Pendant Y-series Acceptors with Well-controlled Morphology Enabled High Performance and Stability All-polymer Solar Cells

Polymer acceptor configuration and aggregation behavior are critical in determining the photovoltaic performance of all-polymer solar cells (all-PSCs). Effectively manipulating polymer self-aggregation through structural design to optimize the blend morphology remains challenging. Herein, we present a simple yet effective design strategy to modulate the aggregation behavior of the Y-series-based polymer acceptor PY-V-γ by introducing a pendant-fluorinated Y-series acceptor (Y2F-ET) into the main-conjugated backbone. Two random copolymer acceptors (PY-EY-5 and PY-EY-20) were synthesized with varying molar fractions of Y2F-ET pendant monomers. Our findings revealed that both the solution-phase and solid-state aggregation behaviors were progressively suppressed as the Y2F-ET content increased. Compared to the highly self-aggregating PY-V-γ-based all-PSCs, the more amorphous PY-EY-5 enabled devices to achieve an increased device efficiency from 17.31% to 18.45%, which is attributed to the slightly smaller polymer phase-separation domain sizes and reduced molecular aggregation in the PM6:PY-EY-5 blend. Moreover, the finely tuned blend morphology exhibited superior thermal stability, underscoring the significant advantages of the Y-series pendant random copolymerization approach.