Non-linear charge transport in polythiophene under high AC field (original) (raw)
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Electrical conductivity and relaxation in poly(3-hexylthiophene)
Physical Review B, 2009
We studied the complex conductivity of regioregular poly͑3-hexylthiophene͒ ͑P3HT͒ in the temperature range between 193-333 K ͑−80°C to 60°C͒ and in the frequency range from the direct current ͑dc͒ to 12 GHz. The identified relaxation process was investigated by quasielastic neutron scattering ͑QENS͒. The dielectric loss peak extracted from complex conductivity corresponds to local molecular motions having an activation energy of about 9 kJ/mol, which agrees well with the QENS results. The molecular motions of the hexyl side groups in poly͑3-hexylthiophene͒ contribute to this relaxation process in P3HT, which is coupled with a cooperative charge transport along the P3HT chains. In the cutoff frequency range, the real part of complex conductivity ͑Ј͒ gradually transitions to a frequency-independent conductivity ͑ ϰ Ј ͒, which is thermally activated. The activation energy of Ј at 50 MHz is about 80 meV. In comparison, the activation energy of the dc conductivity, 0 , is larger, about 280 meV, while the value of 0 , is many orders of magnitude smaller than ϰ Ј We conclude that the local relaxation of the hexyl side groups contribute to a topological disorder in the polymer structure. As a consequence the energy barriers of the charge transport increase and the conductivity decreases. At 190 K the conductivity decreases from the disorder-free ϰ Ј of approximately 5 ϫ 10 −4 S / m to 0 of about 1 ϫ 10 −9 S / m.
Journal of Applied Physics, 2007
In this paper, the direct current and alternating current ͑ac͒ electrical transport properties of doped and undoped regioregular poly͓3-͑4-alkoxyphenyl͒-thiophenes͔, where the alkoxy groups are O-͑CH 2 ͒ n−1 CH 3 with n =1,4,6, and 8, have been investigated. The films have been synthesized by an experimental procedure based on the oxidation of 3-͑4-alkoxylphenyl͒-thiophenes with molecular oxygen in presence of VO͑acac͒2, as the catalyst. Unlike other examples reported in the literature, this approach allows obtaining well structured spin-coated films without the necessity of further processes, such as annealing or exposition to solvent vapors. Direct current-voltage measurements, performed in planar and transverse configuration on 1 m thick films, show both ohmic and space charge limited current behavior, at low and high applied fields, respectively. Due to the film ordered structure, a significant electrical anisotropy was found. In order to deeply investigate the basic conduction mechanisms, ac measurements have been also carried out in the frequency range between 100 Hz and 100 kHz. Finally, direct current and alternating current conductivity temperature dependence is discussed in the framework of thermally activated hopping and tunneling models.
Thin Solid Films, 2008
We have measured dependencies of conductivity and carrier mobility on the temperature and applied electric field in the samples of regioregular poly(3-hexylthiophene) (P3HT) and poly(3-octylthiophene) (P3OT) by the Charge Extraction by Linearly Increasing Voltage (CELIV) method. The samples were produced by the drop-casting and spin-coating methods on the Indium-Tin-Oxide substrate and provided with Al contact at the top. We had observed the "negative" mobility dependence at low electric fields, i.e., the mobility used to decrease with increasing electric field. To our knowledge this is the first time, when such behaviour was confirmed by the CELIV method in P3OT samples, though it was reported earlier by the Time-of-Flight (TOF) in other disordered materials.
Ionic transport and electronic structure in poly(3,4ethylenedioxythiophene)
Solid State Ionics, 1996
A member of the polythiophene family, poly(3,4-ethylenedioxythiophene) (PEDOT), shows interesting electronic, optical and electrochemical properties, making the polymer suitable as electrode material in different electrochromic applications. It has been characterized using standard electrochemical techniques, optical absorption spectroscopy and bending beam methods.
Chemistry of Materials, 1989
We report chemically reversible electrochemical reduction of poly(3-methylthiophene) and electrical and optical properties for the reduced material. It is well-known that large increases in conductivity occur upon oxidation of a number of thiophene-based polymers.'I2 Recently, conducting polymers have been shown to have a finite potential window of high conductivity upon ~x i d a t i o n .~-~ In the case of poly(3-methylthi0phene)~ oxidation to yield the nonconducting oxidized state requires the use of unusual media to minimize degradation. This result has prompted us to examine poly(3-methylthiophene) at the opposite extreme, reduction, to completely define the potential * Author to whom correspondence should be addressed.
Journal of Polymer Science Part B: Polymer Physics, 2010
We present here the evidence for the origin of dc electrical conduction and dielectric relaxation in pristine and doped poly(3-hexylthiophene) (P3HT) films. P3HT has been synthesized and purified to obtain pristine P3HT polymer films. P3HT films are chemically doped to make conducting P3HT films with different conductivity level. Temperature (77-350 K) dependent dc conductivity (r dc ) and dielectric constant (e 0 (x)) measurements on pristine and doped P3HT films have been conducted to evaluate dc and ac electrical conduction parameters. The relaxation frequency (f R ) and static dielectric constant (e 0 ) have been estimated from dielectric constant measure-ments. A correlation between dc electrical conduction and dielectric relaxation data indicates that both dc and ac electrical conductions originate from the same hopping process in this system.
The Journal of Physical Chemistry C, 2010
Conducting polymers have widespread industrial applications owing to a unique combination of mechanical, optical, and electronic properties. Specifically, the family of poly(alkylenedioxythiophene) derivatives has received much attention due to its inherently high conductivity, environmental stability, and tunability. However, although the electron-donating characteristics of the alkoxy moieties are well-known, the source of the differences among these substitutions has been limited to speculative arguments based on bulk properties. To address these issues, a combined electrochemical and density functional theory (DFT) study was undertaken that reveals the significant electronic and geometric characteristics responsible for the comparative properties of these materials. It was found that the geometry of the alkylenedioxy backbone substitution modulates the π-donating character of the oxygen and that this directly influences the onset of p-doped conductivity. These studies also indicate that this framework equally applies to several other heterocyclic polymer systems. An improved theory for these materials is expected to provide the insight and knowledge base for new conducting polymers with enhanced stability and optoelectronic properties.
Molecular Weight Dependent Charge Carrier Mobility in Poly(3,3‘ ‘-dioctyl-2,2‘:5‘,2‘ ‘-terthiophene)
The Journal of Physical Chemistry B, 2006
Poly(3,3′′-dioctyl-2,2′:5′,2′′-terthiophene), a polymer recently used for the fabrication of organic field effect transistors, has been fractionated into five fractions distinctly differing in their molecular weights (M n ), with the goal of determining the influence of the degree of polymerization (DP n ) on its principal physicochemical parameters. It has been demonstrated that within the M n range studied (from 1.5 kDa to 10.5 kDa by SEC), corresponding to DP n from 10 to 38, the polymer band gap steadily decreases with growing molecular weight, which is clearly manifested by an increasing bathochromic shift of the band originating from the π-π* transition. The same trend is observed for the HOMO level, determined from the onset of the p-doping in cyclic voltammetry, which shifts from -5.10 eV to -4.90 eV for the lowest and the highest molecular weight fractions, respectively. The most pronounced influence of DP n has been found for the charge carriers' mobilitys one of the most important parameters of field effect transistors (FETs) fabricated from this polymer. A fourfold increase in DP n results in an increase of the carriers' mobility by more than 3 orders of magnitude. Comparison of these results with those obtained for fractionated regioregular poly(3-hexylthiophene) shows a strikingly similar behavior of both polymers with respect to the molecular weight.
Chemistry of Materials, 2007
Optoelectronic and charge-transport related properties of a series of 3,6-diphenyl-s-tetrazine derivatives, including F, Cl, Br, and CN substituents, have been analyzed. The molecular structure and electronic properties of the new fluorine-containing derivative, bis(3,6-difluorophenyl)-s-tetrazine, were explored by spectroscopic, electrochemical, and theoretical methods. The effects of the substituent on the pristine compound have been assessed from a theoretical perspective, showing that the fluorinated and brominated derivatives have the highest predicted electron mobilities, whereas the cyano derivative is foreseen to undergo the most efficient electron injection process.