Compensation phenomena by ion implantation doping of an electroactive polymer, poly(para‐phenylene)

Abstract

We have shown that poly(para‐phenylene) (PPP) can be obtained either n‐type or p‐type by ion implantation at low energy (E ≦ 50 keV); PPP is primarily an insulator pellet obtained from compacted powder synthetised by the Kovacic method. To compare with the chemical doping effect, we have studied the conductivity and thermopower of PPP samples after two successive ion implantations with Cs+ and I+.The experimental results show that we clearly obtain reversible doping only in the case of an initially I+‐doped sample: the thermopower sign is changed after a Cs+ implantation with a fluence equal to 3 × 1014 ions cm−2. In the other case (Cs+ initial implantation) we observe the change in thermopower sign at higher fluence (2 × 1016 I+ ions cm−2). This last effect can be attributed to a metal transition induced by the accumulation of defects in the material because of too high implantation parameters (graphitisation).

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

“…There is considerable interest in thin-film devices based on polymers and related oligomers (Burroughes, Jones and Friend 1988, Burroughes et al 1990, Garnier, Horovitz, Peng and Fichou 1990, and Some progress has been made in the use of ion implantation to form pnjunctions (Lucas et al 1993a). The effects ofion implantation in this regime have also been shown to be additive, with reversal of the sign of the thermopower from p to n type seen for caesium implantation in PPP previously implanted with iodine (Le Hue et al 1992).…”

“…The associated levels are typical of isolated chains and do not take into account other interactions (external interactions associated with disorder effects or structural defects for example). When modifications of the polymer structure become important, for example, during implantation where damage can be created (Ventkatesan, Calcagno, Elman and Foti 1987) and where doping effects can be also generated (Koshida andHirayama 1991, Le Hue, Moliton, Lucas andFroyer 1992), the previous band scheme is insufficient; a more general model must be proposed where different regimes of behaviour can account for successive transport phenomena.…”

“…It has not, however, proved to be an easy material to process since it cannot be solution processed directly. Pressed pellets PPP synthesized by the method of Kovacic and Kyriakis (1963) and Kovacic and Jones (1987) have been extensively used (Froyer et al 1987, Duroux et al 1988a, Duroux, Moliton and Froyer 1988b, Moliton, Ratier, Guille and Froyer 1990b, Moliton, Ratier, Moreau and Froyer 1991, Le Hue et al 1992, Ratier et al 1992a, b, Ratier, Moliton, Guille and Froyer 1992c. Electrochemical polymerization of para-dibromobiphenyl onto conducting substrates has been used to prepare thin films (Ratier, Pelous, Froyer and Moliton 1991).…”