Contact Corrosion Vulnerability in TOPCon Solar Cells

Researchers have identified new degradation mechanisms in TOPCon solar cells, particularly related to contact corrosion, which are significantly impacted by a mix of ions and aluminum-silver paste. The study highlights how these factors lead to an increase in series resistance, a key degradation pathway for these cells.

Scientists from a prominent university conducted accelerated tests at high temperatures and humidity levels to observe how different sodium-containing salts (sodium bicarbonate and sodium chloride) affect the performance of TOPCon cells. Their findings suggest that these salts trigger varying degrees of efficiency reduction, with sodium chloride causing up to a 92% loss in power conversion efficiency. The research emphasizes that the degradation primarily stems from electrochemical reactions within the silver-aluminum paste.

Photoluminescence images of TOPCon cells taken at various stages during dump heat test

Image: UNSW, Solar Energy Materials and Solar Cells, Common License CC BY 4.0

The tests were conducted on TOPCon cells featuring both front and rear-side architectures. On the front, a boron-diffused emitter was coated with aluminum oxide, silicon nitride, and a silicon oxynitride stack for surface passivation and anti-reflective purposes. On the rear, a tunneling oxide layer paired with a phosphorus-doped silicon layer completed the design. The study revealed differences in how the salts affected the front and rear of the cells, with sodium bicarbonate increasing recombination at the rear and sodium chloride mainly impacting the front.

The researchers suggest that long-term exposure to ion-level contaminants poses a risk to the stability of TOPCon cells, particularly in their metallization layers. They recommend further studies on different ion combinations to better understand and mitigate these degradation mechanisms.

Schematic of the TOPCon cell used in the research

Image: UNSW, Solar Energy Materials and Solar Cells, Common License CC BY 4.0

Their findings provide essential insights for enhancing the reliability and performance of TOPCon technology, which is becoming increasingly prominent in the solar industry. A complementary study also introduced a laser-assisted firing process that could improve contact quality and corrosion resistance while lowering manufacturing costs.