The TOPCon cell using the proposed copper paste
Healy further mentioned that the paste is designed to etch through the silicon nitride layer during the firing process at peak temperatures of around 600°C. The patented formulation prevents the copper from oxidizing during air-firing while ensuring that the copper does not directly contact the silicon. The LECO process finalizes the electrical contact.
BFT has conducted accelerated testing and confirmed that the copper diffusion into the silicon does not occur, which is critical for maintaining the efficiency of the solar cells. The company also reported that a TOPCon cell based on an M10 wafer and metallized with the new copper paste achieved a power conversion efficiency of over 24%.
Healy added: "The combination of the paste formulation and LECO process has also achieved an open-circuit voltage that is the same as a sister cell that featured silver as the back-side contact." This success demonstrates the feasibility of replacing silver paste with a screen-printed, air-fired copper contact on a high-efficiency full-sized TOPCon solar cell.
The company believes the performance of the cell can be further enhanced with careful optimization of paste formulation and firing conditions. BFT is currently collaborating with manufacturing partners to refine the product and optimize processing parameters. The company is also working on scaling up the paste for industrial needs and expects pilot-scale deployment by 2026.
Based in Kentucky, Bert Thin Films, Inc. specializes in copper-based solar cell production across various device architectures. The company was awarded $1 million in funding by the U.S. Department of Energy in 2021.
