21.8% efficient n-type solar cells with industrially feasible plated metallization
Using plated contacts, many of the challenges of metallizing high-efficiency n-type solar cells can be overcome. Very low resistivity contacts on boron emitters are hard to achieve by standard screen printing, and voltage reductions of up to 30 mV with currently available printing paste generations have been reported. In contrast, fully plated contacts have many similarities with evaporated contacts, which so far allow the highest efficiencies shown. Using plated contacts, excellent efficiencies of up to 21.74% are demonstrated in this work, contacting boron emitters with surface doping concentrations as low as 6x1018 cm-3 without significant series resistance losses. Open circuit voltages close to 680 mV show that the detrimental effect as observed for screen printed contacts can be avoided. High adhesive forces >2 N/mm have been achieved for the contacts by the controlled formation of nickel silicide. Simultaneously, very low series resistance was realized (FF of 81.2%). Plating experiments with 156x156 mm2 n-type solar cells in industrial inline tools yielded satisfactory deposition homogeneity over the cell area for contact fingers and busbars (+/- 2 mm deviation), depending on the used ablation method. Fingers were found to systematically plate twice as much as busbars.