The role of elastomer composition in optimizing rubber-toughened organic solar cells

This study explores the use of elastomer additives to increase the mechanical reliability of flexible organic solar cells (OSCs) with minimal impact on device performance. In particular, we compare the addition of styrene-ethylene-butylene-styrene (SEBS) and styrene-ethylene-propylene-styrene (SEPS) co-polymers with varying polystyrene content and molecular weight. Our findings reveal that SEPS exhibits slightly higher miscibility than SEBS. Yet, the miscibility difference is relatively small, and casting conditions that drive local morphology become a larger driver dictating final device performance. In both the SEBS and SEPS additives, we can maintain 95% of the control OSC efficiency. This is achieved while significantly improving the fracture toughness of the OSCs. The fracture energy is shown to be strongly driven by the molecular weight of the additive, and optimized elastomer additives can result in a more than a four-fold increase in OSC fracture toughness.