Electrical transport in doped polyacetylene

Abstract

The results of an experimental study of electrical conductivity and thermopower in doped polyacetylene are reported. Included are measurements on both as‐grown and partially oriented films doped with iodine and AsF₅; [CH(AsF₅)_y]_xand [CH(I₃)_y]_x, where y covers the full doping range. The data indicate three important concentration regimes; the dilute limit (y−5 cm²/V sec) and activated (ΔΕ=0.3 eV). The semiconductor to metal transition is evident in the data and leads to a qualitative change in temperature dependence of the conductivity and to finite zero temperature values above y_c?0.01–0.02. The transport mobility increases by five to six orders of magnitude on going through the transitional region. In the metallic state, the high mobility (∼60 cm²/V sec, assuming unit charge transfer) provides evidence of the validity of a band theory approach with delocalized states in this disordered polymer. The transport in the metallic state is described as metallic strands separated by thin potential barriers. The main effect of orientation appears to be to alter the barriers. In particular, use of oriented cis‐(CH)_x starting material leads to significant improvement in conductivity due to smaller barrier widths and lower barrier heights. Analysis of the temperature dependence of the conductivity within this model leads to an estimate of the intrinsic conductivity in heavily doped metallic [CH(AsF₅)_y]_x, σ?4×10⁴Ω⁻¹ cm⁻¹ at room temperature.