http://www.one-p.eu daily 1 2010-10-05T13:12:14Z http://www.one-p.eu/publication/publication/role-of-ge20120120111942 We report a comparative study of OFET devices based on zone-cast layers of three tetrathiafulvalene (TTF) derivatives in three configurations of electrodes in order to determine the best performing geometry. The first testing experiments were performed using SiO2/Si substrates. Then the optimum geometry was employed for the preparation of flexible OFETs using Parylene C as both substrate and dielectric layer yielding, in the best case, to devices with lFET = 0.1 cm2/V s. With the performed bending tests we determined the limit of curvature radius for which the performance of the OFETs is not deteriorated irreversibly. The investigated OFETs are sensitive to ambient atmosphere, showing reversible increase of the source to drain current upon exposition to air, what can be explained as doping of TTF derivative by oxygen or moisture No publisher Rovira wp1 2012-01-20T10:47:20Z Publication http://www.one-p.eu/publication/publication/mixed-quan20111223100828 The electron-phonon coupling is critical in determining the intrinsic charge carrier and exciton transport properties in organic materials. In this study, we consider a Su-Schrieffer-Heeger (SSH) model for molecular crystals, and perform numerical benchmark studies for different strategies of simulating the mixed quantum-classical dynamics. These methods, which differ in the selection of initial conditions and the representation used to solve the time evolution of the quantum carriers, are shown to yield similar equilibrium diffusion properties. A hybrid approach combining molecular dynamics simulations of nuclear motion and quantum-chemical calculations of the electronic Hamiltonian at each geometric configuration appears as an attractive strategy to model charge dynamics in large size systems “on the fly,” yet it relies on the assumption that the quantum carriers do not impact the nuclear dynamics. We find that such an approximation systematically results in overestimated charge-carrier mobilities, with the associated error being negligible when the room-temperature mobility exceeds ∼4.8 cm2/Vs (∼0.14 cm2/Vs) in one-dimensional (two-dimensional) crystals. No publisher DeHalleux wp1 2011-12-23T09:08:59Z Publication http://www.one-p.eu/publication/publication/belt-shape20111223100151 Linear π-conjugated oligomers have been widely investi- 18 gated, but the behavior of the corresponding cyclic oligomers is poorly 19 understood, despite the recent synthesis of π-conjugated macrocycles such 20 as [n]cycloparaphenylenes and cyclo[n]thiophenes. Here we present an 21 efficient template-directed synthesis of a π-conjugated butadiyne-linked 22 cyclic porphyrin hexamer directly from the monomer. Small-angle X-ray 23 scattering data show that this nanoring is shape-persistent in solution, even 24 without its template, whereas the linear porphyrin hexamer is relatively 25 flexible. The crystal structure of the nanoring
template complex shows that most of the strain is localized in the acetylenes; the 26 porphyrin units are slightly curved, but the zinc coordination sphere is undistorted. The electrochemistry, absorption, and 27 fluorescence spectra indicate that the HOMO
LUMO gap of the nanoring is less than that of the linear hexamer and less than that 28 of the corresponding polymer. The nanoring exhibits six one-electron reductions and six one-electron oxidations, most of which are 29 well resolved. Ultrafast fluorescence anisotropy measurements show that absorption of light generates an excited state that is 30 delocalized over the whole π-system within a time of less than 0.5 ps. The fluorescence spectrum is amazingly structured and red- 31 shifted. A similar, but less dramatic, red-shift has been reported in the fluorescence spectra of cycloparaphenylenes and was 32 attributed to a high exciton binding energy; however the exciton binding energy of the porphyrin nanoring is similar to those of 33 linear oligomers. Quantum-chemical excited state calculations show that the fluorescence spectrum of the nanoring can be fully 34 explained in terms of vibronic Herzberg
Teller (HT) intensity borrowing. No publisher DeHalleux wp2 2011-12-23T09:02:37Z Publication http://www.one-p.eu/publication/publication/supramolec20111223094928 Molecular dynamics (MD) simulations have been coupled to valence bond/Hartree-Fock (VB/HF) quantum-chemical calculations to evaluate the impact of diagonal and offdiagonal disorder on charge carrier mobilities in self-assembled one-dimensional stacks of a perylene diimide (PDI) derivative. The relative distance and orientation of the PDI cores probed along the MD trajectories translate into fluctuations in site energies and transfer integrals that are calculated at the VB/HF level. The charge carrier mobilities, as obtained from time-of-flight numerical simulations, span several orders of magnitude depending on the relative time scales for charge versus molecular motion. Comparison to experiment suggests that charge transport in the crystal phase is limited by the presence of static defects No publisher DeHalleux wp1 2011-12-23T08:49:59Z Publication http://www.one-p.eu/publication/publication/conformati20111220141408 Efficient Cu-catalyzed 1,3-dipolar cycloaddition reactions have been used to prepare two series of three regioisomers of G-1 and G-2 poly(triazole-pyridine) dendrons. The G-1 and G-2 dendrons consist of a branched yet conformationally pre-organized 2,6-bis(phenyl/pyridyl-1,2,3-triazol-4-yl)pyridine (BPTP) monomeric and trimeric core, respectively, carrying one focal and either two or four peripheral alkyl side chains. In the solid state, the conformation and supramolecular organization was studied by means of a single crystal X-ray structure analysis of one derivative. At the liquid-solid interface, the self-assembly behavior was investigated by scanning tunneling microscopy (STM) on graphite surfaces. Based on the observed supramolecular organization it appears that the subtle balance between conformational preferences inherent in the dendritic backbone on the one side and the adsorption and packing of the alkyl side chains on the graphite substrate on the other side dictate the overall structure formation in 2D. No publisher DeHalleux wp4 2011-12-20T13:14:33Z Publication http://www.one-p.eu/publication/publication/controllin20111220130944 The dimensionality of charge transport in an organic electrochemical transistor depends on the degree of advancement of the electrochemical half-reaction at the organic semiconductor/electrolyte interface. A carbon nanotube (CNT) nanoporous gate electrode leads to bulk transport in the semiconductor, while a flat Au gate electrode allows for localizing of the electrochemical oxidation of the semiconducting polymer at the organic semiconductor/electrolyte interface. No publisher DeHalleux wp1 2011-12-20T12:34:12Z Publication http://www.one-p.eu/publication/publication/towards-fl20111220125351 The article reports a promising approach to engineering biocompatible and highly piezoresistive membrane for flexible weightless transparent pressure sensors. The developed membrane is based on a bi layer (BL) film composing a polycarbonate (PC) matrix “self-metallized” with a highly piezoresistive organic molecular metal. The key role of the matrix thickness in the enhancement of the pressure sensitivity of BL film-based membranes was shown. The presented approach permits engineering biocompatible all-organic membranes with pressure sensitivity being of 8 /mmHg. To determine restrictions for BL films applications in biomedical high-tech, the effect of the body temperature on membrane piezoresitive properties was studied. The pressure tests at 26 oC, 33 oC and 40 oC showed that the body temperature does not significantly influence on the membrane pressure sensitivity. Therefore this type of membrane sensors is able to take the place of conventional metal-based strain and pressure gages in monitoring biomedical high-tech. No publisher DeHalleux wp1 2011-12-20T11:54:38Z Publication http://www.one-p.eu/publication/publication/origin-of-20111220122114 Understanding the mechanisms limiting ambipolar transport in conjugated polymer field-effect transistors (FETs) is of both fundamental and practical interest. Here, we present a systematic study comparing hole and electron charge transport in an ambipolar conjugated polymer, semicrystalline poly(3,3-di-n-decylterselenophene) (PSSS). Starting from a detailed analysis of the device characteristics and temperature/charge-density dependence of the mobility, we interpret the difference between hole and electron transport through both the Vissenberg- Matters and the mobility-edge model. To obtain microscopic insight into the quantum mechanical wave function of the charges at a molecular level, we combine charge modulation spectroscopy (CMS) measuring the charge-induced absorption signatures from positive and negative polarons in these ambipolar FETs with corresponding density functional theory (DFT) calculations.We observe a significantly higher switch-on voltage for electrons than for holes due to deep electron trap states, but also a higher activation energy of the mobility for mobile electrons. The CMS spectra reveal that the electrons that remain mobile and contribute to the FET current have a wave function that is more localized onto a single polymer chain than that of holes, which is extended over several polymer chains.We interpret this as evidence that the transport properties of the mobile electrons in PSSS are still affected by the presence of deep electron traps. The more localized electron state could be due to the mobile electrons interacting with shallow trap states in the vicinity of a chemical, potentially water-related, impurity that might precede the capture of the electron into a deeply trapped state. No publisher DeHalleux wp1 2012-01-19T15:04:19Z Publication http://www.one-p.eu/publication/publication/a-benzotri20111213084641 A new benzotrithiophene-containing donor–acceptor type copolymer for polymer solar cells is reported. The promise of benzotrithiophene as a weak donor material is reflected in a polymer band gap of 1.75 eV affording a high Voc of 0.81 V and a moderate PCE of 2.2% in a polymer solar cell. No publisher Rand wp2 2011-12-23T09:24:15Z Publication http://www.one-p.eu/publication/publication/single-ste20111211144311 Here, we report a simple, alternative route towards high-mobility structures of the small-molecular semiconductor 5,11-bis(triethyl silylethynyl) anthradi-thiophene (TES ADT) that requires one single processing step without the need for any post-deposition processing. The method relies on careful control of the casting temperature of the semiconductor and allows rapid production of transistors with uniform and reproducible device performance over large areas. No publisher DeHalleux wp5 2012-01-09T08:11:41Z Publication http://www.one-p.eu/publication/publication/influence-20111211141715 Blends of chemically readily accessible, small-molecular arylacetylene derivatives with poly(vinylidene fluoride) (PVDF) are presented that allow reliable solution processing of field-effect transistor (FET) architectures with electronic characteristics comparable to those of the neat semiconductors. We demonstrate that having the chemical means and corresponding processing protocols to control solid-state microstructures by either adjusting the chemical nature of the organic semiconductor, blend composition or deposition temperature, permit straight-forward comparison between materials and allow probing if electronic characteristics are affected by the chemical structure of the organic semiconductor and/or selected processing protocols. No publisher DeHalleux wp5 2011-12-11T13:51:43Z Publication http://www.one-p.eu/publication/publication/the-influe20111211140939 The influence of solid-state microstructure on the optoelectronic properties of conjugated polymers is widely recognized, but still poorly understood. Here, we show how the microstructure of conjugated polymers controls the yield and decay dynamics of long-lived photogenerated charge in neat films. Poly(3-hexylthiophene) was used as a model system. By varying the molecular weight, we drive a transition in the polymer microstructure from nonentangled, chain-extended, paraffinic- like to entangled, semicrystalline (MW ¼ 5.5–347 kg/mol). The molecular weight range at which this transition occurs (MW ¼ 40–50 kg/mol) can be deduced from the drastic change in elongation at break found in tensile tests. Linear absorption measurements of free-exciton bandwidth and time-resolved microwave conductivity (TRMC) measurements of transient photoconductance track the concomitant evolution in optoelectronic properties of the polymer as a function of MW. TRMC measurements show that the yield of free photogenerated charge increases with increasing molecular weight in the paraffinic regime and saturates at the transition into the entangled, semicrystalline regime. This transition in carrier yield correlates with a sharp transition in free-exciton bandwidth and decay dynamics at a similar molecular weight. We propose that the transition in microstructure controls the yield and decay dynamics of long-lived photogenerated charge. The evolution of a semicrystalline structure with well-defined interfaces between amorphous and crystalline domains of the polymer is required for spatial separation of the electron and hole. This structural characteristic not only largely controls the yield of free charges, but also serves as a recombination center, where mobile holes encounter a bath of dark electrons resident in the amorphous phase and recombine with quasi first-order kinetics. No publisher DeHalleux wp2 2011-12-11T13:52:07Z Publication http://www.one-p.eu/publication/publication/organic-se20111211140300 No publisher DeHalleux wp2 2011-12-11T13:52:33Z Publication http://www.one-p.eu/publication/publication/feffhigh-p20111211135145 In an attempt to disentangle the effects of permittivity and surface energy of the gate insulator (expressed by its dielectric constant k and water contact angle, respectively) on the performance of organic field-effect transistors (FETs), we fabricated top- and bottom-gate FET architectures with poly(3-alkylthiophenes) (P3ATs) of different side-chain lengths, using a range of gate dielectrics. We find that this class of semiconductor, including the short butyl-(C4–) substituted derivative, is significantly less susceptible to the often detrimental effects that high-k dielectrics can have on the performance of many organic FETs. For bottom gate devices we identify the surface energy of the gate dielectric to predominantly dictate the device mobility. No publisher DeHalleux wp1 2011-12-11T13:52:59Z Publication http://www.one-p.eu/publication/publication/tuning-the20111209103704 We report on the fabrication of solution processed organic phototransistors (OPTs) based on perylenebis(dicarboximide)s (PDIs). We found that the responsivity to the photo-illumination depends on the transistor’s channel length and that it can be tuned by varying the device geometry. The analysis of different morphologies of the active semiconducting layer revealed that single PDI fibers exhibit the higher photo-response when compared to more poorly organized films. The highest responsivity value of 4.08±1.65 x 105 A/W was achieved on a multifiber based OPT. These findings represent a step forward towards the use of organic based phototransistors as photosensors. No publisher DeHalleux wp1 2012-01-20T09:37:28Z Publication