Screen printing is widely used in solar cell metallization, but the process can cause degradation that adversely affects device performance. The issue is particularly relevant for copper-plated silicon heterojunction (HJT) solar cells, which offer a promising route to reducing metallization costs and reliance on expensive silver.

The mechanical pressure and thermal treatments involved in screen printing can damage the sensitive passivating contact structures of HJT solar cells, increasing recombination losses and reducing conversion efficiency. Understanding the underlying degradation mechanisms is therefore essential to optimizing metallization processes without compromising cell performance.

Researchers in China have investigated the mechanisms behind screen printing-induced degradation in copper-plated HJT solar cells and developed a method to mitigate the effects, potentially improving their suitability for large-scale manufacturing.

“The screen-printing process for photoresist application in HJT cells differs fundamentally from conventional screen printing of silver paste,” corresponding author Lang Zhou told pv magazine. “In silver paste printing, the screen openings account for only 2–5% of the total area, while the remaining surface is covered by an emulsion layer that prevents direct contact between the mesh and the wafer. In contrast, full-area photoresist coating typically uses a screen without emulsion coverage to ensure uniform resist deposition across the entire wafer surface. As a result, the mesh comes into direct and extensive contact with the wafer during each printing cycle.”

The researchers said previous investigations had revealed a gradual decline in conversion efficiency from 26.2% to 25.7% over 15,000 consecutive printing cycles in commercial solar cell production. The losses were mainly attributed to reductions in open-circuit voltage and fill factor, while short-circuit current density and electrical resistance remained largely unchanged. Further measurements showed that minority carrier lifetime degradation increased from 0.61% with a new screen to 11.0% after 15,000 printing cycles.

The scientists used three-dimensional confocal microscopy to identify progressive wear of the screen mesh knuckles as the main cause of the degradation. As the knuckles wore down, their contact area with the wafer increased, placing greater mechanical stress on the underlying passivation layers. Although scanning electron microscopy revealed no visible surface scratches, photoluminescence measurements confirmed increased recombination losses, suggesting damage to the sensitive amorphous silicon/crystalline silicon interface.

To address the issue, the researchers developed an emulsion buffer layer to prevent direct contact between the screen mesh and the wafer surface. They evaluated six different patterns, with emulsion coverage ratios ranging from 2.9% to 16.6%.

The results showed a trade-off between mechanical protection and photoresist coating uniformity, as higher emulsion coverage reduced damage but impaired ink distribution. An emulsion coverage ratio of 4.7% provided the best balance, limiting minority carrier lifetime degradation to 0.41% after 10,000 printing cycles while maintaining relatively good coating uniformity.

The researchers attributed the improvement to the emulsion layer preventing direct contact between the screen mesh and the wafer surface, thereby reducing cumulative mechanical damage to the sensitive passivation layers.

“The findings demonstrate that a relatively simple modification to screen design can substantially mitigate printing-induced degradation, offering a practical approach to improving the manufacturing reliability of copper-plated HJT solar cells,” Zhou said.

The researchers presented their findings in “Screen-printing photoresist induced efficiency degradation and mitigation in Cu-plated SHJ solar cells,” published in Solar Energy.

The development comes amid growing interest in copper metallization as an alternative to silver-based contacts in HJT solar cells. In April 2026, researchers at China’s Nankai University developed a silver-free HJT solar cell with 25.2% efficiency using plasma-induced interface engineering and copper electroplating. The approach addressed adhesion, contact resistance and stability challenges at the ITO interface, highlighting the potential of copper-based metallization for high-efficiency devices. pv magazine Global

In a separate development, scientists at Germany’s Forschungszentrum Jülich achieved 23.08% efficiency in a fully copper-metallized HJT solar cell. The silver-free device exhibited a relatively small efficiency penalty compared with its silver-metallized counterpart, while cells combining silver-copper paste on the front side with silver contacts on the rear reached 23.95% efficiency. The findings underline the potential of copper to reduce silver consumption, although further improvements in processing and electrical performance remain necessary. pv magazine Global