The interplay between inter-and intrachain charge transport in bulk polythiophene in the hopping regime has been clarified by studying the conductivity s as a function of frequency v͞2p (up to 3 THz), temperature T, and doping level c. We present a model which quantitatively explains the observed crossover from quasi-one-dimensional transport to three-dimensional hopping conduction with increasing doping level. At high frequencies the conductivity is dominated by charge transport on onedimensional conducting chains. PACS numbers: 71.20.Rv, 71.55.Jv, 72.60. + g, 72.80.Le The charge transport mechanisms in conjugated polymers, although extensively studied over the past two decades, are still far from being completely understood. Neither the behavior around the insulator-to-metal transition (IMT), which can be induced in several polymer materials upon appropriate doping, nor the nature of hopping transport in the deeply insulating regime is yet resolved. While some studies indicate that transport is dominated by hops between three-dimensional (3D), well conducting regions [1,2], in other cases the strongly one-dimensional (1D) character of the polymer systems appears to be a crucial factor [3][4][5].In investigating the nature of hopping transport in conjugated polymers, studying the temperature and doping level dependence of the dc conductivity is an important tool. Since the dc conductivity is determined by the weakest links in the conducting path spanning the sample, the study of s dc ͑T ͒ gives insight in the slowest relevant transport processes in the system.On the insulating side of the IMT, the dc conductivity is predicted by many models to follow the well-known hopping expressionwhere the value of g and the interpretation of T 0 depend on the details of the model. The original Mott theory for 3D variable range hopping with a constant density of states (DOS) at the Fermi energy predicts g 1͞4 [6], while several modifications of the model have been proposed to describe the frequently observed value g 1͞2. Studying the dependence of g and T 0 on doping level c provides the opportunity to discriminate between the various hopping models and extract parameters determining the conductive properties such as the DOS and the localization length.While the dc conductivity is sensitive to the slowest transport processes, the ac conductivity s͑v͒ provides information about processes occurring at time scales t ഠ v 21 . Especially in conjugated polymers, where intrachain and interchain transition rates may differ by orders of magnitude, knowledge of s͑v͒ at high frequencies can help to clarify the properties of charge transport on a polymer chain.In this Letter, we present a systematic study of the charge transport in a conjugated polymer far away from the IMT, as a function of frequency, temperature, and doping level. By selecting a polymer system with very low interchain mobility, a separation of interchain and intrachain contributions to the conductivity can be made when the applied frequency is varied over 12 decade...

Dye doping is a promising way to increase the spectral purity of polymer light-emitting diodes (LEDs). Here we analyze the frequency and field dependence of the complex admittance of Al-Ba-PPV-PEDOT-ITO LEDs with and without dye. We compare the charge carrier mobilities of pristine and dye-doped double-carrier and hole-only (Au replacing Al-Ba) devices. Dye doping is shown to significantly influence the electron mobilities while the hole mobilities are left unchanged and thereby changing the carrier balance in a double carrier device towards that of a hole only device. The minimum in the LED capacitance as function of voltage appears to be an excellent probe for the electron trapping phenomenon underlying the reduction of the mobility.

We show how the dielectric response of powders of semiconducting nanocrystals can be used to extract the intrinsic conductivity of the nanocrystals. The method is applied to powders of nanocrystals of semiconductive aquocyanophthalocyaninatocobalt (III) (Phthalcon-11), a promising filler material for conducting composites, and published data of silicon.1 Introduction The intrinsic conductivity of nanosized crystals is difficult to measure. Four points measurements on nanosized particles are hardly possible and have been achieved for carbon nanotubes only because of their considerable length (> 1 µm), while Hall measurements combined with ESR-based techniques need great care and are not simply analyzed [1,2]. DC-conductivity measurements on powders are most likely strongly hindered by the electrical and grain contacts, and dielectric measurements in the radio-frequency range on doped semiconducting crystals without ohmic contacts [3,4] have shown the danger of a simplified analysis even for large single crystals.Here we have set ourselves the goal to estimate the intrinsic Drude and possible other contributions to the conductivity of semiconducting nanosized particles by dielectric spectroscopy over a large frequency range. It is well known that the dielectric response of disordered materials like pressed powders exhibit an astonishingly similar response, even up to the far-infrared [5,6]. For that reason to distill physical relevant parameters seems a quite disappointing enterprize, but by using characteristic frequencies and temperatures was shown to be possible [7][8][9]. For the present samples, which were powders of Phthalcon-11 nanocrystals, such pronounced features are even lacking, and the analysis is primarily based on fitting with physical plausible parameters, of which the consistency with the phase sensitive data could be checked accurately. Published data on silicon are analyzed in a similar way as a consistency check.

Phthalcon-11 (aquocyanophthalocyaninatocobalt (III)) forms semiconducting nanocrystals that can be dispersed in epoxy coatings to obtain a semiconducting material with a low percolation threshold. We investigated the structure-conductivity relation in this composite and the deviation from its optimal realization by combining two techniques. The real parts of the electrical conductivity of a Phthalcon-11/epoxy coating and of Phthalcon-11 powder were measured by dielectric spectroscopy as a function of frequency and temperature. Conducting atomic force microscopy (C-AFM) was applied to quantify the conductivity through the coating locally along the surface. This combination gives an excellent tool to visualize the particle network. We found that a large fraction of the crystals is organized in conducting channels of fractal building blocks. In this picture, a low percolation threshold automatically leads to a conductivity that is much lower than that of the filler. Since the structure-conductivity relation for the found network is almost optimal, a drastic increase in the conductivity of the coating cannot be achieved by changing the particle network, but only by using a filler with a higher conductivity level.

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Please check the document version of this publication:• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: openaccess@tue.nl providing details and we will investigate your claim. Conducting submicron particles are well suited as filler particles in nonconducting polymer matrices to obtain a conducting composite with a low percolation threshold. Going to nanometer-sized filler particles imposes a restriction to the conductivity of the composite, due to the reduction of the density of states involved in the hopping process between the particles, compared to its value within the crystallites. We show how those microscopic parameters that govern the charge-transport processes across many decades of length scales can accurately and consistently be determined by a range of dielectric-spectroscopy techniques from a few hertz to infrared frequencies. The method, which is suited for a variety of systems with restricted geometries, is applied to densely packed 7-nm-sized tin oxide crystalline particles with various degree of antimony doping and the quantitative results unambiguously show the role of the nanocrystal charging energy in limiting the hopping process.

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DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement: