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The transport properties of electrons and holes in a poly(p-phenylene vinylene)-based polymer light-emitting diode (PLED) have been investigated. Using admittance spectroscopy, we are able to simultaneously obtain the electron and hole mobility, μ=μ0 exp(γE), in a single PLED. The dynamics of the electron and hole transport are separated in the frequency domain as a result of the different transit times. At room temperature, we find μ0=5.6×10−11 m2/V s and γ=5.0×10−4 (m/V)1/2 for holes. For electrons μ0=1.0×10−12 m2/V s and γ=8.0×10−4 (m/V)1/2 are obtained.

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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...