Fluorine-Free Transparent Backsheets for Low-Carbon Footprint Photovoltaic Modules

Fluorine-free transparent photovoltaic backsheets were developed via dip-coating polyethylene terephthalate (PET) films with perhydropolysilazane (PHPS), which were subsequently converted to a SiO x N y -based inorganic coating layer on the PET surface.Fourier-transform infrared (FT-IR) spectroscopy confirmed the formation of Si-O, Si-N, and Si-OH bonds, effectively converting the PHPS precursor into a robust SiO x N y network.UV-Vis measurements revealed that the optical transmittance of the coated films was high (>88%), ensuring optical suitability for photovoltaic transparent backsheet applications.The water vapor transmission rate (WVTR) measurements demonstrated that the moisture permeability (<2 g/m 2 day) was lower than that of the untreated PET films, whereas the adhesion tests confirmed strong interfacial bonding between the SiO x N y -coated PET film and the encapsulant.Furthermore, the films retained high transparency and strong moisture barrier performance after accelerated aging under pressure-cooker test (PCT) conditions and UV irradiation, confirming their high durability and environmental stability.Overall, SiO x N y -coated PET films are a sustainable, transparent, and high-performance alternative to conventional fluorine-based backsheets for low-carbon photovoltaic modules.