Monolithic metamorphic multi-junction solar cell

Abstract

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.

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 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.Math.10.sup.18/cm.sup.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.Math.10.sup.17/cm.sup.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.Math.10.sup.17/cm.sup.3 and greater than 1.Math.10.sup.16/cm.sup.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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIG. 1 shows a view of an example of a monolithic metamorphic multi-junction solar cell;

(3) FIG. 2 shows a view of an example of a monolithic metamorphic multi-junction solar cell;

(4) FIG. 3 shows a view of an example of a monolithic metamorphic multi-junction solar cell.

DETAILED DESCRIPTION

(5) The illustration in FIG. 1 shows a first embodiment of a monolithic metamorphic multiple solar cell with a first top subcell SC1 on a second subcell SC2 below. Upon irradiation, the light L first strikes the top side of first subcell SC1

(6) A top tunnel diode TD1 is formed between first subcell SC1 and second subcell SC2.

(7) A third subcell SC3 is arranged below second subcell SC2. A second tunnel diode TD2 is formed between second subcell SC2 and third subcell SC3.

(8) A fourth subcell SC4 is arranged below third subcell SC3. A third tunnel diode TD3 is formed between third subcell SC3 and fourth subcell SC4.

(9) A metamorphic buffer MP is arranged between fourth subcell SC4 and third tunnel diode TD3.

(10) Each of the subcells SC1, SC2, SC3, and SC4 has an n-doped emitter layer materially connected to a p-doped base layer.

(11) Second subcell SC2 has an emitter formed of InGa(As)P and a base formed of InGaAsP. Here, the proportion of arsenic in the emitter is less than in the base or exactly zero. The doping in the emitter of second subcell SC2 is also less than the doping in the base.

(12) The illustration in FIG. 2 shows a second embodiment of a four-junction solar cell. Only the differences from the first embodiment are explained below.

(13) Second subcell SC2 has an emitter formed of InGaP and a base formed of InGaAsP; i.e., the emitter has a ternary compound in contrast to the quaternary compound in the base. As a result, second subcell SC2 is designed as a so-called hetero cell.

(14) The illustration in FIG. 3 shows a third embodiment of a four-junction solar cell. Only the differences to the preceding embodiments will be described below.

(15) A fifth subcell SC5 is arranged between first subcell SC1 and second subcell SC2. A fourth tunnel diode TD4 is arranged between fifth subcell SC5 and second subcell SC2. Fifth subcell SC5 is lattice-matched to the second subcell as well as to the third subcell.

(16) 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.