A protection method for through-holes of a semiconductor wafer having the steps: providing a semiconductor wafer, and comprising a plurality of solar cell stacks, wherein each solar cell stack has a Ge substrate forming a bottom side of the semiconductor wafer, a Ge subcell, and at least two III-V subcells in the order mentioned, as well as at least one through-hole, extending from the top side to the bottom side of the semiconductor wafer, with a continuous side wall and a circumference that is oval in cross section; applying a photoresist layer to a top side of the semiconductor wafer and to at least one region of the side wall of the through-hole, said region adjoining the top side, and applying an organic filler material by means of a printing process to a region of the top side, said region comprising the through-hole, and into the through-hole.

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.

A stacked multi-junction solar cell with a back-contacted front side, having a germanium substrate that forms a rear side of the multi-junction solar cell, a germanium sub-cell and at least two III-V sub-cells, successively in the named order, and at least one passage contact opening that extends from the front side of the multi-junction solar cell through the sub-cells to the rear side and a metallic connection contact that is guided through the passage contact opening. A diameter of the passage contact opening decreases in steps from the front side to the rear side of the multi-junction solar cell. The front side of the germanium sub-cell forms a first step having a first tread depth that circumferentially projects into the passage contact opening. The second step with a second tread depth circumferentially projects into the passage contact opening.

A passivation method for a passage opening of a wafer, at least having the steps of: providing a wafer having a top, a bottom and comprising a plurality of solar cell stacks, wherein each solar cell stack has a Ge substrate that forms the bottom of the wafer, a Ge sub-cell, at least two III-V sub-cells, in the named order, and at least one passage opening extending from the top to the bottom of the wafer, with a contiguous side wall and a circumference that is oval in cross section, and applying a dielectric insulating layer by means of chemical vapor deposition to the top of the wafer, the bottom of the wafer and the side wall of the passage opening.

A marking method for applying a unique identification to each individual solar cell stack of a semiconductor wafer, at least comprising the steps: Providing a semiconductor wafer having an upper side and an underside, which comprises a Ge substrate forming the underside; and generating an identification with a unique topography by means of laser ablation, using a first laser, on a surface area of the underside of each solar cell stack of the semiconductor wafer, the surface area being formed in each case by the Ge substrate or by an insulating layer covering the Ge substrate.

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.

A metallization method for a semiconductor wafer having at least the steps: providing a semiconductor wafer having a top side and a bottom side and comprising a plurality of solar cell stacks, wherein each solar cell stack has a Ge substrate forming the bottom side of the semiconductor wafer, a Ge subcell, and at least two III-V subcells in the order mentioned, as well as at least one through-hole, extending from the top side to the bottom side of the semiconductor wafer, with a continuous side wall and a circumference that is oval in cross section, applying a photoresist layer in certain areas as a resist pattern by means of a printing method to the top side and/or to bottom side of the semiconductor wafer, applying a metal layer in a planar manner to exposed regions of the surface of the semiconductor wafer.

A two-step hole etching method including: providing a semiconductor wafer which has a plurality of solar cell stacks and performing a first and a second processing step. In the first processing step, a first resist layer is applied to a top surface of the semiconductor wafer, at least a first opening is produced in the first resist layer and, via a first etching process, a hole which extends beyond a p/n junction of the Ge sub-cell into the semiconductor wafer is produced in the area of the first opening. In the second process step a second resist layer is applied to the top surface of the semiconductor wafer, a second opening greater than the first opening and surrounding the hole is produced in the second resist layer, and, the hole is widened in an area which extends to the Ge sub-cell serving as an etch stop layer.

Approaches for the foil-based metallization of solar cells and the resulting solar cells are described. In an example, a solar cell includes a substrate. A plurality of alternating N-type and P-type semiconductor regions is disposed in or above the substrate. A conductive contact structure is disposed above the plurality of alternating N-type and P-type semiconductor regions. The conductive contact structure includes a plurality of metal seed material regions providing a metal seed material region disposed on each of the alternating N-type and P-type semiconductor regions. A metal foil is disposed on the plurality of metal seed material regions, the metal foil having anodized portions isolating metal regions of the metal foil corresponding to the alternating N-type and P-type semiconductor regions.

The present invention provides an electroconductive paste for a solar cell electrode, comprising a metal powder, glass frit, a metal oxide, an organic binder, and a solvent, wherein the metal oxide comprises an oxide of at least one kind of metal selected from a group consisting of tungsten (W), antimony (Sb), nickel (Ni), copper (Cu), magnesium (Mg), calcium (Ca), ruthenium (Ru), molybdenum (Mo), and bismuth (Bi).