Carrier Dynamics in Conducting Polymers: Case ofPF6Doped Polypyrrole

Abstract

The carrier dynamics in PF6 doped polypyrrole has been probed by dielectric spectroscopy (from 10(-4) 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.

Doping, density of states, and conductivity in polypyrrole and poly(p-phenylene vinylene)

“…For m * equal to the free electron mass, the number of carriers for PPy M found by Romijn et al was about 3 holes/nm 3 . 8 We collected reflection data on PPy samples with very different room temperature dc conductivities. The outcome of the sum-rule is somewhat arbitrary, because at energies of (∼ 3 eV) intraband excitations start playing a role as well.…”

“…8 The reflection amplitude and phase give the real and imaginary parts of the dielectric constant, see Fig. 5, where the imaginary component of the complex relative dielectric constant ǫ 2 (ω) (or the real part of the conductivity σ(ω) = ωǫ 0 ǫ 2 (ω) with ǫ 0 the vacuum dielectric constant)…”

“…4,5,6 To explain the transport data in conducting polymers in general, key ingredients are the crystalline coherence length (a few nanometers), the volume fraction of crystallinity (> 50%), the doping level, the interchain transfer integral, the energy dependence of the density of states, the extent of disorder in the material, charge repulsion and polaronic effects. 7,8,9,10,11 The relevant values of the transfer integral, the spread in its mean value due to disorder and of the Coulomb correlations are usually all around 0.1 eV or less, which is close to the thermal energy at 300 K. A systematic study of the evolution of density of states (DOS) and charge transport as a function of well controlled doping level is still lacking in several conducting polymers. In this work the difference between FeCl 3 and PF 6 doped OC 1 C 10 -PPV and PF 6 doped PPy, as a function of doping level is investigated in detail by studying both the electrochemical gated transistor (EGT) characteristics and temperature dependence of conductivity using a precise calibration of the amounts of doping.…”

Charge carrier properties below and above the metal–insulator transition in conjugated polymers – recent results

“…Here we show that if one has to explain the strong doping-concentration dependence of the dc conductance below the MIT, the variable-range hopping-mechanism between point-like sites has to be modified to allow for the growing size of the localized regions and indicate how such a modification can be justified theoretically [1]. For a characterization of the metallic state close to the MIT we use dielectric data on PPy from 10 -4 to 4 eV down to 4.2 K [2], to argue that only 1% of the carriers are delocalized. The subtle metallic features and the anomalies in carrier dynamics are modelled by coherent and incoherent transport between short conjugated segments.…”

“…The doping of polypyrrole with PF 6 is done electrochemically [2,3]. The dc-data are always taken in the ohmic regime.…”