Progress in Fine-Line Front-Side Printing for TOPCon Solar Cells

As the silver price sets one record height after another, to curb costs, the need to reduce silver consumption in solar cell metallization increases. This work develops front-side metallization for tunnel oxide passivating contact (TOPCon) solar cells toward fine-line printing, i.e., feature sizes of less than 20 μm in width and a reduction of wet paste laydown. Besides silver reduction, this is motivated by increasing conversion efficiency, which further reduces cost per watt. To reach these goals by screen printing, three different fine-mesh configurations for knotless screens are utilized. Nominal screen opening widths vary from 24 µm to 13 μm. Moreover, printing with a dual-layer stencil featuring a nominal opening width of 9 μm is analyzed. The printed and fired contacts are characterized toward key geometrical and electrical performance indicators. Based on the corresponding findings, M10-sized TOPCon solar cells featuring fine-line grids with a core finger width wc  =  (16 ± 1) μm were fabricated. Compared to the reference group with wc  =  (23 ± 2) μm, a conversion efficiency gain of (0.9 ± 0.2)% <inf>rel</inf> is achieved, which is mainly driven by a reduction of shading-induced losses. Furthermore, wet paste laydown on the front is reduced by ∼30% <inf>rel</inf> using such metallization.