Three dimensionality of ‘‘metallic’’ states in conducting polymers: Polyaniline

Wang, Z. H.; Li, C.; Scherr, E. M.; MacDiarmid, Alan G.; Epstein, Arthur J.

doi:10.1103/physrevlett.66.1745

Cited by 241 publications

(93 citation statements)

References 31 publications

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“…Elusive issues include the non-trivial influence of the multiple sources of disorder (for example, semi-crystallinity, paracrystallinity and nanoscale inhomogeneity [1][2][3][4][5][6][7], the elucidation of the important hopping mechanisms [1][2][3][4][7][8][9][10] , the effects of charge carrier-lattice interactions 3,4 and the identification of the ultimate limits on conductivity and mobility [1][2][3][4][5][6]11 . The latter is particularly important as, in addition to being of considerable fundamental interest the upper limits on conductivity and mobility also limit device performance (for example, transistor output current and operating frequency).…”

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Hopping transport and the Hall effect near the insulator–metal transition in electrochemically gated poly(3-hexylthiophene) transistors

et al. 2012

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Despite 35 years of investigation, much remains to be understood regarding charge transport in semiconducting polymers, including the ultimate limits on their conductivity. Recently developed ion gel gating techniques provide a unique opportunity to study such issues at very high charge carrier density. Here we have probed the benchmark polymer semiconductor poly(3-hexylthiophene) at electrochemically induced three-dimensional hole densities approaching 10 21 cm À 3 (up to 0.2 holes per monomer). Analysis of the hopping conduction reveals a remarkable phenomenon where wavefunction delocalization and Coulomb gap collapse are disrupted by doping-induced disorder, suppressing the insulator-metal transition, even at these extreme charge densities. Nevertheless, at the highest dopings, we observe, for the first time in a polymer transistor, a clear Hall effect with the expected field, temperature and gate voltage dependencies. The data indicate that at such mobilities (B0.8 cm 2 V À 1 s À 1 ), despite the extensive disorder, these polymers lie close to a regime of truly diffusive band-like transport.

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Hopping transport and the Hall effect near the insulator–metal transition in electrochemically gated poly(3-hexylthiophene) transistors

et al. 2012

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“…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.…”

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Dopant-Induced Crossover from 1D to 3D Charge Transport in Conjugated Polymers

et al. 1999

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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...

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“…1 It is reported that the doped charge carriers in the protonated PANI are predominantly localized in the amorphous regions, giving rise to local moments, while a relatively small fraction of the doped carriers has three-dimensionally extended wave-functions in the crystalline parts of the sample. 2 Since, in the doped polyaniline the charge and the spins are associated with the same carrier, 3 magnetic susceptiblity and ESR measurements can provide detailed understanding about the microscopic nature of these carriers. We report here a detailed study of the nature of charge carriers in a recently reported conducting PANI, 4 doped with BF 3 , which has so far been characterized only by spectroscopic methods.…”

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confidence: 99%