Stacked multi-junction solar cell

Abstract

A stacked multi-junction solar cell with a first subcell having a top and a bottom, and with a second subcell. The first subcell is implemented as the topmost subcell so that incident light first strikes the top of the first subcell and after that strikes the second subcell through the bottom. A first tunnel diode is arranged between the bottom of the first subcell and the second subcell. A window layer is arranged on the top of the first subcell, and the band gap of the window layer is larger than the band gap of the first subcell. A cover layer is arranged below metal fingers and above the window layer, and an additional layer is arranged below the cover layer and above the window layer. A thickness of the additional layer is less than the thickness of the window layer.

Claims

1. A stacked multi-junction solar cell comprising: a first subcell having a top and a bottom; a second subcell, the first subcell being implemented as the topmost subcell so that incident light first strikes the top of the first subcell and after that strikes the second subcell through the bottom of the first subcell; a first tunnel diode arranged between the bottom of the first subcell and the second subcell; a window layer arranged on the top of the first subcell, a band gap of the window layer being larger than a band gap of the first subcell; at least two metal fingers spaced apart from one another; a cover layer arranged below the at least two metal fingers and above the window layer; and an additional layer arranged below the cover layer and above the window layer, wherein a thickness of the additional layer is less than a thickness of the window layer, wherein the band gap of the additional layer is smaller than a band gap of the window layer, wherein the window layer and the additional layer have substantially the same elements, wherein the thickness of the additional layer between the metal fingers is smaller than below the metal fingers, wherein the window layer and the additional layer include a compound with at least the constituents InAlP or are made of InAlP, and wherein the additional layer has a higher In concentration and a lower Al concentration in comparison with the window layer.

2. The stacked multi-junction solar cell according to claim 1, wherein a lattice constant of the additional layer is greater than a lattice constant of the window layer, and wherein the lattice constant of the window layer is less than a lattice constant of the first subcell.

3. The stacked multi-junction solar cell according to claim 1, wherein the cover layer is completely absent or at least partially absent between the metal fingers.

4. The stacked multi-junction solar cell according to claim 1, wherein the cover layer is made of GaAs or InGaAs.

5. The stacked multi-junction solar cell according to claim 1, wherein the thickness of the cover layer is in a range between 30 nm and 1 μm, or the thickness of the cover layer is in a range between 250 nm and 500 nm, or the thickness of the cover layer is 300 nm.

6. The stacked multi-junction solar cell according to claim 1, wherein the additional layer has a lower wet chemical etching rate in comparison with the window layer vis-à-vis an etching solution made of citric acid, hydrogen peroxide, and water.

7. The stacked multi-junction solar cell according to claim 1, wherein the additional layer has a thickness, and the thickness of the additional layer is in a range between 0.1 nm and 5 nm, or the thickness of the additional layer is in a range between 0.5 nm and 1.2 nm, or the thickness of the additional layer is exactly 0.7 nm.

8. The stacked multi-junction solar cell according to claim 1, wherein the window layer has a thickness, and the thickness of the window layer is in a range between 10 nm and 25 nm, or the thickness of the window layer is in a range between 14 nm and 20 nm, or the thickness of the window layer is in a range between 15 nm and 17 nm, or the thickness of the window layer is 15 nm.

9. The stacked multi-junction solar cell according to claim 1, wherein the first subcell has a compound of the constituents InP or of the constituents InGaP, or the first subcell is made of InP or of InAlP or of InGaP or of AlGaInP.

10. The stacked multi-junction solar cell according to claim 1, wherein the cover layer and the window layer and the additional layer have an n-doping with the dopants Si and/or Te, and the concentration of the dopants is greater than 5.Math.E17 N/cm.sup.3 and less than 5.Math.E19 N/cm.sup.3.

11. The stacked multi-junction solar cell according to claim 1, wherein the multi-junction solar cell has a third subcell and a fourth subcell, or has exactly four subcells, and wherein an additional tunnel diode is formed between the third and fourth subcells.

12. The stacked multi-junction solar cell according to claim 1, wherein the multi-junction solar cell includes five subcells or the multi-junction solar cell consists of exactly five subcells, and wherein an additional tunnel diode is formed between each two consecutive subcells of the five subcells.

13. The stacked multi-junction solar cell according to claim 1, wherein the multi-junction solar cell is a monolithic multi-junction solar cell.

14. The stacked multi-junction solar cell according to claim 1, wherein the multi-junction solar cell has a semiconductor mirror formed between two subcells.

15. The stacked multi-junction solar cell according to claim 1, wherein the multi-junction solar cell has a metamorphic buffer between the first and second subcells.

16. A stacked multi-junction solar cell comprising: a first subcell having a top and a bottom; a second subcell, the first subcell being implemented as the topmost subcell so that incident light first strikes the top of the first subcell and after that strikes the second subcell through the bottom of the first subcell; a first tunnel diode arranged between the bottom of the first subcell and the second subcell; a window layer arranged on the top of the first subcell, a band gap of the window layer being larger than a band gap of the first subcell; at least two metal fingers spaced apart from one another; a cover layer arranged below the at least two metal fingers and above the window layer; and an additional layer arranged below the cover layer and above the window layer, wherein a thickness of the additional layer is less than a thickness of the window layer, wherein the band gap of the additional layer is smaller than a band gap of the window layer, wherein the thickness of the additional layer between the metal fingers is smaller than below the metal fingers, wherein a lattice constant of the additional layer is greater than a lattice constant of the window layer, and wherein the additional layer and the window layer comprise In, the In content in the additional layer being greater than the In content in the window layer.

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 is a cross-sectional view of an exemplary embodiment according to the invention of a multi-junction solar cell,

(3) FIG. 2 is a cross-sectional view of an exemplary embodiment according to the invention of a multi-junction solar cell,

(4) FIG. 3 is a cross-sectional view of an exemplary embodiment according to the invention of a multi-junction solar cell.

DETAILED DESCRIPTION

(5) The illustration in FIG. 1 shows a view of a first embodiment, having a multi-junction solar cell MS with a first subcell TZ1 and a second subcell TZ2, wherein the first subcell TZ1 is implemented as the topmost subcell. The first subcell TZ1 has a top and a bottom.

(6) Incident light L first strikes the top of the first subcell TZ1 and after that emerges at the bottom and strikes the second subcell TZ2.

(7) Arranged between the bottom of the first subcell TZ1 and the second subcell TZ2 is a first tunnel diode TD. Below the second subcell TZ2, a metal layer M2 is integrally bonded over the full area to a bottom of the second subcell TZ2.

(8) Arranged on the top of the first subcell TZ1 is a window layer FS1. Arranged above the window layer FS1 are two metal fingers M1 that are spaced apart from one another.

(9) Below the metal fingers M1, an additional layer FS2 is formed on the window layer FS1. The additional layer FS2 has a different stoichiometry from the window layer FS1. Arranged above the second window layer FS2, but below the metal fingers M1, is a cover layer AB.

(10) In another embodiment that is not shown, at least a slight thickness of the second window layer FS2 is formed on the first window layer FS1 between the metal fingers M1, wherein the thickness of the additional layer FS2 between the metal fingers M1 is less than the thickness of the additional layer FS2 below the metal fingers M1.

(11) In the illustration in FIG. 2, a cross-sectional view of a second embodiment according to the invention of a multi-junction solar cell MS is shown. Only the differences from the illustration in FIG. 1 are explained below.

(12) The first subcell TZ1 includes or is made of AlInGaP. The second subcell TZ2 includes or is made of AlInGaAs. Arranged below the second subcell TZ2 is a third subcell TZ3. The third subcell TZ3 includes or is made of InGaAs. Arranged between the second subcell TZ2 and the third subcell TZ3 is an additional tunnel diode TD.

(13) Arranged below the third subcell TZ3 is a fourth subcell TZ4. The fourth subcell TZ4 includes or is made of Ge. Arranged between the third subcell TZ3 and the fourth subcell TZ4 is an additional tunnel diode TD.

(14) Optionally, a semiconductor mirror HASP is arranged between the additional tunnel diode TD and the third subcell TZ3 in order to increase the radiation hardness for space applications. It is a matter of course here that the semiconductor mirror HASP is omitted for terrestrial applications.

(15) In another embodiment, a metamorphic buffer MP is arranged between the third subcell TZ3 and the fourth subcell TZ4, wherein the additional tunnel diode TD is either arranged between the metamorphic buffer MP and the third subcell TZ3 or between the metamorphic buffer MP and the fourth subcell TZ4.

(16) Instead of the arrangement of the metal layer M2 below the second subcell TZ2, the metal layer M2 is arranged below the fourth subcell TZ4, and is integrally bonded over the full area to a bottom of the fourth subcell TZ4.

(17) In the illustration in FIG. 3, a cross-sectional view of a third embodiment according to the invention of a multi-junction solar cell MS is shown. Only the differences from the illustration in FIG. 2 are explained below.

(18) The first subcell TZ1 includes or is made of AlInGaP. The second subcell TZ2 includes or is made of GaInP. The third subcell TZ3 includes or is made of AlInGaAs.

(19) The fourth subcell TZ4 includes or is made of InGaAs. Arranged below the fourth subcell TZ4 is a fifth subcell TZ5. The fifth subcell TZ5 includes or is made of Ge.

(20) Arranged between the fourth subcell TZ4 and the fifth subcell TZ5 is an additional tunnel diode TD.

(21) Optionally, a semiconductor mirror HASP is arranged between the additional tunnel diode TD and the fourth subcell TZ4 in order to increase the radiation hardness for space applications.

(22) In another embodiment, a metamorphic buffer MP is arranged between the fourth subcell TZ4 and the fifth subcell TZ5, wherein the additional tunnel diode TD is either arranged between the metamorphic buffer MP and the fourth subcell TZ4 or between the metamorphic buffer MP and the fifth subcell TZ5.

(23) The metal layer M2 is arranged below the fifth subcell TZ5, and is integrally bonded over the full area to a bottom of the fifth subcell TZ5.

(24) 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.