Στην εργασία αυτή μελετάμε διάφορα πολυοξομεταλλικά οξείδια (POMs) τα οποία μπορούν να χρησιμοποιηθούν ως διεπιφανιακά υμένια για την βελτίωση της απόδοσης και των διάφορων χαρακτηριστικών των οργανικών φωτοβολταικών διατάξεων καθώς και ενα νέο πολυμερές (cbz-bt) το οποίο μπορεί να χρησιμοποιηθεί σαν αντικαταστάτης του P3HT για να παίξει τον ρόλο του δότη σε οργανικές φωτοβολταικές διατάξεις. / In the present thesis we studied some polyoxometallates(POMs) which can be used as interfacial films in order to improve the efficiency and other featurew of organic OPVs and we also studied a new polymer (cbz-bt) which can be used instead of P3HT,playing the role of donor in OPVs.

Triarylamine type materials with vastly altered physical properties are synthesized by hybridizing organic semiconducting structures with silicone and siloxane groups. By altering the silicon content of these materials, we can tune their physical composition from free flowing liquids, to amorphous glasses, to cross-linked films. Much of this modification is enabled by the unique use of a metal-free Si-H activation chemistry; the Piers-Rubinsztajn reaction. This chemistry is demonstrated to be a general and rapid way to build up hybrid semiconducting structures. Key to the utility of these materials in electronic devices, it is shown that hybridization with silicon groups has a negligible effect on the useful electrochemical properties of the base materials. Building on this, it is shown that charge carrier mobility through a prototypical liquid organic semiconductor is similar to the base materials and transport is described by existing dispersive transport theories. Finally, two side projects in the area of organic electronics are discussed. New phthalonitrile based fluorophores are characterized and their utility as deep-blue emitting dopants in organic light emitting diodes is demonstrated. These same π-extended phthalonitriles can also be used as precursors to new red-shifted BsubPcs which display exceptional electrochemical stability and tuning.

Triarylamine type materials with vastly altered physical properties are synthesized by hybridizing organic semiconducting structures with silicone and siloxane groups. By altering the silicon content of these materials, we can tune their physical composition from free flowing liquids, to amorphous glasses, to cross-linked films. Much of this modification is enabled by the unique use of a metal-free Si-H activation chemistry; the Piers-Rubinsztajn reaction. This chemistry is demonstrated to be a general and rapid way to build up hybrid semiconducting structures. Key to the utility of these materials in electronic devices, it is shown that hybridization with silicon groups has a negligible effect on the useful electrochemical properties of the base materials. Building on this, it is shown that charge carrier mobility through a prototypical liquid organic semiconductor is similar to the base materials and transport is described by existing dispersive transport theories. Finally, two side projects in the area of organic electronics are discussed. New phthalonitrile based fluorophores are characterized and their utility as deep-blue emitting dopants in organic light emitting diodes is demonstrated. These same π-extended phthalonitriles can also be used as precursors to new red-shifted BsubPcs which display exceptional electrochemical stability and tuning.

The research work presented in this thesis investigates the mechanistic details of conventional as well as electrochemically directed self-assembly of alkylthiosulfates and explores the use of conjugated semiconducting polymers for organic electronic applications. Here, the significance of the use of conjugated polymers is twofold; first, to explore their applications in nanoelectronics and second, the possibility of using them as a top contact on the self-assembled monolayers (SAMs) for molecular electronic applications. Throughout this work, deposition of the organic materials was performed on prefabricated device structures that required no further lithographic or metal deposition steps after modification of the electrodes with the organic molecules. Self-assembly of alkylthiosulfates on gold are reported to form monolayers identical to those formed from the corresponding alkanethiols. However, these self-assembly processes follow more complex mechanisms of monolayer formation than originally recognized. Studies on the mechanism of alkylthiosulfate chemisorption on gold shows that the self-assembly process is influenced by electrolyte and solvent. Plausible mechanisms have been proposed for the role of trace water in the solvent on conventional as well as electrochemically assisted self-assembly of alkylthiosulfates on gold. Electroanalytical and spectroscopic techniques have been used to explore the mechanistic details of electrochemically directed self-assembly of alkylthiosulfates on gold. It has been found that the self-assembly process is dynamic under electrochemical conditions and the heterogeneous electron transfer process between the organosulfur compound and gold is mediated through gold surface oxide and accompanied by corrosion. Conducting polymers are serious candidates for organic electronic applications since their properties can be controlled by the manipulation of molecular architecture. Unique electronic properties of conjugated polypyrrole hybrid materials (PPy0DBS-Li+) with immobile dopant anions and mobile cations have been observed and explained on the basis of movement of the cations in an applied electric field. Based on this principle, functioning polymer resistive memory devices have been demonstrated which can be scalable to lower dimensions for nanoelectronics applications. Finally, proof of concept for using a conducting polymer as a top contact in molecular electronic devices created using electrochemically directed self-assembly is demonstrated.

The research work presented in this thesis investigates the mechanistic details of conventional as well as electrochemically directed self-assembly of alkylthiosulfates and explores the use of conjugated semiconducting polymers for organic electronic applications. Here, the significance of the use of conjugated polymers is twofold; first, to explore their applications in nanoelectronics and second, the possibility of using them as a top contact on the self-assembled monolayers (SAMs) for molecular electronic applications. Throughout this work, deposition of the organic materials was performed on prefabricated device structures that required no further lithographic or metal deposition steps after modification of the electrodes with the organic molecules. Self-assembly of alkylthiosulfates on gold are reported to form monolayers identical to those formed from the corresponding alkanethiols. However, these self-assembly processes follow more complex mechanisms of monolayer formation than originally recognized. Studies on the mechanism of alkylthiosulfate chemisorption on gold shows that the self-assembly process is influenced by electrolyte and solvent. Plausible mechanisms have been proposed for the role of trace water in the solvent on conventional as well as electrochemically assisted self-assembly of alkylthiosulfates on gold. Electroanalytical and spectroscopic techniques have been used to explore the mechanistic details of electrochemically directed self-assembly of alkylthiosulfates on gold. It has been found that the self-assembly process is dynamic under electrochemical conditions and the heterogeneous electron transfer process between the organosulfur compound and gold is mediated through gold surface oxide and accompanied by corrosion. Conducting polymers are serious candidates for organic electronic applications since their properties can be controlled by the manipulation of molecular architecture. Unique electronic properties of conjugated polypyrrole hybrid materials (PPy0DBS-Li+) with immobile dopant anions and mobile cations have been observed and explained on the basis of movement of the cations in an applied electric field. Based on this principle, functioning polymer resistive memory devices have been demonstrated which can be scalable to lower dimensions for nanoelectronics applications. Finally, proof of concept for using a conducting polymer as a top contact in molecular electronic devices created using electrochemically directed self-assembly is demonstrated.

Organic semiconductors have the advantage over traditional inorganic semiconductors, such as Si or GaAs, in that they do not require perfect single crystal films to operate in real devices. Complicated multi-layer structures with nanometer scale thicknesses can thus be easily fabricated from organic materials using low-cost roll-to-roll manufacturing techniques. However, the discrete nature of organic semiconductors also implies that they typically contain almost no intrinsic charge carriers (i.e., electrons or holes), and thus act as insulators until electrical charges are injected into them. In electrical device applications this means that all of the holes and electrons within a device must be injected from the anode and cathode respectively. As a result, device stability, performance, and lifetime are greatly influenced by the interface between the organic materials and the electrode contacts. Despite the fundamental importance of the electrode/organic contacts, much of the basic physical understanding of these interfaces remains unclear. As a result, the current design of state-of-the-art organic optoelectronic devices tends to be based on trial and error experimentation, resulting in overly complicated structures that are less than optimal. In the present thesis, various electrode/organic interfaces relevant to device applications are studied using a variety of different techniques, including photoelectron spectroscopy and the iii temperature dependent current-voltage characteristics of single carrier devices. The fundamental understanding gleaned from these studies has been used to develop new strategies for controlling the energy-level alignment at electrode/organic interfaces. A universal method for tuning the work function of electrode materials using a halogenated organic solvent and UV light has been developed. Application of this technique in organic light emitting diodes enabled the first highly simplified two-layer device with a state-of-the-art record breaking efficiency.

We have synthesized norbornene-functionalized side-chain monomers for potential use as hole transporting and electron transporting/hole blocking materials in organic light-emitting diodes. TPD-norbornenes were prepared. The monomers demonstrated similar electrochemical and absorbance spectra to the parent TPD small molecule. The similarity is promising for using the monomers in OLEDs because TPD is a known blue-emitter with relatively high hole mobility in amorphous thin films. 1,10-Phenanthroline small molecules and monomers were synthesized to explore their potential as hole blocking materials in multilayer devices. We had difficulty purifying the monomers; however, the small molecules were slightly easier to reduce than commonly used hole blocking materials 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline and 4,7-diphenyl-1,10-phenanthroline.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

>Magister Scientiae - MSc / Applications of electrochemiluminescent conjugated polymers offer promising solutions in addressing the problem of light emitting devices. However, the challenging problems that hamper their application in light emitting devices are loss of signal due to diffusion of the electrochemiluminescence (ECL) reagent out of the detection zone, limited ability to repeatedly cycle an individual luminophore and high reagent consumption. In this work, the main objective was to produce conducting polymers with enhanced electrochemiluminescence by tuning the properties of the polymer itself. The electrochemical and photophysical properties of films of polyaniline (PANI) and poly(8-anilino-1- naphthalene sulfonic acids) (PANSA) synthesized through electro- and chemical polymerization methods were also investigated. The electrosynthesis of PANSA undoped and doped with anthracene sulfonic acid (ASA), 1,2-naphthaquinone-4-sulfonic acid (NSA) and carbon nanotubes (CNT) in acid medium was investigated and the cyclic voltammograms (CV) showed the growth of the polymer during polymerization. The CV multiscan characterization displayed that the growth of the polymer was dependent of the scan rate and the three redox couples were observed as indicative of the three redox states of typical polyaniline and its derivatives. The results also showed that the peak currents were diffusion controlled and the electron charge transport coefficient (De) of the electrosynthesized polymers was found to range between 10⁻⁸ and 10⁻⁹ cm² s⁻¹ for PANSA, PANSA-ASA, PANSA-NSA and PANSA-CNT. The De value indicates that the movement of electrons along the polymer chain was averagely fast. The transmission electron microscopy (TEM) was used to investigate the electronic morphology of the polymers and the TEM images showed an intertwinement of tubings which aggregate into a ring with a mixture of tubings and plastic sheets. The chemical synthesis of PANI, PANSA and PANI-NSA was carried out by using monomers analine, 8-anilino-1-naphthalene sulfonic acid, and aniline with 1,2- naphthaquinone-4-sulfonic acid, respectively, using oxidants. All chemically synthesized polymers exhibited quinoid and benzoid bands typically see in polyaniline FTIR and Raman spectra confirmed the successfully formation of polymers. The CV characterization of these polymers showed distinctive redox peaks. This proved that the polymers were electroactive, conductive and exhibited reversible electrochemistry. The De of the electrosynthesized polymers was found to be ~10⁻⁵ cm² s⁻¹ for chemically synthesized polymers. The electric conductivity measurement showed to increase from 10⁻⁴ to 10⁻² when aniline was polymerized with NSA dopant, this might be related to the process of electron transfer from dopant to polymer. Scanning electron microscopy for external morphology showed that the polymers were made of different nano- rods polymeric structures. Photophysical properties of electro- and chemically synthesized PANSA and PANI were investigated through UV-vis absorption, fluorescence behaviour, and lifetime. The UV-vis absorption spectra of these polymers showed that they exhibited absorption bands corresponding to the polyemeraldine redox state of typical polyaniline. The effect of dopants resulted in the increase in solubility of the polymers with a small shift of absorption bands due to incorporation of dopants in to the backbone of the polymer. The fluorescence emission spectra of the electrochemically synthesized PANSA with and without dopants were observed to be similar and mirror image of the excitation spectra and corresponding to the electronic band of the benzoid ring in the polyemeraldine form confirming that the fluorescing molecule in these polymers were the benzoid rings. However, the emission spectra of the chemically synthesized PANSA and PANI were different to excitation spectra due to loss of symmetry upon excitation. The effects of chemically synthesized PANI, PANSA and PANI-NSA addition on the photophysical properties of [Ru(bpy)₂(picCOOH)]²⁺.(ClO₄⁻)₂) were investigated in order to understand the interaction of polymer and [Ru(bpy)₂(picCOOH)]²⁺.(ClO₄⁻)₂. The analysis revealed that the presence of polyaniline and its derivatives enhanced the [Ru(bpy)₂(picCOOH)]²⁺.(ClO₄⁻)2 absorption band, photoluminescence and fluorescence lifetime. The enhancement observed from interaction of [Ru(bpy)₂(picCOOH)]²⁺.(ClO₄⁻)₂ with polyaniline and its derivatives might be due to the excited state electron transfer from the PANI and PANSA excited state to the [Ru(bpy)₂(picCOOH)]²⁺.(ClO₄⁻)₂. It was further demonstrated in this work that it is possible to form polyaniline and PANSA doped with [Ru(bpy)₂(picCOOH)]²⁺.(ClO₄⁻)₂ films on ITO electrode using potentiostatic growth method to favour ECL production. The results showed that all films generated ECL in the presence of Tripropylamine (TPA) as a co-reactant and their emission properties depend on time used to prepare the film. The enhancement of ECL signal was due to a positive electron transfer from the conducting polymer (PANI and PANSA) to [Ru(bpy)₂(picCOOH)]²⁺.(ClO₄⁻)₂ complex. The results highlighted the potential of these polymeric luminophores usage in the manufacturing of the ECL devices.