Fusion New Materials has developed a silver-coated copper busbar paste with 55% Ag content, which is also compatible with 0BB metallization
It expects HJT laydown to reduce to as low as 6 mg/W by 2025
Fusion has customized its paste composition through 3 distinct routes to address the challenges of silver optimization without compromising efficiency
The price delta between HJT and TOPCon cells, with HJT still being the more expensive option, has driven increasing demand from HJT cell manufacturers for metallization pastes with lower silver (Ag) content – a key cost contributor – without compromising cell efficiency. Recently, several PV cell metallization paste manufacturers have been working to develop low-silver-content HJT pastes suitable for mass production to meet the challenging criteria set by cell makers.
At the recent TaiyangNews Annual Flagship Conference, High-Efficiency Solar Technologies 2024, Jasmine Chen, Director of the Organic Research Institute, Fusion New Materials, discussed the latest low silver content paste offerings and their engineering aligning with the company’s HJT cost reduction roadmap (see Fusion New Material presentation here). She also briefly highlighted the new product layout.
Starting in 2015 with an R&D center in Shanghai, the company achieved a breakthrough in the development of both PERC and HJT silver pastes in 2017. This was followed by the initiation of the IPO process and the acquisition of Samsung Solar’s silver paste by 2020, which was completed in 2022, marking the beginning of TOPCon and HJT paste mass production and supply. However, by 2023, the company crossed an annual shipments more than 2,000 tons.
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.
According 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.
To address the challenges of silver optimization in HJT metallization paste without compromising efficiency, Fusion has customized its paste composition through three distinct routes: conductive phase, adhesive phase, and solvent phase. The company emphasized that by optimizing the organic composition of the paste – such as viscosity control, particle dispersion, and shaping – it has achieved excellent grid line shapes without deflection and a high aspect ratio, ultimately improving the paste’s system compatibility. Additionally, it has enhanced interface contact – both interparticle and particle-substrate contact – by optimizing organic resins and powders.
Fusion concluded its presentation with an overview of its paste product portfolio for both finger and busbar pastes compatible with SMBB and 0BB cell designs. The company also provided a brief look at new paste developments, including non-screen printing series, steel plate printing series, and laser-transfer printing series.