Not available / text

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.

Organic electronics have received significant development in the last few decades. p- Type materials are much more in availability than n-type now. There are only a few examples of air-stable n-type materials. The design and synthesis of novel air-stable ntype materials is still a focus of research. Herein is described a study to evaluate the effectiveness of a novel electron-withdrawing group, composed of three electronwithdrawing groups connected in series, to impart material properties known to be favorable for obtaining air-stable n-types. The smaller acenes, naphthalene and anthracene, carrying these electron-withdrawing groups were prepared and studied by UV-Vis absorption spectroscopy and solution electrochemical measurements to estimate changes in frontier molecular orbital energies and single crystal X-ray diffraction to determine packing motif. These measurements suggest that the new materials could be promising as n-type semiconductors in organic field effect transistor (OFET) and as acceptors for organic photovoltaic (OPV) cells. The reasons are based on: (1) the close intermolecular contacts seen in X-ray crystal structures, some of them showing 3D faceto- face stack. (2) Electrochemical measurements indicate LUMO energy levels suitable for air-stable n-type materials.

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.

Boronsubphthalocyanines (BsubPcs) are a class of organic semiconducting materials which are relatively underdeveloped in their synthetic methods and organic semiconducting applications. A comprehensive investigation of these materials is explored in a rigorous and strategic manner progressing through each stage of the materials development cycle: materials selection from computational screening, organic/organometallic synthesis of target materials using known methods or by the development of new synthetic methods, physical and chemical analysis of new materials, and device implementation in organic light emitting diodes and organic photovoltaic cells. The result is the formation of new compositions of BsubPc specifically engineered for application as organic semiconductors in devices. Specifically, phenoxy-boronsubphthalocyanine derivatives are investigated starting with a computational study of their molecular orbitals – a property that dictates their function (donor or acceptor behaviour) in organic electronic devices. The nature of the axial phenoxylate is found to vary the energy level of the frontier molecular orbitals minimally, by up to ~0.4 eV while the nature of the BsubPc periphery can shift the energy levels of the frontier molecular orbitals by >1 eV. The differential sensitivity of the axial phenoxylate and the BsubPc periphery becomes a key design element allowing controlled adjustments of the frontier molecular orbitals by peripheral modification and isolating the design physical chemical properties essential to device fabrication to the axial phenoxylate. Subsequently, an investigation into the solubility and sublimability of these materials is performed, which leads to their investigation in OLED and OPV devices. The success from the phenoxy-BsubPcs study has led to the exploration of new chemistry to expand the available axial nucleophiles beyond phenoxylates. Previously unattainable sulphur and nitrogen nucleophiles are synthesised using two methods (1) the condensation of Cl-BsubPc with phthalimides and (2) the activation of Cl-BsubPc using aluminum chloride to access thiols and anilines. The phthalimido-BsubPcs synthesized from this method are incorporated in OLEDs.

Boronsubphthalocyanines (BsubPcs) are a class of organic semiconducting materials which are relatively underdeveloped in their synthetic methods and organic semiconducting applications. A comprehensive investigation of these materials is explored in a rigorous and strategic manner progressing through each stage of the materials development cycle: materials selection from computational screening, organic/organometallic synthesis of target materials using known methods or by the development of new synthetic methods, physical and chemical analysis of new materials, and device implementation in organic light emitting diodes and organic photovoltaic cells. The result is the formation of new compositions of BsubPc specifically engineered for application as organic semiconductors in devices. Specifically, phenoxy-boronsubphthalocyanine derivatives are investigated starting with a computational study of their molecular orbitals – a property that dictates their function (donor or acceptor behaviour) in organic electronic devices. The nature of the axial phenoxylate is found to vary the energy level of the frontier molecular orbitals minimally, by up to ~0.4 eV while the nature of the BsubPc periphery can shift the energy levels of the frontier molecular orbitals by >1 eV. The differential sensitivity of the axial phenoxylate and the BsubPc periphery becomes a key design element allowing controlled adjustments of the frontier molecular orbitals by peripheral modification and isolating the design physical chemical properties essential to device fabrication to the axial phenoxylate. Subsequently, an investigation into the solubility and sublimability of these materials is performed, which leads to their investigation in OLED and OPV devices. The success from the phenoxy-BsubPcs study has led to the exploration of new chemistry to expand the available axial nucleophiles beyond phenoxylates. Previously unattainable sulphur and nitrogen nucleophiles are synthesised using two methods (1) the condensation of Cl-BsubPc with phthalimides and (2) the activation of Cl-BsubPc using aluminum chloride to access thiols and anilines. The phthalimido-BsubPcs synthesized from this method are incorporated in OLEDs.

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.