcell is greater than 100 nm, wherein the base layer has an arsenic content based on elements of main group V between 22% and 33% and an indium content based on elements of main group III between 52% and 65%, and wherein a lattice constant of the base layer is between 0.572 nm and 0.577 nm.
5. The monolithic metamorphic multi-junction solar cell according to claim 1 , wherein the first subcell up to and including the third subcell is lattice-matched to one another.
6. The monolithic metamorphic multi-junction solar cell according to claim 1 , wherein the first subcell has a band gap in a range between 1.85 eV and 2.07 eV and the second subcell has a band gap in a range between 1.41 eV and 1.53 eV and the third subcell has a band gap in a range between 1.04 eV and 1.18 eV.
7. The monolithic metamorphic multi-junction solar cell according to claim 1 , wherein the first subcell has a compound formed of at least AlInP, in which the indium content based on elements of main group III is between 64% and 75% and the Al content between 18% and 32%.
8. The monolithic metamorphic multi-junction solar cell according to claim 1 , wherein the third subcell has a compound formed of at least InGaAs, in which the indium content based on elements of main group III is greater than 17%.
9. The monolithic metamorphic multi-junction solar cell according to claim 1 , wherein a semiconductor mirror is arranged between the third subcell and the fourth subcell.
10. The monolithic metamorphic multi-junction solar cell according to claim 1 , wherein the thickness of the base layer in the second subcell and the thickness of the base layer in the third subcell are each greater than 0.4 μm or greater than 0.8 μm.
11. The monolithic metamorphic multi-junction solar cell according to claim 1 , wherein the base layer in the second subcell has at least partially a dopant gradient and a dopant concentration thereof increases towards the third subcell to more than 1·10 18 /cm 3 .
12. The monolithic metamorphic multi-junction solar cell according to claim 1 , wherein the base doping of the base layer in the second subcell in the region adjacent to the emitter layer in the second subcell has a dopant concentration of less than 5·10 17 /cm 3 .
13. The monolithic metamorphic multi-junction solar cell according to claim 1 , wherein exactly four subcells or exactly five subcells are provided, or wherein a fifth subcell is formed between the first subcell and the second subcell.
14. The monolithic metamorphic multi-junction solar cell according to claim 1 , wherein the emitter layer of the second subcell has a dopant concentration of less than 2·10 17 /cm 3 and greater than 1·10 16 /cm 3 .
15. The monolithic metamorphic multi-junction solar cell according to claim 1 , wherein the emitter layer in the second subcell comprises InGa(As)P or consists of InGa(As)P and the base layer comprises or consists of InGaAsP, wherein the arsenic content of the emitter layer is at least 5% less than the arsenic content of the base layer or the emitter layer is arsenic-free.