18.7 EMITTER WRAP-THROUGH SILICON SOLAR CELLS WITH SCREEN-PRINTED SILVER CONTACTS ACTING AS A BARRIER FOR EVAPORATED ALUMINIUM METALLIZATION

摘要

Since earlier EWT cells with an evaporated aluminium metallization suffered from an inability ofproviding annealing, a screen-printed silver finger is used to contact the emitter. This silver finger hinders theevaporated aluminium layer, which is used for the laser-fired contacts, from reducing the pseudo fill factor in afinal annealing step. The pseudo fill factor is thereby increased up to over 80% leading to conversion efficienciesup to 18.2% on FZ silicon using an emitter with a sheet resistance of 60 Ω/sq. Front and rear side are passivatedin a short oxidation step. This reduces the phosphorus concentration at the surface while simultaneouslyincreasing the conductivity of the emitter. Furthermore it is shown, that a single side polishing step after the laserdamage removal and texturization process approves to be beneficial for the open-circuit voltage. By using astandard POCl_3 diffusion process conversion efficiencies up to 18.7% are achieved on FZ silicon.