NREL Research Flags Higher UV Degradation In n-Type Modules

A new study by the US National Renewable Energy Laboratory (NREL) warns of accelerated ultraviolet or UV-induced degradation in n-type silicon PV modules. Field tests at a 3 MW commercial site by the team show higher-than-expected power losses, raising questions about current IEC testing standards and module durability. 

Researchers found that commercial passivated emitter rear totally diffused (n-PERT) panels at the site experienced power losses of around 2% per year – far above expectations – linked to UV exposure exceeding the limits of current IEC tests.  

They studied 4 fielded modules after 6 years of deployment and 2 unfielded spares under a suite of electrical and physical tests. Tests revealed 2 main causes of degradation: increased cell surface recombination losses due to UV exposure, and higher series resistance in cells with certain metallization paste, likely caused by encapsulant breakdown. This effect was further worsened by combined UV and damp heat exposure compared to damp heat alone. 

The research highlights the vulnerability of advanced cell types – such as n-PERT, tunnel oxide passivated contact (TOPCon), and silicon heterojunction (SHJ) – to UV-induced degradation (UVID), a risk previously seen mainly in lab settings. 

However, NREL is quick to add that the study does not mean that n-PERT cells are naturally more prone to UV-induced degradation than other types. Rather, many factors, still not fully understood, affect how much a cell or module is affected by UVID. 

“Evidence thus far does not concretely conclude that a certain cell type is more immune than another to UVID, but instead implies that more specific design decisions (e.g., passivation layer properties, screen printed silver paste composition, etc.) are the key factors,” explains NREL.  

The findings emphasize the need for more rigorous UVID qualification standards as solar cell and module designs advance, it adds. The team also highlights the importance of a deeper understanding of UVID degradation mechanisms and the combined effects of stress factors. 

“This study is unique in that it reproduces field observed utility scale UVID with an accelerated test and supports the need for standards development for longer UV exposure combined with other stress factors to catch materials interplay within a module package,” reads the study titled UV + Damp Heat Induced Power Losses in Fielded Utility N-Type Si PV Modules, published in the journal Progress in Photovoltaics.  

NREL calls for a revision of IEC testing protocols to include longer UV exposure and combined stress factors to better predict field performance of emerging PV technologies. 

TaiyangNews delves into the impact of UVID and the solutions in the market in the Cell & Module Technology Trends 2025 Report, which is available for free download here.