Doping, density of states, and conductivity in polypyrrole and poly(p-phenylene vinylene) (original) (raw)
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Wide Energy-Window View on the Density of States and Hole Mobility in Poly(p-Phenylene Vinylene)
Physical Review Letters, 2004
Using an electrochemically gated transistor, we achieved controlled and reversible doping of poly(p-phenylene vinylene) in a large concentration range. Our data open a wide energy-window view on the density of states (DOS) and show, for the first time, that the core of the DOS function is Gaussian, while the low-energy tail has a more complex structure. The hole mobility increases by more than 4 orders of magnitude when the electrochemical potential is scanned through the DOS.
Electronic Conduction in Polymers. I. The Chemical Structure of Polypyrrole
Australian Journal of Chemistry, 1963
The pyrolysis of tetraiodopyrrole in an inert atmosphere at temperatures from 120-700� yields black, infusible, amorphous polymers insoluble in solvents. Depending on the pyrolysis temperature, iodine may be present in the polymers as iodine of substitution and as chemisorbed molecular iodine, which is very tenaciously held. As a first approximation, the structure may be regarded as a three-dimensional network of pyrrole rings cross-linked in a nonplanar fashion by direct carbon to carbon linkages. The secondary nitrogen atoms form a hydroquine type system which may be oxidized by iodine or molecular oxygen under alkaline conditions. The extent of oxidation depends on the hydroxyl ion concentration. The nonplanarity of the oxidized quinonoid system renders it unstable but stability is enhanced, as in the triphenylmethane dyestuffs, by the formation of a carbinol. Despite their nonplanarity polypyrroles are relatively good conductors of electricity. The resistivity ranges from 1-200 ...
Journal of Applied Physics, 2005
We present a systematic study of the influence of the processing conditions on the charge-carrier mobility in hole-only diodes and field-effect transistors ͑FETs͒ based on alkoxy-substituted poly͑p-phenylene vinylene͒ ͑PPV͒. It is demonstrated that by chemical modification from asymmetrically to fully symmetrically substituted PPVs the mobility in both types of devices can be significantly improved. Furthermore, for symmetrical PPVs the mobility is strongly dependent on processing conditions, such as choice of solvents and annealing conditions. The increase in mobility is accompanied by a strong enhancement of the anisotropy in the charge transport. Ultimately, mobility of up to 10 −2 cm 2 / Vs in FETs and 10 −5 cm 2 / Vs in hole-only diodes have been achieved.
dc Conduction in electrochemically synthesized polypyrrole films
1998
DC conductivity measurements were performed by modified four-probe rig on electrochemically synthesized polypyrrole films at a temperature range of -30 • C to 120 • C. Conductivity increased with temperature. The temperature dependence of conductivity was very high for lightly doped polymers, decreasing as the doping level increased. The model used to describe the conduction process was the conduction model originally developed for amorphous silicon by Mott and Davis. When applied to conducting polymers, it assumes that electron transport originates from localized or fixed states within the polymer chain. The charge transfer between the chains takes place by hopping, referred to as phonon-assisted hopping, between two localized states. Plots of DC conductivity versus temperature can be parametrized by Mott's Variable Range Hopping conduction model. The DC conductivity of polypyrrole films doped from light to intermediate levels with p-toluene sulphonic acid were measured in the temperature range of 77K to 300K. The localization length of localized electrons was assumed to be 3Å, which is approximately equal to the length of the pyrrole monomer. Mott parameters of polypyrrole films doped with p-TS were evaluated at 300K and 10K. Results were found to be consistent with the Mott's requirement that αR >> 1 . Theoretical values of α and N (EF ) have been determined at approximately 10 8 cm −1 and 10 19 -10 20 cm −3 eV −1 , respectively. Hence according to Mott parameters determined by the experimental data for the p-TS doped polypyrrole samples, Mott parameters are seen to have a better agreement with those expected from disordered systems, particularly for lightly doped samples, indicating the suitability of Mott's model to these samples. The average hopping distance R decreased from 16Åto 4.4Åwith the increase in the doping level from 0.006 M to 0.03 M at 300K, whereas at 10K, R decreased from 37Å to 10Å over the same dopant range.
Carrier Dynamics in Conducting Polymers: Case of PF6 Doped Polypyrrole
Physical Review Letters - PHYS REV LETT, 2003
The carrier dynamics in PF 6 doped polypyrrole has been probed by dielectric spectroscopy (from 10 ÿ4 to 4 eV), down to 4.2 K. The phase-sensitive sub-THz data have assisted to resolve the discrepancies in Kramers-Kronig analysis in earlier studies. Even in metallic samples, just 1% of the carriers are delocalized, at 300 K; the fraction drops down considerably as a function of disorder, carrier density, and temperature. This subtle metallic feature and the anomalies in carrier dynamics are attributed to coherent and incoherent transport between short conjugated segments.
Electrical Properties of Polypyrrole Conducting Polymer at Various Dopant Concentrations
Polypyrrole conducting polymer was prepared by chemical reaction method with various concentrations of iron (III) chloride (FeCl3) as dopant. The dc conductivity was obtained from current-voltage characteristic by using parallel-plate techniques in the temperature range of 100-300K. With the involvement of chloride, Cl -in the polymeric chain, the conductivity increased as temperature and the dopant concentration increased. To describe the electrical transport process, Mott's 1-D, 2-D and 3-D variable range hopping (VRH) models have been considered. The result gives evidence of transport mechanism based on Mott's 3-D VRH mechanism for all various dopant concentrations studied.
Conducting Polymers—Modern Semiconductors: A Theoretical Overview
In the present manuscript a brief discussion about the new generation of plastic or polymer also called materials of 21 st century, which could be conductive once it undergoes a structural modification process called doping has been presented. Also how theoretical methods utilizing quantum chemical calculations can be employed to study various properties of these new generation polymers and what informations can be drawn from them about their structural and electronic properties has been discussed.
On the structure and transport properties of polypyrroles
1992
Conducting organic polymers have attracted much attention as electronic materials, since Shirakawa et al. reported [1] an increase of several orders of magnitude in the electrical conductivity of polyacetylene after reaction with oxidants. This oxidative process giving positively charged structures is known as ,,doping,, owing to its analogy with the doping process for inorganic semiconductors. However, from a chemical point of view, the two types of doping correspond to different types of chemical transformation [2]: the oxidative process upon the non-conducting neutral polymer results in an positively charged oxidized molecule which in its solid structure requires the incorporation of a counter anion. Obviously, the nature of this anion determines the physical properties of the material. In spite of the high electrical conductivities reported for polyacetylene [3] (see Scheme 1) it rapidly degenerates in air. Other it conjugated organic conductors are thus attracting more attentio...