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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
61

Novel poly(propylene thiophenoimine)-co poly(ethylenedioxythiophene) composites of naphthalene diimide for applications in organic photovoltaic cells

Yonkeu, Anne Lutgarde Djoumessi January 2013 (has links)
Magister Scientiae - MSc / Solar energy generation arises as a result of direct conversion of sunlight into electricity a by solar cell; which is mainly made up of a semiconducting material incorporated into a system. It is emerging as one of the most reliable and cost efficient renewable energy sources. Within the solar field, organic bulk heterojunction photovoltaic cells have proved of being able to have a great impact in the future years; mainly due to the easy processability of the active layer and substrate, their cost effectiveness and above all, a good power conversion efficiency associated to the close 3-dimensional interpenetrating network that is generated from blending donor and acceptor semiconducting materials together in a bulk heterojunction active layer. In this research work, we therefore report on the study of a newly developed organic bulk heterojunction active layer based on a blend of a star-copolymer generation 1 poly(propylenethiophenoimine)-co-poly(ethylenedioxythiophene) (G1PPT-co-PEDOT) as donor material with N,N-diisopropylnaphthalene diimide (NDI) as acceptor material. Both materials were chemically synthesized. The synthesis of G1PPT-co-PEDOT started first by the functionalization of generation 1 poly(propyleneimine) tetramine, G1PPI into G1PPT by condensation reaction in the presence of 2-thiophene carboxaldehyde under Nitrogen gas followed by the copolymerization of G1PPT with ethylene dioxythiophene (EDOT) monomer in the presence of ammonium persulfate, (NH4)2S2O8 as oxidant. On the other hand, NDI was also synthesized via condensation reaction of 1,4,5,8-naphthalene tetracarboxylic dianhydride in the presence of two (2) equivalences of N,N-diisopropylamine at 110 oC overnight in DMF. Both materials were characterized using FT-IR, UV-Vis spectroscopy, Fluorescence spectroscopy, Voltammetry, HRSEM microscopy and XRD. Based on the cyclic voltammetry and UV-Vis results, we were able to calculate the HOMO, LUMO and band gap energy (Eg) values of both the donor and acceptor to be -4.03 eV, -6.287 eV and 2.25 eV for iii the donor G1PPT-co-PEDOT respectively and -4.302 eV, -7.572 eV and 3.27 eV for the acceptor respectively. From these results, the energy diagram for both donor and acceptor was drawn and it comes out that the separation between the HOMO of the donor and the LUMO of the acceptor ΔEg = 1.985 eV, the ideal value for a good donor-acceptor combination. Also the offset energy that is, the energy difference between the LUMO of the donor and the LUMO of the acceptor is 0.302 eV.
62

Lithographic fabrication, electrical characterization and proof-of-concept demonstration of sensor circuits comprising organic electrochemical transistors for in vitro and in vivo diagnostics / Fabrication lithographique, caractérisation électrique et preuve de concept des circuits de capteurs comprenant des transistors organiques électrochimiques, à des fins diagnostiques in vitro et in vivo

Braendlein, Marcel 24 March 2017 (has links)
Grâce à leurs excellentes propriétés mécaniques, électriques et chimiques, les dispositifs organiques électroniques à base de polymères conducteurs peuvent résoudre l’incompatibilité entre les modules électroniques rigides en silicone et les exigences des tissus mous qui constituent l’environnement biologique. Les avancées en matière de semiconducteurs organiques et en microélectronique ont donné naissance à la bioélectronique. Cette discipline emploie des capteurs à des fins diagnostiques, telles que la détection des métabolites ou la mesure d’un potentiel d’action neuronal, et des actionneurs à des fins thérapeutiques, comme l’application locale d’un traitement à l’intérieur même du corps, ou la stimulation cérébrale profonde afin de guérir un trouble neurologique. En bioélectronique, l’utilisation de matériaux organiques, tels que le polymère conducteur poly(3,4-éthylènedioxythiophène) polystyrène sulfonate de sodium (PEDOT:PSS) a permis de développer des composants électroniques biomédicaux de qualité exceptionnelle, comme par exemple le transistor organique électrochimique (OECT), qui ont été testés in vitro et in vivo. Ce manuscrit explique en détail la fabrication, la fonctionnalisation et la caractérisation du OECT à base de PEDOT:PSS. Afin de pouvoir intégrer ce capteur à des systèmes de mesure biomédicaux déjà établis, l’OECT est intégré à des circuits simples, tels qu’un amplificateur de tension ou un pont de Wheatstone. Ces circuits sont mis à l’épreuve de la pratique clinique, dans le cas de mesures électrocardiographiques, ou de détection de métabolites dans des cellules cancéreuses. Cela permet d’apprécier à la fois leur applicabilité, et leurs limites. / Due to their outstanding mechanical, electrical and chemical properties, organic electronic devices based on conducting polymers can bridge the gap between the rigid silicon based read-out electronics and the soft biological environment and will have a huge impact on the medical healthcare sector. The recent advances in the field of organic semiconductors and microelectronics gave rise to a new discipline termed bioelectronics. This discipline deals with sensors for diagnostic purposes, ranging from metabolite detection and DNA recognition all the way to single neuronal firing events, and actuators for therapeutic purposes, through for example active local drug delivery inside the body or deep brain stimulation to cure neurological disorder. The use of organic materials such as the conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) in the field of bioelectronics has brought about a variety of outstanding electronic biomedical devices, such as the organic electrochemical transistor (OECT), that have been implemented for both in vitro and in vivo applications. The present manuscript gives a detailed explanation of the fabrication, functionalization and characterization of OECTs based on PEDOT:PSS. To be able to intercept this sensor element with traditional biomedical recording systems, the OECT is implemented into simple circuit layouts such as a voltage amplifier or a Wheatstone bridge. These sensor circuits are then applied to real-life biomedical challenges, such as electrocardiographic recordings or metabolite detection in tumor cell cultures, to demonstrate their applicability as well as their limitations.
63

Optical studies of the charge localization and delocalization in conducting polymers

Kim, Youngmin 06 January 2005 (has links)
No description available.
64

Charge transport in organic multi-layer devices under electric and optical fields

Park, June Hyoung 17 July 2007 (has links)
No description available.
65

Conjugated Polymer-based Conductive Fibers for Smart Textile Applications

Bashir, Tariq January 2013 (has links)
Electrically conductive or electro-active fibers are the key components of smart and interactive textiles, which could be used in medical, sports, energy, and military applications in the near future. The functionalization of high-performance textile yarns/fibers with conjugated polymers can produce conductive fibers with better electro-mechanical properties, which is difficult with commonly used spinning techniques. In this thesis work, textile-based conductive yarns/fibers were prepared by coating viscose and polyester (PET) yarns with the conjugated polymer PEDOT. For coating purposes, an efficient technique called chemical vapor deposition (CVD) was used, which is a solventless technique and can produce PEDOT polymer layers with high conductivity values. The polymerization of EDOT monomer vapors and coating of oxidant (FeCl3 or FepTS) enriched viscose and PET yarns took place simultaneously. The PEDOT-coated viscose and polyester yarns showed relatively high conductivity values, which could be sufficient for many electronic applications. The polymerization process and the quality of PEDOT polymer strongly depends on different reaction conditions. In this research work, the impact of most of these reaction parameters on the electrical, mechanical, and thermal properties of PEDOT-coated conductive yarns was considered separately. Under specific reaction conditions, it was found that viscose fibers were successfully coated with PEDOT polymer and showed rather high electrical conductivity (≥ 15 S/cm). However, due to the acid hydrolysis of viscose fibers in FeCl3 solutions, the mechanical properties were drastically reduced. In order to improve the mechanical properties of conductive yarns, a relatively stable and chemical-resistant substrate (PET) was coated with PEDOT polymer. Comparative studies between PEDOT-coated viscose and PET conductive yarns showed that the electrical and mechanical properties were enhanced by changing the substrate material. Later on, PEDOT-coated conductive fibers were treated with silicone elastomer solution and due to the thin silicone layers, the hydrophobic properties, flexibility, and durability of coated yarns was improved. Furthermore, a novel electrical resistance-measuring setup was developed, which can be used not only for fibers but also for fabric structures. The electrical characterization of PEDOT-coated conductive yarns showed that it can be used effectively for sensitive fibers without damaging their surface morphology. Finally, the use of conductive yarns as stretch sensors was evaluated. For this purpose, small rectangular knitted patches of conductive yarns were prepared and then the change in electrical resistance values at different extension percentages (5–50%) was investigated. The constant variations in electrical resistance values at different extension and relaxation cycles for longer periods of time revealed that the conductive yarns produced have the potential to be used as stretch sensors for monitoring of vital signs in medical and sports applications. / <p>Thesis for the Degree of Doctor of Philosophy to be presented on March 08, 2013, 10.00 in KA-salen, Kemigården 4, Chalmers University of Technology, Gothenburg</p>
66

SIMULACAO DA ESTRUTURA MOLECULAR E ELETRÔNICA DE POLIMEROS CONDUTORES

Andrade, Ageo Meier de 22 February 2016 (has links)
Made available in DSpace on 2017-07-24T19:37:54Z (GMT). No. of bitstreams: 1 Ageo Meier Andrade.pdf: 3358892 bytes, checksum: c2798e568b2f1bcb11fc21644c783df2 (MD5) Previous issue date: 2016-02-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The search for materials with conductive capacity has been gaining attention in the scienti c community for its many technological applications. Moreover, understanding the charge transport phenomena in these materials it is still seen as a challenge to the scientic community. Poly (3,4-ethylenedioxythiophene), PEDOT features desirable characteristics where planar molecular structure ensures process of charge transfer and charge separation. In the investigation of these properties, computational tools emerge as an alternative with low nancial cost when compared to experimental techniques. Knowing that several semi-empirical methodologiess are available and the class of conductive polymers exhibit unique macromolecular characteristics; the objective of this study was to investigate the structural properties of 1-EDOT to 10-EDOT by the latest methodologies available in MOPAC2012 program, that is, PM6, PM7 and RM1. It was found that among them, PM6 methodology provided good results, especially for presenting the planar polymer chain to oligomers of 2-EDOT to 10-EDOT. DFT calculations have been used for organic polymeric systems with conductive characteristics and has evolved as a major computational tools for electronic properties. Thus, for 1-EDOT to 10-EDOT optimized by PM6 methodology, single point calculations were applied using DFT B3LYP/6-31++G(d,p) obtaining information related to the charge transport, especially reducing band-gap energy, border orbital location and formation of an intramolecular charge hall. From these informations, were investigated electrostatic potential map and Density of States (DOS) based on energy levels. In computational analysis of excited states, calculations based on TDDFT using B3LYP/6-31+G were applied to molecular systems, where it was possible to investigate discrete levels of excitation energy in the UV-visible range. In small oligomers of 1-EDOT to 6-EDOT using PM6 optimized structures such calculations showed the possibility of investigating the main configuration related to discrete levels, showing the reduction in energy required for excitation with increasing polymer chain for this material. Having noted both the reduction of energy band-gap and the singlet excitation energy, relatedto increasing polymeric chain, it was investigated these properties for a macromolecular system considering infinite oligomers. In this analysis, linear regression applied to the results of 2-EDOT to 6-EDOT had the lowest band-gap energy. Subsequently, band-gap energy was related to the wavelength of maximum absorption of the singlet excitation energy. It was concluded that it is possible to apply semi-empirical calculations followed by single-pint DFT and TDDFT calculations in the investigation of conductive properties of polymeric materials providing significant results to understand charge transport and the prediction of structural and electronic properties. / A busca por materiais com capacidades condutoras vem ganhando atenção na comunidade científica por suas inúmeras aplicações tecnológicas. Além disso, o entendimento do fenômeno de transporte de carga continua sendo visto como um desafio para a comunidade cientifica. Poli (3,4-etilenodioxitiofeno), PEDOT apresenta caracteristicas condutoras desejáveis porque sua estrutura molecular planar garante que haja o processo de transferência e separação de carga. Na investigação dessa propriedade, ferramentas computacionais surgem como uma alternativa de baixo custo financeiro quando comparados a técnicas experimentais. Sabendo que diversas metodologias semi-empíricas estão disponíveis e que a classe de polímeros condutores apresentam caracteressticas macromoleculares únicas; objetivou-se neste estudo a investigação das propriedades estruturais de 1-EDOT a 10-EDOT pelas mais recentes metodologias disponíveis no programa MOPAC2012, isto é, PM6, PM7 e RM1. Verificou-se que dentre elas, a metodologia PM6 forneceu bons resultados em relação aos resultados experimentais, principalmente por apresentar a cadeia polimérica planar para oligômeros de 2-EDOT a 10-EDOT. Cálculos em DFT tem sido usados para sistemas poliméricos orgânicos com características condutoras e evoluiu como uma das principais ferramentas computacionais para propriedades eletrônicas. Sendo assim, foram aplicados cálculos pontuais em DFT usando B3LYP/6-31++G(d,p)) de 1-EDOT a 10-EDOT a partir de estruturas otimizadas em PM6 obtendo-se informações relevantes ao transporte de carga, principalmente, redução da energia de band-gap, localizaçãoo dos orbitais de fronteiras e formação de um corredor de carga intramolecular. Investigou-se a partir destas informações o mapa de potencial eletrostático e a Densidade de Estados (DOS) por meio dos níveis discretos de energia. Na análise computacional de estados excitados, cálculos baseados em TDDFT usando B3LYP/6-31+G foram aplicados a sistemas moleculares, onde é possível investigar níveis discretos de excitação na faixa do UV-Visível. Nos pequenos oligomeros de 1-EDOT a 6-EDOT, utilizando a estrutura otimizada em PM6, tais cálculos mostraram a possibilidade de investigar as principais configurações de excitação do estado singlete em níveis discretos, mostrando a redução da energia necessária para excitação com o aumento da cadeia polimérica para esse material. Por ter verificado tanto a redução da energia de band-gap quanto da energia de excitação de singlete, e que ambos s~ao relacionados ao aumento da cadeia polimérica, investigou-se a previsão por extrapolação para um sistema macromolecular com infinitos oligômeros. Nessa análise, a regressão linear aplicada aos resultados de 2-EDOT a 6-EDOT apresentou a menor energia de band-gap. Posteriormente, o band-gap foi relacionado ao comprimento de onda máximo da absorção de singlete. Concluiu-se que é possível aplicar cálculos semi-empíricos em conjunto com cálculos pontuais em DFT e TDDFT na investigação de propriedades condutoras de materiais poliméricos proporcionando resultados expressivos para entender o transporte de carga e a prediação de propriedades estruturais e eletrônicas.
67

Conjugated Polymers for Neural Interfaces : Prospects, possibilities and future challenges

Asplund, Maria January 2009 (has links)
Within the field of neuroprosthetics the possibility to use implanted electrodes for communication with the nervous system is explored. Much effort is put into the material aspects of the electrode implant to increase charge injection capacity, suppress foreign body response and build micro sized electrode arrays allowing close contact with neurons. Conducting polymers, in particular poly(3,4-ethylene dioxythiophene) (PEDOT), have been suggested as materials highly interesting for such neural communication electrodes. The possibility to tailor the material both mechanically and biochemically to suit specific applications, is a substantial benefit with polymers when compared to metals. PEDOT also have hybrid charge transfer properties, including both electronic and ionic conduction, which allow for highly efficient charge injection.   Part of this thesis describes a method of tailoring PEDOT through exchanging the counter ion used in electropolymerisation process. Commonly used surfactants can thereby be excluded and instead, different biomolecules can be incorporated into the polymer. The electrochemical characteristics of the polymer film depend on the ion. PEDOT electropolymerised with heparin was here determined to have the most advantageous properties. In vitro methods were applied to confirm non-cytotoxicity of the formed PEDOT:biomolecular composites. In addition, biocompatibility was affirmed for PEDOT:heparin by evaluation of inflammatory response and neuron density when implanted in rodent cortex.   One advantage with PEDOT often stated, is its high stability compared to other conducting polymers. A battery of tests simulating the biological environment was therefore applied to investigate this stability, and especially the influence of the incorporated heparin. These tests showed that there was a decline in the electroactivity of PEDOT over time. This also applied in phosphate buffered saline at body temperature and in the absence of other stressors. The time course of degradation also differed depending on whether the counter ion was the surfactant polystyrene sulphonate or heparin, with a slightly better stability for the former.   One possibility with PEDOT, often overlooked for biological applications, is the use of its semi conducting properties in order to include logic functions in the implant. This thesis presents the concept of using PEDOT electrochemical transistors to construct textile electrode arrays with in-built multiplexing. Using the electrolyte mediated interaction between adjacent PEDOT coated fibres to switch the polymer coat between conducting and non conducting states, then transistor function can be included in the conducting textile. Analogue circuit simulations based on experimentally found transistor characteristics proved the feasibility of these textile arrays. Developments of better polymer coatings, electrolytes and encapsulation techniques for this technology, were also identified to be essential steps in order to make these devices truly useful.   In summary, this work shows the potential of PEDOT to improve neural interfaces in several ways. Some weaknesses of the polymer and the polymer electronics are presented and this, together with the epidemiological data, should point in the direction for future studies within this field. / QC 20100623
68

Nanofils de silicium pour les cellules solaires hybrides

Zhu, Mingxuan 20 December 2013 (has links) (PDF)
Le contexte énergétique actuel est un enjeu sociétal. L'utilisation de l'énergie solaire au travers de cellules solaires photovoltaïques à bas-coût et à haut rendement, est une des voies envisagées pour répondre aux besoins énergétiques. Ce travail de thèse a permis de démontrer la faisabilité de cellules solaires hybrides, basées sur une jonction de type " cœur/coquille " entre des nanofils de silicium obtenus par gravure chimique et du PEDOT polymérisé par voie électrochimique. Les principaux avantages d'une telle structure sont à la fois la simplicité et le faible coût des méthodes utilisées pour la réalisation de la cellule. Les nanofils de silicium, grâce à leur capacité à piéger la lumière, conduisent à des propriétés d'anti-reflet très intéressantes avec notamment des valeurs de réflexion inférieures à 3% sur toute la gamme spectrale du visible. La réalisation de telles jonctions a fait l'objet d'une étude poussée sur les différentes caractéristiques de dépôt du polymère, tels que l'intensité lumineuse, le potentiel appliqué et la durée du procédé. L'influence de ces paramètres sur la mesure I(V) de la cellule solaire hybride complète a également été étudiée. On peut noter en particulier que l'on obtient ainsi une densité de courant de fuite très faible et une résistance de fuite très élevée, permettant d'émettre l'hypothèse d'une bonne passivation des états de surface. Ceci constitue une voie prometteuse pour obtenir un bon transport de charges en polarisation inverse.
69

Morpological Architecturing of Electroactive Materials in Organic Electronics

Khanum, Khadija Kanwal January 2015 (has links) (PDF)
Morphological architecturing is one of the smart and efficient ways to maximize the number of excitons harvested from the known photoactive materials and existing fabrication technologies. Surfaces and interfaces play a vital role in absorbing light and therefore when patterned regularly, aid in the improvement of light absorption. This thesis deals with the study of light management by morphologically architecturing the organic electroactive materials. Here, morphological architecturing is carried out using electrospinning technique by optimizing various parameters. In the first part, organic photovoltaic system is tailored by morphologically modifying the conjugated polymer active layer and analyzing the enhancement in light collection and hence performance of photovoltaic devices. In the second part, the prospects of using free standing buffer layer instead of thin film buffer layer in a solar cell is evaluated. Furthermore, the study on morphological engineering of conjugated small molecule is carried out, by varying the solvents and derivatives, in order to control morphologies by understanding the underlying mechanism. Overall this thesis attempts to understand the fundamentals in morphological architecturing, by physical architecturing of the small molecules in a device for light management applications as well as demonstrating improvement in light absorption in existing organic photovoltaic systems. In the introduction chapter, a brief description of organic photovoltaics is given followed by highlighting the importance of processing methods in light management and in organic photovoltaics. The significance of structured architecture in improving the device characteristics is presented. The issues and challenges in existing architecturing techniques available in literature are discussed. Electrospinning as a tool for morphological modification for organic photovoltaics is demonstrated. This is followed by an outline of the thesis. In Chapter 2, brief description of procedures carried out for fabrication, characterization and optimization of electrospinning process parameters are discussed. The description of fabrication procedures including electrospinning, spincoating and thermal evaporation are given. Characterization techniques used in this thesis for surface and feature analysis, structural, compositional, optical and opto-electrical analyses are described. Optimization of electrospinning process parameters in obtaining various morphologies are evaluated. In Chapter 3, enhancement of device characteristics of poly (3-hexylthiophene): phenyl C61-butyric acid methyl ester (P3HT: PCBM) by changing active layer film morphology into network structure is elucidated. Network structure is provided by electrospraying assisted hierarchical assembly of short fibrils. Effect of electrospraying parameters such as solvent, polymer blend concentration, applied voltage, tip to collector distance, flow rate and deposition time are analyzed. Solvent and applied voltage are observed to be the major parameters governing the formation of network structure. The optimized conditions are used to investigate the optical and structural properties. Percent reflectance studies showed improvement in light absorption due to increase in surface area. Structural characterization studies indicate an increase in orientation of crystallites and crystallinity as compared to spincoated samples. The optimized conditions along with additional spincoated layer of P3HT:PCBM are used to fabricate bulk heterojunction device. Device characteristics exhibited an increase in short circuit current and thus increase in efficiency from 2.18% to 3.66%. There is a enhancement of 37.5% going from maximum external quantum efficiency of 40%-55% for electrosprayed and spincoated devices. It is anticipated that network morphology could be the next possible structure to be explored in organic photovoltaic materials. In Chapter 4, photonic structure is analyzed and compared. A photonics device requires uniform periodic structural arrangement. Various techniques are used to fabricate these types of structures, employing several steps of fabrication. This work proposes single step hierarchical array of equal submicron size porous structure fabricated by tuning electrospinning processing parameters. The dictating process parameters on evolving structure are high voltage, tip to collector distance and solvent. Morphological and optical investigations suggest that uniform periodic topography helps in light scattering leading to multi reflection and thus enhancement in light absorption. This structure is evaluated as active layer in organic photovoltaic devices using poly (3 hexyl thiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) blend and its device characteristics are analyzed. Consistent and reliable device characteristics obtained through photonic structure is demonstrated. Finally, comparison is drawn to network structure to assess the advantages and limitations of both morphologies as active layer in organic photovoltaics. In Chapter 5, instead of architecturing active layer the next polymer film layer in the organic solar cells, that is the hole transport layer is transformed into free standing nanofiber mats. Morphological, structural and surface wetting properties are assessed for these nanofiber mats followed by fabrication of inverted organic solar cell. The free standing nanofibers mats are obtained by electrospinning the blend of Poly(3,4-ethylenedioxythiophene) Polystyrene sulfonate (PEDOT:PSS) a conducting water soluble polymer with other water soluble polymers such as poly vinyl alcohol (PVA) and poly ethylene oxide (PEO). The study is further extended by employing two batches of PEDOT:PSS of varying conductivity that are analyzed side by side for six ternary and two binary blends each. Electrospinning parameters such as applied voltage and flow rate are optimized and fibers of diameter 150-200 nm are obtained. Maximum content of PEDOT:PSS with which free standing fiber mats could be achieved are 98 and 99%. Subsequent increase in PEDOT:PSS results in formation of beads. Surface wetting behavior showed that hydrophillicity increases with increase in PEDOT:PSS content. Devices are fabricated and the variation in characteristics and charge collection with respect to addition of PEO and PVA are discussed. In Chapter 6, a conjugated small molecule is taken as case study unlike the use of the conjugated polymer studies in previous chapters. A mechanism is proposed for tuning the sphere-spike morphology and also to control the crystallite size through solvent management using a conjugated small molecule. Electrospraying of an organic molecule is carried out using various solvents, obtaining fibril structures along with a range of distinct morphologies. Solvent characteristics play a major role in achieving the morphology of the organic material. A thiophene derivative (7, 9-di (thiophen-2-yl)-8H-cyclopenta [a]acenaphthylen-8-one) (DTCPA) of donor-acceptor-donor (DAD) architecture is used to study this solvent effect. Seven solvents with decreasing vapor pressure are selected for experiments. Electrospraying is conducted at a solution concentration of 1.5 wt % and a constant applied voltage of 15 kV. Gradual transformation in morphology of the electrospun product from spikes-sphere to only spikes is observed. A mechanism describing this transformation is proposed based on the electron micrograph analysis and XRD analysis. These data indicate that the morphological change is due to the synergistic effect of both vapor pressure and dielectric constant of the solvents. Through a reasonable control over the crystallites size and morphology along with supporting transformation mechanism theory, the work in this chapter elucidates electrospraying as a prospective method for designing the architectures in organic electronics. In Chapter 7, light management studies are carried out by morphologically architecturing the carbazole derivatives through electrospraying. The effect of derivatives on morphology is analyzed. The two carbazole derivatives; carbazole-benzothiadiazole (Cz-Bz) resulted in 2D structures and carbazole-benzothiadiazole-bithiophene (Cz-Bz-Bt) resulted in 3D structures after electrospraying. These structures are further analyzed to study the effect of vapor pressure of solvents and solution concentration. Structural characteristics indicate that electrospraying imparts change in molecular structure orientation. Optical studies showed 19 – 31% enhancement in light absorption. Further, three types of organic photovoltaic devices are fabricated and the opto-electrical properties are evaluated. Also, the effect of substrate on morphological formation is assessed. In Chapter 8, the major contributions and conclusions drawn from the morphological architecturing of both conjugated polymers and small molecules are summarized, along with few recommendations for future research.
70

Conducting Redox Polymers for Electrode Materials : Synthetic Strategies and Electrochemical Properties

Huang, Xiao January 2017 (has links)
Organic electrode materials represent an intriguing alternative to their inorganic counterparts due to their sustainable and environmental-friendly properties. Their plastic character allows for the realization of light-weight, versatile and disposable devices for energy storage. Conducting redox polymers (CRPs) are one type of the organic electrode materials involved, which consist of a π-conjugated polymer backbone and covalently attached redox units, the so-called pendant. The polymer backbone can provide conductivity while it is oxidized or reduced (i. e., p- or n-doped) and the concurrent redox chemistry of the pendant provides charge capacity. The combination of these two components enables CRPs to provide both high charge capacity and high power capability. This dyad polymeric framework provides a solution to the two main problems associated with organic electrode materials based on small molecules: the dissolution of the active material in the electrolyte, and the sluggish charge transport within the material. This thesis introduces a general synthetic strategy to obtain the monomeric CRPs building blocks, followed by electrochemical polymerization to afford the active CRPs material. The choice of pendant and of polymer backbone depends on the potential match between these two components, i.e. the redox reaction of the pendant and the doping of backbone occurring within the same potential region. In the thesis, terephthalate and polythiophene were selected as the pendant and polymer backbone respectively, to get access to low potential CRPs. It was found that the presence of a non-conjugated linker between polymer backbone and pendant is essential for the polymerizability of the monomers as well as for the preservation of individual redox activities. The resulting CRPs exhibited fast charge transport within the polymer film and low activation barriers for charge propagation. These low potential CRPs were designed as the anode materials for energy storage applications. The combination of redox active pendant as charge carrier and a conductive polymer backbone reveals new insights into the requirements of organic matter based electrical energy storage materials.

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