Enhancing Adhesion and Reducing Ohmic Contact through Nickel-Silicon Alloy Seed Layer in Electroplating Ni/Cu/Ag

Due to the lower cost compared to screen-printed silver contacts, the Ni/Cu/Ag contacts formed by plating have been continuously studied as a potential metallization technology for solar cells. To address the adhesion issue of backside grid lines in electroplated n-Tunnel Oxide Passivating Contacts (n-TOPCon) solar cells and reduce ohmic contact, we propose a novel approach of adding a Ni/Si alloy seed layer between the Ni and Si layers. The metal nickel layer is deposited on the backside of the solar cells using electron beam evaporation, and excess nickel is removed by H₂SO₄:H₂O₂ etchant under annealing conditions of 300-425 °C to form a seed layer. The adhesion strength increased by more than 0.5 N mm^-1 and the contact resistance dropped by 0.5 mΩ cm² in comparison to the traditional direct plating Ni/Cu/Ag method. This is because the resulting Ni/Si alloy has outstanding electrical conductivity, and the produced Ni/Si alloy has higher adhesion over direct contact between the nickel-silicon interface, as well as enhanced surface roughness. The results showed that at an annealing temperature of 375 °C, the main compound formed was NiSi, with a contact resistance of 1 mΩ cm^-2 and a maximum gate line adhesion of 2.7 N mm^-1. This method proposes a new technical solution for cost reduction and efficiency improvement of n-TOPCon solar cells.