MONOLITHIC METAMORPHIC MULTI-JUNCTION SOLAR CELL

Abstract

A monolithic metamorphic 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 each other in the indicated order, and the first subcell forms the topmost 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 layer of the second subcell is greater than the base layer.

Claims

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 in the indicated order with the first subcell forming the topmost subcell; a metamorphic buffer formed between the third subcell and the fourth subcell; a semiconductor mirror formed between the second subcell and the third subcell, wherein the first, second, third and fourth subcells each have an n-doped emitter layer and a p-doped base layer, wherein a thickness of the emitter layer of the first, third and fourth subcell is less than a thickness of the associated base layer, and wherein, in the second subcell, the thickness of the emitter layer is greater than the thickness of the base layer.

2. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein a second tunnel diode is arranged between the second subcell and the semiconductor mirror.

3. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein the semiconductor mirror is n-doped and the doping is greater than 5⋅10.sup.17/cm.sup.3.

4. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein the thickness of the emitter layer has a thickness greater than 600 nm.

5. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein the base layer has a thickness less than 450 nm and/or a doping greater than 4⋅10.sup.17/cm.sup.3.

6. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein the emitter layer of the second subcell comprises InGaAsP or consists of InGaAsP.

7. The monolithic metamorphic multi-junction solar cell according to claim 4, wherein the emitter layer of the second subcell has an arsenic content based on the elements of main group V of between 22% and 33% and an indium content based on the elements of the main group III between 52% and 65%, and the lattice constant of the emitter layer is between 0.572 nm and 0.577 nm.

8. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein the second subcell is designed as a heterocell.

9. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein the base layer of the second subcell comprises InGaAsP or InGaP or AlInGaP or InAlP or AlInAs, or consists of InGaAsP or InGaP or AlInGaP or InAlP or AlInAs.

10. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein the first subcell has a bandgap in a range between 1.85 eV and 2.07 eV and the second subcell has a bandgap in a range between 1.41 eV and 1.53 eV and the third subcell has a bandgap in a range between 1.04 eV and 1.18 eV.

11. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein the first subcell comprises a compound of at least the elements AlInP and the indium content based on the elements of the main group III is between 64% and 75% and the Al content is between 18% and 32%.

12. 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.

13. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein the emitter layer of the second subcell at least partially has a dopant gradient and the dopant concentration in the direction of the first subcell increases to more than 3⋅10.sup.17/cm.sup.3.

14. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein the emitter layer of the second subcell comprises a first region and a second region, the first region having a different magnitude of doping than the second region and the second region being formed closer to the base than the first region.

15. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein exactly four subcells or exactly five subcells are provided, a fifth subcell being formed between the first subcell and the second subcell.

16. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein the base layer of the second subcell is doped with carbon and/or wherein the carbon concentration in the base layer of the second solar cell is higher than the zinc concentration.

17. The monolithic metamorphic multi-junction solar cell according to claim 1, wherein the emitter doping of the second subcell is less than the base doping by at least a factor of 3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] 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:

[0069] FIG. 1 is a view of an example of a monolithic metamorphic multi-junction solar cell,

[0070] FIG. 2 is a view of an example of a monolithic metamorphic multi-junction solar cell,

[0071] FIG. 3 is a view of an example a monolithic metamorphic multi-junction solar cell.

DETAILED DESCRIPTION

[0072] FIG. 1 shows a first embodiment of a monolithic metamorphic multi-junction solar cell with a first upper subcell SC1 on an underlying second subcell SC2. When irradiated, the light L first strikes the upper surface of the first subcell SC1.

[0073] An upper tunnel diode TD1 is formed between the first subcell SC1 and the second subcell SC2.

[0074] A third subcell SC3 is arranged below the second subcell SC2. Between the second subcell SC2 and the third subcell SC3, a second tunnel diode TD2 is formed.

[0075] A fourth subcell SC4 is arranged below the third subcell SC3. A third tunnel diode TD3 is formed between the third subcell SC3 and the fourth subcell SC4.

[0076] A metamorphic buffer MP is arranged between the fourth subcell SC4 and the third tunnel diode TD3.

[0077] Each of the subcells SC1, SC2, SC3, and SC4 has an n-doped emitter layer which is materially bonded to a p-doped base layer.

[0078] The thickness of the emitter layer at the first, third and fourth subcells SC1, SC3, SC4 is in each case less than the thickness of the associated base layer.

[0079] In the second subcell SC2, the thickness of the emitter layer is greater than the thickness of the base layer.

[0080] FIG. 2 shows a second embodiment of a four-junction solar cell. In the following, only the differences to the first embodiment are explained.

[0081] The second subcell SC2 has an emitter made of InGaP and a base made of InGaAsP, i.e., the emitter has a ternary compound in contrast to the quaternary compound in the base. As a result, the second subcell SC2 is designed as a so-called heterocell.

[0082] FIG. 3 shows a third embodiment of a four-junction solar cell. In the following, only the differences to the preceding embodiments are explained.

[0083] A fifth subcell SC5 is arranged between the first subcell SC1 and the second subcell SC2. A fourth tunnel diode TD4 is arranged between the fifth subcell SC5 and the second subcell SC2. The fifth subcell SC5 is lattice matched to both the second and third subcells.

[0084] 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.