Synthesis of Copolymers Based on Thiazolothiazole and Their Applications in Polymer Solar Cells

Two conjugated alternating copolymers of thiazolothiazole with benzodithiophene ( P1 ) or bithiazole ( P2 ) were synthesized by a palladium(0)-catalyzed Stille coupling reaction. The thermal, electrochemical, optical, charge transport, and photovoltaic properties of these copolymers were examined. Compared with P1, P2 exhibits red shifted absorption, a lower band gap, and a lower HOMO level. The field-effect hole mobility of P1 is as high as 2.8 × 10 −3 cm 2 V −1 s −1, which is 1 order of magnitude higher than that of P2 . Polymer solar cells were fabricated based on the blend of the polymers and methanofullerene6,6-phenyl C61-butyric acid methyl ester (PC 61 BM). The PSC based on P1:PC 61 BM (1:2, w/w) exhibits a power conversion efficiency of 2.72% under AM 1.5, 100 mW cm −2, higher than that reported for the thiazolothiazole-based polymers in the literature.