Simultaneously improving efficiency, stability and intrinsic stretchability of organic photovoltaic films via molecular toughening

A key advantage of intrinsically stretchable organic photovoltaics (IS-OPVs) is that the output power can increase with the enlargement of the photoactive area during stretching. Designing wearable IS-OPV devices that simultaneously possess desirable photovoltaic performance and operational stability under thermal and mechanical stress remains a significant challenge. Herein, we propose a facile strategy to simultaneously enhance efficiency/power output, stability and intrinsic stretchability of high-efficiency polymer:nonfullerene systems by introducing tethered molecules. The introduction of molecular toughening optimizes molecular stacking and phase separation in PM6:eC9, thereby improving charge transport, suppresses recombination, and stabilized the film morphology. Strikingly, the nonhalogenated solvent o-xylene processed optimal ternary blends achieved a champion photovoltaic efficiency of 19.1% for rigid devices and a top efficiency of 15.1% for intrinsically stretchable devices by benign solvents. Furthermore, we unraveled the thickness dependence of mechanical properties in ternary blend films for the first time. Using thick-film toughened blends, we realized intrinsically stretchable OPVs with significantly enhanced flexibility, stretchability and mechanical stability compared to their thin-film counterparts. Thick-film devices (>= 300 nm) retained over 92% of their initial performance after 1000 bending times and over 80% after 1000 stretching cycles. This work provides fresh insights for the construction of high-efficiency and stretchable devices and helps promote wearable photovoltaics.