Binary all-polymer solar cells with efficiency over 17% by fine-tuning halogenated thiophene linkers of polymer acceptors

All-polymer solar cells (APSCs) have achieved significant advances because of the rising of polymerized small molecular acceptors (PSMAs). While, the effect of halogen atoms on PSMAs in linkers has not been systematically studied. Herein, three PSMAs of PZC1, PZC2, and PZC3 are designed and synthesized by introducing fluorine and chlorine atom on the linkers to fine-tune their optoelectronic and molecular packing properties. Both halogenated polymer acceptors exhibit a slightly blue-shifted absorption range as well as deeper-lying frontier energy levels. When compared with non-halogenated PZC1, the fluorinated polymer acceptor (PZC2) presents better co-planar and rigid molecular conformation. The 3,4-dichlorothiophene-based polymer acceptor (PZC3) displays a distinctly twisted molecular chain between terminal groups and 3,4-dichlorothiophene owing to the steric hindrance between chlorine (Cl) and hydrogen (H) atoms. Due to the optimal morphologies in PM6:PZC2 film, the corresponding devices exhibit an excellent PCE of 17.30%, superior to those of PM6:PZC1 (13.83%) and PM6:PZC3 (15.75%) based devices. The mechanical robustness of three blend films is further investigated. PZC2-based films exhibit outstanding mechanical flexibility. Afterwards, the PM6:PZC2-based flexible devices achieve a PCE of 14.24%. Our results demonstrate that the usage of halogenated thiophene offers a practical way to fine-tune the performance of APSCs.