PERC+ solar cells with screen-printed dashed Ag front contacts

Abstract

The efficiency of PERC solar cells is limited by charge carrier recombination at the Ag front contacts on the emitter. To reduce the recombination current, we replaced the conventional continuous Ag contacts by dashed Ag contacts with lengths between 150 µm and 450 µm and a pitch of 600 µm. They are screen-printed using a firing-through Ag paste to establish the contact to the emitter. To provide a current path from the contacts to the busbars, a continuous Ag finger is printed on top using a non-firing through Ag paste with no glass frits or a low content of glass frits. First experiments reveal that the choice of the top Ag paste strongly influences the contact formation. A top Ag paste with a low content of glass frits etches the SiNx layer in between two contacts partially. A top Ag paste with no glass frits intermixes with the bottom paste during fast-firing and thereby dilutes the glass frit content of the bottom paste. As a consequence, the contact formation to the emitter is hindered, resulting in a high contact resistance. The potential of this concept is analyzed using numerical simulations. Depending on the contact resistivity and the fraction of the contacted area on the emitter, the concept can increase the conversion efficiency of future PERC solar cells by up to 0.3%abs.