High electrical conductivity in doped polyacetylene

Abstract

The electrical conductivity of conducting polymers results from mobile charge carriers introduced into the π-electron system through doping^1,2. 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 polyacetylene^1–3, 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).