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 x 10(-3) cm(2) V-1 s(-1), which is I order of magnitude higher than that of P2. Polymer solar cells were fabricated based on the blend of the polymers and methanofullerene[6,6]-phenyl C61-butyric acid methyl ester (PC61BM). The PSC based on P1:PC61BM (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.