Wet chemical single-side emitter etch back for MWT solar cells with AL-BSF and challenges for via paste selection

This work investigates the integration of a wet chemical single-side emitter etching process into the process sequence of screen printed p-type Czochralski-grown silicon MWT-BSF (metal wrap through aluminum back surface field) solar cells. The MWT-BSF solar cells fabricated with single-side emitter etch back achieve a median conversion efficiency of 18.4 % (as processed), while MWT-BSF solar cells isolated by laser grooves show a slightly lower median conversion efficiency of 18.2 % (as processed). Repeated current-voltage (I-V) measurements under forward and reverse bias using stabilized MWT-BSF solar cells with single-side emitter etch back confirm that a novel via paste enables stable results under forward bias (standard operation mode), although the via paste is in direct contact with the p-type base. MWT-BSF solar cells with single-side emitter etch back show increasing current densities under reverse bias without affecting the cell performance after repeated I-V measurements, this behaviour could be used for an integrated bypass approach. The results confirm the successful integration of single-side emitter etch back into the MWT-BSF process sequence allowing for the reduction of the process sequence by one process step compared to MWT-BSF solar cells isolated by laser grooves.