Ternary D1–D2–A–D2 Structured Conjugated Polymer: Efficient “Green” Solvent-Processed Polymer/Neat-C70 Solar Cells

In contrast to the great efforts on developing novel donor (D)–acceptor (A) copolymers, research on investigating the backbone composition of conjugated polymer is rare. In this contribution, we disclose the design and synthesis of a ternary D1–D2–A–D2 structured conjugated polymer PBSF. Compared to the typical D–A polymer with fixed D/A moiety number, the ternary structure can tune the optical and electrical properties more comprehensively and delicately. Precisely control of the ternary fragments relative to the backbone vector was achieved, further promoting sufficient planar structure, strong intermolecular packing, and excellent charge transport. Finally, the additive and annealing-free polymer solar cells based on PBSF and phenyl-C 71 -butyric acid methyl ester ([70]PCBM; PCE = 7.4%) or cheap, nonfunctionalized C 70 (PCE = 5.3%) demonstrate excellent performance using either chlorinated or nonhalogenated “green” solvent. We believe that this novel and efficient ternary structure may spark future polymer design to achieve sustainable-processed photovoltaic devices for practical mass production.