The electrical currents generated in a solar cell are outputted via electrical conductors that are in ohmic contact with the active semiconductor body of the solar cell. Depending on the cell type and on the direction of light incidence, these conductors, which are also referred to as contacts, can be composed of different materials. Whereas the selection of material and the shaping of the conductor of the back side of the solar cell is not problematical, the front side contacts must still assure an adequate light incidence into the semiconductor body.
Transparent, electrically conductive metal oxide layers (TCO) that can be produced by thin-film technology can be applied as front side contacts. As a consequence of their relatively low surface conductivity, however, these TCO contacts are reinforced or replaced by a structured, metallic front side contact or contact grid when higher currents are to be outputted. A structure for the grid is, therefore, desirable wherein an adequate overall grid contact cross section is distributed as uniformly as possible over the surface of the solar cell with a minimum occlusion thereof.
To that end, a finely branched or, respectively, tightly rastered, first grid contact structure is usually first applied on the front side. This is done, for example, with either a thin-film or thick-film technology. A bus structure that is at least composed of a conductor with adequate cross section, which is applied transversely thereto, is then applied on this first grid contact structure. The bus structure can, likewise, be produced by a thin-film technology, but thick-film technology is better. It is also possible to solder the bus structure in the form of solid metallic conductors onto the grid contact structure.
For external connection of crystalline or polycrystalline solar cells, conductor ribbons are soldered onto the bus structure at correspondingly provided terminal locations or pads. These also serve for the series connection of individual solar cells, wherein the conductor ribbons are respectively conducted under the back side of the neighboring solar cell and are soldered to the back side. Due to the mechanical sensivity of the grid contact structures, this had to be done manually and immediately before the interconnection in order to avoid tearing off or other damage. Due to the instability of the ribbon in view of bending, the positioning of the ribbon also requires high precision. A fully automated, cost-beneficial mass production or, respectively, mass interconnection of solar cells is thus made difficult.
USPTO Backgrounds
USPTO Backgrounds