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

In this paper, the d.c. and a.c. (ac) elec. transport properties of doped and undoped regioregular poly[3-(4-alkoxyphenyl)-thiophenes], where the alkoxy groups are O-(CH2)n-1CH3 with n = 1,4,6, and 8, have been investigated. The films have been synthesized by an exptl. procedure based on the oxidn. of 3-(4-alkoxyphenyl)-thiophenes with mol. 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. D.c.-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, resp. Due to the film ordered structure, a significant elec. 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, d.c. and a.c. cond. temp. dependence is discussed in the framework of thermally activated hopping and tunneling models.