Synthesis, Characterization, and Photovoltaic Properties of Dithienylbenzobisazole-Dithienylsilole Copolymers

Three conjugated polymers comprised of dioctyldithieno-[2,3-b:2’,3’-d]silole and a donor-acceptor-donor triad of either cis-benzbisoxazole, trans-benzobisoxazole or transbenzobisthiazole were synthesized via the Stille cross-coupling reaction. The impact of varying the heteroatoms and/or the location within the benzobisazole moiety on the optical and electronic properties of the resulting polymers was evaluated via cyclic voltammetry and UV-Visible spectroscopy. All of the polymers have similar optical band-gaps of 1.9 eV and highest occupied molecular orbital levels of 25.2 eV. However, the lowest unoccupied molecular orbitals (LUMO) ranged from 23.0 to 23.2 eV. Interestingly, when the polymers were used as donor materials in bulk-heterojunction photovoltaic cells with PC71BM as the electron-acceptor, the benzobisoxazole-based polymers gave slightly better results than the benzobisthiazolecontaining polymers with power conversion efficiencies up to 3.5%. These results indicate that benzobisoxazoles are promising materials for use in OPVs. VC 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1533–1540.