Solar cell with combined metallization and process for producing the same

DETAILED DESCRIPTION It is an object of the present invention to provide an improved process for producing front and rear side contacts of silicon solar cells which allows simple production of the rear side contact and by means of which a finely structured and firmly adhering front side contact can be produced without damaging the rear side contact.
This and other objects and advantages are achieved according to the invention by a process for producing front and rear side contacts on a solar cell comprising a monocrystalline or polycrystalline silicon wafer having a flat p/n transition and a passivation layer on the front side, which comprises the steps of: producing a channel structure in the passivation layer; producing a rear side contact by printing on and firing a silver-containing paste which additionally comprises, besides oxidic additives, aluminum as a dopant; treating the wafer with an ionogenic palladium solution containing fluoride ions to produce a nucleation layer on the surface of the wafer exposed in the channel pattern; reinforcing the nucleation layer by deposition of at least one further metal from the solution.
Further embodiments of the invention further define the process, wherein the channel structure is defined by photolithography and is produced by wet chemical etching.
Alternately, the channel structure is produced by laser engraving.
In another embodiment, the channel structure is produced by mechanical removal of passivation layer and of silicon and by subsequent etching.
A preferred development of the process includes the palladium nucleation layer being reinforced by chemical deposition of a nickel layer having a thickness of from 1 to 5 .
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m and subsequently by electroless deposition of a copper layer having a thickness of from 5 to 20 .
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Alternately, the process provides that the palladium nucleation layer is reinforced by deposition of a silver layer having a thickness of from 5 to 20 .
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m.
Preferably, a silicon wafer having a textured surface is used