Reduce or replace silver: Future HJT optimization focuses on minimizing silver usage through fine-line printing and lower silver content in pastes – or replacing it entirely. (Source: Fusion Materials) 
Technology

Refining Paste Composition And Metallization For HJT Cells

Paste formulations, fine-line printing, and copper alternatives for reducing silver use and boosting process efficiency in HJT production

Shravan Chunduri

  • Reliable high-speed printing through ultra-narrow screen openings in HJT requires a well-optimized paste composition

  • Paste formulation plays a critical role in preventing printing defects such as line spreading, finger breakage, and screen clogging

  • In the short term, the industry aims to standardize silver consumption below 10 mg/W by combining ZBB layouts with 30% silver-coated copper pastes

As screen openings become increasingly narrower, maintaining high-speed printing in HJT cell production is becoming more challenging. Therefore, a paste composition that supports both ultra-narrow screen openings and fast printing speeds is crucial, and this largely depends on the optimization of the paste’s organic composition. A typical HJT silver paste consists of 3 key components. The first is the conductive base, typically made of pure silver or silver-coated copper powder. The second component is the resin, which is usually an epoxy type. The third includes organic solvents and additives. Poor compatibility among these ingredients can lead to particle aggregation, preventing uniform dispersion within the system. This, in turn, can lead to printing defects such as line spreading, broken fingers, or – in more severe cases – screen clogging due to high levels of aggregation. The paste formulation must strike the right balance to ensure smooth and reliable printing. This means achieving synergy between optimized particle size and morphology, a well-matched resin, and effective dispersants – all tailored to perform according to the demands of narrow openings and fast production speeds.

Looking ahead, optimization of metallization is the key for HJT. The roadmap for how to bring HJT’s silver consumption on par with TOPCon is clear – ZBB in combination with 30% silver content of silver-coated copper paste. In the short term, the industry’s goal is to make such, or even an ultra-low 10%, silver consumption a standard in mass production. Advanced metallization techniques, such as laser transfer printing, can also help realize ultra-thin fingers below 20 μm with aspect ratios above 50%. Additionally, they can help reduce silver consumption and improve efficiency by at least 0.1%, according to Fusion. But the eventual and ultimate goal is to replace silver altogether, with several paste makers already working in this direction. At the TaiyangNews High Efficiency Solar Technologies Conference, Fusion also showed a glimpse of the copper paste solutions it is working on (see Fusion PV Paste Solutions Come With Lower Silver Concentration).

This text is an excerpt from the TaiyangNews Cell & Module Technology Trends 2025 report, which can be downloaded for free here.