STACKED MULTIJUNCTION SOLAR CELL HAVING A DIELECTRIC INSULATING LAYER SYSTEM

Abstract

A stacked multijunction solar cell having a dielectric insulating layer system, a germanium substrate, which forms an underside of the multijunction solar cell, a germanium subcell and at least two III-V subcells, which follow each other in the specified order, the insulating layer system includes a layer sequence made up of at least one bottom insulating layer, which is integrally connected to a first surface section of the multijunction solar cell and a top insulating layer forming an upper side of the insulating layer system, and a metal coating of the multijunction solar cell is integrally and electrically conductively connected to a second surface section abutting the first surface section of the multijunction solar cell and is integrally connected to a section of the upper side of the insulating layer system, and the top insulating layer comprises amorphous silicon or is made up of amorphous silicon.

Claims

1. A stacked multijunction solar cell comprising: a dielectric insulating layer system having s a layer sequence made of up at least one bottom insulating layer integrally connected to a first surface section of the multijunction solar cell and a top insulating layer forming an upper side of the insulating layer system; a germanium substrate, which forms an underside of the multijunction solar cell; a germanium subcell; and at least two III-V subcells, which follow each other; and a metal coating being integrally and electrically conductively connected to a second surface section abutting the first surface section of the multijunction solar cell and being integrally connected to a section of the upper side of the insulating layer system, wherein the top insulating layer comprises amorphous silicon or is formed substantially of amorphous silicon.

2. The stacked multijunction solar cell according to claim 1, wherein the bottom insulating layer comprises SiO.sub.2 and/or Si.sub.3N.sub.4 or is made up of SiO.sub.2 and/or Si.sub.3N.sub.4.

3. The stacked multijunction solar cell according to claim 1, wherein the insulating layer system includes at least one further middle insulating layer, the at least one further middle insulating layer comprising SiO.sub.2 and/or Si.sub.3N.sub.4 or being formed substantially of SiO.sub.2 and/or Si.sub.3N.sub.4.

4. The stacked multijunction solar cell according to claim 1, wherein the multijunction solar cell has a back side-contacted front side, wherein the semiconductor wafer has a through-contact hole extending from the upper side of the multijunction solar cell through the subcells to the underside, the through-contact hole having a contiguous side wall and an oval circumference in parallel to the surface, and wherein the side wall of the through-contact hole is covered by the dielectric insulating layer system.

5. The stacked multijunction solar cell according to claim 4, wherein the metal coating on the insulating layer system extends from the upper side of the multijunction solar cell along the side wall through the through-contact hole to the under side of the multijunction solar cell.

6. The stacked multijunction solar cell according to claim 1, wherein the metal coating comprises a multilayer system.

7. The stacked multijunction solar cell according to claim 6, wherein the multilayer system comprises an AuGe/Ti/Pd/Ag/Au layer sequence or a Pd/Au/Ge/Ti/Pd/Ag/Au layer sequence.

8. The stacked multijunction solar cell according to claim 1, wherein the multilayer system has a layer comprising a nickel or a layer comprising an aluminum as the bottom layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] 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:

[0038] FIG. 1 shows a detail of a first specific embodiment of a multijunction solar cell having a dielectric insulating layer system;

[0039] FIG. 2 shows an exemplary embodiment of a multijunction solar cell having a dielectric insulating layer system;

[0040] FIG. 3 shows an exemplary embodiment of a multijunction solar cell having a dielectric insulating layer system;

[0041] FIG. 4 shows a back side view of the multijunction solar cell.

DETAILED DESCRIPTION

[0042] The illustration in FIG. 1 shows a detail of a surface of a stacked multijunction solar cell 10. The surface is formed by a semiconductor layer, e.g. a layer comprising a germanium or a III-V semiconductor. A dielectric insulating layer system 24, made up of a bottom insulating layer M1 and an top insulating layer M2, is on a first surface section A1 of upper side 10.1.

[0043] Bottom insulating layer M1 is integrally connected to upper side 10.1 of multijunction solar cell 10. The bottom insulating layer comprises SiO.sub.2 and/or Si.sub.3N.sub.4 or consists of SiO.sub.2 and/or Si.sub.3N.sub.4. An upper side of the insulating layer system 24 is formed by top insulating layer M2, top insulating layer M2 being made up of amorphous silicon.

[0044] A metal coating 12 is formed on a second surface section A2 abutting first surface section A1 as well as on the upper side of insulating layer system 24. The metal coating is integrally and electrically conductively connected to upper side 10.1 of multijunction solar cell 10. Metal coating 12 is also integrally connected to the upper side of insulating layer system 24, i.e. to amorphous silicon layer M2.

[0045] Another specific embodiment is shown in the illustration in FIG. 2. Only the differences from the illustration in FIG. 1 are explained below. The further specific embodiment comprises, as a cutout, part of the surface section A1 and part of the surface section A2.

[0046] In the first surface section A1, the dielectric layer sequence 24 comprises two middle insulating layers M3 and M4 between the lowermost insulating layer M1 and the uppermost insulating layer M2.

[0047] The two middle insulating layers M3 and M4 each comprise SiO2 and/or Si3N4 or each consist of SiO2 and/or Si3N4. The lower insulating layer M1 here has a different material than at least one of the two middle insulating layers M3 and M4.

[0048] In the cutout in the area of the surface section A1, a layer system is formed on the dielectric layer sequence 24 for the metal coating 12 of a layer system of a sequence of five metal layers 12.1, 12.2, 12.3, 12.4 and 12.5 as an AuGe/Ti/Pd/Ag/Au layer sequence or as a Pd/Au/Ge/Ti/Pd/Ag/Au layer sequence, wherein as the first metal layer 12.1 of the layer system, i.e. the AuGe layer or the Pd layer is materially bonded to the surface of the topmost insulating layer M2 of the insulation layer system 24 below. Furthermore, in the area of the surface section A2, the first metal layer 12.1 is materially connected to the electrically conductive semiconductor surface of the multijunction solar cell.

[0049] In other words, the sequences of the five metal layers 12.1, 12.2, 12.3, 12.4, and 12.5 cover the upper side of the insulating layer system 24 in the illustrated section on the upper side 10.1, i.e. the surface of the upper insulating layer M2.

[0050] Furthermore, in the section shown, the metal coating 12 covers the surface of the multijunction solar cell as part of the surface section A2.

[0051] In the illustration of FIG. 3, a cross section through an opening is shown. Only the differences from the illustration in FIG. 1 or from FIG. 2 are explained below.

[0052] The stacked multijunction solar cell 10 has an opening 22 with a side wall 22.1. A plurality of III-V subcells 16, 18, and 20 are formed on the Ge substrate 14, which itself is preferably also embodied as a subcell.

[0053] The insulating layer system 24 extends from the first surface section A1 over the second surface section A2 on the upper side 10.1 through the opening 22 to the underside 10.2. The opening has a larger diameter on the upper side 10.1 than that of the underside 10.2. In other words, the opening is conical.

[0054] Here, the insulating layer system 24 completely covers the side wall 22.1 all around in the opening in order to prevent the metal coating from short-circuiting the individual subcells 14, 16, 18 and 20 in the opening 22.

[0055] The metal coating 12 is materially connected to the front side 10.1 of the multijunction solar cell 10 in an electrically conductive manner and then completely covers the insulating layer system 24 arranged on the front side 10.1 and the side surfaces 22.1 of the opening and a part of the insulating layer system 24 on the underside 10.2 to form a rear contact surface on the underside 10.2. This allows for the front side to be connected electrically from the rear side or from the underside 10.2 by means of the rear side contact surface.

[0056] On the underside 10.2, an electrically conductive semiconductor rear side, i.e. the rear side of the Ge substrate 12, which is spaced apart by an area of the insulating layer system 24, is also covered by the metal coating 12. As a result, both contacts of the multijunction solar cell can be connected from the underside 10.2.

[0057] In the illustration of FIG. 4, a plan view of the underside 10.2 of the embodiment depicted in connection with FIG. 3 is shown. Only the differences from the illustration in FIG. 3 are explained below.

[0058] The underside 10.2 of the multijunction solar cell 10 is predominantly, i.e. more than 70%, covered by the metal coating 12 in order to connect the rear side of the multijunction solar cell 10 with low electrical resistance.

[0059] The front side 10.1 is connected with two through-contacts, i.e. by means of two openings 22 from the rear side. In this case, the two areas around the openings 22, which are designed as rear-side contacts for the front side 10.1, are electrically connected by means of a conductor track.

[0060] For purposes of insulation, the rear-side contact area is separated from the area of the metal coating 12, which electrically connects the rear side of the multiple solar cell 10, by an insulating area.

[0061] 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.