[pt] Este trabalho teve como objetivo fabricar e caracterizar Transistores Orgânicos Emissores de Luz (OLETs, Organic light-Emitting Transistors). Os OLETs combinam em um único dispositivo a funcionalidade elétrica de um transistor de efeito de campo orgânico e a capacidade de geração de luz, representando uma nova classe de dispositivos orgânicos com alto potencial de inovação em aplicações, como sistemas ópticos de comunicação, tecnologia de displays avançada, lasers orgânicos, fontes de luz em nanoescala e optoeletrônica orgânica integrada. Portanto, esta tese possui um caráter pioneiro, tanto para grupo de pesquisa quanto para o país, uma vez que ocorre a junção dos conhecimentos e domínio adquiridos sobre OFETs e OLEDs. Efetivamente, este trabalho de doutorado consistiu na fabricação e caracterização sistemática de diversos dispositivos OLET utilizando variadas arquiteturas e diversos materiais, comerciais e não comerciais, como o NT4N, o P13 e uma bicamada de C8-BTBT com TcTa:Ir(ppy)3. Os dispositivos foram caracterizados através de medidas elétricas e óticas, obtendo-se as curvas características. Também foram determinados seus parâmetros e propriedades de funcionamento, com destaque para as mobilidades de carga e para as eficiências obtidas. Houve também o entendimento e a implementação de um tratamento térmico na camada dielétrica, sendo parte fundamental da fabricação dos dispositivos. Os dispositivos fabricados apresentaram diferentes graus de desempenho, com destaque para a arquitetura bicamada, por apresentar a maior potência luminosa (4 microwatt) e a maior eficiência (0,5 por cento), sendo suficientes para inserir os dispositivos fabricados na categoria de dispositivos orgânicos altamente eficientes. Tal fato demonstra que o domínio da fabricação e da caracterização desta nova classe de dispositivos foi alcançado. / [en] The aim of this work was to achieve the knowledge of the fabrication and the characterization of Organic Light Emitting Transistors, OLETs, considered as one of the innovative technologies nowadays. The OLETs combine in a single device the electrical functionality of an organic field-effect transistor (OFET) and the light-generating capability. They represent a promising new class of organic devices with high potential for innovation in applications such as communication systems, advanced display technology, organic lasers, nanoscale light sources and integrated organic optoelectronics. In some way, this thesis has a pioneer character, both for our research group and for the country, since it combines different knowledge and skills about OFETs and OLEDs to achieve a new device. Actually, this work involved the systematic manufacture and characterization of several OLETs using different architectures employing commercial and noncommercial materials, such NT4N, P13 and a bilayer of C8-BTBT with TcTa:Ir(ppy)3. The devices were then characterized by electrical and optical measurements. The working parameters and properties were determined as well, highlighting the charge carrier mobilities and efficiencies obtained. The understanding and the implementation of a specific heat treatment in the dielectric layer was a fundamental part of this work for the manufacture of the devices which have different degrees of performance. With emphasis on the bilayer architecture, that presented the highest luminous power (4 microwatt) and efficiency (0,5 percent), inserting the devices manufactured in the category of highly efficient organic devices. Such fact shows that the fabrication and characterization of this new class of devices has been achieved.

Neste trabalho estudamos a dinâmica molecular e o empacotamento em semicondutores orgânicos com diferentes tamanhos de cadeias conjugada usando uma estratégia de multi-técnicas, em particular Ressonância Magnética Nuclear (RMN), espalhamento de Raios-X de alto ângulo (WAXS), Calorimetria Exploratória Diferencial (DSC), espectroscopia Raman e espectroscopias Ópticas de absorção UV-Vis e fluorescência. Nestes estudos utilizamos oligômeros de fluorenos, com 3, 5 e 7 unidades repetitivas e copolímeros multibloco conjugados/não-conjugados com as unidades conjugadas constituídas por unidades de fenileno de vinileno (PV) e as não-conjugadas formadas por unidades metilênicas. No estudo com oligômeros, foi mostrado que a capacidade e a forma de ordenamento das cadeias dependem do número de unidades repetitivas, com o Pentâmero possuindo uma tendência muito maior de cristalização. Essa conclusão foi suportada por cálculos teóricos ab-initio, que mostraram que a conformação de menor energia do pentâmero favorece as interações intercadeias e, portanto, o ordenamento de longo alcance. Os resultados referentes aos estudos de dinâmica molecular corroboraram essas características e mostraram que a ativação dos movimentos moleculares nas fases amorfas dos oligômeros são predominantemente dependentes dos comprimentos das cadeias oligoméricas, em concordância com o comportamento encontrado para as suas Tg´s. No estudo referente aos copolímeros multiblocos, foi encontrado que a presença dos grupos espaçadores alifáticos inibem a forte tendência de cristalização das unidades de PV, porém não impedem a agregação dessas unidades. Foi verificado que, a dispersão de tamanhos das unidades agregadas afeta fortemente as características de emissão dos copolímeros, onde a emissão nas cadeias maiores é privilegiada. No que diz respeito a dinâmica molecular, foi observado que a presença de movimentos na região alifática contribui para o aparecimento de processos de relaxação não radiativos o qual inibem a emissão dos copolímeros e provocam alargamento das bandas vibrônicas. Por fim, foi observado que movimentos isotrópicos das cadeias de PV são responsáveis pela transição vítrea dos copolímeros, sendo que as energias necessárias para ativar esses movimentos aumentam com o tamanho da cadeia. Portanto, de forma geral, nossos resultados indicam que mesmo em sistemas com comprimento de cadeias muito bem controlados, as fortes interações intermoleculares presentes em polímeros conjugados, podem tornar a morfologia em estado sólido desses sistemas bastante complexa, sendo que muitas das propriedades ópticas (e provavelmente também elétricas) são afetadas pela forma de empacotamento, desordem conformacional e térmica, além da própria constituição das cadeias. / In this dissertation we present a study of the molecular dynamics and packing in organics semiconductor with different conjugated chains lengths using a of multi-techniques approach, in particular, Nuclear Magnetic Resonance (NMR), Wide Angle X-ray Scattering (WAXS), Differential Scanning Calorimetry (DSC), Raman spectroscopy, UV-Vis absorption and fluorescence spectroscopy. The studies were carried-in fluorene oligomers with 3, 5 and 7 repeat units and multi-block conjugated/non-conjugated copolymers with the conjugated part formed by phenylene-vinylene units (PV) and the non-conjugated block formed by methylene units. Concerning the oligomers studies, it was shown that the ability of the chain to form ordered domains as well as the domain structure depend on the number of repeat units, with the pentamer having a higher tendency to crystallization. This conclusion was supported by theoretical ab-initio calculations, which showed that the pentamer conformation favors inter-chain interactions and therefore long-range ordering. The molecular dynamics studies support these characteristics and showed that the activation of molecular motions in oligomers amorphous phase are predominantly dependent on the oligomeric chain lengths, in agreement with the behavior observed for their glass transitions (Tg´s). In the study concerning the multi-block copolymers, it was found that presence of the aliphatic chains inhibit the strong tendency to crystallization of the PV units, but do not prevent their aggregation. It was found that the dispersion in aggregated units sizes strongly affects the copolymers emission, with the emission of larger chains being privileged. Regarding the molecular dynamics, we observed that the presence of motion on aliphatic region contributes to the appearance of non-radiative relaxation processes that inhibit the emission of the copolymers and produce broadening of the vibronic bands. Finally, we observed that isotropic motions of the PV chains are responsible for the copolymers glass transition and the energy required to activate these movements increase with length of the chain. In summary, our results indicate that even in systems with well controlled chains length, the strong intermolecular interactions present in conjugated polymers, can make the solid state morphology of these systems quite complex, which may affect many optical (and probably electric) properties are affected by the packaging structure, thermal and conformational disorder, in addition to the constitution of the chains composition.

Les propriétés électroniques et d'autoassemblage de deux composés organiques, le DHTAP et le bis-pyrène, ont été étudiées par microscopie à effet tunnel (STM), sous ultra-vide et à basse température. Les propriétés optiques ont été étudiées par spectroscopie en cavité résonnante (CRD), également sous ultravide.La croissance du DHTAP a été étudiée sur différents métaux nobles. La croissance du bis-pyrène a été étudiée sur Au(111). Dans chaque cas, les conditions de température idéales pour la formation d’une première couche organisée ont été déterminées. Différents modèles sont proposés pour les structures observées en première couche. La formation de la seconde couche moléculaire à également été étudiée.L'évolution des propriétés optiques, étudié par CRD, du bis-pyrène déposé sur du verre borosilicate combinée aux informations obtenues par STM ont permit d’associer ces modifications aux interactions des moments dipolaires de transition des molécules de la première et de la seconde couche et on également permit de déterminer le mode de croissance.Finalement, la possibilité d’induire des modifications chimique de la molécule de DHTAP, intégrée dans une couche auto-assemblée, en utilisant le courant tunnel du STM a été observé. Il s’avère que la molécule de DHTAP intégrée en première couche peut subir une double déshydrogénation pour conduire à la formation d’un composé identifié comme étant le 5,7,12,14-tetraazapentacene (TAP). En seconde couche, la formation de deux radicaux, en plus du TAP, a été observé. La molécule de TAP présente un certain intérêt du fait qu’elle n’est pas synthétisable pas les méthodes conventionnelle de chimie organique. / Electronic and self-assembling properties of two organic compound, the DHTAP and the bis-pyrene, have been studied by the means of low temperature scanning tunnelling microscopy (STM) under ultrahigh vacuum conditions. Optical properties have been studied by cavity ring-down (CRD) spectroscopy, also under ultrahigh vacuum conditions.The growth of DHTAP has been studied on different metallic substrate. The growth of bis-pyrene has been studied on Au(111). In each case, the optimal temperature conditions for the formation of a well-ordered first monolayer have been determined. The formation of second monolayers has also been studied. The evolution of the optical properties, studied by CRD, of bis-pyrene deposited on borosilicate glass combined with information obtained from STM allow us to identify these modifications as interactions between transition dipole moments of molecules in the first and in the second layer, and also determine the growth mode.Finally, the possibility to induce chemical modification of DHTAP molecules embedded in an ordered monolayer using the tunnelling current of the STM has been studied. It appears that the molecule embedded in the first ML can be doubly dehydrogenated which leads to the formation of a compound identified as 5,7,12,14-tetraazapentacene (TAP). In the second layer, the formation of two radicals in addition to the TAP has been observed. The TAP molecule is interesting because of that it cannot be synthesized using common organic chemical methods.

Master of Science / Department of Chemistry / Daniel A. Higgins / Three water-soluble perylene diimides (PDIs) were investigated to examine differences in their thin film forming properties. The PDI thin films investigated in this thesis are formed in an electrostatic-self-assembled (ESA) layer-by-layer (LBL) process by the use of a dip coater. The three PDIs employed are sodium bis (sulfonatopropyl) perylene diimide (PDISO[subscript]3[superscript]2-), bis (trimethylammonioethyl) perylene diimide diiodide (PDIDI[superscript]2+), and N-(butoxypropyl)-N'-(2-(N,N,N-trimethylammonio)-ethyl) perylene-3,4,9,10-tetracarboxylic diimide iodide (C[subscript]7OPDI[superscript]+). Thin films were made by alternately depositing the PDIs with counter polyelectrolyte (PEs). The PEs employed were poly(diallyldimethylammonium chloride) (PDDA[superscript]+) and poly(acrylic acid) (PA[superscript]-), depending on the charge of the PDI. PDIs were determined to be aggregated in all three PDI precursor solutions. The fraction of PDI aggregated in each was found to be 0.972, 0.903, and 0.993, for the PDISO[subscript]3[superscript]2-, PDIDI[superscript]2+, and C[subscript]7OPDI[superscript]+, respectively. The C[superscript]7OPDI[superscript]+ solution was the most aggregated only having one charge group, which makes it more hydrophobic. Thin films prepared from the solutions all displayed an absorbance spectrum similar to the aggregated form. All the composites displayed linear growth in film thickness and fiber width with bilayer number. However, the three composites gave unique surface morphologies. The PDISO[subscript]3[supercript]2-[dot in middle of line]PDDA+ composite was found to incorporate highly curled intertwined fibers compared to the PDIDI[superscript]2+[dot in middle of line]PA[superscript]- composite, where the fibers were not intertwined. The fiber structure was found to change after 15 bilayers. This change in morphology was attributed to the fibers grafting together and overlapping causing the loss of original fiber structure. The two symmetric composites differed in the film thickness with the PDISO[subscript]3[superscript]2-[dot in middle of line]PDDA[superscript]+ being thicker than the PDIDI[superscript]2+[dot in middle of line]PA[superscript]- composite. This was attributed to the molecular weights (MW) of the polyelectrolytes investigated during thin film deposition, with the PDDA[superscript]+ having a much higher MW. C[subscript]7OPDI[superscript]+[dot in middle of line]PA[superscript]- thin film composite had a film thickness approximately equal to the PDISO[subscript]3[superscript]2-[dot in middle of line]PDDA[superscript]+ composite, indicating precursor aggregation also influences deposition rate. The C[subscript]7OPDI[superscript]+[dot in middle of line]PA[superscript]- composite incorporated wavy thin fibers that appeared aligned in the dipping direction. This alignment was visible for bulk samples in UV-vis absorption dichroism studies. The alignment was parallel to the dipping direction of the substrate.

This thesis deals with organic materials and determining their electrical parameters. In the thesis are discussed methods of deposition of organic layers and their measurement. Described are the aspects, which are characteristic for organic materials. They will briefly mention some new components and commercial systems. Special attention is given to conducting polymers and determining their parameters. In the experimental part were measured VA and impedance characteristics of the conductive polymer PEDOT-PSS. The research was also about material degradation in time and effects of thickness on the electrical parameters.

No description available.

Der zunehmende Bedarf nach digitalen Speichermedien macht die Erforschung von neuen Materialien für zukünftige Technologien von nichtflüchtigen Speichern nötig. Hierfür eignen sich zum Beispiel Metall-Nanopartikel, die in organischen Halbleiterschichten eingebettet sind. Aufgrund der bistabilen Schaltbarkeit der Leitfähigkeit von Metall-Nanopartikeln lassen sie sich in Abhängigkeit der elektrischen Umgebungsbedingungen entweder in einen niedrig- oder einen hochleitenden Zustand schalten. Bisher wurden verschiedene Modelle entwickelt, um den Schaltmechanismus von Speichern mit einem organischen Matrixmaterial zu erklären, jedoch fehlt bislang ein konsistentes Bild zum Verständnis des Schaltvorgangs. Die vorliegende Arbeit  untersucht die Rolle des Raumladungsfeldes ausgehend von Metall-Nanopartikeln in Bauelementen. Dazu wurde eine Reihe von Experimenten zur Bestimmung der elektronischen und elektrischen Eigenschaften durchgeführt, um die tatsächliche Rolle des Raumladungsfeldes aufzuklären. Mit Hilfe von Röntgen- und UV-Photoelektronenspektroskopie wurde die Wechselwirkung zwischen den Metall-Nanopartikeln und den prototypischen organischen Halbleiterschichten detailliert untersucht. Unter Verwendung der bereits untersuchten Materialien wurden Bauelemente hergestellt und charakterisiert. Die Ergebnisse zeigen, dass der allgemein vorgeschlagene Mechanismus bezüglich der Aufladung/Entladung von Metall-Nanopartikeln als Ursache für die elektrische Bistabiliät in einem zweipoligen Bauteil ausgeschlossen werden kann. Stattdessen stützt dieses Ergebnis den alternativen Mechanismus der Filamentbildung. Zur Untersuchung der Skalierbarkeit der Speicher im Nanometerbereich wurden die Strukturen durch das Abscheiden der Materialien bei streifendem Einfall präpariert. Die entsprechenden Nanospeicher wurden elektrisch charakterisiert und zeigten Bistabilität. Folglich sind diese Nanspeicher besonders attraktiv für zukünftige Technologien in Hinblick auf hohe Speicherdichten. / The increasing need to store digital information has triggered research into the exploration of new materials for future non-volatile memory (NVM) technologies. For instance, metal nanoparticles (MNPs) embedded into organic semiconductors are suitable for novel memory applications because they were found to display bistable resistive switching. Different switching models were hitherto developed to explain the fundamental mechanisms at work in resistive NVMs. This thesis explores specifically the role of space-charge field due to the charging of MNPs as rationale for resistive switching in two-terminal devices. A series of experiments on the electronic and electrical properties of devices were conducted in order to reveal whether this mechanism is, indeed, at play in resistance switching. Photoelectron spectroscopy provided detailed information about the interaction between gold nanoparticles (AuNPs) with prototypical organic semiconductors used in optoelectronics. The study of the electronic valence structures provided evidence of a space-charge due to the charging of AuNPs. Furthermore, it is found that charge-neutrality of AuNPs can be dynamically re-established upon illumination, through electron transfer from excitons. Devices were built with the same materials investigated by photoemission spectroscopy and electrical characterization was conducted. Despite the previously demonstrated ability to optically change the charging state of the AuNPs, the devices do not display any bistability. This finding provides evidence that the commonly proposed charging/decharging mechanism of MNPs can be excluded as cause for electrical bistability in NVM devices. In order to explore the scaling of resistive NVMs into the nanometric range, glancing angle deposition technique was employed. The nano-NVMs were electrically characterized and it is proved to manifest resistive bistability. These finding make nano-NVMs highly appealing for future high-density memory technology.

Organische Halbleiterbauelemente sind eine vielversprechende Technologie, die das Spektrum der optoelektronischen Halbleiterbauelemente erweitert und etablierte Technologien basierend auf anorganischen Halbleitermaterialien ersetzen kann. Für Display- und Beleuchtungsanwendungen werden sie z. B. als organische Leuchtdioden oder Transistoren verwendet. Eine entscheidende Eigenschaft organischer Halbleitermaterialien ist, dass die Ladungstransporteigenschaften stark von der Temperatur im Bauelement beeinflusst werden. Insbesondere nimmt die elektrische Leitfähigkeit mit der Temperatur zu, so dass Selbsterhitzungseffekte, einen großen Einfluss auf die Leistung der Bauelemente haben. Mit steigender Temperatur nimmt die elektrische Leitfähigkeit zu, was wiederum zu größeren Strömen führt. Dies führt jedoch zu noch höheren Temperaturen aufgrund von Joulescher Wärme oder Rekombinationswärme. Eine positive Rückkopplung liegt vor. Im schlimmsten Fall führt dieses Verhalten zum thermischen Durchgehen und zur Zerstörung des Bauteils. Aber auch ohne thermisches Durchgehen führen Selbsterhitzungseffekte zu interessanten nichtlinearen Phänomenen in organischen Bauelementen, wie z. B. die S-förmige Beziehung zwischen Strom und Spannung. In Regionen mit negativem differentiellen Widerstand führt eine Verringerung der Spannung über dem Bauelement zu einem Anstieg des Stroms durch das Bauelement. Diese Arbeit soll einen Beitrag zur mathematischen Modellierung, Analysis und numerischen Simulation von organischen Bauteilen leisten. Insbesondere wird das komplizierte Zusammenspiel zwischen dem Fluss von Ladungsträgern (Elektronen und Löchern) und Wärme diskutiert. Die zugrundeliegenden Modellgleichungen sind Thermistor- und Energie-Drift-Diffusion-Systeme. Die numerische Diskretisierung mit robusten hybriden Finite-Elemente-/Finite-Volumen-Methoden und Pfadverfolgungstechniken zur Erfassung der in Experimenten beobachteten S-förmigen Strom-Spannungs-Charakteristiken wird vorgestellt. / Organic semiconductor devices are a promising technology to extend the range of optoelectronic semiconductor devices and to some extent replace established technologies based on inorganic semiconductor materials. For display and lighting applications, they are used as organic light-emitting diodes (OLEDs) or transistors. One crucial property of organic semiconductor materials is that charge-transport properties are heavily influenced by the temperature in the device. In particular, the electrical conductivity increases with temperature, such that self-heating effects caused by the high electric fields and strong recombination have a potent impact on the performance of devices. With increasing temperature, the electrical conductivity rises, which in turn leads to larger currents. This, however, results in even higher temperatures due to Joule or recombination heat, leading to a feedback loop. In the worst case, this loop leads to thermal runaway and the complete destruction of the device. However, even without thermal runaway, self-heating effects give rise to interesting nonlinear phenomena in organic devices, like the S-shaped relation between current and voltage resulting in regions where a decrease in voltage across the device results in an increase in current through it, commonly denoted as regions of negative differential resistance. This thesis aims to contribute to the mathematical modeling, analysis, and numerical simulation of organic semiconductor devices. In particular, the complicated interplay between the flow of charge carriers (electrons and holes) and heat is discussed. The underlying model equations are of thermistor and energy-drift-diffusion type. Moreover, the numerical approximation using robust hybrid finite-element/finite-volume methods and path-following techniques for capturing the S-shaped current-voltage characteristics observed in experiments are discussed.

A high performance vertical organic transistor based on the organic semiconductor C60 is developed in this work. The sandwich geometry of this transistor, well known from organic light-emitting diodes or organic solar cells, allows for a short transfer length of charge carriers in vertical direction. In comparison to conventional organic field-effect transistors with lateral current flow, much smaller channel lengths are reached, even if low resolution and low-cost shadow masks are used. As a result, the transistor operates at low voltages (1 V), drives current densities in the range of 10 A/cm², and enables a switching speed in the MHz range. The operation mechanism is studied in detail. It is demonstrated that the transistor can be described by a nano-porous permeable base electrode insulated by a thin native aluminum oxide film on its surface. Thus, the transistor has to be understood as two metal-oxide-semiconductor diodes, sharing a common electrode, the base. Upon applying a bias to the base, charges accumulate in front of the oxide, similar to the channel formation in a field-effect transistor. Due to the increased conductivity in this region, charges are efficiently transported toward and through the pinholes of the base electrode, realizing a high charge carrier transmission. Thus, even a low concentration of openings in the base electrode is sufficient to ensure large transmission currents. The device concept turns out to be ideal for applications where high transconductance and high operation frequency are needed, e.g. in analog amplifier circuits. The full potential of the transistor is obtained if the active area is structured by an insulating layer in order to perfectly align the three electrodes. Besides that, molecular doping near the charge injecting contact is essential to minimize the contact resistance. Due to the high power density in the vertical C60 transistor, Joule self-heating occurs, which is discussed in this work in the context of organic semiconductors. The large activation energies of the electrical conductivity observed cause the presence of S-shaped current-voltage characteristics and result in thermal switching as well as negative differential resistances, as demonstrated for several two-terminal devices. A detailed understanding of these processes is important to determine restrictions and proceed with further optimizations. / In dieser Arbeit wird ein vertikaler organischer Transistor mit hoher Leistungsfähigkeit vorgestellt, der auf dem organischen Halbleiter C60 basiert. Die von organischen Leuchtdioden und organischen Solarzellen bekannte \'Sandwich’-Geometrie wird verwendet, so dass es möglich ist, für die vertikale Stromrichtung kurze Transferlängen der Ladungsträger zu erreichen. Im Vergleich zum konventionellen organischen Feldeffekttransistor mit lateralem Stromfluss werden dadurch viel kleinere Kanallängen erreicht, selbst wenn preisgünstige Schattenmasken mit geringer Auflösung für die thermische Verdampfung im Vakuum genutzt werden. Daher kann der Transistor bei einer Betriebsspannung von 1 V Stromdichten im Bereich von 10 A/cm² und Schaltgeschwindigkeiten im MHz-Bereich erreichen. Obwohl diese Technologie vielversprechend ist, fehlt bislang ein umfassendes Verständnis des Funktionsmechanismus. Hier wird gezeigt, dass der Transistor eine nanoporöse Basiselektrode hat, die durch ein natives Oxid auf ihrer Oberfläche elektrisch isoliert ist. Daher kann das Bauelement als zwei Metall-Oxid-Halbleiter-Dioden verstanden werden, die sich eine gemeinsame Elektrode, die Basis, teilen. Unter Spannung akkumulieren Ladungsträger vor dem Oxid, ähnlich zur Ausbildung eines Ladungsträgerkanals im Feldeffekttransistor. Aufgrund der erhöhten Leitfähigkeit in dieser Region werden Ladungsträger effizient zu und durch die Öffnungen der Basis transportiert, was zu hohen Ladungsträgertransmissionen führt. Selbst bei einer geringen Konzentration von Löchern in der Basiselektrode werden so hohe Transmissionsströme erzielt. Das Bauelementkonzept ist ideal für Anwendungen, in denen eine hohe Transkonduktanz und eine hohe Schaltgeschwindigkeit erreicht werden soll, z.B. in analogen Schaltkreisen, die kleine Signale verarbeiten. Das volle Potential des Transistors offenbart sich jedoch, wenn die aktive Fläche durch eine Isolatorschicht strukturiert wird, um den Überlapp der drei Elektroden zu optimieren, so dass Leckströme minimiert werden. Daneben ist die Dotierung der Molekülschichten am Emitter essentiell, um Kontaktwiderstände zu vermeiden. Aufgrund der hohen Leistungsdichten in den vertikalen C60-Transistoren kommt es zur Selbsterwärmung, die in dieser Arbeit im Kontext organischen Halbleiter diskutiert wird. Die große Aktivierungsenergie der Leitfähigkeit führt zu S-förmigen Strom-Spannungs-Kennlinien und hat thermisches Umschalten sowie negative differentielle Widerstände zur Folge, was für verschiedene Bauelemente demonstriert wird. Ein detailliertes Verständnis dieser Prozesse ist wichtig, um Beschränkungen für Anwendungen zu erkennen und um entsprechende Verbesserungen einzuführen.

Nous investiguons dans ce travail la dynamique des excitons dans une couche mince d’agrégats H autoassemblés hélicoïdaux de molécules de sexithiophène. Le couplage intermoléculaire (J=100 meV) place ce matériau dans la catégorie des semi-conducteurs à couplage de type intermédiaire. Le désordre énergétique et la forte interaction électronsphonons causent une forte localisation des excitons. Les espèces initiales se ramifient en deux états distincts : un état d’excitons autopiégés (rendement de 95 %) et un état à transfert de charge (rendement de 5%). À température de la pièce (293K), les processus de sauts intermoléculaires sont activés et l’anisotropie de la fluorescence décroît rapidement à zéro en 5 ns. À basse température (14K), les processus de sauts sont gelés. Pour caractériser la dynamique de diffusion des espèces, une expérience d’anisotropie de fluorescence a été effectuée. Celle-ci consiste à mesurer la différence entre la photoluminescence polarisée parallèlement au laser excitateur et celle polarisée perpendiculairement, en fonction du temps. Cette mesure nous donne de l’information sur la dépolarisation des excitons, qui est directement reliée à leur diffusion dans la structure supramoléculaire. On mesure une anisotropie de 0,1 après 20 ns qui perdure jusqu’à 50ns. Les états à transfert de charge causent une remontée de l’anisotropie vers une valeur de 0,15 sur une plage temporelle allant de 50 ns jusqu’à 210 ns (période entre les impulsions laser). Ces résultats démontrent que la localisation des porteurs est très grande à 14K, et qu’elle est supérieure pour les espèces à transfert de charge. Un modèle numérique simple d’équations différentielles à temps de vie radiatif et de dépolarisation constants permet de reproduire les données expérimentales. Ce modèle a toutefois ses limitations, notamment en ce qui a trait aux mécanismes de dépolarisation des excitons. / In this work, we investigate exciton dynamics in a thin film of sexithiophene molecules in self-assembled chiral H-aggregate supramolecular stacks. The intermolecular coupling energy J=100 meV places those molecules in the intermediate coupling regime. The energetic disorder and the strong phonon-electron interactions leads to high localization of the photoexcitations. The initial photoexcited species branches into two distinct states : self-trapped exciton (95% yield) and charge-transfer excitons (5% yield). At room temperature (293K), the intermolecular hopping processes are thermaly activated and the fluorescence anisotropy goes to zero within 5 ns. At low temperature (14K), hopping processes are frozen. To characterize exciton diffusion mechanisms, a fluorescence anisotropy experiment has been done. This measurement consists of monitoring the difference between the parallel and perpendicular composants of the photoluminescence (with respect to the laser beam), as a function of time. The fluorescence anisotropy gives us information about the depolarization of the excitons, which is directly connected with their diffusion within the supramolecular stack. We measure an anisotropy of 0,1 after 20 ns which stays constant for 50 ns. Chargetransfer states induce a rise of the anisotropy up to 0,15 between 50 ns and 210 ns (the period between adjacent laser pulses). Those measurements shows that exciton localization is very strong at 14K and higher for the charge-transfer states than the self-trapped ones. A simple mathematical model based on the resolution of a system of differential equations with constants radiative and depolarization lifetimes can reproduce the experimental data. This model has some limitations, especially for the description of the depolarization mechanisms of the self-trapped excitons.