Synthesis, Characterization, And Photovoltaic Properties Of Dithienylbenzobisazole-Dithienylsilole Copolymers

Three conjugated polymers comprised of dioctyl-dithieno-[2,3-b:2',3'-d]silole and a donor-acceptor-donor triad of either cis-benzbisoxazole, trans-benzobisoxazole or trans-benzobisthiazole 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 approximate to 1.9 eV and highest occupied molecular orbital levels of -5.2 eV. However, the lowest unoccupied molecular orbitals (LUMO) ranged from -3.0 to -3.2 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 benzobisthiazole-containing polymers with power conversion efficiencies up to 3.5%. These results indicate that benzobisoxazoles are promising materials for use in OPVs. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1533-1540