New Polymeric Acceptors Based on Benzo[1,2‐<i>b</i>:4,5‐<i>b</i>′] Difuran Moiety for Efficient All‐Polymer Solar Cells

In order to realize high-performance bulk-heterojunction (BHJ) all-polymer solar cells, achieving appropriate aggregation and moderate miscibility of the polymer blends is one critical factor. Herein, this study designs and synthesizes two new polymer acceptors (P_As), namely PYF and PYF-Cl, containing benzo[1,2-b:4,5-b'] difuran (BDF) moiety with/without chlorine atoms on the thiophene side groups. Thanks to the preferred planar structure and high electronegativity of the BDF units, the resultant P_As generate strong intermolecular interactions and π-π stacking in both the neat and blend films. At the same time, the BDF moieties flanked with bulky 2D side groups increase intermolecular space and restrain the excessive entanglement of polymer chains for developed heterojunction miscibility attributes. Consequently, appropriate polymer crystallinity and moderate miscibility between P_As and polymer donor (P_D) contribute to harmonious blending morphologies. Eventually, the PM6:PYF-based solar cells achieve an optimal efficiency of 11.82%. More encouragingly, the PYF serves as an efficient guest acceptor and realizes an improved efficiency of 17.05% in the PM6:PYIT:PYF ternary systems, which is much higher than that of the host system (15.87%). This study highlights the importance of BDF moiety in designing new P_As for high-performance all-polymer solar cells.