High electrical conductivity in doped polyacetylene

The electrical conductivity of conducting polymers results from mobile charge carriers introduced into the π-electron system through doping1,2. Because of the large infra-chain transfer integrals, the transport of charge is believed to be principally along the conjugated chains, with inter-chain hopping as a necessary secondary step. In conducting polymers, as in all metals and semiconductors, charge transport is limited by a combination of intrinsic electron–photon scattering and sample imperfection. Although relatively high conductivities (σ ≈ 1,000 S cm−1) have been reported for partially orientated and heavily doped polyacetylene1–3, the absence of a metal-like temperature dependence implies that the observed values are not intrinsic. In doped polyacetylene, (CH)x, electrical transport can be limited both by microscopic defects (leading to scattering and localization) and by the more macroscopic complex fibrillar morphology12 and associated interfibrillar contacts. Thus, with improvements in material quality, one might anticipate corresponding improvements in the electrical conductivity. Here we report the synthesis of polyacetylene with fewer sp3 defects than in material prepared by other methods. The higher-quality material exhibits substantially higher electrical conductivity; maximum values of >20,000 S cm−1 are obtained after doping with iodine. The conductivity has been measured as a function of temperature and pressure: at 0.48 K and 10 kbar, iodine-doped samples remain highly conducting (σ ≈ 9,000 S cm−1).