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 vapor. The conductivity anisotropy is dependent on the degree of orientation and the absolute conductivity. An anisotropy value of 2.4 is obtained for an elongation of four 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.