π-Conjugation Effects of Oligo(thienylenevinylene) Side Chains in Semiconducting Polymers on Photovoltaic Performance

Abstract

Semiconducting copolymers based on benzo[1,2-b:4,5-b′]dithiophene and thieno[3,4-c]pyrole-4,6-dione containing oligo(thienylenevinylene) side chains with different lengths were synthesized to examine the effect of the π-conjugated side chains on the performance of polymer solar cells (PSCs). Using the copolymers that had π-conjugated side chains as the PSC electron donor resulted in a higher short circuit current and fill factor compared with the reference copolymers, which had no side chain or an analogous side chain with no π-conjugation, resulting in an increase of power conversion efficiency of 10–22%. Measurements of hole mobility by space-charge-limited current and internal quantum efficiency indicated that introducing the π-conjugated side-chain units can facilitate both charge transport and charge separation in the polymer:PC71BM blend films.