Tunable Donor Aggregation Dominance in a Ternary Matrix of All‐Polymer Blends with Improved Efficiency and Stability

Abstract Using two structurally similar polymer acceptors in constructing high‐efficiency ternary all‐polymer solar cells is a widely acknowledged strategy; however, the focus thus far has not been on how polymer acceptor(s) would tune the aggregation of polymer donors, and furthermore film morphology and device performance (efficiency and stability). Herein, it is reported that matching of the celebrity acceptor PY‐IT and the donor PBQx‐TCl results in enhanced H‐aggregation in PBQx‐TCl, which can be finely tuned by controlling the amount of the second acceptor PY‐IV. Consequently, the efficiency‐optimized PY‐IV weight ratio (0.2/1.2) leads to a state‐of‐the‐art power conversion efficiency of 18.81%, wherein light‐illuminated operational stability is also enhanced along with well‐protected thermal stability. Such enhancements in the efficiency and operational and thermal stabilities of solar cells can be attributed to morphology optimization and the desired glass transition temperature of the target active layer based on comprehensive characterization. In addition to being a high‐power conversion efficiency case for all‐polymer solar cells, these enhancements are also a successful attempt for using combined acceptors to tune donor aggregation toward optimal morphology, which provides a theoretical basis for the construction of other types of organic photovoltaics beyond all‐polymer solar cells.