Coefficient seebeck et méanismes de conduction dans les polymères (PPP) electroactifs dopés par implantation ionique

Abstract

A study of the Seebeck coefficient has shown that doping of polyparaphenylene by ion implantation makes it possible to obtain an electronically doped semiconductor at low energy: n‐type with alkali metal ions and p‐type with halide ions. At the highest energies (E > 100 keV) the p‐type conductivity is due to the creation of defects by irradiation. Generally the semiconductor obtained is degenerate with a Seebeck coefficient close to that obtained by chemical doping. Study of the mechanisms of conduction suggests plots of log σ = (T−l/n); the greater n is, the better is the agreement between the experimental curve and theory. Representation of the conductivity is proposed according to Mott's theories, which are applicable to amorphous semiconductors and involve several conduction processes in the temperature space. For the variable‐range‐hopping (VRH) mechanism at low temperature, two parameters, α−1 (representing the spatial separation of hopping sites) and N(EF) (the density of states at the Fermi Level) are obtained.

Ion implantation in conjugated polymers: Mechanisms for generation of charge carriers

“…This is consistent with the conductivity data which also show universal behaviour at these implantation parameters. Information on the thermopower for PPP implanted with inert-gas ions is also consistent with the trends observed in the conductivity; implantation with argon at 50 keV of 10'6ionscm-2 gives a value of S = +51 pVK-' and implantation with xenon at lOOkeV of 10'6ionscm-2 gives a value of S = + 38 pV K-' (Moliton, Duroux, Ratier and Froyer 1990a). Temperature dependence of the conductivity of PPP implanted with caesium ions at 30keV.…”

“…The temperature dependence of the thermopower has been reported for PPP pellets (Moliton et al 1990a. It is found that below room temperature there is a very weak variation down to 180 K, although there are stronger variations above 300 K .…”

“…The temperature dependence of both conductivity (Moliton et al 1990a) and thermopower (Moliton et al 1990a can provide important information about the nature of the transport processes. The temperature dependence of the conductivity of PPP films prepared by the polystyrene-PPP precursor method is shown in fig.…”