ABSTRACT:We report the synthesis and polymerization of a novel thieno[3,2-b]thiophene-diketopyrrolopyrrolebased monomer. Copolymerization with thiophene afforded a polymer with a maximum hole mobility of 1.95 cm 2 V -1 s -1 , which is the highest mobility from a polymer-based OFET reported to date. Bulk-heterojunction solar cells comprising this polymer and PC 71 BM gave a power conversion efficiency of 5.4%. T here is considerable interest in the synthesis of narrow-bandgap conjugated polymers for use in organic photovoltaic (OPV) and organic field-effect transistor (OFET) devices. Their solution processability and mechanical properties allow access to a new generation of cheap and flexible transistors and solar devices. Current state of the art polymeric materials have allowed for the fabrication of OFETs with mobilities of ∼1 cm 2 V -1 s -1 1 and OPV devices with power conversion efficiencies (PCEs) of over 7%.2 Diketopyrrolopyrrole (DPP)-based copolymers have emerged as extremely attractive materials for both thin-film transistors and solar cell devices in recent years. The DPP core's electrondeficient nature has been exploited for the synthesis of extremely narrow band gap donor-acceptor-type materials that are wellsuited for use in OPVs with high PCEs reported from both small molecules and polymers.3-6 Furthermore, the planarity of the DPP skeleton and its ability to accept hydrogen bonds (and other types of electrostatic interactions) result in copolymers that encourage π-π stacking. Typically, these DPP-based copolymers are prepared via either Suzuki or Stille coupling of the 3,6-bis(5-bromothiophen-2-yl)-2,5-dialkylpyrrolo[3,4-c]pyrrole-1,4-(2H,5H)-dione core with the desired comonomer, which as a result means that the electron-deficient DPP unit is always flanked by two thiophenes. Variation of the comonomer has yielded polymers with extremely attractive properties for both OPV and OFET devices. For instance, copolymerization with thiophene derivatives or benzothiadiazole resulted in polymers with impressive ambipolar charge-carrier mobilities. 7,8 Recently, a copolymer of 3,6-bis(5-bromothiophen-2-yl)-N,N 0 -bis(2-octyl-1-dodecyl)-1,4-dioxopyrrolo[3,4-c]pyrrole and 2,5-bis(trimethylstannyl)thieno[3,2-b]thiophene showed an impressive hole mobility of ∼0.9 cm 2 V -1 s -1 . 9 In terms of materials for OPVs, copolymerization of the same DPP monomer (albeit having a slightly different solubilizing alkyl chain) with phenylene-1,4-diboronic acid bispinacol ester afforded a polymer that was used to fabricate OPV devices with efficiencies of ∼5.5%. 10Despite the significant number of reports on DPP-based copolymers, there have been very few studies on the effect of modifying the 3,6-bis(5-bromothiophen-2-yl)-2,5-dialkylpyrrolo-[3,4-c]pyrrole-1,4-(2H,5H)-dione monomer. One very recent example was the replacement of the flanking thiophenes by furans, which resulted in polymers with high PCEs in solar cell devices. 11 We were interested in increasing the intermolecular association of DPP-based copolymers by repla...

One of the most inspiring and puzzling developments in the organic electronics community in the last few years has been the emergence of solution-processable semiconducting polymers that lack significant long-range order but outperform the best, high-mobility, ordered semiconducting polymers to date. Here we provide new insights into the charge-transport mechanism in semiconducting polymers and offer new molecular design guidelines by examining a state-of-the-art indacenodithiophene-benzothiadiazole copolymer having field-effect mobility of up to 3.6 cm 2 V À 1 s À 1 with a combination of diffraction and polarizing spectroscopic techniques. Our results reveal that its conjugated planes exhibit a common, comprehensive orientation in both the non-crystalline regions and the ordered crystallites, which is likely to originate from its superior backbone rigidity. We argue that charge transport in high-mobility semiconducting polymers is quasi one-dimensional, that is, predominantly occurring along the backbone, and requires only occasional intermolecular hopping through short p-stacking bridges.

The electrical performance of organic semiconducting polymers in field-effect transistor devices is now sufficient for initial low complexity circuit applications. To achieve high performance, either operation in an inert atmosphere or a hydrophobic surface treatment and annealing step is typically required. In this communication we report a strategy to prepare fully air stable, amorphous semiconducting polymers which can achieve charge carrier mobilities in the range of 0.04 cm(2)/(V s), remaining over a period of over 3 months in ambient conditions.