Preparation of hindered amine-grafted EVA and its effect on the photoaging behavior of EVA photovoltaic encapsulation films

During prolonged operation of photovoltaic modules, the Ethylene-Vinyl Acetate Copolymer (EVA) encapsulant film is prone to aging and degradation, which significantly reduces the service life of the modules. In this study, reactive hindered amine light stabilizers (rHALS) were chemically grafted onto EVA backbone to prepare hindered amine-grafted EVA (EVA-g-HALS) and the influence of EVA-g-HALS on the photoaging behavior of EVA photovoltaic encapsulant films was systematically investigated. Firstly, the strategy of directly forming EVA-g-HALS during the crosslinking process of EVA photovoltaic encapsulant film was investigated. Fourier-transform infrared spectrum (FTIR) results revealed that rHALS underwent self-polymerization before crosslinking, making it impossible to form EVA-g-HALS during the crosslinking process. Subsequently, reactive extrusion was employed to prepare EVA-g-HALS and X-ray photoelectron spectroscopy results confirmed the successful synthesis of EVA-g-HALS. Then the effect of EVA-g-HALS on the photoaging behavior of EVA photovoltaic encapsulant films was investigated. The FTIR results indicated that after 800 h of photoaging, the addition of EVA-g-HALS reduced the growth amplitude of degradation-induced carbonyl absorption peak intensity by 70 %, whereas direct addition of rHALS only achieved a 23 % reduction. Rheological and crystallization behavior studies revealed that EVA-g-HALS effectively prevented the degradation of the crosslinked network in EVA photovoltaic encapsulant films, as evidenced by nearly unchanged storage modulus and crystallization temperature. These findings confirm the superior anti-aging performance of EVA-g-HALS compared to several commercial HALS. Finally, mechanism of superior anti-photoaging performance of EVA-g-HALS was revealed by combination of experiment and molecular simulation method. The EVA-g-HALS possesses enhanced migration resistance and outstanding compatibility with the EVA matrix, thereby exhibiting superior anti-photoaging performance. This research could provide a new strategy and inspiration for developing high efficiency anti-aging additives for EVA photovoltaic encapsulant films.