Direct current and alternating current electrical transport properties of regioregular poly[3-(4-alkoxyphenyl)-thiophenes]

In this paper, the direct current and alternating current (ac) electrical transport properties of doped and undoped regioregular poly[3-(4-alkoxyphenyl)-thiophenes], where the alkoxy groups are O-(CH2)(n-1)CH3 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-alkoxylphenyl)-thiophenes with molecular oxygen in presence of VO(acac)2, 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 mu 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. (C) 2007 American Institute of Physics.