STACK-LIKE MULTI-JUNCTION SOLAR CELL

Abstract

A multi-junction solar cell having at least three partial cells having an emitter and a base. The first partial cell comprises a first layer of a compound containing at least the elements GaInP, and the energy band gap of the first layer is greater than 1.75 eV, and wherein the second partial cell has a second layer of a compound having at least the elements GaAs and the lattice constant of the second layer is in the range between 5.635 and 5.675 , and wherein the third partial cell has a third layer of a compound having at least the elements GaInAs and the energy band gap of the third layer is smaller than 1.25 eV and the lattice constant of the third layer is greater than 5.700 .

Claims

1. A stack-like multi-junction solar cell comprising: at least a first, second, and third partial cell, each of the first, second, and third partial cells having an emitter and a base; and a metamorphic buffer formed between the second partial cell and the third partial cell, the metamorphic buffer having a sequence of at least three layers, and lattice elements of the buffer layers being greater than a lattice constant of the second layer, and the lattice constant of the buffer layers in the sequence increasing in a direction towards the third partial cell from layer to layer, wherein the first partial cell comprises a first layer of a compound having at least the elements GaInP and an energy band gap of the first layer being greater than 1.75 eV, and the lattice constant of the first layer being in a range between 5.635 and 5.675 , wherein the second partial cell comprises a second layer of a compound having at least the elements GaAs and an energy band gap of the second layer being in a range between 1.35 eV and 1.70 eV, and the lattice constant of the second layer being in the range between 5.635 and 5.675 , wherein the third partial cell comprises a third layer of a compound having at least the elements GaInAs and an energy band gap of the third layer being less than 1.25 eV, and the lattice constant of the third layer being greater than 5,700 , wherein a thickness of the three layers is greater than 100 nm and the three layers are designed as part of the emitter and/or as part of the base and/or as part of the space charge zone of the corresponding three partial cells situated between the emitter and base, wherein at least the second layer and/or the third layer is formed of a compound with at least the elements GaInAsP and has a phosphorus content of greater than 1% and has an indium content of greater than 1%, and wherein no semiconductor bond is formed between two partial cells of the stack.

2. The multi-junction solar cell according to claim 1, wherein the lattice constant of the first layer and/or the lattice constant of the second layer are in a range between 5.640 and 5.670 .

3. The multi-junction solar cell according to claim 1, wherein the lattice constant of the first layer and/or the lattice constant of the second layer lie in a range between 5.645 and 5.665 .

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

5. The multi-junction solar cell according to claim 1, wherein the lattice constant of the third layer is greater than 5.730 .

6. The multi-junction solar cell according to claim 1, wherein at least the second layer and/or the third layer are formed of a compound with at least the elements GaInAsP and has a phosphorus content of less than 35%.

7. The multi-junction solar cell according to claim 1, wherein both layers have a thickness greater than 0.4 m or greater than 0.8 m.

8. The multi-junction solar cell according to claim 1, wherein the second layer and the third layer formed of a compound with at least the elements GaInAsP and have a phosphorus content of greater than 1% and an indium content of greater than 1%.

9. The multi-junction solar cell according to claim 1, wherein the multi-junction solar cell has a fourth partial cell, the fourth partial cell having a fourth layer of a compound with at least the elements GaInAs and an energy band gap of the fourth layer being at least 0.15 eV smaller than an energy band gap of the third layer, and the thickness of the fourth layer being greater than 100 nm, and the fourth layer being a part of the emitter and/or a part of the base and/or a part of the space charge zone between the emitter and the base.

10. The multi-junction solar cell according to claim 9, wherein the fourth layer is formed of a compound with at least the elements GaInAsP and has a phosphorus content greater than 1% and less than 35% and an indium content greater than 1%.

11. The multi-junction solar cell according to claim 1, wherein a semiconductor mirror is formed between two partial cells and/or the semiconductor mirror is arranged below the lowest partial cell with the lowest energy band gap.

12. The multi-junction solar cell according to claim 1, wherein the first layer of the first partial cell is formed of a compound with at least the elements AIGaInP.

13. The multi-junction solar cell according to claim 1, wherein the multi-junction solar cell has no Ge partial cell.

14. The multi-junction solar cell according to claim 1, wherein a second metamorphic buffer is formed between the third partial cell and the fourth partial cell.

15. The multi-junction solar cell according to claim 1, wherein a fifth partial cell is provided.

16. The multi-junction solar cell according to claim 1, wherein the multi-junction solar cell has at least four partial cells, wherein the third layer is formed a compound having at least the elements GaInAsP, and has a phosphorus content greater than 50%, and wherein the multi-junction solar cell has exactly one metamorphic buffer and/or lattice constants of the fourth layer differ from lattice constant of the third layer by less than 0.3%.

17. The multi-junction solar cell according to claim 1, wherein no substrate is arranged between the two partial cells.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] 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:

[0040] FIG. 1a is a cross section of an embodiment according to the invention as a triple-function solar cell in a first alternative,

[0041] FIG. 1b is a cross section of an embodiment according to the invention as a triple-function solar cell in a second alternative,

[0042] FIG. 1c is a cross section of an embodiment according to the invention as a triple-junction solar cell in a third alternative,

[0043] FIG. 2a is a cross section of an embodiment according to the invention as a four-junction solar cell in a first alternative,

[0044] FIG. 2b is a cross section of an embodiment according to the invention as a four-junction solar cell in a second alternative,

[0045] FIG. 2c is a cross section of an embodiment according to the invention as a four-junction solar cell in a third alternative, and

[0046] FIG. 2d is a cross section of an embodiment according to the invention as a four-junction solar cell in a fourth alternative.

DETAILED DESCRIPTION

[0047] The illustration in FIG. 1a shows a cross section of an embodiment according to the invention of a stack-like monolithic multi-junction solar cell MS; in the following, the individual solar cells of the stack are referred to as a partial cell. The multi-junction solar cell MS has a first partial cell SC1, wherein the first partial cell SC1 formed of a GaInP compound and has the largest band gap of the entire stack above 1.75 eV. A second partial cell SC2, formed of a GaInAsP compound, is arranged underneath the first partial cell SC1. The second partial cell SC2 has a smaller band gap than the first partial cell SC1. Under the second partial cell SC2, a third partial cell SC3 formed of an InGaAs compound is arranged under the second partial cell SC2, wherein the third partial cell SC3 has the smallest band gap. In the present case, the third partial cell SC3 has an energy band gap of less than 1.25 eV.

[0048] A metamorphic buffer MP1 is formed between the second partial cell SC2 and the third partial cell SC3. The buffer MP1 is formed of a plurality of layers, wherein the lattice constant within the buffer MP1 generally decreases from layer to layer of the buffer MP1 in the direction of the third partial cell SC3. Introducing the buffer MP1 is advantageous if the lattice constant of the third partial cell SC3 does not match the lattice constant of the second partial cell SC2.

[0049] It is understood that a tunnel diode can be formed between the individual partial cells SC1, SC2 and SC3.

[0050] It is also understood that each of the three partial cells SC1, SC2 and SC3 each have an emitter and a base, wherein the thickness of the second partial cell SC2 is designed to be greater than 0.4 m.

[0051] The lattice constant of the first partial cell SC1 and the lattice constant of the second partial cell SC2 are matched to one another or are the same. In other words, the partial cells SC1 and SC2 are lattice-matched to one another.

[0052] Since the band gap of the first partial cell SC1 is greater than the band gap of the second partial cell SC2, and the band gap of the second partial cell SC2 is greater than the band gap of the third partial cell SC3, solar irradiation takes place through the surface of the first partial cell SC1.

[0053] FIG. 1b shows a cross section of an embodiment according to the invention as a triple-junction solar cell in a second alternative. In the following, only the differences from the embodiment shown in conjunction with FIG. 1a are explained. Hereafter, the second partial cell SC2 formed of a GaAs compound and the third partial cell SC3 formed of a GaInAsP compound.

[0054] FIG. 1c shows a cross section of an embodiment according to the invention as a triple-junction solar cell in a third alternative. In the following, only the differences from the embodiment illustrated in conjunction with FIG. 1a are explained. Hereafter, the second partial cell SC2 and the third partial cell SC3 each formed of a GaInAsP compound.

[0055] FIG. 2a shows a cross section of an embodiment according to the invention as a four-junction solar cell in a first alternative. In the following, only the differences from the embodiment shown in conjunction with FIG. 1a are explained. Below the third partial cell SC3, a fourth partial cell SC4 is formed on a GaInAs compound. The lattice constant of the fourth partial cell SC4 and the third partial cell SC3 are matched with one another or are the same.

[0056] The fourth partial cell SC4 has a smaller band gap than the third partial cell SC3.

[0057] FIG. 2b shows a cross section on an embodiment according to the invention as a four-junction solar cell in a second alternative. In the following, only the differences from the preceding embodiments will be explained. The second partial cell SC2 formed of a GaAs compound and the third partial cell SC3 now formed of an InGaAsP compound.

[0058] FIG. 2c shows a cross section of an embodiment according to the invention as a four-junction solar cell in a third alternative. In the following, only the differences from the embodiment shown in FIG. 2a are explained. The third partial cell SC3 formed of a GaInAsP compound.

[0059] FIG. 2d shows a cross section of an embodiment according to the invention as a four-junction solar cell in a fourth alternative. In the following, only the differences from the embodiment shown in FIG. 2a are explained. The third partial cell SC3 and the fourth partial cell SC4 each formed of a GaInAsP compound.

[0060] 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.