Filament stretching during parallel dispensing - A way to reduce silver consumption in SHJ metallization

In the field of silicon heterojunction (SHJ) solar cells, great successes on improving production processes have been achieved in the last years, however further improvements in the case of metallization are required to obtain higher market share. Therefore, lower Ag laydowns and higher process throughput are demanded. This study presents the impact of filament stretching on Ag-electrode shapes and laydown during temperature-controlled micro-extrusion, known as parallel dispensing. Dispensed metal grids ensure higher cell performances than screen-printed grids. It has been discovered that the maximum use of filament stretching benefits the solar cell efficiency due to narrower Ag-electrodes and less silver consumption. We have shown a low Ag laydown per 157.35 mm line of mAg = 0.27 mg electrode-1 in average. An efficiency gain of ΔηA = + 0.26%abs. has been demonstrated by the maximum usage of filament stretching. Further, a novel parameter that values the effectiveness of silver usage and enables the comparison between different printing processes has been introduced. We have demonstrated that silver is used more effectively by up to +74%rel. when the low-temperature curing paste is dispensed compared to screen printing because dispensed electrodes show an almost perfectly homogeneous shape.