Rear Contact and BSF Formation for Local Al-BSF Solar Cells

This work studies the performance of commercially available Al pastes for the rear side contact formation with an industrially feasible process. The pastes are specifically designed for local Al-BSF/PERC (Passivated emitter and rear cell) cells. With this type of metallization, fill factors (FF) up to 80% are demonstrated, to our knowledge, the highest FF ever reported on fully screen printed PERC cells with industrial type emitter. Additionally, the use of an AlSi eutectic (12.7% Si) target for PVD sputtering is evaluated in comparison to a reference process using a pure Al target with the same kind of deposition technique. It was found that the thickness of the Al p+ BSF layer realized with the 12.7% Si containing Al target is systematically thicker than the reference due to a smaller metal Si interface. With this method, solar cells have been fabricated showing a potential efficiency above 20%, with standard Ag front screen printing on 60 Ω/□ emitter.