Over 10% efficient screen printed RGS solar cells

The ribbon-growth-on-substrate (RGS) technology has the potential to produce wafers for PV at low cost and high speed without silicon losses related to wafer cutting. Up to now a discontinuously operating R&D machine produces test wafers with high oxygen content. Special care had therefore to be taken to prevent the formation of recombination centres related to oxygen formed at high temperatures during cell processing. Solar cells fabricated from RGS material with high oxygen content using an evaporation process resulted in efficiencies of up to 12.8%. An industrial-type screen printing process led to efficiencies of up to 10.5%. To further increase efficiency, the oxygen content has to be reduced. After a rebuilding of the RGS machine wafers reveal significantly lower oxygen contents. First screen printed cells made from that material show higher currents and open circuit voltages but not yet higher efficiencies due to shunting problems caused by current collecting structures.