Fineline Printing Options for High Efficiencies and Low Ag Paste Consumption

AbstractIn this paper, we investigate and compare three different fine line printing techniques for the silver front side metallization of industrial-type silicon solar cells: single print, dual print and print-on-print. We produce solar cells using the same screen or stencil aperture of 40μm and about 92 fingers and obtain finger widths below 60μm for all three approaches. The print-on-print process achieves the highest finger heights of 20μm after firing but with quite strong finger height variation. In contrast, the dual printed fingers have a very flat surface with a finger height of 14.5μm which leads to the highest cross-section area of 530μm2 of the three techniques. The single print shows the lowest cross-section area of 390μm2 due to the lowest average finger height. The measured finger line resistance correlates with the finger cross-section area. The dual print allows us to use a non-firing through bus bar paste which increases the Voc by 2mV and hence achieves the highest efficiency of 19.1% using full-area Al-BSF cells. Due to an optimized bus bar screen print in combination with only 30μm finger aperture, the dual print has the lowest Ag paste consumption of only 75mg/wafer, one of the lowest Ag paste consumption that has been reported so far. A first batch of PERC solar cells with dual-printed Ag front contacts shows efficiencies up to 19.6%