Considering N type modules? If so, why its important to go for double glass?

Research conducted by Dutch scientists has shed light on the differing degradation risks between n-type and p-type bifacial TOPCon cells. The study, led by Paul Sommeling from the Netherlands Organisation for Applied Scientific Research (TNO), examined the impact of moisture degradation on PV modules encapsulated with various materials.

Published in Solar Energy Materials and Solar Cells, the study compared three encapsulants commonly used in PV module production: ethylene vinyl acetate (EVA), polyolefin elastomers (POE), and thermoplastic polyolefins (TPO). Previous research hinted at the potential superiority of POE and TPO over EVA due to their lack of acidic components, which can lead to corrosion. However, concrete evidence of their field durability remains elusive.

The researchers subjected laminates made with these encapsulants to damp heat testing lasting up to 2,500 hours under controlled conditions (85°C/85% relative humidity). Using commercially available n-type and p-type bifacial cells (TOPCON and PERC, respectively), they conducted tests under controlled conditions. Analysis through techniques like scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDX) revealed significant differences.

The results indicated that TPO encapsulants offered superior protection against moisture-induced degradation compared to EVA and POE. Notably, the front-side metallization of n-type TOPCon cells exhibited higher vulnerability to degradation than their p-type counterparts, particularly in EVA-based laminates.

The study attributed these differences to the composition of cell metallization, with the degradation of lead glass, containing lead oxide (PbO), being a significant factor. Sommeling emphasized that corrosion issues, often linked to the release of acetic acid from EVA, are well-documented. However, the study highlighted novel insights into corrosion behavior based on metallization types and cell compositions.

The findings suggest that the combination of n-type TOPCon cells and EVA encapsulation presents a higher risk of degradation. To mitigate this risk, alternatives to EVA or corrosion-resistant metallization for TOPCon cells should be considered. Ultimately, employing more corrosion-resistant materials could enhance the durability of n-type PV panels.

A few samples taken out of a mini PV panel by the coring technique, Image credit: TNO