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Researchers at the University of New South Wales say they have identified three types of failures in TOPCon panels that are absent in PERC products. They explain that these failures can occur when modules are exposed to high humidity and contaminants before encapsulation.
Scientists at the University of New South Wales (UNSW) in Australia say they have identified three new types of failures in TOPCon solar modules that have never been detected in PERC panels.
“We were quite surprised by the results,” the lead author of the research, Bram Hoex, told pv magazine . “We expected that polyolefin elastomer (POE) would generally perform well, but we found that some POEs performed very poorly. “This is probably due to the different additives used in POE, which react with the soldering flux and metallization, causing contact corrosion.”
The scientists explained that their work initially aimed to evaluate the impact of bills of materials (BOM) on the reliability of PERC and TOPCon solar cells available on the market. They specified that all modules were encapsulated in a pilot line within an unspecified industrial facility.
“These processes included soldering to connect the ribbon and lug wires to the bus bars and laminating to join the modules that make up the bill of materials,” they explained, noting that all panels underwent damp heat testing ( DH) at 85 ºC and 85% relative humidity for a maximum of 1,000 h. They said all BOM components such as glass, polymer backsheet, ethyl vinyl acetate (EVA) and POE were procured from various manufacturers around the world and were considered for high volume manufacturing. The names of the suppliers were not revealed for “confidentiality reasons.”
The team performed current-voltage (IV) measurements with an Eternalsun Spire module flash tester and captured open-circuit photoluminescence (PLLS) and line-scan electroluminescence (ELLS) images using a BTi-M1 luminescence line-scan system. before and after the DH test. "ELLS image ratios were obtained by dividing the ELLS images captured before and after 1,000 h of DH testing using Lumitools, an advanced image processing software," he stressed.
The series of tests demonstrated that the methods used to encapsulate high-quality (POE) and low-quality (EVA) panels had a "negligible" impact on the performance and reliability of the PERC cells, with the observed alterations defined as "of minimal nature.
On the contrary, the TOPCon cells tested showed a greater loss of peak power compared to their PERC counterparts, with peak power values ??decreasing from around 30% to 25 values ??for modules encapsulated with different types of POE and from approximately 29% to 26% for EVA encapsulated panels. These losses were mainly attributed to an increase in series resistance.
"Our findings indicate that PERC modules demonstrate stability, with only a 1-2% decrease in peak power after 1000 h of DH testing, regardless of the bill of materials used," the research group stated. "In contrast, TOPCon modules experience significant degradation, with a relative decrease in maximum power of 4 to 65% after the same duration of DH testing."
Through the tests, the scientists identified, in particular, three types of failures: A failure located at one point; a failure mode that occurs at the point of interconnection between the flat cables and the bus bars of the cells; and a complete failure in the entire cell and module area.
They attributed the cause of the first failure to the electrochemical reaction between humidity, cell metallization, and contaminants likely present in the cells before encapsulation. As for the second type, they said it was observed in modules with TOPCon cells encapsulated with EVA or POE, starting at the interconnection point and then spreading to the surrounding area of ??the cell after a prolonged DH test.
Regarding the Type 3 failure type, it was observed to occur in modules with TOPCon cells encapsulated with POE, probably due to an electrochemical reaction between the metallization of the cell, humidity, solder flux and the released critical elements.
According to the academics, these results demonstrate the vulnerability of TOPCon solar cells when exposed to high humidity and contaminants before encapsulation. “Great care must be taken when handling and selecting encapsulants for TOPCon modules,” they warned.
Their conclusions are presented in the study " Buyer aware: Three new failure modes in TOPCon modules absent from PERC technology ", recently published in Solar Energy Materials and Solar Cells.
The same research group last year identified four failure modes caused by wet heat in heterojunction solar panels with a glass backsheet configuration. These failures could cause power losses of between 5% and 50%. |
