The Fraunhofer Institute for Solar Energy Systems ISE (Fraunhofer ISE) announced that its latest research has found that ultraviolet (UV) tests rate degradation of tunnel oxide passivated contact (TOPCon) silicon solar modules significantly higher than performance reduction in real-life conditions.

The research shows that common UV tests can significantly exaggerate the degradation effect.

The institute conducted tests to check the validity of reports of UV-induced degradation in TOPCon-based photovoltaic modules, which is currently a concern for the solar industry.

Fraunhofer ISE said the solar modules must be stabilized after testing to ensure accurate results. Such steps will help distinguish UV-sensitive modules from less sensitive types to evaluate them comparably.

Daniel Philipp, Head of the Department for Module Characterization and Reliability, Fraunhofer ISE, said, “Unfortunately, many module types of the current generation of commercial TOPCon PV modules react sensitively to UV irradiation. This is confirmed by modules returning from the field and comparisons between modules aged in the laboratory and the field. However, the degradation rate does not appear as drastic as previously assumed.”

He recommended that users test modules based on the latest findings. Further analysis of the phenomenon is necessary to predict the long-term effects of UV-induced degradation on module yield more accurately.

The research indicates that UV irradiation during the tests destabilizes the modules enough to lose significant efficiency during dark storage after exposure. However, subsequent irradiation with sunlight leads to a considerable recovery.

Some modules barely showed any degradation after UV testing at 60 kW hours/sq m, approximately equal to the UV exposure in one year in Germany and subsequent stabilization under sunlight. Other modules still showed significant power losses of up to 5% even after stabilization.

The research concludes that the degradation is significantly less drastic than the standard UV tests suggest.

Field tests at the Fraunhofer ISE Outdoor Performance Lab with TOPCon modules and analyses of field returns at the institute’s CalLab PV Modules indicated that the stabilization process provides degradation measurements significantly closer to the values measured in practice.

In 2024, Fraunhofer ISE produced a TOPCon solar cell in the large-area M10 silicon wafer format, achieving an efficiency of 24%.

The institute also collaborated with solar cell manufacturing company Oxford PV and reported a 25% conversion efficiency for its perovskite solar modules.