Combining Energy Transfer and Optimized Morphology for Highly Efficient Ternary Polymer Solar Cells

Aimed at achieving ideal morphology, illuminating morphology-performance relationship, and further improving the power conversion efficiency (PCE) of ternary polymer solar cells (TSCs), a ternary system is designed based on PTB7-Th: PffBT4T-2OD:PC71BM in this work. The PffBT4T-2OD owns large absorption cross section, proper energy levels, and good crystallinity, which enhances exciton generation, charge dissociation and transport and suppresses charge recombination, thus remarkably increasing the short-circuit current density (J(sc)) and fill factor (FF). Finally, a notable PCE of 10.72% is obtained for the TSCs with 15% weight ratio of PffBT4T-2OD. As for the working mechanism, it confirmed the energy transfer from PffBT4T-2OD to PTB7-Th, which contributes to the improved exciton generation. And morphology characterization indicates that the devices with 15% PffBT4T-2OD possess both appropriate domain size (25 nm) and enhanced domain purity. Under this condition, it affords numerous D/A interface for exciton dissociation and good bicontinuous nanostructure for charge transport simultaneously. As a result, the device with 15% PffBT4T-2OD exhibits improved exciton generation, enhanced charge dissociation possibility, elevated hole mobility and inhibited charge recombination, leading to elevated Jsc (19.02 mA cm(-2)) and FF (72.62%) simultaneously. This work indicates that morphology optimization as well as energy transfer plays a significant role in improving TSC performance.