A recent study has found that tunnel oxide passivated contact (TOPCon) solar modules, despite their increasing popularity, show three distinct failure modes that are not present in traditional passivated emitter and rear cell (PERC) modules. This research was conducted by a team at the University of New South Wales, Australia, and published in the journal Solar Energy Materials & Solar Cells. The study compared the reliability of TOPCon and PERC solar modules under damp heat testing conditions, which simulate prolonged exposure to high humidity and temperature, commonly experienced in the field.

The researchers used different materials in the construction of both PERC and TOPCon modules, such as polyolefin elastomer (POE) and ethyl-vinyl acetate (EVA), along with various polymer backsheets. While PERC modules remained stable under testing, with only a minimal power loss of about 1 to 2 percent, the TOPCon modules showed significantly more degradation. The TOPCon modules experienced a decline in power output ranging from 4 to as much as 65 percent after 1000 hours of damp heat exposure. This performance drop occurred even when POE, an encapsulant known for its low water vapor transmission rate, was used.

Three types of failures were identified in the TOPCon modules. The first failure mode is point-localized, appearing as dark spots in electroluminescence imaging. The second failure occurs at or around the connection points between the ribbon wires and busbars, while the third type involves widespread failure across the entire module area. These issues are thought to result from electrochemical reactions caused by the presence of moisture, cell metallization, ribbon wires, soldering flux, and other contaminants. Contaminants such as sodium and chlorine, often introduced during the manufacturing process or from handling, are suspected to play a major role in accelerating the degradation of TOPCon cells.

The findings show that the TOPCon technology, although considered to be the future of solar cell design, is highly sensitive to humidity and contaminants. The study suggests that the type of POE used for encapsulation can have a large impact on the reliability of TOPCon modules. Specifically, certain POE types were found to negatively affect TOPCon performance, leading to serious power losses.

Further research is needed to better understand the effects of different encapsulation materials and how they interact with the components of TOPCon cells. The authors stress the importance of strict quality control during manufacturing and handling processes to prevent contamination. They also highlight the need for extensive testing of encapsulants and module designs before large-scale deployment of TOPCon technology.

In contrast, PERC modules demonstrated much better stability and lower susceptibility to damp heat conditions. Their power output declined minimally, regardless of the materials used in the module construction. This suggests that PERC technology, although older, may still offer advantages in terms of durability in certain environmental conditions.

The researchers conclude that while TOPCon technology holds promise for higher efficiency in solar power generation, more work is needed to ensure its long-term reliability. Developers and manufacturers are encouraged to exercise caution when selecting materials and to prioritize improving the design and protection of TOPCon solar modules. Without addressing these failure modes, the benefits of TOPCon may be undermined by its potential for early degradation in real-world conditions.