SPLTRAK Abstract Submission
Vinyl acetate content tailoring in ethylene vinyl acetate improves the resilience against environmental stressors
Umang Desai1,2, Bhuwanesh Kumar Sharma3, Aparna Singh1
1Department of metallurgical engineering and materials science, Indian Institute of Technology Bombay, Mumbai, India
/2National centre for photovoltaic research and education, Indian Institute of Technology Bomby, Mumbai, India
/3Faculty of Science, Department of Chemistry, MUIS, Ganpat University, Mehsana, India

   The most common encapsulant used in the photovoltaic (PV) modules is ethylene vinyl acetate (EVA). The properties of EVA can be tailored by modulating its vinyl acetate (VA) content. As a rule of thumb, EVA containing 28 to 33% VA content is used as an encapsulant in PV industry. It is well known that the EVA films degrade due to the environmental stressors like humidity, temperature and solar radiation during the field operation of the modules. The immediate consequence of the EVA’s degradation is the loss of its optical properties which ultimately reduce the electrical performance of the PV modules.
   In this work, we summarize the effect of damp-heat and ultraviolet ageing on the free-standing films of EVA that contain the VA content outside the most commonly used and accepted range. The VA contents discussed here include 18, 24, 33, and 40 wt. % with the necessary additives. These films have been cured at 150 C under vacuum and subsequently subjected to accelerated damp-heat (85 C and 85% RH) aging and UV aging at a wavelength of 340 nm for 1000 and 2000 h. Tensile strength, thermal stability and degree of crosslinking have been found to be greater for EVA containing lower VA content (18 and 24%) and diminished for EVA with higher VA content (33 and 40%) due to DH aging. However, inadequate % transmittance and relatively high stiffness after 2000 h of DH aging discourages EVA18 as an encapsulant. Moreover, EVAs with higher VA content (33 and 40%) have been degraded significantly after 2000 h of DH aging resulting in significant loss in transmittance and mechanical integrity. The effect of UV aging up to 2000 h suggests that the optimum range of VA content in EVA should be between 18 and 33% by weight. VA content beyond 40% degrades almost all properties needed for an encapsulate material after aging of only 2000 h. VA content of around 18% is the most stable under UV aging conditions but has a slightly lower value of transmittance for the unaged sample although the difference in transmittance between different specimens decreases with UV aging.
   Therefore, from the findings of the above-mentioned studies, it is recommended to the PV community to decrease the VA content in EVA films up to 24 % by weight for better performance against the environmental stressors.