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Product Briefing Outline: RENA GmbH has launched a new novel electroplating tool for all solar cell types and formats. The CupCellPlate system enables a reduction in paste width and thickness to boost conversion efficiencies. During the plating operation each solar cell is positioned on top of a separate cup. The cell lies on contact pins above the cup and electrolyte or rinsing water flows against the cell. Due to this configuration it was possible to optimize the flow and thus the plating homogeneity. In addition, the wetting of the upper side is avoided, thus eliminating extensive protective actions to prevent chemical attacks on the non-processed cell side. With this design any metal like Ni, Cu, Sn or Ag can be plated.

Problem: In today’s Back-End process of solar cell production, the contacts which transport the current out of the cell are printed with metal paste onto the cell. After a thermal treatment, there is a porous structure which has only a fraction of the conductivity of pure metal. Due to the reduced conductivity, the maximum efficiency of the solar cell cannot be achieved.

Solution: The idea of the RENA Integrated Metallization Solution is the reduction of the paste width and thickness and use of the printed contact as seed/start layer for the following conductivity-enhancement with high conductive electroplated metal layers. Thus the efficiency of the solar cell is increased – viz. more current is flowing. In addition the CupCellPlate opens the chance to integrate low-cost and innovative metal sequences like nickel/copper/tin instead of silver into production. To derive the full advantage from the higher conductivity it is necessary to have a line width reduction, because in that case the shadowing of the effective area is reduced. Therefore RENA has in cooperation with NBTechnologies GmbH and Frintrup GmbH developed novel fine line screens. With these fine line screens it is possible to print 60μm structures, instead of up to now 100-120μm, with classic paste printing. With this combination of novel fine line printing and single side electroplating with the CupCellPlate efficiency increases of 0.5% can be realized.

Applications: Solar cell electroplating of Ni, Cu, Sn and Ag.

Platform: The automatic process control guarantees 24 hour operation with a throughput of 2400 wafers per hour. The transport of the solar cells from one process step to the next is performed with a special handling unit which transfers a complete row in parallel. The equipment is therefore neither inline nor batch, but it can be integrated like an inline tool into a production line.

Availability: April 2009 onwards.