Zachariah, M.; Romanini, M.; Zygouri, P.; Gournis, D.; Tamarit, J. Ll.; Del Barrio, M.; Macovez, R. Synthetic metals Vol. 217, p. 123-128 DOI: 10.1016/j.synthmet.2016.03.028 Data de publicació: 2016-07-01 Article en revista
Dielectric spectroscopy is employed to probe the frequency-dependent conductivity and dipolar dielectric response of solid C60Br6. Below approximately 215 K, charge conduction is electronic and well described by Mott's variable-range polaron hopping model, with effective hopping activation energy Ea varying between 0.12 eV at 125 K and 0.16 eV at 220 K, and most probable hopping range varying between 100 and 125% of the decay length of the localized polaron's wavefunction. Above 215 K a new contribution appears in the conductivity, accompanied by a weak endothermic feature in the calorimetric thermogram, which might signal a solid-solid phase transition. A broad dielectric loss feature is observed in the imaginary part of the permittivity. Such feature stems largely from a conductivity-related frequency-dependent loss associated with polaron hopping, as confirmed by the validity of the Barton-Nakajima-Namikawa condition. (C) 2016 Elsevier B.V. All rights reserved.
P-type organic thin-film transistors (OTFTs), in which the active semiconductor is made of pentacene with silicon dioxide as a gate insulator, were fabricated and characterized. The effects of humidity on the electrical characteristics of pentacene based thin-film transistors (pentacene-TFTs) in the linear and saturation regimes were investigated. We report the variation of the electrical parameters by relative humidity (RH) extracted from the experimental electrical characteristics current–voltage of pentacene-TFT devices. We show that the diffusion of water molecules (H2O), the creation of acceptor states due to the presence of oxygen and the formation of clusters in the pentacene active layer considerably affect the stability and the performances of pentacene-TFTs. The degradation of electrical parameters of the pentacene-TFTs under relative humidity (RH) can be recovered with a simple pumping under vacuum (3 × 10-5 to 5 × 10-5 mbar). We also show that the changes introduced by the effects of humidity are reversible. Moreover the pentacene-TFT presents an intensive response for a high relative humidity (RH = 57%), which could be used for a humidity detection device technology.
Picene has recently attracted much attention as the active layer in organic thin-film transistors because of its good performance in air. In this work, we have fabricated picene thin-film transistors that exhibit field-effect mobilities up to 1.3 cm2 V−1 s−1 and on/off ratios above 105 in ambient conditions. These devices have been electrically characterized over the temperature range 300–360 K in air and also under vacuum conditions. In particular, the thermal activation energy of the channel conductance as a function of the gate bias has been measured. The dependence of the activation energy on the gate bias corresponds to a gradual shift of the Fermi level towards the HOMO level as more gap states are filled by trapped holes. The density-of-states can be estimated from the derivative of the activation energy with respect to gate bias. The calculated density-of-states is compared for devices measured in air and under vacuum conditions. These results can help to understand the gas sensing capability of picene, together with its enhanced electrical performance after air exposure.
Aleman, C.; Armelin, E.; Iribarren, J.; Liesa, F.; Laso, M.A.G.; Casanovas Salas, Jordi Synthetic metals Vol. 149, num. 2-3, p. 151-156 DOI: 10.1016/j.synthmet.2004.12.012 Data de publicació: 2005-03 Article en revista
We report the results of a series of ab initio and DFT quantum mechanical calculations on the structure and on the electronic spectral of 2,3-ethylenedioxythiophene-, thiophene- and 2,3-ethylenedithiafurane-containing oligomers. Calculations were performed on oligomers formed by n repeating units, where n ranges from 1 to 8. The bond-length alternation patterns in the p-system, the importance of long-range interactions in the stabilization of oligomer chains, the energies of the HOMO and LUMO orbitals and the values of the lowest transition energy have been examined allowing a systematic comparison among the three families of conducting polymers.
Puigdollers, J.; Voz, C.; Martin, I.; Vetter, M.; Orpella, A.; Alcubilla, R. Synthetic metals Vol. 146, num. 3, p. 355-358 DOI: 10.1016/j.synthmet.2004.08.027 Data de publicació: 2004-11 Article en revista
Pentacene thin films obtained by thermal evaporation at room temperature have been incorporated as the active layer in bottom-gate thin-film transistors (TFTs). The dielectric was spin-cast polymethyl methacrylate (PMMA) baked at only 170 °C. Crystalline silicon wafers and polyethylenenaphtalate (PEN) polymer foils were used as substrates. These devices were electrically characterised by measuring the output and transfer characteristics at different temperatures. Both the channel conductance and field-effect mobility evidenced similar thermal activation energies around 0.15 eV. These results could indicate that electrical transport is mainly controlled by trapping and thermal release of carriers from localised states.