Structuring of Metal Layers by Electrochemical Screen Printing for Back-Contact Solar Cells

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Reduction in production costs is essential for newsolar cell concepts to be competitive. A large cost factor in interdigitated back-contact solar cell manufacturing is the metallization. Several process steps are needed to form an interdigitated metal pattern out of a full faced metal layer to realize n- and p-metal contacts. Generating electrically separated conductor tracks is not only a challenge in PV but also in the circuit board sector. To drive down the costs for metal structuring, an innovative approach called electrochemical screen printing (ESP), which combines screen printing and electrochemical etching is developed in this paper. It permits localized etching of aluminum layers with very short process durations. The process speed yields 100 mm/s and is comparable with the conventional screen printing speed in solar cell manufacturing. Hence, it is faster than conventional structuring processes using masks and chemical etchants. By using a self-made water-based NaNO3 paste, narrow etched grooves (<80 μm) are formed in an aluminum layer by ESP, resulting in electrically separated aluminum regions. To increase the conductivity of the thin formed Al pattern, selective thickening is demonstrated by aluminum activation and plating nickel and copper. In this way, Al/Ni/Cu conductor tracks separated by a 70 μm trench are made out of a full faced aluminum layer using a short and simple process sequence. By electron microscopy and X-ray spectroscopy, the quality of etched regions and the structure of the formed metal stack are characterized in detail in order to assess the process sustainability.