The ISE (Fraunhofer Institute for Energy Systems) in carried out a study on TOPCon cells and detected reliability issues such as degradation caused by exposure to light, heat, humidity and UV radiation.
In total, 20 types of TOPCon modules manufactured by various companies were analyzed. The study identified some failure modes that do not pose serious risks, such as light- and temperature-induced degradation.
However, the study identified that during accelerated aging tests of PV modules, moisture ingress (DH, Damp Heat) and exposure to UV radiation can cause more critical damage.
According to the Fraunhofer Institute, this is because the currents in the metallization pastes are sensitive to humidity. According to the analysis, this problem could be solved in the next generations of modules.
During UV radiation testing, TOPCon modules showed a degradation pattern where performance dropped significantly but then partially recovered.
“During UV exposure, a new degradation pattern was observed during indoor testing, showing severe power losses (up to -12% after 120 kWh/m2), followed by recovery after humidity freeze (HF) testing, which may influence outdoor performance and certification test results (IEC 61730-2, Sequence B),” explained study authors Paulo Gebhardt, Ulli Kräling, ster Fokuhl, Ingrid Hadrich and Daniel Filipp.
Degradation depended on how the module was being operated (whether it was short-circuited or open-circuited), while recovery was influenced by factors such as temperature, electrical current and, possibly, light. The researchers are conducting further tests to better understand the impact of light on this process.
Despite these issues, TOPCon modules have shown superior performance in of efficiency, ability to generate power from both sides (bifaciality) and temperature coefficients when compared to older PERC cell technology.
The study recommends that companies conduct additional testing to ensure quality before purchasing large quantities of TOPCon modules. They also believe that over time, the reliability of TOPCon modules will improve as more testing is done.
Relative degradation to baseline during the combined UV/HF test sequence: P MPP (left) and V OC (right). Types 14 and 19 were subjected to only parts of the test sequence.Graphic: Fraunhofer ISE/Disclosure.
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