Chinese scientists identify degradation pathways in low-silver heterojunction solar cells

Chinese researchers have confirmed that thermal aging leads to significant degradation in low-silver heterojunction solar cell electrodes, primarily driven by silver-copper interdiffusion and defect formation, affecting long-term device reliability.

The research, conducted by scientists from the East China University of Science and Technology, focused on the microstructural and electrical changes occurring in silver-coated copper electrodes used in heterojunction (HJT) solar cells under accelerated aging conditions. They found that contact resistance and sheet resistance increase with aging time, with interdiffusion between silver and copper layers being the primary cause of electrical degradation.

The team used a silver-coated copper paste composed of core-shell particles, submicron silver powder, and an epoxy resin matrix, applying it onto n-type monocrystalline silicon wafers. The electrodes underwent drying and curing processes before electrical performance was assessed using the transmission line method (TLM). Results indicated that both line resistance and contact resistivity rose with increasing aging duration and temperature, with contact resistivity showing higher sensitivity to thermal stress.

Advanced characterization techniques, including energy-dispersive X-ray spectroscopy (EDS), focused ion beam scanning electron microscopy (FIB-SEM), and X-ray diffraction (XRD), confirmed that the primary degradation mechanism was interdiffusion of silver and copper, leading to defect formation and void evolution. These microstructural changes cause the initially continuous conductive network to fragment, severely impairing electrical pathways and accelerating performance decline.

Implications for Long-Term Solar Module Reliability

This discovery highlights the importance of improving interfacial stability in low-silver electrodes to enhance the durability of heterojunction solar modules. As the industry seeks to reduce silver content for cost savings, understanding these degradation pathways is vital for balancing affordability with long-term performance. The findings provide critical guidance for designing more reliable metallization strategies, potentially influencing manufacturing practices and material selection in commercial HJT modules.

Degradation Challenges in Silver-Coated Copper Electrodes

Heterojunction solar cells are increasingly adopting low-silver electrodes to cut costs, but limited understanding of their aging behavior has hindered widespread adoption. Prior studies indicated that silver-copper interdiffusion could compromise electrical contact quality over time, but detailed mechanisms remained unclear. This research builds on earlier work by providing a comprehensive analysis of microstructural evolution under accelerated thermal conditions, emphasizing the role of interdiffusion and defect formation in electrical failure.

“Our study clarifies the underlying degradation mechanisms and offers guidance for designing cost-effective, reliable metallization strategies for HJT solar modules.”

— an anonymous researcher

Remaining Questions on Degradation Dynamics

It is not yet clear how different material compositions, layer thicknesses, or manufacturing processes influence the degradation pathways observed. Long-term field data and real-world testing are needed to confirm whether these accelerated aging results fully replicate operational conditions.

Next Steps in Improving Electrode Stability

Future research will likely focus on developing interfacial barriers or alternative materials to prevent silver-copper interdiffusion. Additionally, testing under real-world conditions and exploring new metallization designs will be critical for translating laboratory findings into commercial applications.

Key Questions

How does interdiffusion affect the performance of heterojunction solar cells?

Interdiffusion between silver and copper layers causes defect formation and microstructural fragmentation, increasing contact resistance and leading to electrical performance decline over time.

Why is reducing silver content important in solar cell electrodes?

Lowering silver content reduces material costs, making solar modules more affordable, but it can also compromise long-term reliability if degradation mechanisms are not properly managed.

What methods did researchers use to analyze microstructural changes?

The team employed energy-dispersive X-ray spectroscopy (EDS), focused ion beam scanning electron microscopy (FIB-SEM), and X-ray diffraction (XRD) to confirm interdiffusion and defect formation.

Are these findings applicable to commercial solar modules?

The study provides valuable insights, but further testing under actual operational conditions is necessary to confirm applicability to commercial modules.

Source: PV Magazine