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SummaryEfficient fibre formation for all regioregular poly(3-alkylthiophene)s (P3ATs) with alkyl chain lengths (A) between 3 and 9 carbon atoms has been accomplished in several solvents. It was observed that for the aliphatic and (chlorinated) aromatic hydrocarbon solvents used, the solvent refractive index offers some rationale to predict the feasibility of a solvent for fibre formation. The fibres were separated from remaining non-organised polymer by centrifugation. This enabled the characterisation of the isolated fibres in function of alkyl chain length (A) with TEM, AFM, XRD and UV-Vis spectroscopy. The fibres are 20 +/− 5 nm wide and 0.5 to >4 µm long and mainly crystallize in the common type I crystal phase. The order within the fibres was probed with XRD, SAED, and UV-Vis and was found to strongly improve with increasing alkyl chain length in going from P33T to P35T, resulting in a longer conjugation length. For P35T to P39T the improvement in order is only marginal.Fibres from P37T, were found to mainly crystallize in a crystal phase slightly different from type I that we refer to as type I'. This new crystal structure has a lattice constant a that is marginally shorter than that of phase I and a slightly longer lattice constant b of 4.0 Å and thus in XRD can hardly be distinguished from phase I. It is furthermore characterized by a blue-shifted absorption band in UVVis spectroscopy. The type I' fibres were converted in normal type I fibres in the solid state at 70 °C and in solution around 50 °C.

The mass production technique of gravure contact printing is used to fabricate state‐of‐the art polymer field‐effect transistors (FETs). Using plastic substrates with prepatterned indium tin oxide source and drain contacts as required for display applications, four different layers are sequentially gravure‐printed: the semiconductor poly(3‐hexylthiophene‐2,5‐diyl) (P3HT), two insulator layers, and an Ag gate. A crosslinkable insulator and an Ag ink are developed which are both printable and highly robust. Printing in ambient and using this bottom‐contact/top‐gate geometry, an on/off ratio of >104 and a mobility of 0.04 cm2 V−1 s−1 are achieved. This rivals the best top‐gate polymer FETs fabricated with these materials. Printing using low concentration, low viscosity ink formulations, and different P3HT molecular weights is demonstrated. The printing speed of 40 m min−1 on a flexible polymer substrate demonstrates that very high‐volume, reel‐to‐reel production of organic electronic devices is possible.

Conductive atomic force microscopy (CAFM) is introduced to perform electrical characterization of organic photovoltaic blends with high spatial resolution. Reference blends used in organic bulk heterojunction solar cells are investigated. The ability of CAFM to electrically evidence phase separated donor and acceptor regions is demonstrated. Furthermore, local spectroscopy is performed to analyze charge transport mechanisms in the blends. Significant modifications of the electrical properties of the semiconducting polymers are shown to occur after blending with fullerene derivatives. Finally, the sensitivity of CAFM to photoelectrical phenomena is revealed. Current variations of few picoamperes are locally observed under illumination of P3HT:PCBM.

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Label-free detection of DNA molecules on chemically vapor-deposited diamond surfaces is achieved with spectroscopic ellipsometry in the infrared and vacuum ultra-violet range. This non-destructive method has the potential to yield information on the average orientation of single as well as double stranded DNA molecules, without restricting the strand length to the persistence length. The orientational analysis based on electronic excitations in combination with information from layer thicknesses, provides a deeper understanding of biological layers on diamond. The π-π* transition dipole moments, corresponding to a transition at 4.74 eV, originate from the individual bases. They are in a plane perpendicular to the DNA backbone with an associated n-π* transition at 4.47 eV. For 8-36 bases of single and double stranded DNA covalently attached to ultra-nanocrystalline diamond, the ratio between in-and out-of-plane components in the best fit simulations to the ellipsometric spectra yields an average tilt angle of the DNA backbone with respect to the surface plane ranging from 45° to 52°. 2We comment on the physical meaning of the calculated tilt angles. Additional information is gathered from atomic force microscopy, fluorescence imaging, and wetting experiments. The results reported here are of value in understanding and optimizing the performance of the electronic read-out of a diamond-based label-free DNA hybridization sensor.

The morphology and electrical properties of hybrids of a semiconducting polymer (namely poly(3-hexylthiophene) P3HT) and carbon nanotubes are investigated at the nanoscale with a combination of Scanning Probe Microscopy techniques, i.e., Conductive Atomic Force Microscopy (C-AFM) and time-resolved Current Sensing Force Spectroscopy Atomic Force Microscopy (CSFS-AFM, or PeakForce TUNA™). This allows us to probe the electrical properties of the 15 nm wide P3HT nanofibers as well as the interface between the polymer and single carbon nanotubes. This is achieved by applying controlled, low forces on the tip during imaging, which allows a direct comparison between the morphology and the electrical properties at the nanometre scale.

New functionalized poly(3-hexylthiophene)s (P3HT) have been designed and synthesized with the aim of increasing the dispersion of carbon nanotubes (CNT) in solutions and in thin films of semiconducting polymers. Dispersion in solution has been assessed by sedimentation tests while the thin film morphology has been analyzed by TEM and AFM. Both the physisorption of P3HT chains (via pyrene end-groups) or their chemical grafting (onto amine functions generated on the CNT surface) lead to a much better dispersion in solution and in the solid. In thin films, P3HT fibrils are observed to arrange perpendicular to the CNT surface, which can be understood on the basis of molecular modeling simulations. Finally, the effect of dispersing those P3HT/CNT nanocomposites in bulk-heterojunction P3HT-based photovoltaic devices has been evaluated.