What does HJT paste demand?The cell maker uses narrower screen openings and thinner fingers to reduce silver consumption, along with faster printing speeds and curing, to enhance production efficiency. Despite the cost reduction, the need to maintain cell efficiency and performance requires the HJT cell's bulk resistance to be lower than 5 μΩ·cm, regardless of silver content, and to be equivalent to that of pure silver paste, noted Chen. Additionally, busbar pastes must meet strict reliability criteria, including a tensile strength greater than 1 N/mm, as well as excellent chemical and physical stability under UV exposure, heat, and humidity. They must also withstand high welding temperatures between 200°C and 300°C, as well as lamination temperatures.Evolving trendsAccording to Fusion’s HJT busbar paste cost reduction roadmap, the number of busbars increased from 9BB with a 50 µm screen opening in 2022 to up to 20BB with a 30 µm screen opening by 2023, followed by a further reduction in the screen opening to 27 µm in Q1 2024. Recently, Fusion developed a silver-coated copper busbar paste with 55% Ag content, which is also compatible with 0BB metallization and is already in mass production.However, the company’s HJT cost reduction roadmap for finger paste highlights a consistent trend in the development of silver-coated copper paste, compatible with both the front and rear sides of SMBB and 0BB busbar designs. Silver content was reduced from 50% to 30% by Q3 2024, with a further reduction to up to 20% reached by the end of 2024, with compatibility limited to the rear side. Chen further stated that, according to the company's HJT cost reduction roadmap, starting with a 22 µm screen opening and a silver laydown of 21 mg/W using pure Ag paste on an SMBB design, the laydown is expected to reduce to as low as 6 mg/W with a 10 µm screen opening using steel plate + 0BB metallization technology and 30% silver-coated copper paste by 2025.
