Terpolymer Strategy toward High-Efficiency Polymer Solar Cells: Integrating Symmetric Benzodithiophene and Asymmetrical Thieno[2,3‑f]benzofuran Segments

While a large number of terpolymers have been developed for polymer solar cells, very few studies have directly focused on the rational selection of the third component to balance the miscibility and crystallinity for forming the desired morphology, and universal terpolymer strategies for preparing different donor/acceptor systems are lacking. Herein, we employ a new strategy involving the integration of benzodithiophene (BDT) and thieno­[2,3-f]­benzofuran (TBF) segments to construct a series of terpolymer donors, and a profound influence on the crystallinity and miscibility of the blend films as well as on the ultimate device performance is observed. Incorporating highly crystalline TBF segments into a low-crystalline BDT-based alternating copolymer can not only increase the order of the microstructure, conserve the favorable face-on orientation, and promote the formation of proper phase-separation features but also generate high exciton dissociation and suppress charge recombination. This strategy was successfully applied in the reported J52 system and provided a remarkable 2-fold boost in performance. Finally, competitive power conversion efficiencies of 11.9, 12.4, and 12.2% accompanied by high fill factors of 73, 71, and 76% were recorded for TBFCl50-FTAZ/ITIC-, TBFCl50-BDD/ITIC-, and TBFCl50-BDD/IDIC-C4Ph-based devices, respectively, via the above terpolymer strategy. Thus, our discovery provides a promising and innovative method for finely controlling the microstructure of heterojunctions for designing high-performance terpolymers.