Ambipolar Organic Thin Film Transistors of Cationic and Anionic Phthalocyanines Fabricated Using Layer-by-Layer Deposition from Aqueous Solution

Organic thin film field effect transistors of water soluble phthalocyanine derivatives containing both cationic and anionic end groups were successfully prepared using the layer-by-layer deposition technique. The alternating growth of the films and subsequent transistor properties were studied with a variety of techniques including ellipsometry, UV-vis spectroscopy, polarized UV-vis spectroscopy, and field effect measurements. A stepwise and regular deposition of Alcian Blue, pyridine variant amd Copper (II) phthalocyanine tetrasulfonic acid, tetrasodium salt multilayers in both pure water and 0.03 M NaCl solution was observed. Polarized UV-vis spectra indicated that the conjugated phthalocyanine ring lies almost flat on the substrate surface with a random orientation within the plane of the substrate. Unusual "ambipolar" transistor behavior was found for the films fabricated from solution that we believe involves an ion-modulated electrical conduction mechanism.