Quaterthiophene Benzobisazole Copolymers for Photovoltaic Cells: Effect of Heteroatom Placement and Substitution on the Optical and Electronic Properties Achala Bhuwalka, Jared F. Mike, Meng He, Jeremy J. Intemann, Toby Nelson, Monique D. Ewan, Robert A. Roggers, Zhiqun Lin, and Malika Jeffries-EL* Department of Chemistry, Iowa State University, Ames Iowa 50011, United States Department of Mate...