Roles of Quinoidal Character and Regioregularity in Determining the Optoelectronic and Photovoltaic Properties of Conjugated Copolymers

This work describes an efficient synthetic method for creating ladder-type, oligomeric donor monomers with fused thienobenzothiophene structures. These monomers are copolymerized with fluorinated thieno[3,4-b]thiophene ester to form a series of polymers which are investigated as donor materials in polymer/fullerene solar cells. Photophysical and electrochemical characterizations are used in conjunction with quantum-chemical calculations to identify the interplay of quinoidal and charge transfer character in the optical gaps of conjugated copolymers, providing broadly applicable design rules for tuning the excitation character of conjugated copolymers. X-ray diffraction, mobility measurements, and solar cell device characterization are used to analyze neat films and bulk heterojunctions of these copolymers, demonstrating the importance of the spatial symmetry of the donor and acceptor unit in determining the charge transport characteristics of conjugated copolymers.