We have produced and characterized poly(3-hexylthiophene) (PHT) thin films by electrochemical deposition onto tin–oxide (TO) or gold covered glass substrates. PHT film thickness and roughness depend on deposition charge density and are also dependent on substrate material. From electrical measurements we determine an electrical conductivity of 9×10−5 S cm−1 when Ni and Au electrodes are used. An energy barrier of 0.8 eV for positive charge carrier injection into PHT at Al/PHT and TO/PHT interfaces was determined. We estimate the mobility of positive charge carriers in electrochemically deposited PHT as being 1×10−4 cm2 V−1 s−1. An energy diagram of PHT is proposed.

We investigate the electronic characteristics and the absorption spectra of poly(3-octylthiophene), POT, films grown by electrochemical methods onto Au substrates. We discuss the results considering the morphological factor. POT films thickness can be controlled by current density in the electropolymerization process. The film roughness depends on the thickness, being about 12% of film thickness. The samples for electrical measurements were made in sandwich structure, Au/POT/metal (metal: Ni, Al). Analyzing current-voltage data we were able to estimate the positive charge carrier mobility (5×10 −4 cm 2 V −1 s −1 ) and the potential barrier height in the metal/polymer interfaces (0.1 eV for Au/POT and Ni/POT and 0.85 eV for Al/POT). I IntroductionConjugated polymers have been object of intense research in the last years. These organic semiconductors present good mechanical features, facility of production and offer the possibility of construction of devices with larger active areas than their inorganic counterparts. Among these polymers, polythiophene and its derivatives have received special considerations. Polythiophenes have a good chemical stability upon environmental conditions and produce stable interfaces with electrode metals commonly used in electronics, like aluminum and gold [1,2]. Another important feature of polythiophene films is a large absorption coefficient in the visible range of the electromagnetic spectrum [3,4,5]. These characteristics make polythiophene and its derivatives interesting materials for solar cell applications [6]. One of the major problems in polymer devices is the small charge carrier mobility. The morphology of the polymer film takes important place in this situation. In amorphous materials the transport occurs via hopping between localized states and disorder contributes to a further reduction of mobility. Many methods have been used to improve the order degree or the crystallinity in polymer films [7,8]. The use of polymers with large side chain segments is one of the methods employed with this intent. The increase in the side chain length improves the order and the planarity of the polymer chains [9]. So, the order is expected to be higher in poly(3-octylthiophene), POT, than in other polythiophene derivatives, like poly(3-metylthiophene) and consequently, also the charge carrier mobility.When a potential barrier energy ϕ for the charge carriers injection at the interface between the electrode and the polymer is so that ϕ >> kT (k is the constant of Boltzmann and T is the absolute temperature) the transport is better described by Simmons current density expression, derived for thermionic injection into low mobility materials [10].

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