Thèses

Mercredi 29 Septembre 2021 à 14h00.

transport electrothermique au travers de nano objects (partenaire : commission europeenne/ EFINED)

''Thermoelectricity is the conversion of heat to electricity and vice versa. As Seebeck discovered, a voltage applied to an electronic device generates a heat current, while a temperature difference can generate electricity. During the past decades, the size of consumer electronics has been continuously decreasing. The down-sizing of the electronic devices requires a more efficient heat management. An interesting route towards this goal is the idea of using single molecules as electronic components which gave rise to "molecular electronics". In fact, the usage of organic molecules in thermoelectric applications has at tracted a great deal of attention due to their flexibility, relatively low price and their eco-friendly nature. In this work, the thermoelectric properties of molecular junctions based on oligo(phenyleneethynylene) (OPE3) derivatives were studied. With the help of Density Functional Theory (DFT) calculations, models for the molecular junctions were constructed. The electronic transport properties were obtained using Non Equilibrium Green’s Function-Density Functional based Tight-Binding (NEGF-DFTB). Firstly, the effect of side groups on the electronic conductance and thermopower of OPE3 derivatives was quantified. It is shown that these derivatives provide structural properties that are needed for highly efficient thermoelectric materials. Next,the effect of cross-linking molecules on the thermoelectric efficiency was investigated. Classical Molecular Dynamics (MD) was used to compute the phonon transport across the junctions. Combining the results from ab-initio and MD for electron and phonon transport, respectively, the thermoelectric efficiency in terms of the figure of merit ZT was computed for OPE3 derivatives. We have found that cross-linked molecules show a high ZT value, which makes them good candidates to be used as cooling systems. Finally, we introduce a circuit model that combines electron and phonon transport channels. This model allows to determine optimal parameter ranges in order to maximize cooling. Overall, our results demonstrate that the OPE3 derivatives display the necessary structural rigidity and compatible electronic structure to enable high performance devices for cooling applications.

Directeurs de thèse :
Niehaus Thomas (Professeur),
Merabia Samy (Directeur de recherche) co-directeur de thèse

Membres du jury / members of the jury:
- Banfi Francesco (Professeur)
- Gotsmann Bernd (Chercheur), Examinateur
- Martine Evelyne (Directrice de recherché), Rapporteur
- Merabia Samy (Directeur de recherche), co-directeur de thèse
- Michelini Fabienne (Maitre de conférences), Examinatrice
- Niehaus Thomas (Professeur), Directeur de thèse
- Pecchia Alessandro (Chercheur), Rapporteur.

Invités :
- Chapuis Pierre-Olivier (Chargé de recherche)
- Saint-Martin Jérôme (Maître de conférences

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