Industrially feasible mc-Si metal wrap through (MWT) solar cells with high emitter sheet resistances exceeding 16% efficiency

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 ohm/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.