Investigation of the charge transport through disordered organic molecular heterojunctions

We develop a new three-dimensional multiparticle Monte Carlo ({\it 3DmpMC}) approach in order to study the hopping charge transport in disordered organic molecular media. The approach is applied here to study the charge transport across an energetically disordered organic molecular heterojunction, known to strongly influence the characteristics of the multilayer devices based on thin organic films. The role of energetic disorder and its spatial correlations, known to govern the transport in the bulk, are examined here for the bilayer homopolar system where the heterojunction represents the bottleneck for the transport. We study the effects of disorder on both sides of the heterojunction, the effects of the spatial correlation within each material and among the layers. Most importantly, the {\it 3DmpMC} approach permits us to treat correctly the effects of the Coulomb interaction among carriers in the region where the charge accumulation in the device is particularly important and the Coulomb interaction most pronounced. The Coulomb interaction enhances the current by increasing the electric field at the heterojunction as well as by affecting the thermalization of the carriers in front of the barrier. Our MC simulations are supplemented by the master equation (ME) calculations in order to build a rather comprehensive picture of the hopping transport over the homopolar heterojunction.Comment: 26 pages, 11 figures, LaTe

The Impact of Molecular Polarization on the Electronic Properties of Molecular Semiconductors

In a molecular semiconductor, the carrier is dressed with a polarization cloud that we treat as a quantum field of Frenkel excitons coupled to it. The consequences of the existence of this electronic polaron on the dynamics of an extra charge in a material like pentacene can thus be evaluated.Comment: 7 pages, 1 figure, LaTe

Polarization effects in the channel of an organic field-effect transistor

We present the results of our calculation of the effects of dynamical coupling of a charge-carrier to the electronic polarization and the field-induced lattice displacements at the gate-interface of an organic field-effect transistor (OFET). We find that these interactions reduce the effective bandwidth of the charge-carrier in the quasi-two dimensional channel of a pentacene transistor by a factor of two from its bulk value when the gate is a high-permittivity dielectric such as $(\textrm{Ta}_{2}\textrm{O}_{5})$ while this reduction essentially vanishes using a polymer gate-insulator. These results demonstrate that carrier mass renormalization triggers the dielectric effects on the mobility reported recently in OFETs.Comment: 19 pages, 3 figure

Spin dependent transport in organic light-emitting diodes

Electrically Detected Magnetic Resonance (EDMR) was used to study a series of multilayer organic devices based on aluminum (III) 8-hydroxyquinoline. These devices were designed to identify the micoscopic origin of different spin dependent process, i.e. hopping and exciton formation. EDMR is demonstrated to probe molecular orbitals of charge, and thus indirectly explore interfaces, exciton formation, charge accumalation and electric fields in operating organic based devices

Thermopower measurements on pentacene transistors

We present the first thermoelectric measurements on pentacene field effect transistors. We report high values of the Seebeck coefficient at room temperature between 240 and 500 micro V/K depending on the dielectric surface treatment. These values are independent of the thickness of the channel and of the applied gate voltage. Two contributions to the Seebeck coefficient are clearly identified: the expected contribution that is dependent on the position of the transport level and reflects the activated character of carrier generation, and an unexpected intrinsic contribution of 265 plus minus 40 micro V/K that is independent of the temperature and the treatment of the oxide surface. This value corresponds to an unusually large lattice vibrational entropy of 3 kB per carrier. We demonstrate that this intrinsic vibrational entropy arises from lattice hardening induced by the presence of the charge-carrier. Our results provide direct evidence of the importance of electronic polarization effects on charge transport in organic molecular semiconductors.Comment: 7 pages, 8 figures, LaTe

Science et technologie comme auxiliaires d'une nouvelle violence

Où l’on tente de montrer sur quelques exemples, qu’en déformant la réalité, la « technoscience » contribue à alimenter la logique de guerre économique et de guerre totale, tentation ultime d’un monde dirigé par le marché. Où l’on voit aussi qu’Hannah Arendt avait déjà abordé cette question par morceaux dans plusieurs de ses oeuvres

Miglioramento dell'efficienza energetica in sistemi aggregati di edilizia pre-industriale di base, tra istanze conservative e prestazionali. Valutazione quantitativa del fabbisogno di energia in alcuni aggregati nel centro urbano di Ferrara

The energy performance of buildings, their needs and the possibilities of energy saving, have long been an issue in the debate of construction and real estate sectors. The transposition of the Directive 2002/91/EC (EPBD), as well as of the Directive 2010/31/EU, has modified the relationship between building and energy, also in existing buildings. On the other hand, the energy performance certificate (EPC) spreading has changed the real estate perception. Energy upgrade is a good way for retrofit existing buildings of the second half of the 20th century, but not for all existing buildings. The cultural heritage and preindustrial basic building should be a special case to discuss. Several studies discuss energy performance of single building, building stock, heritage building and also urban comfort. The planning of actual energy policies and the organization of targeted action in the structural planning, can only start from the knowledge of the real state of things. With the aim of validating the real need for improvement of energy performance in preindustrial basic building, my dissertation provides an in-depth quantitative analysis of the thermal energy demand and the improvement of energy efficiency in preindustrial basic building, through the analytical investigation of the case studies in the urban center of Ferrara