Reducing TOPCon Solar Cell Degradation via Copper Plating: Key Findings from UNSW Research

Researchers at the University of New South Wales (UNSW) have introduced an innovative approach to combat contaminant-induced degradation in tunnel oxide passivated contact (TOPCon) solar cells. By employing a 1 µm copper (Cu) plating layer on the front silver grid, they created a robust protective barrier that significantly enhances the durability and reliability of these cells under challenging conditions.

The Challenge: Corrosion in TOPCon Solar Cells

TOPCon solar cells are sensitive to corrosion, particularly in their front metallization. This degradation is exacerbated by damp heat (DH) and exposure to contaminants, making long-term performance stability a concern. UNSW’s breakthrough addresses this issue while also reducing reliance on silver—a costly material—thereby contributing to a lower levelized cost of electricity (LCOE).

The Copper Plating Solution

The team applied a 1 µm Cu plating layer to the front silver grid using a bias-assisted light-induced plating (LIP) technique. This layer acts as a protective barrier, minimizing the penetration of contaminants like sodium chloride (NaCl) and reducing oxidation.

• Plating Process: Utilized a Conifer plating tool, immersing the front side in a CuSO4 plating solution with illumination and constant current for enhanced deposition.
• Capping Materials: Silver (Ag) or tin (Sn) layers capped the Cu plating to improve soldering and further shield the contacts.

Experimental Highlights

1. Materials Used:
   • Bifacial nine-busbar (9BB) 158 mm TOPCon cells.
   • Screen-printed silver grids on both the rear and front sides.
   • Carrier-selective passivating contacts (CSPCs) based on polysilicon and silicon monoxide (poly-SiOx).
2. Initial Efficiency Improvement:
   Plated cells demonstrated a 0.39% relative efficiency increase, attributed to reduced grid resistance and an enhanced fill factor.
3. Durability Testing:
   • Damp Heat (DH) Testing: After 6 hours, unprotected cells experienced an 80% relative efficiency degradation, while Cu-plated cells retained 88.5% of their performance.
   • Contact Resistivity: A 10-fold increase in resistivity was observed in bare cells after 0.5 hours, compared to stable resistivity in Cu-plated cells over extended periods.
4. Advanced Analysis:
   • SEM and EDS Imaging: Revealed that Cu plating filled voids in the silver contact, creating a denser and more stable interface.
   • Parasitic Recombination: Reduced due to the improved contact quality.

TOPCon solar cells. It highlights the following:

Initial Efficiency Improvement: Copper-plated cells show a notable improvement in initial efficiency.
Key Takeaways

Efficiency Retention: Copper-plated cells retain significantly higher efficiency under damp heat (DH) testing.

Contact Resistivity: A much lower increase in contact resistivity for copper-plated cells compared to unprotected ones.

• The copper plating layer effectively mitigates NaCl-induced degradation, significantly improving the stability and efficiency of TOPCon cells under adverse conditions.
• This method also accelerates the research and development cycle by focusing on cell-level testing rather than module-level testing, enabling faster and more detailed failure analyses.

Future Implications

This breakthrough aligns with global efforts to make solar energy more sustainable and cost-effective. By reducing silver usage and enhancing cell stability, this research not only advances the field of photovoltaics but also underscores the potential for innovative manufacturing processes to lower costs and increase efficiency.

For further details, the full study, “Alleviating contaminant-induced degradation of TOPCon solar cells with copper plating,” is published in Solar Energy Materials and Solar Cells.