Rubber-Toughened Organic Solar Cells: Miscibility-Morphology-Performance Relations

Toughorganic solar cell (OSC) active layers are necessary to achieverobust, flexible, and stretchable devices. A major challenge is thatthe brittle small molecule acceptor (SMA) in polymer/SMA bulk heterojunctionsresults in films prone to mechanical failure. To improve mechanicaltoughness, we investigate the use of a thermoplastic elastomer (styrene-b-ethylene-butylene-styrene) (SEBS) as an additive in high-performancephotoactive layers. We find a consistent transition of all measuredparameters [e.g., fracture energy (G (c))and power conversion efficiency (PCE)] at a SEBS concentration of5-10 wt %, which is driven by the miscibility of the SEBS.We use this insight to optimize the SEBS loading for PCE and toughness.Optimized OSCs are found to increase G (c) significantly with a marginal decrease in PCE, resulting in a record G (c)& BULL;PCE metric, considering all OSC photoactivelayers. The pronounced miscibility-function relationship providesa framework to optimize elastomer addition in OSCs for performanceand toughness.

Automated summary

The addition of a thermoplastic elastomer (SEBS) in organic solar cells (OSC) can improve the mechanical strength without significantly decreasing the conversion efficiency. The optimal SEBS concentration for the best fracture energy and power conversion efficiency is found to be 5-10 wt %. This study provides a framework for optimizing elastomer addition in OSCs for improved performance and toughness.