Anisotropic dc-conductivity in stretch-oriented iodine doped poly[3-(4-octylphenyl)-2,2′- bithiophene]

A square four point probe is constructed to measure anisotropic conductivity of small samples. The method is applied to measurements of the anisotropic conductivity of a conjugated polymer. The polymer poly[3-(4-octylphenyl)-2,2′-bithiophene] is stretch oriented to various elongations and doped with I2 vapour. The conductivity anisotropy is dependent on the degree of orientation and the absolute conductivity. Anisotropy values of 2.4 is obtained for an elongation of 4 times. For a given elongation the conductivity anisotropy decreases during the spontaneous undoping. The experimental results are discussed in terms of varying charge hopping distances.