Fluorinated Benzothienoisoindigo Copolymers for Organic Solar Cells: A Comparative Study on Polymer Orientation and Device Performance

We report the synthesis and characterization of a new conjugated polymer composed of fluorinated benzothienoisoindigo (F-BTIDG) and benzobisthiazole (BBTz). The fluorination brought about a significant change in the crystallinity and orientation of the polymer, which results in unfavorable decrease in power conversion efficiency (ca. 1.6%). We discuss Herman's orientation parameters, unsymmetry of the unit, and planarity of the polymer backbone based on density functional theory. The work suggests that fluorination does not always lead to improvements in polymer orientation and device performance.