Heraeus Photovoltaics boosting evolution of TOPCon metallization

By Heraeus Photovoltaics

The quest to find the ideal balance between efficiency and cost optimization is never ending in the photovoltaics industry. N-type cells, well known for their high efficiency, have started to come to the fore, with the industry placing a major bet on the technology. According to the Institute for Solar Energy Research in Hamelin (ISFH), the maximum theoretically possible efficiency for PERC, HJT and TOPCon cells is 24.5%, 27.5% and 28.7% respectively.

Among N-type technologies, TOPCon cells are developing extremely rapidly. However, their  increased efficiency in mass production would not be possible without the use of front and rear side metallization.

At the 2022 PV CellTech conference in Berlin, Andreas Henning, Head of Heraeus Photovoltaics (HPT) R&D in Germany, presented the company’s latest developments in TOPCon technology. In his address to the attendees, Henning provided a thorough understanding of front-side/back-side silver pastes.

How to make effective contact with the front-side boron emitter while reducing metal recombination has become a major topic in the industry, with HPT experts having their own unique insights into this challenge. Through joint research with external universities and via in-house experiments, Heraeus has developed SOL 9400, a newly formulated system. With optimized cell processing, SOL9400 offers outstanding electrical contact, enabling higher Voc and FF to provide significantly improved efficiency. With regard to compatibility with fine line printing, the new formulation, combined with ultra-fine-line knotless screen printing, allows for significant improvements in line pattern.

Contact and Line performance for front side Ag/Al paste from Heraeus Internal Data

The contact mechanism for silver paste on the TOPCon P-doped region is similar to that for front side PERC cell pastes. However, the presence of poly-Si and tunnel oxide layers involves precise adaption of the silver paste. To solve this challenge, HPT has developed SOL 7400. Building on the outstanding properties of its predecessors, this paste series offers a better match with different poly-Si processes and thicknesses and compatibility with various polishing processes. It has demonstrated excellent contact performance on different structures, while also addressing wrap-around in the manufacturing process.

2022 will be a milestone year for the dynamic development of N-type cells. Staying on top of industry trends, HPT is well positioned to help drive the progress of the PV industry with its latest TOPCon solutions.

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