Non‐Fused Polymerized Small Molecular Acceptors for Efficient All‐Polymer Solar Cells

The development of polymer acceptors is critical to promote the power conversion efficiencies (PCEs) of all‐polymer solar cells (all‐PSCs). Herein, two novel polymer acceptors (PBTz–TT and PFBTz–TT) derived from non‐fused small molecules, which possess synthetic simplicity, narrow optical bandgap, and high absorption coefficients, are reported for the first time. The all‐PSCs are fabricated by a layer‐by‐layer deposition technique with PBDB‐T as donor, and the device performance is improved by the synergistic effect of solvent additive and thermal annealing. As a result, the all‐PSCs offer PCEs of 10.14% and 6.85% for PFBTz‐TT and PBTz‐TT, respectively. Further morphological and electrical characterizations unveil that the higher device performance of PFBTz‐TT originates from more efficient exciton separation and charge transport as a result of more ordered polymer packing in solid state. Herein, it is demonstrated that polymerizing non‐fused small molecular acceptors is an effective strategy to develop polymer acceptors for high‐performance all‐PSCs.