Synthetic Metals, 55-57 (1993) 1453--1458 14 5 3 ELECTROCHEMICAL STUDY ON POLYPYRROLE - POLY(3-OCTYLTIIIOPHENE) BILAYER FILMS JOItAN BOBACKA, ZHIQIANG GAO 1 and ARI IVASKA Laboratory of Analytical Chemistry, ,~bo Akademi University, SF-20500 Turku-/~bo, Finland 1 On leave from Henan University, Kaifeng, China ABSTRACT Bilayer film electrodes of polypyrrole and poly(3-octylthiophene) were prepared by electrochemical poly- merization of the corresponding monomers. The electrochemical behaviour of the electrodes in LiBF4-propylene carbonate solution was studied by cyclic voltammetry and impedance spectroscopy. The impedance data, ob- tained at different dc potentials, were fitted to equivalent electrical circuits providing information about charge transfer and diffusion processes across the bilayer film electrodes. KEYWORDS: polypyrrole, poly(3-octylthiophene), bilayer, cyclic voltammetry, impedance INTRODUCTION Bilayer electrodes of redox polymers were introduced by Murray et al. [1]. It was shown that charge transfer between the metal substrate and the outer polymer layer is mediated by the inner polymer layer at potentials close to the redox potentials (E*') of the redox centers in the inner layer. It was suggested that the rectifying and charge trapping behaviour of these bilayers may be used for fabrication of diodes, transistors, optical switches and solar collectors without using any semiconducting material [1]. The switching of the bilayers from one redox state to another was found to be limited by electron diffusion in the inner layer and not by the interfacial electron transfer between the two layers [2]. The same conclusion was reached also recently by Hillman el al. [3], for a bilayer where the inner film was a conducting polymer, poly(2,2'-bithiophene). Due to the high electronic conductivity of this polymer it was suggested that the bilayer switching may be limited by diffusion of charge compensating counterions [3]. Bilayer structures where two layers of conducting polymers are sandwiched between two solid contacts have also been reported [4-7]. Combination of polypyrrole (PPy) with polythiophene (PT) [4], or PPy with polyaniline [5], resulted in rectifying heterojunctions, while pn-junctions were prepared by combination of p- 0379-6779/93/$6.00 © 1993- Elsevier Sequoia. All fights reserved