MULTI-JUNCTION SOLAR CELL

Abstract

A stacked multi-junction solar cell having a first subcell and second subcell, the second subcell having a larger band gap than the first subcell. A third subcell has a larger band gap than the second subcell, and each of the subcells include an emitter and a base. The second subcell has a layer which includes a compound formed at least the elements GaInAsP, and a thickness of the layer is greater than 100 nm, and the layer is formed as part of the emitter and/or as part of the base and/or as part of the space-charge zone situated between the emitter and the base. The third subcell has a layer including a compound formed of at least the elements GaInP, and the thickness of the layer is greater than 100 nm.

Claims

1. A stacked multi-junction solar cell comprising: a first subcell including germanium; a second subcell having a larger band gap than the first subcell; a third subcell having a larger band gap than the second subcell, the first, second and third subcells having an emitter and a base; a metamorphic buffer formed between the first subcell and the second subcell, the metamorphic buffer having a sequence of at least three layers, and a lattice constant increasing from layer to layer in a sequence in a direction of the second subcell, wherein the second subcell comprises a layer formed of a compound that includes at least the elements GaInAsP, a thickness of the layer being greater than 100 nm, the layer being formed as part of the emitter and/or as part of the base and/or as part of a space-charge zone situated between the emitter and the base, and a lattice constant of the layer is less than 5.84 , wherein the third subcell includes a layer having a compound formed of at least the elements GaInP, a thickness of the layer being greater than 100 nm, the layer being formed as part of the emitter and/or as part of the base and/or as part of the space-charge zone situated between the emitter and the base, a lattice constant of the layer of the third subcell differing from the lattice constant of the layer of the second subcell by less than 0.2%, wherein no semiconductor bond is formed between two subcells, and wherein, in the second subcell, a phosphorus content of the layer is greater than 1% and less than 45%, and an indium content of the layer of the second subcell is less than 50%.

2. The multi-junction solar cell according to claim 1, wherein the multi-junction solar cell includes exactly three subcells, and/or wherein the layer of the second subcell have an energy gap in a range of 1.2 eV to 1.3 eV.

3. The multi-junction solar cell according to claim 1, wherein two directly consecutive subcells include different elements.

4. The multi-junction solar cell according to claim 1, wherein a fourth subcell is disposed between the second subcell and the third subcell, a layer of the fourth subcell has a compound which includes at least the elements AlGaInAs or GaInAsP, a thickness of the layer is greater than 100 nm, the layer is formed as part of the emitter and/or as part of the base and/or as part of the space-charge zone situated between the emitter and the base; or wherein the fourth subcell is disposed between the first subcell and the second subcell, and the layer of the fourth subcell if formed of a compound which includes at least the elements GaInAs or GaInNAs, and a thickness of the layer is greater than 100 nm, and is formed as part of the emitter and/or as part of the base and/or as part of the space-charge zone situated between the emitter and the base.

5. The multi-junction solar cell according to claim 1, wherein the layer of the third subcell is formed of a compound which includes at least the elements AlGaInP.

6. The multi-junction solar cell according to claim 1, wherein a semiconductor mirror is provided, and the semiconductor mirror is disposed between the first subcell and the second subcell or between the first subcell and the fourth subcell.

7. The multi-junction solar cell according to claim 1, wherein the layer of the second subcell or the layer of the fourth subcell is formed of a compound having at least the elements AlGaInAsP.

8. The multi-junction solar cell according to claim 1, wherein the multi-junction solar cell includes exactly four subcells, and/or the layer of the second subcell has an energy gap in the range of 1.43 eV to 1.6 eV.

9. The multi-junction solar cell according to claim 1, wherein a fifth subcell is disposed between the second subcell and the third subcell, and the fifth subcell comprises a layer including a compound of at least the elements AlGaInAs or AlGaInAsP or GaInP, and a thickness of the layer is greater than 100 nm, and the layer is formed as part of the emitter and/or as part of the base and/or as part of the space-charge zone situated between the emitter and the base, or wherein the fifth subcell is disposed between the second subcell and the fourth subcell, and the layer of the fifth subcell is formed of a compound which includes at least the elements GaInAs, and the thickness of the layer of the fifth subcell is greater than 100 nm and is formed as part of the emitter and/or as part of the base and/or as part of the space-charge zone situated between the emitter and the base.

10. The multi-junction solar cell according to claim 1, wherein the multi-junction solar cell includes exactly five subcells and/or the layer of the second subcell has an energy gap in the range of 1.3 eV to 1.4 eV or in the range of 1.43 eV to 1.7 eV.

11. The multi-junction solar cell according to claim 1, wherein, in the second subcell, a phosphorus content of the layer is less than 35%, and an indium content of the layer is less than 45%, and/or the lattice constant of the layer is less than 5.81 .

12. The multi-junction solar cell according to claim 1, wherein, in the second subcell, a phosphorus content of the layer is less than 25%, and an indium content of the layer is less than 45%, and/or the lattice constant of the layer is less than 5.78 .

13. The multi-junction solar cell according to claim 1, wherein, in the second subcell, the thickness of the layer is greater than 0.4 m or greater than 0.8 m.

14. The multi-junction solar cell according to claim 1, wherein the second subcell does not include a multi-junction quantum well structure.

15. The multi-junction solar cell according to claim 1, wherein the lattice constant of the layer of the fourth subcell differs from the lattice constant of the layer of the second subcell by less than 0.2%.

16. The multi-junction solar cell according to claim 1, wherein the lattice constant of the layer of the fifth subcell differs from the lattice constant of the layer of the second subcell by less than 0.2%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0046] FIG. 1 shows a cross-sectional view of an embodiment according to the invention as a triple-junction solar cell;

[0047] FIG. 2a shows a cross-sectional view of an embodiment according to the invention as a four-junction solar cell in a first alternative;

[0048] FIG. 2b shows a cross-sectional view of an embodiment according to the invention as a four-junction solar cell in a second alternative;

[0049] FIG. 2c shows a cross-sectional view of an embodiment according to the invention as a four-junction solar cell in a third alternative;

[0050] FIG. 2d shows a cross-sectional view of an embodiment according to the invention as a four-junction solar cell in a fourth alternative;

[0051] FIG. 3a shows a cross-sectional view of an embodiment according to the invention as a five-junction solar cell in a first alternative;

[0052] FIG. 3b shows a cross-sectional view of an embodiment according to the invention as a five-junction solar cell in a second alternative;

[0053] FIG. 3c shows a cross-sectional view of an embodiment according to the invention as a five-junction solar cell in a third alternative;

[0054] FIG. 3d shows a cross-sectional view of an embodiment according to the invention as a five-junction solar cell in a fourth alternative;

[0055] FIG. 3e shows a cross-sectional view of an embodiment according to the invention as a five-junction solar cell in a fifth alternative; and

[0056] FIG. 3f shows a cross-sectional view of an embodiment according to the invention as a five-junction solar cell in a sixth alternative.

DETAILED DESCRIPTION

[0057] The illustration in FIG. 1 shows a cross-sectional view of an embodiment according to the invention of a stacked, monolithic multi-junction solar cell MS, the individual solar cells of the stack being referred to below as subcells. Multi-junction solar cell MS includes a first subcell SC1, first subcell SC1 formed of germanium. A second subcell, formed of an GaInAsP compound, is disposed so as to rest on first subcell SC1. Second subcell SC2 has a larger band gap than first subcell SC1. A third subcell, formed of a GaInP compound or an AlGaInP component, is disposed so as to rest upon second subcell SC2, third subcell SC3 having the largest band gap. In the present case, second subcell SC2 has an energy gap between 1.2 eV and 1.3 eV.

[0058] A metamorphic buffer MP1 and a semiconductor mirror HS1 are formed between first subcell SC1 and second subcell SC2. Buffer MP1 is formed of a large number of layers, which are not illustrated individually, the lattice constant within buffer MP1 generally increasing from layer to layer of buffer MP1 in the direction of second subcell SC2. An introduction of buffer MP1 is advantageous if the lattice constant of second subcell SC2 does not match the lattice constant of first subcell SC1.

[0059] The reflection profile of first semiconductor mirror HS1 is matched to the band gap of second subcell SC2. In other words, the wavelengths absorbable by second subcell SC2 are reflected back to the absorption area of second subcell SC2.

[0060] The thickness of the absorption area of second subcell SC2 may be significantly reduced and the radiation stability increased thereby.

[0061] It is understood that a tunnel diodenot illustratedis formed between individual subcells SC1, SC2 and SC3.

[0062] It is also understood that each of the three subcells SC1, SC2 and SC3 includes an emitter and a base, the thickness of second subcell SC2 being greater than 0.4 m.

[0063] In that the band gap of first subcell SC1 is smaller than the band gap of second subcell SC2, and the band gap of second subcell SC2 is smaller than the band gap of third subcell SC3, the sunlight shines through the surface of third subcell SC3.

[0064] FIG. 2a shows a cross-sectional view of a embodiment according to the invention as a four-junction solar cell in a first alternative. Only the differences from the embodiment shown in connection with FIG. 1 are explained below. A fourth subcell SC4, formed of AlInGaAs compound, is formed between second subcell SC2 and third subcell SC3. The lattice constants of second subcell SC2, fourth subcell SC4 and third subcell SC3 are matched to each other or coincide with each other. In other words, subcells SC2, SC4 and SC3 are lattice-matched to each other. Fourth subcell SC4 has a larger band gap than second subcell SC2 but a smaller band gap than third subcell SC3.

[0065] FIG. 2b shows a cross-sectional view of a embodiment according to the invention as a four-junction solar cell in a second alternative. Only the differences from the preceding embodiments are explained below. Fourth subcell SC4 now formed of an AlInGaAsP compound.

[0066] FIG. 2c shows a cross-sectional view of a embodiment according to the invention as a four-junction solar cell in a third alternative. Only the differences from the embodiment illustrated in FIG. 2b are explained below. Fourth subcell SC4 formed of a GaInAs compound and is formed between semiconductor mirror HS1 and second subcell SC2, second subcell SC2 now having an energy gap between 1.43 eV and 1.6 eV and formed of an AlInGaAsP compound.

[0067] FIG. 2d shows a cross-sectional view of a embodiment according to the invention as a four-junction solar cell in a fourth alternative. Only the differences from the embodiment illustrated in FIG. 2c are explained below. Fourth subcell SC4 formed of a GaInNAs compound, and second subcell SC2 formed of an InGaAsP compound. All four subcells SC1, SC4, SC2 and SC3 are now lattice-matched to each other and essentially have the lattice constant of germanium. In other words, multi-junction solar cell MS does not include a metamorphic buffer MP1.

[0068] FIG. 3a shows a cross-sectional view of a embodiment according to the invention as a five-junction solar cell in a first alternative. Only the differences from the embodiment illustrated in FIG. 2a are explained below. A fifth subcell SC5, comprising a GaInP compound, is formed between fourth subcell SC2 and third subcell SC3. The lattice constants of second subcell SC2, fourth subcell SC4, fifth subcell SC5 and third subcell SC3 are matched to each other or coincide with each other. In other words, subcells SC2, SC4, SC5 and SC3 are lattice-matched to each other. Fifth subcell SC5 has a larger band gap than fourth subcell SC4 but a smaller band gap than third subcell SC3.

[0069] FIG. 3b shows a cross-sectional view of an embodiment according to the invention as a five-junction solar cell in a second alternative. Only the differences from the embodiment illustrated in FIG. 3a are explained below. Fourth subcell SC4 now formed of an AlInGaAsP compound.

[0070] FIG. 3c shows a cross-sectional view of an embodiment according to the invention as a five-junction solar cell. Only the differences from the embodiment illustrated in FIG. 3b are explained below. Fourth subcell SC4 formed of a GaInAs compound and is formed between semiconductor mirror HS1 and second subcell SC2, second subcell SC2 now having an energy gap between 1.3 eV and 1.4 eV and formed of an AlInGaAsP compound.

[0071] FIG. 3d shows a cross-sectional view of an embodiment according to the invention as a five-junction solar cell in a fourth alternative. Only the differences from the embodiment illustrated in FIG. 3c are explained below. Fourth subcell SC4 formed of a GaInNAs compound and is formed between semiconductor mirror HS1 and second subcell SC2, second subcell SC2 now having an energy gap between 1.43 eV and 1.74 eV and formed of an InGaAsP compound. Fifth subcell SC5 formed of an AlGaInAs compound. All five subcells SC2, SC4, SC5 and SC3 are now lattice-matched to each other and essentially have the lattice constant of germanium. In other words, multi-junction solar cell MS does not include a metamorphic buffer MP1.

[0072] FIG. 3e shows a cross-sectional view of a embodiment according to the invention as a five-junction solar cell in a fifth alternative. Only the differences from the embodiment illustrated in FIG. 3d are explained below. Fifth subcell SC5 formed of an AlGaInAsP compound.

[0073] FIG. 3f shows a cross-sectional view of a embodiment according to the invention as a five-junction solar cell in a sixth alternative. Only the differences from the embodiment illustrated in FIG. 3e are explained below. Fifth subcell SC5 formed of a GaInAs compound and is formed between fourth subcell SC4 and second subcell SC2, second subcell SC2 formed of an AlInGaAsP compound.

[0074] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.