Electrical and magnetic properties of “molecularly-engineered” amorphous films

Abstract

Eletrical and magnetic properties of a molecularly doped polymer system, tri-p-tolylamine (TTA) / polycarbonate (Lexan®), are described. In these amorphous, hole-transporting polymer films, transport occurs via hopping between molecular units doped into the polymer. By selective chemical oxidation of a fraction of the transport molecules, increases in the dc electrical conductivity initially increases of magnitude have been observed. The conductivity of several orders with TTA + cation concentration but exhibits a maximum. These electrical conductivity studies have been co-ordinated with ESR measurements on controlled, variable concentrations of TTA and TTA + in the polymer films. For a given concentration of spins in the range 1×10 19 cm −3 < N S< 5×10 20 cm −3, pronounced exchange narrowing is discovered as the density of neutral molecules is systematically increased. The temperature dependence of the ESR linewidth and the conductivity eliminates motional narrowing due to diffusive hopping of spins as the mechanism, since in these systems the paramagnetic ions are also the source of mobile charge.