Sintesi, caratterizzazione e proprietà ottiche di derivati bisimmidici simmetrici ed asimmetrici del perilene per applicazione nel campo delle celle fotovoltaiche organiche

I derivati perilenici tetracarbossi-bisimmidici sono di particolare interesse nel campo delle celle fotovoltaiche organiche in quanto costituiscono materiali semiconduttori organici di tipo n con elevata mobilit´a di carica ed in grado di assorbire luce in un ampio intervallo dello spettro della radiazione solare. La tendenza alla formazione di aggregati molecolari attraverso interazioni tipica dei derivati perilenici a formare strutture supramolecolari ordinate, `e auspicabile per poter migliorare il rendimento in dispositivi fotovoltaici organici dove la fase attiva `e costituita da una eterogiunzione accettore-donatore a dispersione di massa. In questo lavoro di tesi sono stati sintetizzati derivati perilenici bisimmidici di tipo ammide-immide ed estere-immide, simmetrici ed asimmetrici. I sostituenti sugli azoti immidici sono stati scelti per favorire la formazione di aggregati molecolari e portare a composti con caratteristiche liquido-cristalline in grado, quindi, di formare strutture ordinate. Per conferire propriet´a liquido-cristalline sono stati utilizzati derivati dell’acido gallico con catene alchiliche lineari a 6 atomi di C. Attraverso microscopia a luce polarizzata e analisi calorimetrica DSC sono state valutate le propriet´a liquidocristalline dei composti sintetizzati. In particolare, il derivato estere-immide (Estere triC6OBC6-PBI-C6BOtriC6) ha mostrato un comportamento liquido-cristallino colonnare a crescita dendritica. Sono state studiate, inoltre, le propriet´a ottiche attraverso analisi UV-Vis e fluorescenza, sia in soluzione che allo stato solido, per investigare la tendenza a formare aggregati dei composti in esame. L’analisi allo stato solido del derivato estereo ha mostrato tendenza a formare aggregati di tipo H, con notevole quenching di fluorescenza ed emissione nel rosso. La stabilit´a termica dei derivati `e stata valutata attraverso analisi termodegradativa TGA che ha evidenziato elevata stabilit´a per i derivati sintetizzati. Analisi elettrochimiche tramite voltammetria ciclica del derivato asimmetrico ammideimmide triC6OBC6-PBI-C5OH e del derivato estere-immide Estere triC6OBC6- PBI-C6BOtriC6 hanno mostrato buona reversibilit´a del trasferimento elettronico e propriet´a elettron-accettrici (ELUMO) in linea con quelle dei composti attualmente impiegati nelle celle OPV

Polymer Nanocomposites Containing Anisotropic Metal Nanostructures as Internal Strain Indicators

Polymer/metal nanocomposite containing intrinsically anisotropic metal nanostructures such as metal nanorods and nanowires appeared extremely more sensitive and responsive to mechanical stimuli than nanocomposites containing spherical nanoparticles. After uniaxial stretching of the supporting polymer matrix (poly(vinyl alcohol)), the elongated silver nanostructures embedded at low concentration into the polymer matrix (<1 wt % of Ag) assume the direction of the drawing, yielding materials with a strong dichroic response of the absorption behavior. Accordingly, the film changed its color when observed under linearly polarized light already at moderate drawings. The results obtained suggest that nanocomposite films have potential in applications such as color polarizing filters, radiation responsive polymeric objects and smart flexible films in packaging applications

Incorporation of fullerene into polymers for photovoltaic applications

Photovoltaic technology (PV) makes it possible to directly convert sunlight into electricity and it is seen as a very promising solution to the current energy crisis. Although the PV market is dominated by inorganic-based devices, those systems present high production costs and deployment issues that limit their application. Polymer-based organic solar cells (OPVs) are promising sources of renewable energy due to their facile, low cost production, and formable nature. Due to its electronic properties and high electron mobility, small molecule fullerene (C60) derivatives are widely used in large scale OPVs. However the morphological properties of C60 derivatives decrease device stability as C60 easily undergoes self-aggregation during OPV use. The processibility of C60 can be improved by incorporating it into a polymer. These systems are already described in literature but have in general a multistage synthesis that could affect the electronic properties of C60 as well as give insoluble products due to reticulative reactions. The objective of the work here presented was to prepare innovative polymers based on C60 for photovoltaic and electronic devices using reliable, well-known C60 chemistry. At the University of Pau (EPCP Lab), after the syntheses of small molecules to be used as co-monomers, two synthetic routes were used in order to obtain main- chain oligo- and polyfullerenes. The first route is based on the atom transfer radical addition polymerization (ATRAP), which has already been used for the preparation of main-chain polyfullerenes. With this method, soluble compounds with various molecular weights were prepared. The second route was discovered in this work and exploits a well-known fullerene chemistry to prepare soluble polyfullerenes with reasonably high molecular weights. Preliminary studies to understand the effect of the reaction parameters (reagents, reagents concentration, temperature, time and solvent) and the kinetics of the polymerisation were performed. Material characterisations were carried out via GPC chromatography, NMR spectroscopy, and UV-visible and IR spectroscopies. Thermal analyses (TGA and DSC) were also run to complete the characterisations. Both C60 and its derivative, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), have been exploited as monomers in the reactions. A nine-month (cotutelle) stay at Tübingen University, Germany, permitted a study of the synthesized materials by means of XPS and UPS spectroscopies. The aim of these studies was to obtain a better understanding of the energy levels pictures of the oligo- and polyfullerenes. Thin films of the compounds were deposited on different substrates via solution processes (doctor blade or spin coating) to obtain ex-situ samples for characterisation. Samples of polyfullerene-containing active layers were prepared during a short stay (1 week) at BELECTRIC OPV GmbH, Nuremberg (Germany), and analysed by optical microscopy and AFM microscopy during thermal-degradation studies at Tübingen University. These studies were completed thanks to collaborations with researchers at BELECTRIC OPV GmbH, who have incorporated the compounds into devices and performed complementary and comparable experiments. As general trends, the compounds are found to improve the stability of the devices upon thermal stresses

Incorporation of fullerene into polymers for photovoltaic applications

La technologie photovoltaïque (PV) est considérée une solution très prometteuse à la crise de l'énergie. Bien que le marché du PV soit actuellement dominé par des dispositifs à base de minéraux, ces systèmes présentent des coûts de production élevés et de nombreux problèmes environnementaux. Ces aspects limitent leur application. Les cellules solaires organiques à base de polymères (OPV) sont de prometteuses sources d'énergie renouvelable en raison de leur faible coût de production et grâce à leur nature déformable. En raison de ses propriétés électroniques et de la haute mobilité d'électrons, de petites molécules dérivées du fullerène C60 sont largement utilisées dans la production OPV à grande échelle. Toutefois, les propriétés morphologiques des dérivés du C60 diminuent la stabilité des dispositifs. En effet, le C60 subit facilement le phénomène d’auto-agrégation lors de l'utilisation de la cellule. L'aptitude au traitement du C60 peut être améliorée en l’incorporant dans un polymère. Ces systèmes sont déjà décrits dans la littérature, mais reposent en général sur une synthèse en plusieurs étapes qui pourraient affecter les propriétés électroniques du C60 ainsi que donner des produits insolubles en raison de la réaction de réticulation. L'objectif de ce travail est de préparer des polymères innovants basés sur le fullerène (C60) pour les dispositifs photovoltaïques et électroniques, à l'aide d’une chimie du C60 bien connue et en se basant sur des procédés fiables. À l'Université de Pau (au sein de l’équipe EPCP), après les synthèses de petites molécules qui ont étés utilisées en tant que co-monomères, deux différentes voies de synthèse ont été exploitées afin d'obtenir oligo- et polyfullerènes contenant le C60 dans leur chaîne principale. La première voie exploitée, est basée sur la réaction « Atom Transfer Radical Addition Polymerisation » (ATRAP), qui a déjà été utilisée pour la préparation de main-chain polyfullerenes. Avec cette méthode, des composés très solubles ayant des poids moléculaires variables ont été préparés. La deuxième voie a été découverte dans ce travail de thèse et exploite une chimie du C60 bien connue pour obtenir des « main-chain » polyfullerènes qui présentent un haut poids moléculaire et qui sont bien solubles dans les solvants courants. Des études préliminaires ont été effectuées dans le but de comprendre les effets des paramètres de réaction et la cinétique de la polymérisation. Les matériaux ont été caractérisés par chromatographie d’exclusion stérique, SEC, spectroscopie RMN, et à travers spectroscopie UV-vis et IR. Des analyses thermiques (TGA et DSC) complètent les caractérisations. Le C60, ainsi que son dérivé, [6,6] -phényl-C61-butyrique ester méthylique d'acide (PCBM), ont été exploités en tant que monomères dans les réactions de polymérisation. Un séjour de neuf mois (cotutelle) à l'université de Tübingen, en Allemagne, a permis d'étudier les matériaux synthétisés par spectroscopies XPS et UPS. Le but de ces études était d'obtenir une meilleure compréhension des niveaux énergétiques des oligo- et polyfullerènes. Des couches minces de composés ont été déposées sur différents substrats par des procédés en solution (doctor blade ou spin coating) pour obtenir des échantillons ex-situ pour les analyses. Des échantillons de couches actives contenant des polyfullerène ont également été préparés lors d'un court séjour (une semaine) à BELECTRIC OPV GmbH, Nuremberg (Allemagne). Les échantillons ont été analysés par microscopie optique et microscopie AFM dans le cadre d’une étude sur la stabilité thermique de la couche active à l'Université de Tübingen. Ces études ont été réalisées aussi grâce à la collaboration avec des chercheurs de BELECTRIC OPV GmbH, qui ont intégré les composés dans des dispositifs et réalisé des expériences complémentaires et comparables. Comme tendances générales, les composés améliorent la stabilité des dispositifs quand les derniers sont soumis à un stress thermique.Photovoltaic technology (PV) makes it possible to directly convert sunlight into electricity and it is seen as a very promising solution to the current energy crisis. Although the PV market is dominated by inorganic-based devices, those systems present high production costs and deployment issues that limit their application. Polymer-based organic solar cells (OPVs) are promising sources of renewable energy due to their facile, low cost production, and formable nature. Due to its electronic properties and high electron mobility, small molecule fullerene (C60 ) derivatives are widely used in large scale OPVs. However the morphological properties of C60 derivatives decrease device stability as C60 easily undergoes self-aggregation during OPV use. The processibility of C60 can be improved by incorporating it into a polymer. These systems are already described in literature but have in general a multistage synthesis that could affect the electronic properties of C60 as well as give insoluble products due to reticulative reactions. The objective of the work here presented was to prepare innovative polymers based on C60 for photovoltaic and electronic devices using reliable, well-known C60 chemistry. At the University of Pau (EPCP Lab), after the syntheses of small molecules to be used as co-monomers, two synthetic routes were used in order to obtain main- chain oligo- and polyfullerenes. The first route is based on the atom transfer radical addition polymerization (ATRAP), which has already been used for the preparation of main-chain polyfullerenes. With this method, soluble compounds with various molecular weights were prepared. The second route was discovered in this work and exploits a well-known fullerene chemistry to prepare soluble polyfullerenes with reasonably high molecular weights. Preliminary studies to understand the effect of the reaction parameters (reagents, reagents concentration, temperature, time and solvent) and the kinetics of the polymerisation were performed. Material characterisations were carried out via GPC chromatography, NMR spectroscopy, and UV-visible and IR spectroscopies. Thermal analyses (TGA and DSC) were also run to complete the characterisations. Both C60 and its derivative, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), have been exploited as monomers in the reactions. A nine-month (cotutelle) stay at Tübingen University, Germany, permitted a study of the synthesized materials by means of XPS and UPS spectroscopies. The aim of these studies was to obtain a better understanding of the energy levels pictures of the oligo- and polyfullerenes. Thin films of the compounds were deposited on different substrates via solution processes (doctor blade or spin coating) to obtain ex-situ samples for characterisation. Samples of polyfullerene-containing active layers were prepared during a short stay (1 week) at BELECTRIC OPV GmbH, Nuremberg (Germany), and analysed by optical microscopy and AFM microscopy during thermal-degradation studies at Tübingen University. These studies were completed thanks to collaborations with researchers at BELECTRIC OPV GmbH, who have incorporated the compounds into devices and performed complementary and comparable experiments. As general trends, the compounds are found to improve the stability of the devices upon thermal stresses

Polymer Nanocomposites Containing Anisotropic Metal Nanostructures as Internal Strain Indicators

Polymer/metal nanocomposite containing intrinsically anisotropic metal nanostructures such as metal nanorods and nanowires appeared extremely more sensitive and responsive to mechanical stimuli than nanocomposites containing spherical nanoparticles. After uniaxial stretching of the supporting polymer matrix (poly(vinyl alcohol)), the elongated silver nanostructures embedded at low concentration into the polymer matrix (&lt;1 wt % of Ag) assume the direction of the drawing, yielding materials with a strong dichroic response of the absorption behavior. Accordingly, the film changed its color when observed under linearly polarized light already at moderate drawings. The results obtained suggest that nanocomposite films have potential in applications such as color polarizing filters, radiation responsive polymeric objects and smart flexible films in packaging applications