Le travail rapporté dans ce mémoire de thèse concerne la synthèse et la caractérisation de nouveaux semi-conducteurs organiques basés sur un coeur bithiophène. Ce travail s'inscrit dans le prolongement de précédents travaux réalisés au laboratoire portant sur des dérivés du type distyryl-oligothiophènes. Au cours de ce travail, plusieurs voies de synthèse ont été développées afin de fonctionnaliser un coeur bithiophène, rigide ou non, avec différents groupements fonctionnels, principalement pour trois types d'applications : (i) la réalisation de transistors à base de couche mince organique (OFETs), (ii) l'élaboration de cellules solaires à partir de composés push-pull et (iii) le développement de capteurs. Le premier chapitre est consacré à la fonctionnalisation du benzo-[2,1-b:3,4-b']dithiophène-4,5-dione soit par des groupements mésogéniques soit par des motifs aminostyryles. L'objectif est la possibilité de préparer des OFETs par la voie liquide et de tirer profit des propriétés cristal liquide pour améliorer les performances électriques. Les propriétés cristal liquides ont été décrites, et les transistors réalisés. Malheureusement aucune mobilité de porteur de charge n'a pu être enregistrée. Dans un deuxième temps, des modifications structurales ont été apportées sur certaine des structures synthétisées afin d'améliorer les propriétés recherchées. Toutefois, au moment de la rédaction de ce manuscrit, les OFETs n'étaient pas réalisés. Dans le deuxième chapitre, de nouvelles molécules push-pull de type cruciformes ont été synthétisées dans le but d'évaluer leurs performances en tant que composés organiques actifs dans des dispositifs photovoltaïques. / The work reported herein concerns the synthesis and the characterization of new organic semiconductors built around the bithiophene core. It was relied on an extended work carried out previously in our laboratory on distyryloligothiophene derivatives. The main part of this work was dedicated to develop new functionalized organic semi-conductors with the aim to improve their properties for optoelectronic applications, mainly for: i) the realization of transistors with organic thin layer (OFETs), ii) the elaboration of solar cells from push-pull derivatives and iii) the development of sensors. The first chapter is devoted to the functionalization of the benzo-[2,1-b:3,4-b ']bithiophene-4,5-dione core either by mesogenic or aminostyryl groups with the purpose to improve, using liquid crystal properties, the microscopic ordering and the electrical performances of the synthetized organic semiconductors as well as their solution processability. Besides the liquid crystal properties characterization showing interesting behavior, the OFET devices have been made from those semiconductors but unfortunately have led to, as unexpected, poor charge transport properties. Some structural modifications have been done in order to optimize the charge transport characteristics nevertheless their electrical characterization still under progress up to now. In a second part, some push-pull derivatives, having a cruciform-like structure, have been synthetized and characterized in order to use them as an active organic layer in photovoltaic devices. Their optoelectronic properties have been evaluated and reported.

In this work, well-defined and stable thin films based on polythiophene and its derivative, are employed as the hole-injection contact of organic light-emitting diodes (OLED). The polymer films are obtained by the electropolymerization or the electrochemical doping/dedoping of a spin-coated layer. Their electrical properties and energetics are tailored by electrochemical adjustment of their doping levels in order to improve the hole-injection from the anode as well as the performance of small molecular OLEDs. By using dimeric thiophene and optimizing the electrodeposition parameters, a thin polybithiophene (PbT) layer is fabricated with well-defined morphology and a high degree of smoothness by electro-polymerization. The introduction of the semiconducting PbT contact layer improves remarkably the hole injection between ITO anode and the hole- transport layer (NPB) due to its favourable energetic feature (HOMO level of 5.1 eV). The vapor-deposited NPB/Alq3 bilayer OLEDs with a thin PbT interlayer, show a remarkable reduction of the operating voltage as well as enhanced luminous efficiency compared to the devices without PbT. Investigations have also been made on the influence of PbT thickness on the efficiency and I-V feature as well as device stability of the OLED. It is demonstrated that the use of an electropolymerization step into the production of vapor deposited molecular OLED is a viable approach to obtain high performance OLEDs. The study on the PbT has been extended to poly(3,4-ethylenedioxythiophene) (PEDT) and the highly homogenous poly(styrenesulfonate) (PSS) doped PEDT layer from a spin-coating process has been applied. The doping level of PEDT:PSS was adjusted quantitatively by an electrochemical doping/dedoping process using a p-tuoluenesulfonic acid containing solution, and the redox mechanism was elucidated. The higher oxidation state can remain stable in the dry state. The work function of PEDT:PSS increases with the doping level after adjusting at an electrode potential higher than the value of the electrochemical equilibrium potential (Eeq) of an untreated film. This leads to a further reduction of the hole-injection barrier at the contact of the polymeric anode/hole transport layer and an ideal ohmic behavoir is almost achieved at the anode/NPB interface for a PEDT:PSS anode with very high doping level. Molecular Alq3-based OLEDs were fabricated using the electrochemically treated PEDT:PSS/ITO anode, and the device performance is shown to depend on the doping level of polymeric anode. The devices on the polymer anode with a higher Eeq than that for the unmodified anode, show a reduction of operating voltage as well as a remarkable enhancement of the luminance. Furthermore, it is found that the operating stability of such devices is also improved remarkably. This originates from the removal of mobile ions such as sodium ions inside the PEDT:PSS by electrochemical treatment as well as the planarization of the ITO surface by the polymer film. By utilizing an Al/LiF cathode with an enhanced electron injection and together with a high Eeq- anode, a balanced injection and recombination of hole and electron is achieved. It leads to a further reduction of the operating voltage and to a drastic improvement of EL efficiency of the device as high as 5.0 cd/A. The results demonstrate unambiguously that the electrochemical treatment of a cast polymer anode is an effective method to improve and optimize the performance of OLEDs. The method can be extended to other polythiophene systems and other conjugated polymers in the fabrication of the OLEDs as well as organic transistors and solar cells.

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.

Im Rahmen der vorliegenden Arbeit wurden Schottky-Dioden mittels Rolle-zu-Rolle-Verfahren hergestellt und charakterisiert. Die Dioden bestanden dabei aus einer Kathode (Aluminium oder Kupfer), die durch Sputtern aufgebracht wurde, einer Halbleiterschicht aus Polytriphenylaminen (PTPA3), die mittels Tiefdruck aufgebracht wurde und einer im Flexodruck hergestellten Anode (PEDOT:PSS, Pani oder Carbon Black). Aus elektrischer Sicht wiesen dabei Dioden mit Kupfer und Carbon Black die besten Eigenschaften auf. Mit Hilfe dieser Elektrodenmaterialien und bei Halbleiterschichtdicken von ca. 200 nm konnten Grenzfrequenzen der Dioden von über 1 MHz realisiert werden. Weiterhin wiesen diese Dioden eine gute Langzeitstabilität sowie eine gute Stabilität gegenüber UV-Licht, Feuchtigkeit und Temperatur auf. / Aim of this work was to demonstrate that Schottky-Diodes can be fabricated by means of Roll-to-Roll-Methods and to characterize these diodes. The diodes consists of a sputtered cathode (Aluminum or Copper), a gravure printed semiconducting layer of Polytriphenylamine (PTPA3) and a flexo printed anode (PEDOT:PSS, Pani, Carbon Black). Best electrical characteristics were obtained with diodes consisting Copper and Carbon Black as electrodes. With a thickness of the semiconducting layer of ~200 nm diodes with a cut-off frequency above 1 MHz could be demonstrated. These diodes showed also a good stability when exposed to UV-light, moisture and temperature.

Les appareils de haute technologie (ordinateurs, télévisions, téléphones, …) sont fabriqués à partir de composants relativement simples (transistors, diiodes électroluminescentes, …) qui utilisent du silicium comme semiconducteur. En électronique moléculaire, les composés organiques π- conjugués qui ont un écart HOMO-LUMO faible peuvent présenter cette propriété. Dans le cadre de ce travail, nous avons étudié la synthèse de nouveaux semiconducteurs organiques parpolymérisation par métathèse d’alcynes. Pour cela, des composés de type dialcynylaromatique ont été préparés. Leur étude en polymérisation ainsi que leurs propriétés électroniques ont été réalisées dans des laboratoires collaborateurs d’un projet ANR (CADISCOM). Dans une seconde partie, indépendante de la première, les couplages croisés catalysés par le palladium sont d’une importance capitale dans la chimie organique de synthèse actuelle. De nombreux travaux ont été menés sur le partenaire organométallique de la réaction, mais très peu en ce qui concerne le partenaire électrophile. Lors de ce travail, nous avons élaboré un nouveau groupe partant à partir de précurseurs très peu onéreux que nous avons pu appliquer dans les quatre "grands couplages" les plus utilisés (Suzuki, Stille, Sonogashira et Heck). / High-technology devices (computers, TV, mobile phones, …) are manufactured from simple components (transistors, LED, …) which use silicium as semiconductor. In organic electronics, π- conjugated organic compounds with low HOMO-LUMO gap can show this property. This work is dealing with the synthesis of new organic semiconductors via alkyne metathesis polymerization.Dialkynyl compounds were synthetized. Their polymerization studies as well as electronic characterization were conducted by collaborating groups in an ANR project (CADISCOM). In an independent second part, palladium-catalyzed cross-coupling are of great importance in actual organic synthesis. Many studies have been focused on the organometallic partner of the reaction,but the electrophilic partner have received much less attention. In this work, we developed a new leaving group from cheap precursors that we applied in the four most well-known couplings (Suzuki, Stille, Sonogashira, Heck).

This thesis deals with the research work carried out for the development of novel applications by integrating biomolecules with various nanostructures. The thesis is organized as follows: Chapter 1 reviews the properties of nanomaterials which are important to consider while developing them for various biological and other applications. It discusses the factors which affect the cytotoxicity of nanocrystals towards living cells, photocatalytic mechanisms of nanocrystals that work behind the inactivation of bacterial cells and gas sensing properties of nanocrystals. It also mentions about the integration of biomolecules with nanomaterials which is useful for the development of biosensors, materials that are presently used for fabricating biosensors and the challenges associated with designing successful biosensors. Chapter 2 presents the antibacterial and anticancer properties of ZnO/Ag nanohybids. In this study a simple route to synthesize ZnO/Ag nanohybrids by microwave synthesis has been established where ZnO/Ag nanohybrids have shown synergistic cytotoxicity towards mammalian cells. The observed synergism in the cytotoxicity of ZnO/Ag nanohybrids could lead to the development of low dose therapeutics for cancer treatment. Chapter 3 presents photocatalytic inactivation of bacterial cells by pentavalent bismuthates class of materials. AgBiO3 which was obtained from KBiO3 by ion-exchange method was investigated for its photocatalytic inactivation properties towards E.coli and S.aureus cells under dark and UV illumination conditions. Chapter 4 presents the integration of DNA molecules with ZnO nanorods for the observation of Mott-Gurney characteristics. In this study, ZnO nanorods were synthesized hydrothermally and were characterized by TEM and XRD analysis. DNA molecules were immobilized over ZnO nanorods which were confirmed by UV-Vis spectroscopy and confocal florescence microscopy. Solution processed devices were fabricated by using these DNA immobilized nanostructures and I-V characteristics of these devices were taken in dark and under illumination conditions at different wavelengths of light at fixed intensity. Interestingly, Mott-Gurney law was observed in the I-V characteristics of the devices fabricated using DNA immobilized ZnO nanorods. Chapter 5 presents the chemical synthesis of molecular scale ultrathin Au nanowires. These nanostructures were then used for fabricating electronic biosensors. In this study, the devices were fabricated over Au nanowires by e-beam lithography and a methodology to functionalize Au nanowires and then characterize them by florescence microscopy as well as AFM has been established. The fabricated biosensors were employed for the label free, electrical detection of DNA hybridization process. Chapter 6 presents a simple, cost effective and solution processed route to fabricate devices using ultrathin Au nanowires. The devices were then used for sensing ethanol, H2 and NH3. An important property of these devices is that they can sense these gases at room temperature which reduce their operation cost and makes them desirable to use under explosive conditions.

L'objectif de cette thèse était de démontrer les potentialités de l'impression à jet d'encre pour le pilotage d'une HLED contenant des clusters métalliques phosphorescents dans le rouges, par des transistors organiques à effet de champs. Pour atteindre ce but, le projet a été divisé en deux parties : I) La fabrication et l'optimisation de transistors organiques de type n par photolithographie puis le transfert technologique vers l'impression à jet d'encre. II) Parallèlement au développement des transistors, je me suis attaché à la conception de matériaux hybrides luminescents pour la réalisation d'HLED. Pour la partie transistor, nous avons obtenu une meilleure compréhension des facteurs influençant l'injection de charges mais aussi la stabilité électrique pour un transistor de géométrie grille basse/contacts bas avec le fullerène C60 évaporé. Nous avons démontré que la résistance de contact est d'une part gouvernée par la morphologie du SCO au niveau des électrodes et d'autre part indépendante du travail de sortie du métal. En outre, nous avons vu que la stabilité électrique des transistors est fortement impactée par la nature du contact source et drain. L'optimisation des transistors fabriqués par photolithographie, qui a essentiellement consisté à modifier les interfaces, nous a permis de développer des transistors de type n performants avec des mobilités à effet de champ saturées allant jusqu'à 1,5 cm2/V.s pour une température maximum de procédé de 115 °C. Le transfert vers un transistor fabriqué par impression à jet d'encre a ensuite été effectué. Nous avons ensuite démontré que les morphologies de l'électrode de grille et de l'isolant, fabriqués par impression à jet d'encre, ont un impact négligeable sur les performances des transistors. Pour notre structure imprimée, l'injection de charges aux électrodes S/D est en fait le facteur clé pour la réalisation de transistors performants. Finalement, des matériaux phosphorescents rouges à base de cluster métalliques octaédrique de molybdène ont été développés. Le copolymère hybride résultant présentait un rendement quantique de photoluminescence de 51 %. La réalisation de l'HLED a ensuite été effectuée par combinaison d'une LED bleue commercial et du copolymère dopé avec des clusters octaédriques de molybdène pour des applications possibles en biologie ou dans l'éclairage. / The objective of this thesis was to demonstrate the potentialities of inkjet printing for driving an HLED containing red phosphorescent metallic clusters, with organic field effect transistors. To achieve this goal, the project was divided into two parts: I) The fabrication and optimization of n-type organic transistors by photolithography and then transfer to inkjet printing. II) Parallel to the development of transistors, I focused on designing luminescent hybrid materials for HLED realization. Concerning transistors, we obtained a better understanding of the factors influencing the charge injection but also the electrical stability for bottom gate/ bottom contact geometry transistor with evaporated C60 semiconductor. We have demonstrated that the contact resistance is on the one hand governed by the morphology of the SCO at the electrodes and on the other hand independent of the metal work function. In addition, we have observed that transistors electrical stability of is strongly impacted by the source and drain contact nature. The optimization of photolithography transistors, which essentially consisted of modifying the interfaces, allowed us to develop efficient n-type transistors with saturated field effect mobilities of up to 1.5 cm2/V.s for a maximal process temperature of 115 °C. The technological transfer to inkjet printed transistors was then performed. We then demonstrated that gate electrode and insulator morphologies deposited by inkjet printing, have a negligible impact on transistors performances. For our printed structure, charges injection at the S/D electrodes is in fact the key factor for high performance transistors realization. Finally, red phosphorescent materials based on molybdenum octahedral metal cluster have been developed. The resulting hybrid copolymer showed photoluminescence quantum yield up to 51%. The realization of the HLED was then carried out by combining a commercial blue LED and the copolymer doped with octahedral molybdenum clusters for possible applications in biology or lighting.

Les semi-conducteurs organiques à base d’aluminium ont été systématiquement synthétisés et caractérisés par méthodes photo-physiques et électrochimiques. Une étude de leur relation structure-propriétés électroniques a été menée. Les orbitales frontières ont été comparées à celles obtenues par calcul. De nouvelles méthodes ont été utilisées permettant une description de la morphologie des SCOs et un calcul de mobilité des porteurs de charges associés. La mobilité des trous dans Al(Op)3 a été mesurée sur des transistors en film minces: 0.6-2.1×10−6cm2V−1s−1. Par des techniques de spectroscopie en photoémission, la surface de l’hybride Co/Al(Op)3 a été sondée, révélant deux états d’interfaces hybrides, où la polarisation de spin de HIS1 est 8% plus élevée comparée au cobalt nu, et 4% plus faible dans HIS2. Enfin, des aimant moléculaires à base de phénalényle ont été étudiés. [Dy(Op)2Cl(HOp)(EtOH)] présente notamment un gap énergétique de 43.8K et un temps de relaxation de 5x10-4 s. / Aluminum-based organic semiconductors (OSCs) were systematically synthesized and studied by photophysical and electrochemical methods to identify a relationship between their chemical structure and electronic properties, using Alq3 as benchmark. Experimental HOMO and LUMO were compared to those computed. In addition, newly developed methods were implemented to generate morphologies and calculate charge carrier mobilities. The hole mobility of Al(Op)3 was measured in thin film transistors: 0.6-2.1×10−6 cm2V−1s−1. By photoemission spectroscopy techniques, the Co/Al(Op)3 hybrid interface was probed. Two hybrid interface states (HISs) were unraveled; the SP (spin polarization) of HIS1 is 8% higher than bare cobalt, whereas the SP of HIS2 is 4% lowered. At last, phenalenyl-based dysprosium SMMs (single-molecule magnet) were investigated. [Dy(Op)2Cl(HOp)(EtOH)] showed an energy gap of 43.8K and a quantum relaxation time of 5x10-4s.

[pt] Nesta dissertação foram estudadas as propriedades ópticas, eletroquímicas, elétricas e morfológicas de novos compostos fluorescentes para o desenvolvimento de OLEDs. Para isto, foram estudadas algumas sondas moleculares fluorescentes utilizadas na área biomédica como agentes antitumorais e marcadores ópticos fluorescentes: a) N,N - diisonicotinoil-2-hidroxi-5 metilisoftaldeído diidrazona (DMD); b) 2-(5 -isotiocianato-2 -hidroxifenil)benzoxazol, (5ONCS); c) 1,1 -dipireno (DIPI) e d) 7,7 -terc-butil-1,1- dipireno (TDIPI). Todos estes compostos foram sintetizados por Grupos de pesquisa brasileiros e depositados termicamente em forma de filmes finos no nosso Laboratório. No decorrer do estudo de fabricação dos OLEDs, os dispositivos bicamada baseados no DMD e no 5ONCS se mostraram pouco eficientes devido principalmente à baixa condutividade do DMD e à elevada rugosidade da camada de 5ONCS. A solução destes problemas foi encontrada na técnica de codeposição, que consiste na evaporação simultânea de uma matriz orgânica e de um dopante (DMD ou 5ONCS) numa única camada. Desta forma, foi possível alcançar um aumento da mobilidade das cargas nas camadas co-depositadas alem de favorecer a transferência de energia da matriz para o dopante. Os OLEDs fabricados nestas condições permitiram observar, pela primeira vez, a eletroluminescência dos compostos DMD e 5ONCS. Já os OLEDs baseados nas moléculas DIPI e TDIPI apresentaram eletroluminescência sem a necessidade da co-deposição. Em particular, no caso do OLED baseado no TDIPI foi possível alcançar uma luminância de 1430 cd/m2 com uma eficiência de 2,65 porcento a 1mA. Os resultados deste trabalho evidenciam a potencialidade do uso destes materiais para a fabricação de OLEDs para aplicações na área de iluminação. / [en] In this study the optical, electrochemical, electrical and morphological properties of new fluorescent compounds were studied in order to develop OLEDs based upon these materials. For this purpose some fluorescent molecular probes used in the biomedical field as antitumor agents and fluorescent optical probes were studied: a) N,N diisonicotinoyl-2-hydroxy-5-methylisophthalaldehyde dihydrazone (DMD ), b) 2 - (5 -isothiocyanato -2-hydroxyphenyl) benzoxazole ( 5ONCS ), c) 1,1 - dipyrene (DIPI) and d) 7,7 -tertbutyl- 1,1-dipyrene (TDIPI ). All these compounds were synthesized by Brazilian research groups and then thermally deposited as thin films in our Laboratory. During the study for the fabrication of OLEDs, bilayer devices based on DMD and 5ONCS proved to have low efficiency mainly due to the low conductivity of the DMD and the high roughness of the 5ONCS layer. The solution of these problems was found in the codeposition technique, which consists in the simultaneous evaporation of an organic matrix (host) and a dopant (guest) (5ONCS or DMD) in a single layer. Thus, it was possible to achieve an increase in the charge mobility in the co-deposited layers as well as energy transfer from the guest to the host. The OLEDs fabricated in these conditions allowed the observation, for the first time, of the electroluminescence of DMD and 5ONCS. On the other hand, the DIPI and TDIPI based OLEDs presented good electroluminescence without the need for co-deposition. In particular, in the case of the TDIPI it was possible to achieve a luminance of 1430 cd/m2 with an efficiency of 2.65 percent at 1 mA. The results of this work showed the potential of these materials for the fabrication of OLEDs for lighting applications.

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.:CONTENTS Publications, patents and conference contributions 9 1 Introduction 13 2 Theory 19 2.1 From small molecules to conducting thin films . . . . . . . . . . . . . . . . . . . . 19 2.1.1 Aromatic hydrocarbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.1.2 Solid state physics of molecular materials . . . . . . . . . . . . . . . . . . . 24 2.1.3 Energetic landscape of an organic semiconductor . . . . . . . . . . . . . . 26 2.1.4 Charge transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2.2 Semiconductor structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.2.1 Semiconductor statistics and transport . . . . . . . . . . . . . . . . . . . . 42 2.2.2 Charge injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 2.2.3 Limitations of the current . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 2.2.4 Metal-oxide-semiconductor structures . . . . . . . . . . . . . . . . . . . . . 57 2.3 Self-heating theory of thermistor device . . . . . . . . . . . . . . . . . . . . . . . . 61 3 Organic transistors 65 3.1 The organic field-effect transistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.1.1 Basic principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.1.2 Device characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.1.3 Device geometries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 3.1.4 Device parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 3.1.5 Issues of OFETs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 3.1.6 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 3.2 Overview over vertical organic transistors . . . . . . . . . . . . . . . . . . . . . . . 76 3.2.1 VOTs with an unstructured base electrode . . . . . . . . . . . . . . . . . . . 76 3.2.2 VOTs with structured base electrode . . . . . . . . . . . . . . . . . . . . . . 79 3.2.3 Charge injection modulating transistors . . . . . . . . . . . . . . . . . . . . 82 3.2.4 Vertical organic field-effect transistor . . . . . . . . . . . . . . . . . . . . . . 85 3.2.5 Development of the scientific output . . . . . . . . . . . . . . . . . . . . . . 87 3.2.6 Competing technologies and approaches . . . . . . . . . . . . . . . . . . . 88 3.3 Vertical Organic Triodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 3.3.1 Stucture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 3.3.2 Electronic configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 3.3.3 Energetic alignment of the diodes . . . . . . . . . . . . . . . . . . . . . . . 92 3.3.4 Current flow in the on and the off-state . . . . . . . . . . . . . . . . . . . . 94 3.3.5 Definition and extraction of parameters . . . . . . . . . . . . . . . . . . . . 95 4 Experimental 101 4.1 General processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 4.1.1 Thermal vapor deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 4.1.2 Processing tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 4.1.3 Processing information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 4.2 Mask setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 4.3 Measurement setups and tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 4.3.1 Current-voltage measurements . . . . . . . . . . . . . . . . . . . . . . . . . 108 4.3.2 Frequency-dependent measurements . . . . . . . . . . . . . . . . . . . . . 108 4.3.3 Impedance Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 4.3.4 Ultraviolet and X-ray Photoelectron Spectroscopy . . . . . . . . . . . . . . . 110 4.3.5 Thermal imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 4.4 Materials used in C60 triodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 4.4.1 Buckminsterfullerene C60 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 4.4.2 Tungsten paddlewheel W2(hpp)4 . . . . . . . . . . . . . . . . . . . . . . . . 116 4.4.3 Aluminum and its oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 4.4.4 Spiro-TTB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 4.5 Materials used in Organic Light-emitting Diodes . . . . . . . . . . . . . . . . . . . 121 5 Introduction of C60 VOTs 123 5.1 Sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 5.2 Diode characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 5.3 Base sweep measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 5.4 Determination of parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 5.5 Common-base connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 5.6 Output characteristic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 5.7 Frequency-dependent measurement . . . . . . . . . . . . . . . . . . . . . . . . . . 137 5.8 Intermediate summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 6 Effect of annealing 141 6.1 Charge carrier transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 6.2 Sheet resistance and transmittance of the base electrode . . . . . . . . . . . . . . 142 6.3 Investigation of morphological changes . . . . . . . . . . . . . . . . . . . . . . . . 144 6.4 Photoelectron spectroscopy of the base electrode . . . . . . . . . . . . . . . . . . 153 6.5 Influence of air exposure and annealing onto the dopants . . . . . . . . . . . . . . 159 6.6 Electrical characteristics of the diodes . . . . . . . . . . . . . . . . . . . . . . . . . 162 6.7 Intermediate summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 7 Working Mechanism 167 7.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 7.2 Diode characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 7.3 Simulation and modeling of the diode characteristics . . . . . . . . . . . . . . . . . 173 7.4 Interpretation of the operation mechanism . . . . . . . . . . . . . . . . . . . . . . . 181 7.5 Intermediate summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 8 Optimization of VOTs 183 8.1 Misalignment of the electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 8.2 Use of doping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 8.3 Variation of the intrinsic layer thickness . . . . . . . . . . . . . . . . . . . . . . . . . 190 8.4 Structuring the active area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 8.5 High-frequency operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 8.6 Intermediate summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 9 Self-heating in organic semiconductors 209 9.1 Temperature activation in C60 triodes . . . . . . . . . . . . . . . . . . . . . . . . . . 210 9.2 nin-C60 crossbar structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 9.3 Thermal switching in organic semiconductors . . . . . . . . . . . . . . . . . . . . . 216 9.4 Self-heating in large area devices: Organic LEDs . . . . . . . . . . . . . . . . . . . 218 9.5 Intermediate summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 10 Conclusion and Outlook 227 10.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 10.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 A Appendix 233 A.1 Appendix 1: Accuracy of the current gain . . . . . . . . . . . . . . . . . . . . . . . 233 A.2 Appendix 2: Fit of XRR measurements . . . . . . . . . . . . . . . . . . . . . . . . . 234 A.3 Appendix 3: Atomic force microscopy . . . . . . . . . . . . . . . . . . . . . . . . . 236 A.4 Appendix 4: Transmission electron microscopy . . . . . . . . . . . . . . . . . . . . 236 A.5 Appendix 5: Drift-diffusion simulation of nin devices . . . . . . . . . . . . . . . . . 239 A.6 Appendix 6: A simple parallel thermistor circuit . . . . . . . . . . . . . . . . . . . . 241 List of Figures 245 References 290 / 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.:CONTENTS Publications, patents and conference contributions 9 1 Introduction 13 2 Theory 19 2.1 From small molecules to conducting thin films . . . . . . . . . . . . . . . . . . . . 19 2.1.1 Aromatic hydrocarbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.1.2 Solid state physics of molecular materials . . . . . . . . . . . . . . . . . . . 24 2.1.3 Energetic landscape of an organic semiconductor . . . . . . . . . . . . . . 26 2.1.4 Charge transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2.2 Semiconductor structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.2.1 Semiconductor statistics and transport . . . . . . . . . . . . . . . . . . . . 42 2.2.2 Charge injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 2.2.3 Limitations of the current . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 2.2.4 Metal-oxide-semiconductor structures . . . . . . . . . . . . . . . . . . . . . 57 2.3 Self-heating theory of thermistor device . . . . . . . . . . . . . . . . . . . . . . . . 61 3 Organic transistors 65 3.1 The organic field-effect transistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.1.1 Basic principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 3.1.2 Device characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.1.3 Device geometries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 3.1.4 Device parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 3.1.5 Issues of OFETs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 3.1.6 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 3.2 Overview over vertical organic transistors . . . . . . . . . . . . . . . . . . . . . . . 76 3.2.1 VOTs with an unstructured base electrode . . . . . . . . . . . . . . . . . . . 76 3.2.2 VOTs with structured base electrode . . . . . . . . . . . . . . . . . . . . . . 79 3.2.3 Charge injection modulating transistors . . . . . . . . . . . . . . . . . . . . 82 3.2.4 Vertical organic field-effect transistor . . . . . . . . . . . . . . . . . . . . . . 85 3.2.5 Development of the scientific output . . . . . . . . . . . . . . . . . . . . . . 87 3.2.6 Competing technologies and approaches . . . . . . . . . . . . . . . . . . . 88 3.3 Vertical Organic Triodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 3.3.1 Stucture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 3.3.2 Electronic configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 3.3.3 Energetic alignment of the diodes . . . . . . . . . . . . . . . . . . . . . . . 92 3.3.4 Current flow in the on and the off-state . . . . . . . . . . . . . . . . . . . . 94 3.3.5 Definition and extraction of parameters . . . . . . . . . . . . . . . . . . . . 95 4 Experimental 101 4.1 General processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 4.1.1 Thermal vapor deposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 4.1.2 Processing tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 4.1.3 Processing information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 4.2 Mask setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 4.3 Measurement setups and tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 4.3.1 Current-voltage measurements . . . . . . . . . . . . . . . . . . . . . . . . . 108 4.3.2 Frequency-dependent measurements . . . . . . . . . . . . . . . . . . . . . 108 4.3.3 Impedance Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 4.3.4 Ultraviolet and X-ray Photoelectron Spectroscopy . . . . . . . . . . . . . . . 110 4.3.5 Thermal imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 4.4 Materials used in C60 triodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 4.4.1 Buckminsterfullerene C60 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 4.4.2 Tungsten paddlewheel W2(hpp)4 . . . . . . . . . . . . . . . . . . . . . . . . 116 4.4.3 Aluminum and its oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 4.4.4 Spiro-TTB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 4.5 Materials used in Organic Light-emitting Diodes . . . . . . . . . . . . . . . . . . . 121 5 Introduction of C60 VOTs 123 5.1 Sample preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 5.2 Diode characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 5.3 Base sweep measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 5.4 Determination of parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 5.5 Common-base connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 5.6 Output characteristic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 5.7 Frequency-dependent measurement . . . . . . . . . . . . . . . . . . . . . . . . . . 137 5.8 Intermediate summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 6 Effect of annealing 141 6.1 Charge carrier transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 6.2 Sheet resistance and transmittance of the base electrode . . . . . . . . . . . . . . 142 6.3 Investigation of morphological changes . . . . . . . . . . . . . . . . . . . . . . . . 144 6.4 Photoelectron spectroscopy of the base electrode . . . . . . . . . . . . . . . . . . 153 6.5 Influence of air exposure and annealing onto the dopants . . . . . . . . . . . . . . 159 6.6 Electrical characteristics of the diodes . . . . . . . . . . . . . . . . . . . . . . . . . 162 6.7 Intermediate summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 7 Working Mechanism 167 7.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 7.2 Diode characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 7.3 Simulation and modeling of the diode characteristics . . . . . . . . . . . . . . . . . 173 7.4 Interpretation of the operation mechanism . . . . . . . . . . . . . . . . . . . . . . . 181 7.5 Intermediate summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 8 Optimization of VOTs 183 8.1 Misalignment of the electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 8.2 Use of doping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 8.3 Variation of the intrinsic layer thickness . . . . . . . . . . . . . . . . . . . . . . . . . 190 8.4 Structuring the active area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 8.5 High-frequency operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 8.6 Intermediate summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 9 Self-heating in organic semiconductors 209 9.1 Temperature activation in C60 triodes . . . . . . . . . . . . . . . . . . . . . . . . . . 210 9.2 nin-C60 crossbar structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 9.3 Thermal switching in organic semiconductors . . . . . . . . . . . . . . . . . . . . . 216 9.4 Self-heating in large area devices: Organic LEDs . . . . . . . . . . . . . . . . . . . 218 9.5 Intermediate summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 10 Conclusion and Outlook 227 10.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 10.2 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 A Appendix 233 A.1 Appendix 1: Accuracy of the current gain . . . . . . . . . . . . . . . . . . . . . . . 233 A.2 Appendix 2: Fit of XRR measurements . . . . . . . . . . . . . . . . . . . . . . . . . 234 A.3 Appendix 3: Atomic force microscopy . . . . . . . . . . . . . . . . . . . . . . . . . 236 A.4 Appendix 4: Transmission electron microscopy . . . . . . . . . . . . . . . . . . . . 236 A.5 Appendix 5: Drift-diffusion simulation of nin devices . . . . . . . . . . . . . . . . . 239 A.6 Appendix 6: A simple parallel thermistor circuit . . . . . . . . . . . . . . . . . . . . 241 List of Figures 245 References 290