Synthesis and photovoltaic properties of the acceptor pended push–pull conjugated polymers incorporating thieno[3,2–b] thiophene in the backbone chain or side chains

• Introducing thieno[3,2-b]thiophene to the acceptor pended conjugated polymers.
• The effects of the location of thieno[3,2-b]thiophene on the properties.
• The effects of the numbers of thieno[3,2-b]thiophene in one repetitive unit.

Two novel acceptor pended push–pull conjugated polymers PTT–DTBT and PT–DTTBT，incorporating thieno[3,2–b] thiophene in the backbone chain and conjugated side chains respectively, were designed and synthesized. The effects of the location of thieno[3,2–b]thiophene units on the thermal, photophysical, electrochemical and photovoltaic properties of the polymers were investigated. Compared to the polymer PTT–DTBT, the polymer PT–DTTBT with thieno[3,2–b]thiophene units in the side chains shows more broadened and red–shifted absorption, smaller band gap and higher hole mobility. Bulk heterojunction solar cells with the polymers as electron donors and (6,6)–phenyl–C61–butyric acidmethyl ester as the electron acceptor were fabricated, and the PT–DTTBT–based device exhibits a higher power conversion efficiency of 4.07% than that of the PTT–DTBT–based device (3.05%) without any processing additives or posttreatments.

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