Paste-based silver reduction for iTOPCon rear side metallization

• Published in: Solar energy materials and solar cells 2024-03, Vol.266, p.112646, Article 112646
• Main Authors: Ourinson, Daniel, Brand, Andreas, Lorenz, Andreas, Dhamrin, Marwan, Tepner, Sebastian, Linse, Michael, Göttlicher, Nathalie, Haberstroh, René, Tsuji, Kosuke, Huyeng, Jonas D., Clement, Florian
• Format: Article
• Language: English
• Subjects: Aluminum; Copper; Silver reduction; Solar cell; TOPCon
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2023.112646

This work presents two approaches to reduce the silver (Ag) amount on the rear side of M2-sized industrial tunnel oxide passivated contact (iTOPCon) solar cells by (partially) substituting conventional Ag pastes with copper (Cu) and aluminum (Al) pastes. The first approach is Cu-based and works by screen printing an Ag layer with ca. 75% Ag paste reduction compared to a conventional Ag layer (functioning as a contact and Cu barrier layer) and screen printing a full-area Cu layer on top of the Ag layer (functioning as a conduction layer compensating the reduced Ag amount). This Cu-based approach yields similar power conversion efficiency (η) compared to the conventional approach, showing the Cu-based approach is promising for iTOPCon solar cells. The second approach is Al-based and works by laser contact opening of the dielectric layers and screen printing a full-area layer with an Al paste – adapted to properly contact an n+-poly-Si layer –, substituting Ag on the rear side entirely. This Al-based approach exhibits a 0.9%absη gap to the conventional approach, mainly stemming from the Al paste damaging the poly-Si layer, while – on a positive note – neither rear p+ layer formation nor tunnel oxide layer penetration by the Al paste is detected. Even though the abovementioned η gap must be eliminated in the future, it shows the principal functionality and potential of such type of contact for iTOPCon solar cells.