Developing a high throughput printing technology for silicon solar cell front side metallisation using flexography

Most crystalline silicon solar cells feature a front and rear side metallisation, which is usually applied by flatbed screen printing. Rotational printing methods represent a highly interesting alternative approach to realize the front side metallization with a considerably higher throughput. Particularly flexographic printing has proven to be well-suited for fine line contact fingers down to 25 mm width on textured silicon wafers. Within this work, flexographic printing has been applied for a seed layer front side metallisation of silicon solar cells. Three silver based inks with varying viscosity have been prepared for the experiment. Printing tests have been carried out to investigate the impact of printing pressure, material tolerances and ink viscosity on the printed contact finger width. A considerable impact of material tolerances on the printing result has been observed. It was further found that a variation of the ink viscosity did not significantly influence the finger width. Fingers down to a minimum width of 32 mm have been achieved by applying the optimum process parameters. Fully functional solar cells have been produced by reinforcing the flexo printed seed layer metallisation with silver light-induced plating. The solar cells revealed very promising results with a maximum conversion efficiency of i = 18.8%.