Systematic Fluorination of P3HT: Synthesis of P(3HT-co-3H4FT)s by Direct Arylation Polymerization, Characterization, and Device Performance in OPVs

We present a strategy for tuning physical properties of P3HT-based copolymers by incorporating a fluorinated thiophene repeat unit. The synthesis and characterization of a series of fluorinated polythiophene P(3HT-co-3H4FT) materials are described, where the percentage of fluorinated repeat units in the polymer backbone is systematically varied from 0 to 100%. These P(3HT-co-3H4FT)s (P0, P25, P50, P75, and P100) were synthesized via direct arylation polymerization (DArP) methods. By varying the feed ratio of the two monomers, the percent of fluorinated repeat units (3H4FT) could be precisely controlled. As fluorination is increased, there is a strong effect on the electronic properties of the polymers, evidenced by a 0.4 eV drop in the EHOMO level for P100 when compared to P0. GIWAXS and TEM were used to determine the crystallinity and morphology. TEM analysis of thin film polymer/PCBM bulk-heterojunction blends indicates that increased fluorination does not result in stronger phase separation. Organic ph...