Why is it more important to use pure POE film for N-modules?

In recent years, with the rapid development of PV industry technology, N-type cells are gradually on the rise, and the rapid expansion of TOPCon and HJT production capacity and demand has brought a broad market space for pure POE encapsulation adhesive film.

With the rapid development of new PV cell technology in 2022, TOPCon has undoubtedly become the most mainstream choice for the current expansion of high-efficiency cell technology in the industry, judging from the capacity planning and actual landed capacity of head module and cell manufacturers. In the TOP10 efficiency list of PV module mass production products released by Taiyang News for 2 consecutive years, a clear trend can be seen, whether it is TOPCon, HJT or xBC route, the module efficiency is much higher than the current mainstream PERC products. According to market estimates, the expansion scale of TOPCon will be 150-200GW in 2023, and the expansion scale of HJT will be 60GW+.

In the context of accelerated expansion of N-type cells, the evolution of cell technology has a greater impact on the choice of supporting auxiliary materials, especially encapsulation films.

As the encapsulation process of solar cells is irreversible, and the operational life of modules is usually required to be above 25 years, once the light transmission of the film decreases during operation, problems such as photodegradation, corrosion or delamination can cause module failure, so although the film only accounts for about 5% of the PV industry chain, it directly determines the quality and life of the modules.

At present, the main encapsulation films used for PV modules include EVA film, EPE film and POE film. Due to the continuous acid release, water vapour transmission rate and water absorption rate of EVA film, even during normal use, there will still be water vapour transmission, light transmission rate reduction, acid release and delamination and other failures, thus reducing the power generation of PV modules.

In particular, the release of acetic acid molecules from the decomposition of EVA adhesive film not only corrodes components such as glass and backsheets, but also has a much greater impact on the corrosion of metallised grid lines in N-type cells than in traditional P-type cells, leading to an increased risk of long-term reliability of N-type high-efficiency modules. In recent years, it has also been found in the operation of PV plants that EVA films suffer from severe PID - Potential Induced Degradation - resulting in a significant reduction in PV plant output.

Compared to EVA film, pure POE film has excellent resistance to PID, and its high resistivity and non-hydrolysis properties ensure the safety and long-term ageing resistance of PV modules in high temperature and high humidity environments, enabling the modules to be used more permanently and efficiently.
According to research, although EPE film takes into account the lamination performance of EVA film and the anti-PID performance of POE film, but the disadvantages are also very obvious, the middle layer of POE thickness control is not uniform, POE layer additives are easy to migrate to EVA layer, after the migration of additives, the cross-linking speed of POE becomes slower, the lamination process makes the POE in the EPE film is extruded by the EVA on both sides, thus producing The risk of delamination, etc., and the fact that EPE is not yet technically proven on a large scale in N-cells.

More importantly, the continued acidic release of EVA has not been eliminated from the EPE film, which casts a shadow over the long-term reliability of the EPE film for N-cell applications. At least in current N-type single-glass modules, the EVA film is still not in direct contact with the front of the cell.