Variable range hopping in polypyrrole films of a range of conductivities and preparation methods

Abstract

The electronic transport mechanism in polypyrrole is discussed in terms of Mott variable range hopping (VRH) in samples with a wide range of conductivities and which have been formed using different doping techniques. Samples were synthesized in both aqueous and organic media and samples were either doped during polymerization or dedoped afterwards giving a three order of magnitude range of conductivities at 300 K and a range of sample morphologies. No difference in behavior is observed for materials with different morphologies, suggesting that transport predominantly involves monomer units and occurs independent of structure. The various transport parameters obtained appear reasonable with the exception of the apparent ‘‘hopping attempt frequency,’’ related to the phonon frequency in VRH, some values of which are anomalously high. The density of states at the Fermi level was found to be between 5×1018 and 1×1022 eV−1 cm−3 for a range of samples and the mean hopping distances ranged between 2 and 34 monomer units. The minimum hopping distance of 2 monomer units is consistent with electron delocalization on individual monomer units. An upper limit of conductivity in polypyrrole of no more than 400 S cm−1 is suggested in the limit of the VRH regime in which hopping occurs between adjacent monomer units.

Conduction mechanism in H‐type polysiloxane‐polypyrrole block copolymers

“…The hopping parameters do not follow any systematic change with the supporting electrolyte concentration; however, they are found to satisfy the Mott requirements of ␣R ӷ 1 and W ӷ kT for the variable range hopping mechanism. When compared to the electrical conduction studies in amorphous materials 16,19,20 and pristine PPy and its derivatives, [21][22][23] we observed that the values of the Mott parameters for H-type polysiloxane PPy block copolymers are consistent with the hopping theory and the hopping parameters in the literature. Therefore, we conclude that in the studied temperature range conduction was predominantly provided by the Mott variable range hopping mechanism.…”

Mechanism of charge transport in poly(2,5-dimethoxyaniline)

“…͑10͒-͑13͒ and are reported in Table II. It has been assumed 13,19,26,29 that the electron wave function localization length, i.e., ␣ −1 ͑r p ͒ is equal to the width of poly͑o-methoxyaniline͒ monomer unit, i.e., ϳ5.995 Å, 24 since the electrons are always at least delocalized to the extent of the -orbitals on the monomer units. This parameter yields the density of states at the Fermi level; ͓N͑E F ͔͒ on the assumption that the wave function localization length remains independent of temperature and conductivity.…”

CdS Nanoparticles: Glucose/Starch Synthesis Method and Non Linear Electrical Properties Disperse in Polypyrrole Matrix

“…localization length of the polypyrrole monomer unit about 3Å [42,43]. The higher values of density of states at the Fermi level are found with increase of PPY content.…”