Dithienothiophene-diketopyrrolopyrrole-containing copolymers with alkyl side-chain and their application to polymer solar cells

We synthesized a series of dithieno[3,2-b:2',3'-d]thiophene and diketopyrrolopyrrole (DPP) based alternating copolymers, PDTTDPPs, with one of three branched alkyl side-chains (2-ethylhexyl, 2-butyloctyl, or 2-decyltetradecyl chains) tethered to the DPP moiety. These branched alkyl side-chains of various sizes were anchored to the DPP moiety owing to the relatively facile synthesis of DPP-based building blocks. We investigated the characteristics of the new PDTTDPP-based conjugated polymers bearing different alkyl chain substituents and the effect of the side chain on the device performance. A PDTTDPP-DT-based thin film transistor (TFT) exhibited the highest mobility of 6.88 x 10(-2) cm(2)V(-1) s(-1) whereas the mobilities of TFTs made with PPTTDPP-EH and PDTTDPP-BO polymers were 6.13 x 10(-3) and 7.65 x 10(-3) cm(2)V(-1) s(-1), respectively. A polymer solar cell based on PDTTDPP-DT:[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) (1:1.5 w/w) showed the highest power conversion efficiency of 3.44%. (C) 2015 Elsevier B.V. All rights reserved.