title: Bis(thienothiophenyl) diketopyrrolopyrrole-based conjugated polymers with various branched alkyl side chains and their applications in thin-film transistors and polymer solar cells.
abstract: New thienothiophene-flanked diketopyrrolopyrrole and thiophene-containing π-extended conjugated polymers with various branched alkyl side-chains were successfully synthesized. 2-Octyldodecyl, 2-decyltetradecyl, 2-tetradecylhexadecyl, 2-hexadecyloctadecyl, and 2-octadecyldocosyl groups were selected as the side-chain moieties and were anchored to the N-positions of the thienothiophene-flanked diketopyrrolopyrrole unit. All five polymers were found to be soluble owing to the bulkiness of the side chains. The thin-film transistor based on the 2-tetradecylhexadecyl-substituted polymer showed the highest hole mobility of 1.92 cm2 V(-1) s(-1) due to it having the smallest π-π stacking distance between the polymer chains, which was determined by grazing incidence X-ray diffraction. Bulk heterojunction polymer solar cells incorporating [6,6]-phenyl-C71-butyric acid methyl ester as the n-type molecule and the additive 1,8-diiodooctane (1 vol %) were also constructed from the synthesized polymers without thermal annealing; the device containing the 2-octyldodecyl-substituted polymer exhibited the highest power conversion efficiency of 5.8%. Although all the polymers showed similar physical properties, their device performance was clearly influenced by the sizes of the branched alkyl side-chain groups.
authors.affiliation: Department of Chemistry, Research Institute for Natural Sciences, Korea University , 5 Anam-dong, Sungbuk-gu, Seoul 136-701, Korea.
authors.forename: Jicheol
authors.initials: J
authors.lastname: Shin
authors.forename: Gi Eun
authors.initials: GE
authors.lastname: Park
authors.forename: Dae Hee
authors.initials: DH
authors.lastname: Lee
authors.forename: Hyun Ah
authors.initials: HA
authors.lastname: Um
authors.forename: Tae Wan
authors.initials: TW
authors.lastname: Lee
authors.forename: Min Ju
authors.initials: MJ
authors.lastname: Cho
authors.forename: Dong Hoon
authors.initials: DH
authors.lastname: Choi
keywords: branched alkyl side chain; diketopyrrolopyrrole; polymer semiconductor; polymer solar cell; thin-film transistor