New Research Shows UV Tests Overstate Degradation in TOPCon PV Modules

The Fraunhofer Institute for Solar Energy Systems ISE has presented new findings indicating that current ultraviolet (UV) testing protocols for TOPCon photovoltaic (PV) modules may significantly overestimate real-world degradation. These insights, revealed this week at the SiliconPV conference, stem from extensive comparative studies involving both indoor simulations and field-based outdoor performance testing.

Reports of UV-induced degradation in n-type Tunnel Oxide Passivated Contact (TOPCon) modules have sparked concern among solar project developers and financiers. However, Fraunhofer ISE researchers found that standard UV testing—used to simulate long-term exposure—can produce misleading results unless the tested modules are stabilized after exposure but before performance evaluation.

According to Daniel Philipp, head of the Department for Module Characterization and Reliability at Fraunhofer ISE, “Many commercial TOPCon PV modules show a strong sensitivity to UV irradiation, but our investigations suggest the degradation is not as severe as once thought. Proper stabilization after UV exposure is critical to obtain meaningful and comparable results.”

The research revealed that while intense artificial UV radiation destabilizes module performance—especially during subsequent dark storage—exposure to natural sunlight triggers a notable recovery effect. This recovery aligns more closely with what is observed in real-world module performance, as validated by Fraunhofer ISE’s Outdoor Performance Lab and CalLab PV Modules.

Tests showed that while some modules experienced negligible losses after exposure equivalent to one year of German sunlight (60 kWh/m²), others still demonstrated up to 5% power loss even after recovery. Despite these variations, degradation rates were notably lower than those projected by traditional accelerated UV aging tests.

The Fraunhofer ISE team emphasizes the need for the industry to refine current testing standards to better reflect the actual behavior of TOPCon modules in the field. As the solar sector continues to adopt new technologies, such nuanced testing will be essential for accurate performance forecasting and risk