Influence of Silver-Aluminium Alloy at Solar Cell Rear Side on Series Resistance and Open Circuit Voltage

The rear side metallization of industrial PERC solar cells was investigated regarding the implication on the silver-aluminium-alloy formation, in particular the effect of the high resistivity alloy formation and the etching of surface passivation layer. By changing the dimensions of the printed silver-pads the size of the silver-aluminium-overlap region at the pad-aluminium interface were varied. The influence on fill factor and open circuit voltage are evaluated. For a three busbar cell design with six pads per busbar, the fill factor decreases up to 2.2%abs, if the overlap length between aluminium and silver pad is reduced from 12.5 mm to 1 mm, whereas the open circuit voltage increases by 2.5 mV. These results are additionally confirmed by a 3D simulation which validates the measurement results and shows perspectives for reducing the series resistance effect of the silver-aluminium overlap region up to 40% by increasing the busbar count from 3 to 5.