Pilot-line processing of screen-printed Cz-Si MWT solar cells exceeding 17% efficiency

On the way to higher efficiencies, back contact solar cells are a promising alternative to conventional screen-printed solar cells. Especially, the MWT (metal wrap through) solar cell concept with only a few additional process steps compared to the conventional cell process is appropriate for a fast transfer to industry. The focus of this work is to change the conventional cell process as little as possible and to reduce the time-to-market. Hence, a MWT process with only three screen-printing steps and without efficiency losses is realized by combining the via and the solder pad metallization steps. In comparison with the conventional cell process the number of screen-printing steps is not increased and thus the costs for metallization rise only marginally due to somewhat increased paste consumption. In comparison to a previous approach the additional costs of the MWT process can be significantly reduced. A successful MWT process transfer from Fraunhofer ISE's Photovoltaic Technology Evaluation Center (PV-TEC) pilot-line to the pilot-line of ersol Solar Energy AG is shown. Mean cell efficiencies above 17% and maximum efficiencies of 17.3% are achieved for Cz-Si MWT solar cells within pilot-line production. Moreover, an efficiency gain compared to simultaneously processed, conventionally screen-printed solar cells of 0.3% absolute has already been reached. Furthermore, the influence of p-contact solder pads on the cell efficiency is analyzed in detail by current voltage (IV-) and photoluminescence (PL-) measurements within this work.