Identifying structure formation in semicrystalline conjugated polymers is the fundamental basis to understand electronic processes in these materials. Although correlations between physical properties, structure formation, and device parameters of regioregular, semicrystalline poly(3-hexylthiophene) (P3HT) have been established, it has remained difficult to disentangle the influence of regioregularity, polydispersity, and molecular weight. Here we show that the most commonly used synthetic protocol for the synthesis of P3HT, the living Kumada catalyst transfer polycondensation (KCTP) with Ni(dppp)Cl(2) as the catalyst, leads to regioregular chains with one single tail-to-tail (TT) defect distributed over the whole chain, in contrast to the hitherto assumed exclusive location at the chain end. NMR end-group analysis and simulations are used to quantify this effect. A series of entirely defect-free P3HT materials with different molecular weights is synthesized via new, soluble nickel initiators. Data on structure formation in defect-free P3HT, as elucidated by various calorimetric and scattering experiments, allow the development of a simple model for estimating the degree of crystallinity. We find very good agreement for predicted and experimentally determined degrees of crystallinities as high as ∼70%. For Ni(dppp)Cl(2)-initiated chains comprising one distributed TT unit, the comparison of simulated crystallinities with calorimetric and optical measurements strongly suggests incorporation of the TT unit into the crystal lattice, which is accompanied by an increase in backbone torsion. Polydispersity is identified as a major parameter determining crystallinity within the molecular weight range investigated. We believe that the presented approach and results not only contribute to understanding structure formation in P3HT but are generally applicable to other semicrystalline conjugated polymers as well.

cells today. While the majority of donoracceptor polymers are hole-conducting (p-type), [3][4][5] important progress has been achieved in the development of high performance, n-type polymeric semiconductors in recent years. [6][7][8] In 2009, Facchetti and co-workers introduced a novel n-type, donor-acceptor polymer, poly{[N,N′-bis(2-octyldodecyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} P(NDI2OD-T2), which exhibits excellent electron mobilities as high as 0.85 cm 2 V −1 s −1 in top gate transistor devices under ambient conditions; [ 6 ] bulk-mobilities were found in the range of 5 × 10 −3 cm 2 V −1 s −1 for timeof-fl ight and electron-only current measurements. [ 9 ] Promising results have been further shown for all-polymer solar cells based on poly(3-hexylthiophene)s (P3HT) and P(NDI2OD-T2) as donor and acceptor, respectively, reaching power conversion effi ciencies of 1.4%. [ 10 ] Publications on P(NDI2OD-T2) initially focused on the chemistry, [ 7 ] charge transport and injection in multiple devices, [ 9,11,12 ] whereas little was reported about the structure of the semiconductor layer. While at fi rst it was assumed that P(NDI2OD-T2) forms mainly amorphous layers, [ 6 ] X-ray diffraction analysis and transmission electron microscopy (TEM) revealed the semicrystalline character of P(NDI2OD-T2) thin fi lms in recent years. [13][14][15][16][17] Rivnay et al. were the fi rst to show a remarkable degree of in-plane order in as-cast fi lms with an unconventional face-on texture in the bulk. [ 13 ] A striking texture change was observed upon melt-annealing, when the polymer chains undergo a transition from mainly face-on to edge-on. [ 15,18 ] A very recent study by Schuettfort et al. reports on a preferential edge-on texture at the top surface both for as-cast and melt-annealed layers. [ 16 ] Using mainly spectroscopic measurements, Steyrleuthner et al. demonstrated the strong tendency for aggregation not only in thin fi lms but also in solution, thereby identifying two different kinds of aggregates. [ 19 ] The precise stacking mode of the naphthalene diimide (NDI) and bithiophene (T2) units within the crystalline lattice was investigated via TEM by Brinkmann and coworkers [ 17 ] and Heeger and coworkers. [ 20 ] Highly oriented thin fi lms of P(NDI2OD-T2) were prepared by directional epitaxial crystallization (DEC) on 1,3,5-trichlorobenzene (TCB) and epitaxy on aligned fi lms of poly(tetrafl uoroethylene) (PTFE). Two polymorphs were identifi ed: i) in form I, the NDI and T2 which is up to 10 times higher than those perpendicular to the polymer chain.

Solvent-induced aggregation of regioregular head-to-tail poly(3-alkylthiophene)s (PATs) have been studied by means of AFM and UV−vis spectroscopy. In hexane, which is a good solvent for alkyl side chains but poor for polythiophene backbones, PAT molecules undergo ordered main-chain collapse driven by solvophobic interaction. Well-pronounced concentration-independent red shift of λ max and good resolved fine vibronic structure in the electronic absorption spectra observed upon addition of hexane indicate that planarization occurs on the singlemolecule level. A helical conformation of the man chain of PATs with 12 thiophene rings per each helical turn has been proposed. At the higher concentration of PATs the collapsed molecules undergo unexpected one-dimensional aggregation. Length of the particles varies from several nanometers to several hundreds nanometers and can be easily adjusted by the solvent composition or concentration of PATs.

We describe a new method to grow conductive polymer (CP) brushes of regioregular head-to-tail poly(3-alkylthiophenes) (P3AT) via surface-initiated polycondensation of 2-bromo-5-chloromagnesio-3-alkylthiophene. A simple procedure for the preparation of the Ni(II) macroinitiator by the reaction of Ni(PPh3)4 with photocross-linked poly-4-bromostyrene films was developed. Exposure of the initiator layers to the monomer solution leads to selective chain growth polycondensation of the monomer from the surface, resulting in P3AT brushes in a very economical way. In contrast to the P3AT films prepared by traditional solvent casting methods, our approach leads to mechanically robust CP films, stable against delamination. We believe that our approach will be helpful in the fabrication of all-plastic devices.