D–A copolymers based on dithienosilole and phthalimide for photovoltaic materials

Two D–A copolymers containing dithienosilole (DTS) donor unit and phthalimide (Ph) acceptor unit, PDTSPh and PDTSBTPh, were synthesized by the Pd-catalyzed Stille-coupling method. The copolymers have a strong absorption ranging from 350 to 650 nm, exhibit good solubility and thermal stability. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of the copolymers determined by cyclic voltammetry were about −5.2 and −3.0 eV, respectively. The power conversion efficiency of the polymer solar cells based on PDTSBTPh:PC70BM (1:2, w/w) reached 2.1% with open-circuit voltage of 0.83 V and a short-circuit current of 6.27 mA/cm2, under the illumination of AM1.5, 100 mW/cm2.