Synthesis and Photovoltaic Properties of 2,6-Bis(2-Thienyl) Benzobisazole and 4,8-Bis(thienyl)-Benzo[1,2-B:4,5-B0]Dithiophene Copolymers

In an effort to design efficient low-cost polymers for use in organic photovoltaic cells the easily prepared donor– acceptor–donor triad of a either cis-benzobisoxazole, transbenzobisoxazole or trans-benzobisthiazole flanked by two thiophene rings was combined with the electron-rich 4,8bis(5-(2-ethylhexyl)-thien-2-yl)-benzo[1,2-b:4,5-b0]dithiophene. The electrochemical, optical, morphological, charge transport, and photovoltaic properties of the resulting terpolymers were investigated. Although the polymers differed in the arrangement and/or nature of the chalcogens, they all had similar highest occupied molecular orbital energy levels (25.2 to 25.3 eV) and optical band gaps (2.1–2.2 eV). However, the lowest unoccupied molecular orbital energy levels ranged from 23.1 to 23.5 eV. When the polymers were used as electron donors in bulk heterojunction photovoltaic devices with PC71BM ([6,6]phenyl C71-butyric acid methyl ester) as the acceptor, the transbenzobisoxazole polymer had the best performance with a power conversion efficiency of 2.8%. VC 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 00, 000–000