Investigation of contact formation mechanism and application of copper-based front contact paste for crystalline silicon solar cells

To ensure of the fabrication crystalline Si (c-Si) solar cells at affordable costs, research has been actively conducted on the use of Cu-based pastes as alternatives to their Ag counterparts, which are currently being used as front electrode materials. However, only limited studies have reported on the use of Cu pastes in processes involving high-temperature firing, primarily owing to the issues caused by Cu oxidization and the resulting products acting as deep-level impurities. In this study, the applicability and limitations of Cu-based pastes containing Cu–Ag core–shell particles as the front electrodes of Si solar cells were investigated. A double printing structure with a seed layer of Ag paste was adopted to prevent direct contact between Si and Cu. By analyzing the morphological and electrical properties, the O-mediated electrode-formation mechanism of the Cu-based paste during high-temperature firing under ambient air conditions was evaluated and compared with that of the conventional Ag paste. The electrical parameters of c-Si solar cells were found to always deteriorate when the Cu paste was used, regardless of the electrode structure, owing to the reduction of Cu involved in Ag crystallite formation. Moreover, only contact formation under inert ambient conditions presented electrical parameters similar to those for commercial Ag paste when using high-temperature firing. Finally, the limitations of applying a front electrode paste primarily containing Cu were assessed.