Study on the Structure and Properties of Polyvinyl Butyral (PVB) Films for Photovoltaic (PV) System

Abstract

Polyvinyl butyral (PVB) films are promising encapsulation materials for photovoltaic (PV) modules because of their mechanical properties and electrical insulation. However, achieving favorable flexibility and volume resistivity remains an important consideration in the formulation of PVB films. Focusing on regulating these two properties, this study investigates the effects of molecular structure and plasticizer formulations on PVB performance. As acetoxy content increased from 2% to 12%, the glass transition temperature of the PVB resin decreased from 70.7°C to 64.4°C, while film flexibility and volume resistivity both showed favorable trends. Regarding plasticizer formulations, increasing plasticizer content generally reduces volume resistivity while significantly improving flexibility. For the triethylene glycol bis(2-ethylhexanoate) (3G8) system, PVB films maintain volume resistivity above 1.0 × 10¹⁶ Ω·mm when plasticizer content is below 17.0%. The plasticizer type critically influences performance. At equivalent content, the system exhibits decreasing volume resistivity from dioctyl phthalate (DOP) to dioctyl sebacate (DOS), diisononyl phthalate (DINP), and triethylene glycol bis(2-ethylhexanoate) (3G8), while the flexibility follows the reverse sequence. Consistently, the through-cracked tensile (TCT) tests show that enhanced plasticization improves interlayer flexibility but reduces the adhesion-related load-bearing and crack-bridging capability of PVB/glass laminates. These findings highlight the inherent trade-offs in plasticizer formulations for optimizing both properties.