We present metal wrap through passivated emitter and rear cells (MWT-PERC) on p-type Czochralski silicon (Cz-Si) using advanced metallization approaches. Front surface metallization is performed either with a one-step approach (conventional thick film screen printing) or with a more advanced two-step approach, consisting of aerosol printing of a silver seed layer and subsequent silver electroplating. High short circuit current densities of up to 39.9mA/cm2 indicate excellent light trapping and decreased front side shading due to the absence of busbars as well as high quality surface passivation. Both metallization technologies allow for conversion efficiencies of 18.7% for 125 x 125 mm2 sized Cz-Si MWT-PERC solar cells. Furthermore, we show the possibility of via metallization by the use of two-step seed and plate technology. Via resistances similar to those for screen printed via metallization are achieved. The seed and plate technology therefore forms a promising approach for via metallization of next generation MWT-PERC solar cells.

On the way to higher efficiencies, back contact solar cells seem to be a promising alternative to conventional screen-printed solar cells. Especially, the MWT (metal wrap through) solar cell concept with only two additional process steps compared with the conventional cell process is appropriate for a fast transfer to industry. Hence, a pilot-line process based on a new contact design was developed and tested. Several batches of about 1000 mc-Si MWT solar cells were successfully produced at ISE's PV-TEC pilot-line. Cell efficiencies up to 16.2% are achieved with an emitter sheet resistance of 65 Ω/sq. Compared with conventionally processed cells made of the same mc Si-block, an efficiency gain up to 0.5% is observed. The main reason for the high efficiency is a high short circuit current due to the absence of the bus bars on the front. Furthermore, a cell interconnection only on the back is possible and thus less serial resistance losses in the tabs. Therefore, an additional efficiency gain of about 0.2%abs. compared with standard module technology is achieved using the new MWT tabbing technology.

The industrial standard process for producing solar cell front sides includes several drawbacks. First of all the screen-printed front side metallisation with silver paste leads to contacts with a poor aspect ratio and a low conduction quality due to the composition of a printable paste. Additionally, the poor contact resistance requires high surface doping concentrations of the emitter. When using further developed cell concepts like the laser-fired contacted rear side (LFC) featuring dielectric passivation and a local point contact structure, the high-temperature step for establishing the front contact is detrimental too. A solution for this problem could be the use of alternative front side metallisation techniques. Without firing through they all require a selective opening of the front side antireflection coating. The approach studied in this paper is the selective laser ablation of this layer