Stacked monolithic upright metamorphic multijunction solar cell

Abstract

A stacked monolithic upright metamorphic multijunction solar cell, comprising at least one first subcell having a first band gap, a first lattice constant and being made up of germanium by more than 50%, a second subcell, which is disposed above the first subcell and has a second band gap and a second lattice constant, a metamorphic buffer disposed between the first subcell and the second subcell, including a sequence of at least three layers having lattice constants which increase from layer to layer in the direction of the second subcell, and a first tunnel diode, which is situated between the metamorphic buffer and the second subcell and which has an n.sup.+ layer and a p.sup.+ layer, the second band gap being larger than the first band gap, the n.sup.+ layer of the first tunnel diode comprising InAlP, the p.sup.+ layer of the first tunnel diode comprising an As-containing III-V material.

Claims

1. A stacked monolithic upright metamorphic multijunction solar cell comprising: at least one first subcell having a first band gap, a first lattice constant, and is made of germanium by more than 50%; a second subcell, which is disposed above the first subcell, has a second band gap and a second lattice constant, and is made of AlInGaP; a metamorphic buffer disposed between the first subcell and the second subcell; and a first tunnel diode that includes an n+ layer and a p+ layer, the first tunnel diode being arranged between the metamorphic buffer and the second subcell, the p.sup.+ layer of the first tunnel diode comprising an As-containing III-V material, wherein the second band gap is larger than the first band gap, wherein the second lattice constant is larger than the first lattice constant, wherein the n.sup.+ layer of the first tunnel diode comprises In.sub.xAl.sub.1-xP, where x>0.6, wherein an intermediate layer is disposed between the n.sup.+ layer and the p.sup.+ layer, wherein the intermediate layer is thinner than the n.sup.+ layer and the p.sup.+ layer, wherein the intermediate layer has a thickness of less than 6 nm or less than 4 nm, wherein the intermediate layer comprises GaAs or AlGaAs or AlInAs or InGaAs or AlInGaAs, wherein the intermediate layer is doped with silicon having a dopant concentration of at least 10.sup.18 N/cm.sup.3, wherein an As content of the intermediate layer is higher than an As content of the n.sup.+ layer, and wherein the intermediate layer suppresses cross contamination of dopants between the n.sup.+ layer and the p.sup.+ layer of the tunnel diode.

2. The multijunction solar cell according to claim 1, wherein the intermediate layer has an energy gap of 1.08 eV.

3. The multijunction solar cell according to claim 1, wherein the n.sup.+ layer of the first tunnel diode is doped with silicon and/or with tellurium and/or with selenium and/or with sulfur having a dopant concentration of 10.sup.19 N/cm.sup.3.

4. The multijunction solar cell according to claim 1, wherein the p.sup.+ layer of the first tunnel diode comprises AlInAs.

5. The multijunction solar cell according to claim 1, wherein the p.sup.+ layer of the first tunnel diode comprises Al.sub.xGa.sub.yIn.sub.1-x-yAs, where x>0.4.

6. The multijunction solar cell according to claim 1, wherein the p.sup.+ layer of the first tunnel diode is doped with carbon.

7. The multijunction solar cell according to claim 1, wherein a lattice constant of the n.sup.+ layer of the first tunnel diode corresponds to the second lattice constant of the second subcell, and wherein a lattice constant of the p.sup.+ layer of the first tunnel diode is equal to or less than the second lattice constant of the second subcell.

8. The multijunction solar cell according to claim 1, wherein the multijunction solar cell comprises additional subcells, each having a band gap, the additional subcells being disposed between the first tunnel diode and the first subcell, and the band gaps of the additional subcells each being larger than the first band gap of the first subcell and each being smaller than the second band gap of the second subcell.

9. The multijunction solar cell according to claim 8, wherein the multijunction solar cell comprises at least one additional tunnel diode.

10. The multijunction solar cell according to claim 9, wherein the at least one additional tunnel diode comprises an additional intermediate layer, an n.sup.+ layer of the additional tunnel diode comprising InAlP or InGaP, a p.sup.+ layer of the additional tunnel diode comprising an As-containing III-V material, the additional intermediate layer being disposed between the n.sup.+ layer and the p.sup.+ layer of the additional tunnel diode, and the additional intermediate layer being thinner than the n.sup.+ layer and the p.sup.+ layer of the additional tunnel diode.

11. The multijunction solar cell according to claim 1, wherein the multijunction solar cell is a 4-junction Ge/InGaAs/AlInGaAs/AlInGaP cell.

12. The multijunction solar cell according to claim 1, wherein the multijunction solar cell is a 5-junction Ge/InGaAs/AlInGaAs/InGaP/AlInGaP cell.

13. The multijunction solar cell according to claim 1, wherein the intermediate layer operates to counteract a reduction in a tunnel current of the first tunnel diode due to the n+ layer.

14. A stacked monolithic upright metamorphic multijunction solar cell comprising: at least one first subcell having a first band gap, a first lattice constant and is made of germanium by more than 50%; a second subcell, which is disposed above the first subcell, has a second band gap and a second lattice constant, and is made of AlInGaP; a metamorphic buffer disposed between the first subcell and the second subcell; and a first tunnel diode that includes an n+ layer and a p+ layer, the first tunnel diode being arranged between the metamorphic buffer and the second subcell, the p.sup.+ layer of the first tunnel diode comprising an As-containing III-V material, wherein the second band gap is larger than the first band gap, wherein the second lattice constant is larger than first lattice constant, wherein the n.sup.+ layer of the first tunnel diode comprises In.sub.xAl.sub.1-xP, where x>0.6, wherein an intermediate layer is disposed between the n.sup.+ layer and the p.sup.+ layer, wherein the intermediate layer is thinner than the n.sup.+ layer and the p.sup.+ layer, wherein the intermediate layer has a thickness of less than 6 nm or less than 4 nm, wherein the intermediate layer comprises GaAs or AlGaAs or AlInAs or InGaAs or AlInGaAs such that the intermediate layer counteracts a reduction in a tunnel current of the first tunnel diode due to the n+ layer, and wherein the intermediate layer suppresses cross contamination of dopants between the n.sup.+ layer and the p.sup.+ layer of the tunnel diode.

15. The multijunction solar cell according to claim 1, wherein the second subcell is a topmost subcell.

16. The multijunction solar cell according to claim 14, wherein the second subcell is a topmost subcell.

17. The multijunction solar cell according to claim 1, wherein the second subcell is made entirely of AlInGaP.

18. The multijunction solar cell according to claim 1, wherein the intermediate layer has a one-part design and is made by metalorganic vapor phase epitaxy.

19. The multijunction solar cell according to claim 1, wherein the metamorphic buffer layer comprises a sequence of three layers, each of the three layers having a lattice constant, and wherein the lattice constant of the three layers increases layers to layer in a direction of the second subcell.

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 schematic view of an example embodiment according to the invention of a stacked monolithic upright metamorphic multijunction solar cell;

(3) FIG. 2 shows a schematic view of an example embodiment according to the invention of the multijunction solar cell;

(4) FIG. 3 shows a schematic view of an example embodiment according to the invention of the multijunction solar cell; and

(5) FIG. 4 shows a schematic view of an example embodiment according to the invention of the multijunction solar cell.

DETAILED DESCRIPTION

(6) The illustration in FIG. 1 shows a stacked monolithic upright metamorphic multijunction solar cell S, comprising a first subcell SC1 as the bottom subcell, followed by a metamorphic buffer MP1, a tunnel diode TD1 and a second subcell SC2 as the top subcell.

(7) First subcell SC1 has a first band gap EG1 and a first lattice constant A1 and is made up of germanium by more than 50%.

(8) The second subcell has a second band gap EG2 and a second lattice constant A2, second band gap EG2 being larger than first band gap EG1, and second lattice constant A2 differing from first lattice constant A1.

(9) Metamorphic buffer MP1 balances out the differences between lattice constants A1 and A2 and, for this purpose, includes a sequence of at least three layers having lattice constants which increase from layer to layer in the direction of second subcell SC2.

(10) Tunnel diode TD1 is disposed between metamorphic buffer MP1 and second subcell SC2 and includes an n.sup.+ layer, a p.sup.+ layer and an intermediate layer ZW disposed between the n.sup.+ layer and the p.sup.+ layer.

(11) The n.sup.+ layer of first tunnel diode TD1 comprises InAlP, and the p.sup.+ layer of first tunnel diode TD1 comprises an As-containing III-V material.

(12) Intermediate layer ZW is designed to be thinner than the n.sup.+ layer and the p.sup.+ layer in each case.

(13) Another example is shown in the illustration in FIG. 2. Only the differences from the illustration in FIG. 1 are explained below.

(14) Multijunction solar cell S additionally comprises a third subcell SC3 and a fourth subcell SC4, the two additional subcells SC3 and SC4 each being designed to be lattice-matched to second subcell SC2 and being disposed between metamorphic buffer MP1 and tunnel diode TD1.

(15) Another example is shown in the illustration in FIG. 3. Only the differences from the illustration in FIG. 2 are explained below.

(16) The multijunction solar cell S comprises another tunnel diode TD3, including an intermediate layer according to the invention, in addition to third and fourth subcells SC3 and SC4. The n.sup.+ layer of the additional tunnel diode comprises InAlP, the p.sup.+ layer of the additional tunnel diode comprising an As-containing III-V material.

(17) While a second tunnel diode TD2 between metamorphic buffer MP1 and first subcell SC1 comprises an n.sup.+ layer and a p.sup.+ layer but no intermediate layer, third tunnel diode TD3 is built up between third subcell SC3 and fourth subcell SC4 according to first tunnel diode TD1.

(18) Accordingly, third tunnel diode TD3 has another intermediate layer ZW2 between a p.sup.+ layer and an n.sup.+ layer.

(19) First subcell SC1 is designed as a Ge solar cell or substrate, third subcell SC3 comprises InGaAs, fourth subcell SC4 comprises InAlGaAs and the second subcell comprises InAlGaP. The p.sup.+ layer of first tunnel diode TD1 comprises AlInGaAs, the n.sup.+ layer comprises InAlP and intermediate layer ZW comprises Ga(Al)As.

(20) Another example is shown in the illustration in FIG. 4. Only the differences from the illustration in FIG. 3 are explained below.

(21) The multijunction solar cell is designed as a 5-junction cell. A second tunnel diode TD2 is disposed on first subcell SC1 designed as a Ge substrate, second tunnel diode TD2 not including an intermediate layer.

(22) Second tunnel diode TD2 is followed by metamorphic buffer MP1, a third subcell SC3 made up of InGaAs, a third tunnel diode TD3, a fourth subcell made up of InAlGaAs, a fourth tunnel diode TD4, a fifth subcell made up of InGaP, first tunnel diode TD1 and the second subcell made up of InAlGaP.

(23) The first tunnel diode includes an AlInGaAs layer as the p.sup.+ layer, an InAlP layer as the n.sup.+ layer and an intermediate layer ZW made up of Ga(Al)As between the n.sup.+ layer and the p.sup.+ layer.

(24) Second tunnel diode TD2 does not have an intermediate layer.

(25) Like second tunnel diode TD2, third and fourth tunnel diodes TD3 and TD4 do not have an intermediate layer in the illustrated exemplary embodiment. In the illustrated exemplary embodiment, the n.sup.+ layer of the third and fourth tunnel diodes comprises InGaP or InAlP.

(26) Alternatively, the fourth tunnel diode also comprises an intermediate layer. Alternatively, in addition to fourth tunnel diode TD4, third tunnel diode TD3, in turn, also comprises an intermediate layer.

(27) 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.