Stacked multi-junction solar cell with a metallization comprising a multilayer system

Abstract

A stacked multi-junction solar cell with a metallization comprising a multilayer system, wherein the multi-junction solar cell has a germanium substrate forming a bottom side of the multi-junction solar cell, a germanium subcell, and at least two III-V subcells, the multilayer system of the metallization has a first layer, comprising gold and germanium, a second layer comprising titanium, a third layer, comprising palladium or nickel or platinum, with a layer thickness, and at least one metallic fourth layer, and the multilayer system of the metallization covers at least one first and second surface section and is integrally connected to the first and second surface section, wherein the first surface section is formed by the dielectric insulation layer and the second surface section is formed by the germanium substrate or by a III-V layer.

Claims

1. A stacked multi-junction solar cell comprising: a germanium substrate forming a bottom side of the multi-junction solar cell; a germanium subcell; at least two III-V subcells following one another; and a metallization having a multilayer system including a first layer comprising gold and germanium, with a layer thickness of at least 2 nm and at most 50 nm, a second layer comprising titanium with a layer thickness of at least 10 nm and at most 300 nm, a third layer comprising palladium or nickel or platinum with a layer thickness of at least 5 nm and at most 300 nm, and at least one metallic fourth layer with a layer thickness of at least 2 μm, wherein the multilayer system of the metallization covers at least one first surface section and a second surface section and is integrally connected to both the first surface section and the second surface section, wherein the first surface section is formed by a dielectric insulation layer and the second surface section is formed by the germanium substrate or by a III-V layer, and the second surface section has a back-contacted front side, wherein the germanium substrate, the germanium subcell, and the at least two III-V subcells have at least one contact through-hole extending from a top side of the multi-junction solar cell through the at least two III-V subcells to the bottom side, the at least one contact through-hole having a continuous side wall, the continuous side wall of the contact through-hole being covered by the dielectric insulation layer, and wherein the titanium layer has local connections with the dielectric insulation layer.

2. The stacked multi-junction solar cell according to claim 1, wherein the at least one contact through-hole is oval in cross section.

3. The stacked multi-junction solar cell according to claim 1, wherein the fourth layer comprises silver and has a layer thickness of at least 2.5 μm and of at most 6 μm.

4. The stacked multi-junction solar cell according to claim 1, wherein the multilayer system has a fifth layer comprising gold, with a layer thickness of at least 50 nm and at most 1 μm.

5. The stacked multi-junction solar cell according to claim 1, wherein the dielectric insulation layer comprises SiO.sub.x and/or SiN.sub.x or consists of SiO.sub.x and/or SiN.sub.x.

6. The stacked multi-junction solar cell according to claim 1, wherein the dielectric insulation layer comprises an a-Si layer.

7. The stacked multi-junction solar cell according to claim 1, wherein the multi-junction solar cell comprises a III-V cover layer forming the backcontacted front side, with a thickness of 150-500 nm and a band gap of at least 1.86 eV.

8. The stacked multi-junction solar cell according to claim 1, wherein the multilayer system of the metallization extends from the backcontacted front side of the multi-junction solar cell along the continuous side wall through the contact through-hole to the bottom side of the multi-junction solar cell.

9. The stacked multi-junction solar cell according to claim 1, wherein the local connections between the titanium layer and the dielectric insulation layer are formed by rapid thermal annealing.

10. The stacked multi-junction solar cell according to claim 1, wherein the local connections between the titanium layer and the dielectric insulation layer provide localized permeability.

11. The stacked multi-junction solar cell according to claim 1, wherein the metallization extends beyond the dielectric insulation layer on the front side, the metallization directly contacting the stacked multi-junction solar cell on the front side.

12. The stacked multi-junction solar cell according to claim 1, wherein a portion of the metallization is disposed directly on the germanium substrate on the bottom side.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more fully understood from the detailed description given herein below 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 cross section of an exemplary embodiment of the invention of a stacked multi-junction solar cell with a back-contacted front side and a multilayer system as metallization;

(3) FIG. 2 is a back-side view of the multi-junction solar cell; and

(4) FIG. 3 shows a cross section of the multilayer system of the metallization.

DETAILED DESCRIPTION

(5) The diagram in FIG. 1 shows a detail of a stacked multi-junction solar cell 10 with a metallization comprising a multilayer system 12 and a back-contacted front side in a cross section.

(6) Multi-junction solar cell 10 has a top side 10.1 and a bottom side 10.2 as well as a through-hole 22 extending from top side 10.1 to bottom side 10.2. Multi-junction solar cell 10 comprises a germanium substrate 14 forming bottom side 10.2, a germanium subcell 16 following the germanium substrate, a first III-V subcell 18, and a second III-V subcell 20, forming top side 10.1 in the illustrated exemplary embodiment, in the order mentioned.

(7) Through-hole 22 has a side surface 22.1, wherein side surface 22.1 is formed continuous like a circumferential surface of a cylinder and has an oval shape, e.g., circular or elliptical, in cross section.

(8) Side surface 22.1 of through-contact hole 22 and a region of top side 10.1, said region adjoining through-hole 22, and bottom side 10.2 are covered with a dielectric insulation layer 24.

(9) Multilayer system 12 of the metallization is formed on dielectric insulation layer 24, wherein multilayer system 12 extends from a region, adjacent to dielectric insulation layer 24, on top side 10.1 of semiconductor wafer 10, along side surface 22.1 of through-hole 22 to a region of dielectric insulation layer 24 formed on bottom side 10.2, said region adjoining the through-hole.

(10) Multilayer system 12 therefore extends beyond dielectric insulation layer 24 on top side 10.1 of semiconductor wafer 10 and is integrally connected to both dielectric insulation layer 24 and to top side 10.1 of semiconductor wafer 10, here therefore second III-V subcell 20.

(11) A part of bottom side 10.2, said part which is not covered by dielectric insulation layer 24, is also covered with multilayer system 12 of the metallization.

(12) A back-side view of the multi-junction solar cell according to the first embodiment is shown in the diagram in FIG. 2. Only the differences from the diagram in FIG. 1 will be explained below.

(13) Multi-junction solar cell 10 has exactly two through-holes 22. The regions of multilayer system 12 formed around through-holes 22 are connected by a web-shaped section of multilayer system 12 of the metallization and are surrounded by dielectric insulation layer 24.

(14) A remaining surface of bottom side 10.2 of the semiconductor wafer is covered in a planar manner with multilayer system 12.

(15) The multilayer system according to a first embodiment is shown in more detail in the diagram in FIG. 3. Only the differences from the diagram in FIG. 1 will be explained below.

(16) Multilayer system 12 comprises five layers. A first layer M1, comprising gold and germanium, with a layer thickness of at most 50 nm forms the lowermost layer, adjacent to dielectric layer 24 and semiconductor wafer 10.

(17) The first layer M1 is followed by a second layer M2, comprising titanium, with a layer thickness of at least 10 nm. A third layer M3 comprises palladium or nickel or platinum and has a layer thickness of at least 5 nm.

(18) A fourth metallic layer comprising silver, for example, has a layer thickness of at least 2 μm. As the uppermost layer, multilayer system 12 in the exemplary embodiment shown comprises a fifth metallic layer, e.g., comprising gold, with a layer thickness of at least 50 nm.

(19) 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.