Charge transfer in conducting polymers. Striving toward intrinsic properties

Abstract

A principal goal of the field of conducting polymers is to strive for advances in materials quality that will enable the exploration of the intrinsic electrical properties. In this context, we summarize the requirements for achieving high performance conducting polymers with electrical conductivities greater than that of copper. To avoid localization onto one-dimensioal polymer chains (with bandwidth 4t₀), interchain charge transfer (t_3d) is required. For crystalline materials in which the chains have precise phase order, the mean distance along the chain between defects must be L/a_crystalline≫t₀/t_3d. In the case where there is good chain extension and good chain alignment, but when that alignment is nematic (i.e. with random interchain phase along the chain), the criterion is more severe: L/a_nematic≫(t₀/t_3d)². When the appropriate inequality is satisfied the transport is that of an anisotropic three-dimensional metal, and the conductivity will increase in proportion to the mean distance between chain interruptions, cross-links, sp³ defects etc. If the mean defect scattering time, τ_def=(L/v_F), becomes sufficiently long that phonon scattering limits the mean free path, then the conductivity takes on a metallic temperature dependence, and the system is in the clean and intrinsic transport limit.