Design and synthesis of the quinacridone-based donor polymers for application to organic solar cells

[Display omitted] •D-π-A type copolymers PQCfTB and PQCfTQx for efficient organic solar cells.•Each polymer was synthesized by varying acceptor unit with benzothiadiazole and quinoxaline.•PQCfTB showed higher molecular weight and crystallinity, resulting higher PCE.•Backbone shape change strategy in rational design of D-π-A type copolymer was suggested. D–π–A type quinacridone-based polymers were designed with different acceptor moieties and successfully synthesized via a Suzuki coupling reaction. Depending on the introduction of benzothiadiazole and quinoxaline moieties, the synthesized polymers, poly(quinacridone-thienothiphene-benzothiadiazole) (PQCfTB) and poly(quinacridone-thienothiphene-quinoxaline) (PQCfTQx), showed different physical, optical and electrochemical properties. PQCfTB had a more extended π-conjugation length and a higher number average molecular weight (Mn, 365.1 kDa) than that of PQCfTQx (167.5 kDa). Furthermore, each polymer showed different optical behavior and optical band gaps (Egopt: 1.91 eV for PQCfTB; 1.87 eV for PQCfTQx) in the film state. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of PQCfTB and PQCfTQx were calculated as −5.20 eV and −5.22 eV, as well as −3.29 eV and −3.35 eV, respectively. The XRD measurement results showed that the polymers for PQCfTB and PQCfTQx had bimodal and face-on structures, respectively. Finally, organic solar cells for both polymers were fabricated and optimized with respect to the acceptor. In summary, the PQCfTB-based devices showed higher power conversion efficiencies (w/PC71BM 3.9%; w/IT-M 5.2%; w/PM6:Y6-BO-4Cl 11.0%) than PQcfTQx (2.3%, 4.7%, and 10.0%).