Plated Ni/Cu/Ag for TOPCon Solar Cell Metallization
Passivating Contacts is the next step in reducing recombination effects and improving c-Si solar cell efficiency. This work demonstrates the application of laser structuring and Ni/Cu/Ag electroplating as a new method to metallize solar cells with Tunnel Oxide Passivated Contact (TOPCon)  layers. Critical contact properties such as contact adhesion, contact resistance, contact recombination and optics of the metallization concept are characterized and evaluated for the application as bifacial metallization for TOPCon solar cells. Front and rear side contact TOPCon solar cells with plated Ni/Cu/Ag metallization on the TOPCon layer showed the feasibility of the plating process allowing efficiencies up to 22.7 % with FF = 82.4 % and Voc = 690 mV. The application in a full area rear side metallization design with planar TOPCon surface revealed limitations in contact adhesion (planar surface) and optics (Jsc, poor reflection of Ni). Both limitations can be prevailed by applying a bifacial contact design and implementing textured TOPCon surfaces. It could be demonstrated that the requirements on contact resistance and contact recombination for a locally plated metal contact on TOPCon can be fulfilled by laser structuring and plated Ni/Cu/Ag with average contact resistivity of c = (0.2 ± 0.1) mO∙cm² and no noticeable iVoc-loss after laser ablation.