Rectifying behaviour of n-titanium dioxide–polybithiophene semiconductor–polymer bilayers: an electrochemical quartz crystal microbalance investigation

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We report the first electrochemical quartz crystal microbalance (EQCM) study of an inorganic semiconductor–conducting polymer bilayer. The bilayers were prepared by electrochemically depositing polybithiophene (PBT) onto TiO2 thin films supported on Ti. TiO2 films prepared by electrochemical oxidation of titanium and by sputtering gave indistinguishable results. The current–voltage characteristics are those of a rectifying interface. Interpretation of the EQCM data for bilayer redox switching under voltammetric conditions reveals qualitative and quantitative information on the fate of electronic and ionic charge injected into the TiO2–PBT bilayer. The charge transfer mechanism in the depletion layer at the semiconductor/polymer interface was investigated with respect to anion ingress into and egress from the cation PBT film. Comparison with a previous EQCM investigation on single PBT films deposited on platinum suggests the participation of impact ionization processes at the TiO2/PBT interface.