Al-induced variation to Ag crystal orientation of Ag–Al pastes during metallization

It has been reported that adding Al to Ag metallization paste can reduce the contact resistivity on boron-doped emitters of n-type c-Si solar cells such as Tunnel Oxide Passivated Contact solar cell(TOPCon), because Al can assist forming Ag–Al spikes and dope into the p + emitter. However, Al addition also increases surface recombination and grid line resistivity. Therefore, a comprehensive understanding to the effect of Al on reducing contact resistivity is crucial for optimization of metallization process. In this paper, we investigated the contact characteristics between Ag–Al pastes with p-Si in comparison with those between Ag paste with p-Si. It was revealed that the driving forces for forming electrical contacts between Ag–Al pastes with p-Si is different from those between Ag pastes with p-Si. Moreover, we found that Al will induce the variation of Ag crystal orientation from (111) plane to (200) plane during firing. This induction process is firmly related to the melting amount of Ag during firing, accompanied by the disappearance of Ag3Al. Finally, the effect of Al addition on the contact potential reduction of metal electrodes/p-Si was studied so as to figure out the solution to improving contact properties, which is of great significance for the development of advanced Ag–Al pastes.