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A conducting network of crystalline [bis(ethylenodithio)tetrathiafulvalene]2I3 (ET2I3) can be formed within the surface layer of polycarbonate by exposure of films containing 2 wt.% of molecularly dispersed ET to vapours of iodine solution in CH2Cl2, THF or TCE. The relationship between the microstructure and properties of conducting networks formed under different conditions is reported. Depending on the iodine concentration in the solution, the kind of solvent and the treatment time, networks of a‐ET2I3 or β‐ET2I3 crystallites are formed. Their preferential orientation (c‐axis perpendicular to the film plane) can be deduced from X‐ray diffraction. Morphological studies performed using a scanning electron microscope revealed a nanoscopic size of crystallites and different habits: plate‐like or river‐stone‐like. The presence of a less organised layer covering the crystallites, possibly formed of salts of another composition, is also discussed. The conductivity of the films is higher than that reported for polycrystalline layers obtained by the evaporation method and for pressed pellets of ET2I3. Films with a‐ET2I3 show semiconducting behaviour with some deviation of the temperature dependence of conductivity at 160–200 K. Films with β‐ET2I3 show metallic conductivity down to 60 K. Studies of the optical absorption have shown that the conducting network does not contribute much to the UV‐VIS spectra of conducting films.

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