Chlorination and thiophene strategies to adjust molecular energy levels for high-performance organic polymer solar cells

Three BT-based polymers were built through effective side-chain chlorination strategies and thiophene-induced approaches. The devices based on polymer delivered the best efficiency of 5.73 %. [Display omitted] •Polymers were built through chlorination and thiophene-induced approachs.•The efficiency of device is improved.•PBDBT-1 gave the best device efficiency of 5.73 %. Three novel polymers with D-A (π)-BT backbone, PBDBT-0, PBDBT-1, and PBDBT-2, were built through effective side-chain chlorination strategies and thiophene-induced approaches. Meanwhile, the effect of different thiophene numbers was studied. As expected, all of the chlorinated polymers showed low HOMO levels. The introduction of the thiophene unit improved the solubility of the polymer and slightly adjusted the energy level of the molecule. Furthermore, polymers as donors and PC71BM as acceptors are used to construct organic solar cell devices. The devices based on polymer PBDBT-1 with one thiophene unit delivered the best efficiency of 5.73 % with an open-circuit voltage of 0.85 V, a short-circuit current density of 13.07 mA cm−2 and a fill factor of 51.6 %, which is superior to that of PBDBT-0 and PBDBT-2.