Dissertations / Theses on the topic 'Zinc oxide/polymer'
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Wilke, Philipp Verfasser], Andrij Z. [Akademischer Betreuer] [Pich, and Doris [Akademischer Betreuer] Klee. "Zinc oxide based polymer hybrid materials / Philipp Wilke ; Andrij Pich, Doris Klee." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/1126646393/34.
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Wilke, Philipp [Verfasser], Andrij Z. [Akademischer Betreuer] Pich, and Doris [Akademischer Betreuer] Klee. "Zinc oxide based polymer hybrid materials / Philipp Wilke ; Andrij Pich, Doris Klee." Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/1126646393/34.
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Matsumura, Masashi. "Synthesis, electrical properties, and optical characterization of hybrid zinc oxide/polymer thin films and nanostructures." Birmingham, Ala. : University of Alabama at Birmingham, 2007. https://www.mhsl.uab.edu/dt/2009r/matsumura.pdf.
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Thesis (Ph. D.)--University of Alabama at Birmingham, 2007.Title from PDF t.p. (viewed Feb. 3, 2010). Additional advisors: Derrick R. Dean, Sergey B. Mirov, Sergey Vyazovkin, Mary Ellen Zvanut. Includes bibliographical references (p. 122-145).
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Olenych, I. B., O. I. Aksimentyeva, and Yu Yu Horbenko. "Electrical Properties of Hybrid Composites Based on Poly(3,4-ethylenedioxythiophene) with ZnO and Porous Silicon Nanoparticles." Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42552.
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The electrical properties of hybrid nanosystem based on poly(3,4 ethylenedioxythiophene) with ZnO and porous silicon nanoparticles were studied by the methods of current-voltage characteristics and thermally stimulated conductivity. The dependence of electrical parameters of hybrid films on their composition has been found. The analysis of the temperature dependences of the composites conductivity in the temperature range of 80-330 К indicates the activation character of charge transfer and presence the trapping of unequilibrium carriers at the porous silicon and ZnO nanoparticle – polymer interface.
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Olson, Grant T. "Improving Hybrid Solar Cells: Overcoming Charge Extraction Issues In Bulk Mixtures of Polythiophenes and Zinc Oxide Nanostructures." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1257.
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Organic photovoltaics (OPVs) have received a great deal of focus in recent years as a possible alternative to expensive silicon based solar technology. Current challenges for organic photovoltaics are centered around improving their lifetimes and increasing their power conversion efficiencies. One approach to improving the lifetime of such devices has been the inclusion of inorganic metal oxide layers, but interaction between the metal oxides and common conjugated polymers is not favorable. Here we present two methods by which the interactions between polythiophenes and nanostructured ZnO can be made to be more favorable. Using the first method, direct side on attachment of polythiophene to ZnO nanowires via chemical grafting, we demonstrate chemical linkage between the polymer and ZnO phases. The attachment was confirmed to affect the morphological properties of the polymer layer as well, inducing highly ordered regions of the polymer at the ZnO surface via chemical attachment and physical adsorption. Using the second method to improve polythiophene ZnO interactions, we have functionalized ZnO nanowires with organic molecules that favorably interact with conjugated polymer and organic solvents. Photovoltaic devices were made using a blended active layer of functionalized ZnO nanowires and P3HT. Electrical analysis of the resultant devices concluded that the devices were functional photovoltaic cells and isolated the dominant loss mechanisms for further device improvement.
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Awada, Hussein. "Elaboration des matériaux hybrides, organiques/ oxydes métalliques pour le photovoltaique organique." Thesis, Pau, 2014. http://www.theses.fr/2014PAUU3016/document.
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The performance and life time of organic solar cells are critically dependent on the properties of active layer materials and device interfaces. In this manuscript, we developed new organic-inorganic hybrid materials to create intimate contact between donor and acceptor phases and facilitate the interfacial electronic charge transfer through the device. First, the synthesis of versatile triethoxysilane-terminated poly(3-hexylthiophene) P3HT for direct anchoring (grafting-onto) in one step procedure to various metallic oxides was reported. Electro-optical analysis showed an efficient charge transfer from the polymer to nanoparticles; suggesting that these materials are suitable candidates for photovoltaic application. In the second part, we demonstrate for the first time the elaboration of low band gap polymer brushes on metallic oxide surfaces via surface initiated step growth polymerization (grafting-through). In both cases, a higher grafting density, better packing of polymer chains and enhanced optical properties were observed due to the grafting methodology and polymer characteristics. Finally, P3HT brushes were elaborated on indium tin oxide surface (ITO) as hole transporting layer of organic solar cells. Photovoltaic performances showed that P3HT self-assembled monolayer (SAMs) could be promising alternatives to PEDOT:PSSLes performances et la durée de vie des cellules solaires organiques sont fortement dépendantes de la qualité des matériaux de la couche active et des interfaces dans le dispositif. Dans ce manuscrit, nous avons développé des nouveaux matériaux hybrides organiques-inorganiques pour favoriser le contact entre les matériaux donneur/accepteur d’électrons et ainsi faciliter le transfert de charges à travers le dispositif. Tout d'abord, la synthèse de poly(3-hexylthiophène) P3HT fonctionnalisé par le triéthoxysilane a permis le greffage direct (« grafting-onto ») sur des oxydes métalliques. L’analyse des propriétés électro-optiques montre un transfert de charge efficace du polymère aux nanoparticules; ce qui suggère que ces matériaux sont des candidats potentiels pour l'application photovoltaïque. Dans la deuxième partie, nous avons montré pour la première fois, l’élaboration de brosses de polymères dits à faible bande interdite sur des surfaces d’oxydes métalliques par la technique « grafting-through ». Une densité de greffage élevée, un meilleur empilement des chaines de polymères et des propriétés optiques améliorées ont été obtenus grâce à la technique de greffage et aux caractéristiques du polymère greffé. Enfin, des brosses de P3HT ont été élaborées sur la surface d’oxyde d'indium et d’étain (ITO) en tant que couche de transport de trous de cellules solaires organiques. Les performances photovoltaïques ont montré que les monocouches auto-assemblées de P3HT (SAM) peuvent être une alternative au PEDOT: PSS
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Yoon, Sang Hoon Kim Dong Joo. "Growth and characterization of ZNO and PZT films for micromachined acoustic wave devices." Auburn, Ala, 2009. http://hdl.handle.net/10415/1719.
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Lubuna, Beegum Shafeek. "Organic-Inorganic Hetero Junction White Light Emitting Diode : N-type ZnO and P-type conjugated polymer." Thesis, Linköping University, Department of Science and Technology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11195.
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The purpose of this thesis work is to design and fabricates organic-inorganic hetero junction White Light Emitting Diode (WLED). In this WLED, inorganic material is n- type ZnO and organic material is p-type conjugated polymer. The first task was to synthesise vertically aligned ZnO nano-rods on glass as well as on plastic substrates using aqueous chemical growth method at a low temperature. The second task was to find out the proper p- type organic material that gives cheap and high efficient WLED operation. The proposed polymer shouldn’t create a high barrier potential across the interface and also it should block electrons entering into the polymer. To optimize the efficiency of WLED; charge injection, charge transport and charge recombination must be considered. The hetero junction organic-inorganic structures have to be engineered very carefully in order to obtain the desired light emission. The layered structure is composed of p-polymer/n-ZnO and the recombination has been desired to occur at the ZnO layer in order to obtain white light emission. Electrical characterization of the devices was carried out to test the rectifying properties of the hetero junction diodes.
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Tas, Huseyin. "Coordination Polymerization Of Cyclic Ethers By Metal Xanthates And Carbamates." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1225028/index.pdf.
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Zinc xanthates are active catalysts in stereoregular polymerization of propylene oxide and markedly more stable than that of known classical stereoregular catalysts. But steric control of zinc xanthates is weaker. To find more effective catalyst systems the isopropyl xanthates of Cu, Pb, Ni, Fe, Al and Sn are investigated and only copper (Cu(isoPr)Xt) and tin (Sn(isoPr)Xt) isopropyl xanthates were appeared to be active, but Cu(isoPr)Xt yielded only low molecular weight product. Therefore Sn(isoPr)Xt system was investigated in detail in polymerization of propylene oxide (PO). Polymerization of PO with this catalyst produced two contrasting polymershigh molar mass, crystalline (K-polymer) and low molar mass (D-polymer). Formation of double bonds in D-polymer was thought to be due to as an anionic process. Polymerization reactions were studied by changing polymerization conditions and reacting catalyst with predetermined amount of water. It&
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s found that Sn(isoPr)Xt have considerably low efficiency than that of Zn(isoPr)Xt catalyst. The yield linearly increases by increasing catalyst concentration. The propagation is competed by termination or transfer process hence overall activation energy is negative. Some mechanistic features of this system was also discussed. The catalytical activity of carbamates in this field has also been reported, without any information about catalytical efficiency and stereoregularity of the process. Therefore zinc diethyl dithiocarbamate was also studied and found as an active catalyst in stereoregular polymerization but it showed weaker efficiency in the PO polymerization than that of Zn(isoPr)Xt catalyst (about 12 times weaker).
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Rhodes, Rhys William. "Controlling the morphology of nanoparticle-polymer composite films for potential use in solar cells." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/controlling-the-morphology-of-nanoparticlepolymer-composite-films-for-potential-use-in-solar-cells(6bc2a3cc-7c11-4615-a202-bead6360af99).html.
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This thesis presents an investigation into the factors affecting the morphology of hybrid inorganic/organic photoactive layers used in photovoltaic cells. Although optimisation of the organic (polymer) phase has received substantial attention, research into the morphology of the inorganic phase (semiconducting nanocrystals) remains limited. It is believed that there is a strong link between the morphology of the final photoactive film and the quality of the initial nanocrystal dispersion. To this end, two nanocrystal systems were investigated; zinc oxide (ZnO) and lead sulphide (PbS). ZnO nanocrystals were synthesised and found to possess reproducible characteristics. It was determined that colloid stability was initially dependent upon the presence of acetate groups bound to the surface, which in turn required a small quantity of methanol to be present in the organic dispersant. It was also discovered that while methanol evaporated readily from the surface of the nanocrystals, another molecule, 1-propylamine (1-PA), did not. Further investigations showed that while methanol only weakly physisorbed to the surface of ZnO nanocrystals, 1-PA formed strong, dative covalent bonds with Zn2+, preventing evaporation despite a low boiling point. Subsequent investigations into the effects of different ligands upon colloid stability found that amine-based groups typically possessed superior stabilising capabilities compared to alcohol-based analogues. The characteristics of nanocrystal / polymer blends were also investigated. It was determined that the nanocrystal dispersion became unstable at higher concentrations of polymer due to depletion aggregation. Films of nanocrystal / polymer blends were cast from dispersions containing either alcohol or amine-based ligands, and it was observed that dispersions stabilised with 1-PA possessed smooth morphologies on the micrometer scale. Investigations at the nanometer scale, however, revealed aggregates large enough to favour recombination.The latter half of this thesis regards the characterisation of PbS nanocrystals and investigations into triggered aggregation. It was determined that while PbS nanocrystals possessed reproducible characteristics, the stabilising molecule, oleic acid (OA) was insulating. The effects of exchanging the OA groups for a shorter ligand, butylamine (BA) were investigated.Finally, PbS nanocrystals were treated with a bidentate ligand, 1,2-ethanedithiol (EDT) to induce triggered aggregation. It was observed that the system was highly sensitive to the concentration of EDT in dispersion, forming small, relatively dispersed aggregates at low [EDT], and micrometer-sized crystalline structures at high [EDT]. The characterisation and entrapment of these nanocrystal structures within semi-conducting polymer films is also discussed.
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Choppali, Uma. "Low Temperature Polymeric Precursor Derived Zinc Oxide Thin Films." Thesis, University of North Texas, 2006. https://digital.library.unt.edu/ark:/67531/metadc5504/.
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Zinc oxide (ZnO) is a versatile environmentally benign II-VI direct wide band gap semiconductor with several technologically plausible applications such as transparent conducting oxide in flat panel and flexible displays. Hence, ZnO thin films have to be processed below the glass transition temperatures of polymeric substrates used in flexible displays. ZnO thin films were synthesized via aqueous polymeric precursor process by different metallic salt routes using ethylene glycol, glycerol, citric acid, and ethylene diamine tetraacetic acid (EDTA) as chelating agents. ZnO thin films, derived from ethylene glycol based polymeric precursor, exhibit flower-like morphology whereas thin films derived of other precursors illustrate crack free nanocrystalline films. ZnO thin films on sapphire substrates show an increase in preferential orientation along the (002) plane with increase in annealing temperature. The polymeric precursors have also been used in fabricating maskless patterned ZnO thin films in a single step using the commercial Maskless Mesoscale Materials Deposition system.
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Kim, Yong Hyun. "Alternative Electrodes for Organic Optoelectronic Devices." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-113279.
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This work demonstrates an approach to develop low-cost, semi-transparent, long-term stable, and efficient organic photovoltaic (OPV) cells and organic light-emitting diodes (OLEDs) using various alternative electrodes such as conductive polymers, doped ZnO, and carbon nanotubes. Such electrodes are regarded as good candidates to replace the conventional indium tin oxide (ITO) electrode, which is expensive, brittle, and limiting the manufacturing of low-cost, flexible organic devices. First, we report long-term stable, efficient ITO-free OPV cells and transparent OLEDs based on poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) electrodes by using a solvent post-treatment or a structure optimization. In addition, a high performance internal light out-coupling system for white OLEDs based on PEDOT:PSS-coated metal oxide nanostructures is developed. Next, we demonstrate highly efficient ITO-free OPV cells and OLEDs with optimized ZnO electrodes doped with alternative non-metallic elements. The organic devices based on the optimized ZnO electrodes show significantly improved efficiencies compared to devices with standard ITO. Finally, we report semi-transparent OPV cells with free-standing carbon nanotube sheets as transparent top electrodes. The resulting OPV cells exhibit very low leakage currents with good long-term stability. In addition, the combination of various kinds of bottom and top electrodes for semi-transparent and ITO-free OPV cells is investigated. These results demonstrate that alternative electrodes-based OPV cells and OLEDs have a promising future for practical applications in efficient, low-cost, flexible and semi-transparent device manufacturingDie vorliegende Arbeit demonstriert einen Ansatz zur Verwirklichung von kostengünstigen, semi-transparenten, langzeitstabilen und effizienten Organischen Photovoltaik Zellen (OPV) und Organischen Leuchtdioden (OLEDs) durch die Nutzung innovativer Elektrodensysteme. Dazu werden leitfähige Polymere, dotiertes ZnO und Kohlenstoff-Nanoröhrchen eingesetzt. Diese alternativen Elektrodensysteme sind vielversprechende Kandidaten, um das konventionell genutzte Indium-Zinn-Oxid (ITO), welches aufgrund seines hohen Preises und spröden Materialverhaltens einen stark begrenz Faktor bei der Herstellung von kostengünstigen, flexiblen, organischen Bauelementen darstellt, zu ersetzten. Zunächst werden langzeitstabile, effiziente, ITO-freie Solarzellen und transparente OLEDs auf der Basis von Poly(3,4-ethylene-dioxythiophene):Poly(styrenesulfonate) (PEDOT:PSS) Elektroden beschrieben, welche mit Hilfe einer Lösungsmittel-Nachprozessierung und einer Optimierung der Bauelementstruktur hergestellt wurden. Zusätzlich wurde ein leistungsfähiges, internes Lichtauskopplungs-System für weiße OLEDs, basierend auf PEDOT:PSS-beschichteten Metalloxid-Nanostrukturen, entwickelt. Weiterhin werden hoch effiziente, ITO-freie OPV Zellen und OLEDs vorgestellt, bei denen mit verschiedenen nicht-metallischen Elementen dotierte ZnO Elektroden zur Anwendung kamen. Die optimierten ZnO Elektroden bieten im Vergleich zu unserem Laborstandard ITO eine signifikant verbesserte Effizienz. Abschließend werden semi-transparente OPV Zellen mit freistehenden Kohlenstoff-Nanoröhrchen als transparente Top-Elektrode vorgestellt. Die daraus resultierenden Zellen zeigen sehr niedrige Leckströme und eine zufriedenstellende Stabilität. In diesem Zusammenhang wurde auch verschiedene Kombinationen von Elektrodenmaterialen als Top- und Bottom-Elektrode für semi-transparente, ITO-freie OPV Zellen untersucht. Zusammengefasst bestätigen die Resultate, dass OPV und OLEDs basierend auf alternativen Elektroden vielversprechende Eigenschaften für die praktische Anwendung in der Herstellung von effizienten, kostengünstigen, flexiblen und semi-transparenten Bauelement besitzen
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Tyombo, Nolukholo. "Synthesis and Luminescence of Zinc Oxide Nanorods-Blended Thiopheno-Organosilicon Polymers." University of the Western Cape, 2017. http://hdl.handle.net/11394/6230.
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Magister Scientiae - MSc (Chemistry)The increasing cost of fossil fuel energy production and its implication in environmental pollution and climate change created high demand for alternative and renewable sources of energy. This has led to great interest in research in the field of photovoltaic or solar cells Due to the abundance of sunlight, the technology is sustainable, non-polluting and can be implemented at places where power demand is needed, for example in rural areas. Solar cell devices that have been commercialized are currently based on silicon technology, involving the use of monocrystalline, polycrystalline and amorphous silicon. Although they produce highly efficient solar cells, the cost of Si solar cells is too high. Second generation solar cell materials such as cadmium telluride and third generation materials such as perovskites and organic polymers have been receiving much attention recently. However, they lack the efficiency of Si solar cells. This research proposes the development of high energy conservation photovoltaic cells from novel low-cost organosilicon polymers. The aim was to develop novel highly branched organosilane polymers such as poly(3-hexythiophene), polydi(thien-2-yl)dimethylsilane, poly(3-hexyl- [2,2'] bithiophenyl-5-yl)-dimethyl-thiophen-2yl-silane) as electron donors along with zinc oxide nanorod as the electron acceptor which were able to bring the efficiency of the resultant photovoltaic cell close to that of current Si solar cell.
2021-08-31
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Mbambisa, Gcineka. "Polymeric-bimetallic oxide nanoalloy for the construction of photovoltaic cells." University of the Western Cape, 2014. http://hdl.handle.net/11394/4364.
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Philosophiae Doctor - PhDResearch in renewable energy has become a focal point as a solution to the energy crisis. One of renewable forms of energy is solar energy, with the main challenge in the development of the solar cells being the high cost. This has led to the exploration of the use of organic molecules to construct solar cells since it will lead to lowered costs of construction. The focus of this research is on the synthesis and characterisation of the polyaniline derivatives materials and zinc gallate for application in the construction of hybrid solar cells with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as an acceptor. The polyaniline (PANi) and doped polyaniline derivatives, polyaniline phenathrene sulfonic acid (PANi-PSA), poly[ortho-methyl aniline] phenanthrene sulfonc acid (POMA-PSA) poly[ortho-methyl aniline] anthracene sulfonc acid (POMA-ASA) were produced via chemical synthetic procedures. The zinc gallate (ZnGa2O4) was also produced using a chemical method. The vibrational and electronic spectra of the polymers and zinc gallate were interrogated independently and dependently. Electronic transitions due to charge defects (polarons and bipolarons) were observed for the polymers that are doped. The PANi was the one with the lowest band gap of 2.4 eV with the POMA-ASA having the widest bandgap of 3.0 eV. The XRD and TEM analysis of the polymers revealed characteristics that show that the PANi has the highest level of crystallinity and the POMA-ASA displayed the least level of crystallinity. The electronic data, XRD, TEM data led to the conclusion that the conductivity of the polymers is decreasing in the following sequence, PANi > PANi-PSA > POMA-PSA > POMA-ASA. The photoluminescence of the polymers alone and with the nanoparticles was investigated in solution and on an ITO coated glass substrate. Photoluminescence was observed for the polymers due to relaxation of the exciton and also from the formation of excimers. The relaxation due to the exciton was observed at higher energy levels, while the one that is as a result of the excimer formation was seen at lower energy levels. Enhancement of the peak due to the excimer was observed when the compound is mixed with the nanoparticles in solution. When the analysis was done on the ITO coated glass substrate, it was found that zinc gallate does not lead to quenching of the emission of the polymers; hence it can not be used as an acceptor in this particular system. The electrochemical behaviour of the polyaniline derivatives was investigated using cyclic voltammetry and electrochemical impedance spectroscopy. Interaction of the polymers with the PCBM (acceptor) was investigated using UV-visible absorption spectroscopy and photoluminescence spectroscopy. It was able to quench the photoluminescence of the polymers. Hence it was used as an acceptor in the construction of the photovoltaic cells. The polymers alone and with the nanoparticles were used in the formation of bulk heterojunction photovoltaic cells with PCBM as an acceptor. The photovoltaic behaviour was investigated and PANi was the one that displayed the highest efficiency.
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Al, Kadi Jazairli Mohamad. "Growth of Zinc Oxide Nanoparticles on Top of Polymers and Organic Small Molecules as a Transparent Cathode in Tandem Photovoltaic Device." Thesis, Linköping University, Department of Science and Technology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11391.
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Organic solar cells have caught considerable attention in the past few years due to their potential for providing environmentally safe, flexible, lightweight, inexpensive, and roll-to-roll feasible production solar cells. However, the efficiency achieved in current organic solar cells is quite low, yet quick and successive improvements render it as a promising alternative. A hopeful approach to improve the efficiency is by exploiting the tandem concept which consists of stacking two or more organic solar cells in series.
One important constituent in tandem solar cells is the middle electrode layer which is transparent and functions as a cathode for the first cell and an anode for the second cell. Most studies done so far have employed noble metals such as gold or silver as the middle electrode layer; however, they suffered from several shortcomings especially with respect to reproducibility.
This thesis focuses on studying a new trend which employs an oxide material based on nano-particles as a transparent cathode (such as Zinc-oxide-nano-particles) along with a transparent anode so as to replace the middle electrode.
Thus, this work presents a study on solution processable zinc oxide (ZnO) nanostructures, their proper handling techniques, and their potential as a middle electrode material in Tandem solar cells in many different configurations involving both polymer and small molecule materials. Moreover, the ZnO-np potential as a candidate for acceptor material is also investigated.
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Jasso, Salcedo Alma Berenice. "Synthèse et mise en oeuvre de nanocomposites à base d’oxyde de zinc utilisés pour le traitement photocatalytique de l’eau contaminée par des disrupteurs endocriniens." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0297/document.
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Le présent travail porte sur la photodégradation de polluants aqueux utilisant des catalyseurs à base de ZnO. La première étape a consisté à fonctionnaliser ZnO avec des nanoparticules d'argent. Deux méthodes ont été utilisées : la photodéposition et l'imprégnation des particules d'argent sur ZnO. L’activité des catalyseurs obtenus vis-à-vis de la dégradation du bisphenol-A, du triclosan et de la rhodamine-B a été ensuite étudiée. L'effet du pH, des concentrations du photocatalyseur et du polluant et de la longueur d'onde sur la dégradation du bisphenol-A a été analysée et la constante cinétique déterminée. L'optimisation a montré qu'une teneur faible en argent et un pH alcalin, tant pour la fonctionnalisation de ZnO que pour la photodégradation, maximisent la constante cinétique de dégradation du bisphenol-A. Un modèle a également prédit que le système obtenu par photodéposition présente une activité photocatalytique supérieure à celle de celui obtenu par imprégnation. D'autre part, pour surmonter des problèmes d'agrégation, les particules d’Ag/ZnO ont été immobilisées grâce à leur incorporation dans une matrice d'acide polyacrylique réticulé. La surface des particules de catalyseur a, au préalable, été modifiée grâce à un agent de couplage silané qui a permis (i) la dispersion et l'ancrage par estérification des nanoparticules sur la matrice polyacrylique (ii) de promouvoir la cristallisation du polymère. Les composites obtenus ont été testés avec succès sous rayonnement UV avec une efficacité comparable à celle des particules non-immobilisées. L'immobilisation permet par ailleurs d'empêcher la photocorrosion du catalyseur et d'utiliser ces composites en mode continuThe present work concerns photodegradation of water contaminants using ZnO-based catalysts. The first step consisted in designing a new catalytic system by functionalizing ZnO with silver nanoparticles. Two methods were used: photodeposition and impregnation of silver nanoparticles (AgNPs) on ZnO. The photocatalytic activity of the resulting catalyst towards the degradation of bisphenol-A, triclosan and rhodamine-B was studied. The effect of pH, photocatalyst and contaminant concentrations and wavelength, on bisphenol-A degradation was studied and the kinetic rate constant was determined. The optimization showed that a low silver content and an alkaline pH, during both functionalization of ZnO and photodegradation, maximized the kinetic rate constant of bisphenol-A degradation. A model also predicted that Ag/ZnO obtained by photodeposition showed higher photocatalytic activity that of Ag/ZnO obtained by impregnation.On the other hand, to overcome aggregation problems, Ag/ZnO were immobilized owing to their incorporation in a cross-linked poly(acrylic acid) matrix . The surface of Ag/ZnO was previously modified, using a silane coupling agentwhich allowed (i) dispersing and anchoring NPs on the polyacrylic matrix by formation ester bonds (ii) promoting crystallization of the polymer. The composites were successfully tested under UV light with an efficiency comparable to that of non-immobilized NPs. The immobilization provides additional advantages e.g. hindrance of catalyst photocorrosion and possible use of the composite in continuous mode
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Tarkin, Eylem. "Characterization And Study Of Solution Properties Of Poly(propylene Oxide) Synthesized By Metal Xanthate Catalysts." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1086099/index.pdf.
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Zinc xanthates polymerize propylene oxide into high polymer (PPO) with coordination mechanism. In order to identify structure and stereoisomerisms of this polymer, PPO was subjected to thermal and column fractionation. Obtained fractions were characterized by end-group analysis, cryoscopy, viscometry, IR and 13C-NMR spectroscopy, melting temperature. PPO is composed of a high molecular weight, stereoregular, crystallizable polymer (K-polymer) with low molecular weight (=500 g/mol) D-polymer. Presence of double bonds and hydroxyl terminals was interpreted as the product of an anionic mechanism.
K-Polymers can be thermally fractionated on the basis of their melting temperature (Tm) rather than molecular weight (Mwt). It’
s found that higher Tm fractions have lower Mwt, but they precipitate at higher temperatures than higher Mwt but lower Tm fractions. In column fractionation, K-polymers were deposited on glass beads from isooctane solution in a narrow temperature interval. Then the precipitated samples were split into a number of fractions by using again isooctane but at a higher temperature than the precipitation temperature by increasing residence time from 5 minutes to several hours. It&
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s found that rate of solubility is not controlled by molecular weight, but controlled by percentage crystallinity and Tm. Highest Tm polymers, with relatively higher Mwt showed faster rate of solution than that of lower Tm, lower Mwt but higher percent crystalline fractions. This discrepancy was accounted by suggesting a stereo-block structure where tactic blocks are bound each other with non-crystallizable atactic blocks. The mechanism of polymerization was also discussed in some detail.
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Masghouni, Nejib. "Hybrid Carbon Fiber/ZnO Nanowires Polymeric Composite for Stuctural and Energy Harvesting Applications." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/64354.
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Despite the many attractive features of carbon fiber reinforced polymers (FRPs) composites, they are prone to failure due to delamination. The ability to tailor the fiber/matrix interface FRPs is crucial to the development of composite materials with enhanced structural performance. In this dissertation, ZnO nanowires (NWs) were grown on the surface of carbon fibers utilizing low temperature hydrothermal synthesis technique prior to the hybrid composite fabrication. The scanning electron microscopy revealed that the ZnO nanowires were grown uniformly on the surface of the carbon fabric. The surface grown ZnO NWs functionally-graded the composite material properties and ensured effective load transfer across the interface. To assess the influence of the ZnO NWs growth, reference samples were also prepared by exposing the carbon fabric to the hydrothermal conditions. The damping properties of the hybrid ZnO NWs-CFRP composite were examined using the dynamic mechanical analysis (DMA) technique. The results showed enhanced energy dissipation within the hybrid composite. Quasi-static tensile testing revealed that the in-plane and out-of-plane strengths and moduli of the hybrid FRP composite were also boosted.
The interlaminar shear strength (ILSS) measurements suggested the improvement in the mechanical properties of the composite to the enhanced adhesion between the ZnO nanowires and the other constituents (carbon fiber and epoxy). It was necessary thus, to utilize the molecular dynamics simulations (MD) to investigate the adhesion within the CFRP structure upon growing the ZnO nanowires on the surface of the carbon fibers. Molecular models of the carbon fibers, the epoxy matrix and the ZnO nanowires were built. The resulting molecular structures were minimized and placed within a simulation box with periodic boundary conditions. The MD simulations were performed using the force field COMPASS to account for the empirical energy interactions between the different toms in the simulation box. Proper statistical thermodynamics were employed to relate the dynamics of the molecular model to the macroscale thermodynamic states (pressure, temperature and volume). Per the computed potential energies of the different components of the composite, it was found that the polar surfaces in the ZnO structures facilitates good adhesion properties in the graphite-epoxy composite.
Besides the attractive mechanical properties of the ZnO nanowires, their piezoelectric and semiconductor properties were sought to design an energy harvesting device. To ensure sufficient charges collection from the mechanically stressed individual ZnO nanowires, a copper layer was sputtered on top of the ZnO nanowires which introduced also a Schottky effect. The mechanical excitation was provided by exposing the device to different vibration environment. The output voltage and currents were measured at the conditions (in terms of frequency and resistive load). It was demonstrated that the electrical output could be enhanced by stacking up similar devices in series or in parallel.
Finally, in an attempt to exploit the reversibility of the electromechanical coupling of the energy harvesting device, the constitutive properties of the hybrid ZnO nanowires-CFRP composite were estimated using the Mori-Tanaka approach. This approach was validated by a finite element model (FEM). The FEM simulations were performed on a representative volume element (RVE) to reduce the computational time. The results demonstrated that the mechanical properties of the hybrid ZnO NWs-CFRP composite were better than those for the baseline CFRP composite with identical carbon fiber volume fraction (but with no ZnO NWs) which confirmed the experimental findings. Furthermore, the electro-elastic properties of the hybrid composite were determined by applying proper boundary conditions to the FE RVE.
The work outlined in this dissertation will enable significant advancement in the next generation of hybrid composites with improved structural and energy harvesting multifunctionalties.Ph. D.
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Abdelli, Marwen. "Élaboration et caractérisations des cellules photovoltaïques organiques nano-architecturées." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALI040.
Full textAbstract:
La recherche dans le domaine du photovoltaïque connait une évolution importante grâce au développement de nouveau matériaux/concepts. Dans le cadre de cette thèse, nous avons proposé de réaliser des cellules solaires à architecture proche la structure interpénétrée idéale combinant un réseau de nanofils de ZnO synthétisés « sur mesure » et une couche active organique à base d’une hétérojonction D/A en volume. La compréhension des mécanismes de croissance des nanofils de ZnO et la maitrise de la synthèse ont abouti à un protocole expérimentale optimal permettant une fabrication reproductible de substrats ITO/nano-fils de ZnO avec des morphologies maitrisées (L ≈ 200 nm et D ≈ 30 nm) proches des distances et tailes critiques nécessaires pour l’élaboration des cellules solaires. Après la phase d’optimisation de l’assemblage des cellules solaire et leurs caractérisations, une densité de courant 22 mA/cm² (2 fois meilleure que la cellule 2D) a été obtenue a été obtenu avec une architecture à base de nanofils de ZnO conduisant un rendement photovoltaïque de 7.7 % (1.4 fois meilleur que la cellule 2D) validant ainsi l’efficacité du concept de la nano-texturation des substrats, les caractéristiques morphologiques choisies de la nano-texture, la méthode d’assemblage des cellules et l’ensemble des matériaux utilisésThanks to the development of new materials and innovative concepts, the photovoltaic research field constantly growing. This thesis aims at developing solar cells based on architecture close to interpenetrating structure, which combine synthetized ZnO nanowires and an active layer composed of a volume heterojunction donor/acceptor. We developed an efficient experimental protocol to synthetize via hydrothermal growing in mastered and reproducible manner ZnO nanowires on ITO substrate. An optimal morphology on ZnO nanowires with length close to 200 nm and diameter close to 30nm, required for photovoltaic application, was targeted and successfully obtained. After the optimization of solar cells assembly and their characterizations, short-circuit current density of 22 mA/cm² (2 times better than the 2D cells) and power conversion efficiency of 7.7% (1.4 times better than the 2D cells) were obtained for solar cells based on ZnO nanowires architecture. This result validates the efficiency of the concept of nanotexturing of substrates, the method of solar cells assembly, the chosen morphological characteristics of the nanotexture and the selected materials
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Ozturk, Elif. "Copolymerisation Of Carbon Disulfide, Carbon Dioxide And Other Carbonic Acid Derivatives With Cyclic Ethers By Using Metal Xanthate Catalysts." Phd thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/3/12607227/index.pdf.
Full textAbstract:
The synthesis of high molecular weight copolymer of carbon disulphide (CS2) and propylene oxide (PO) has not reported in literature. In the present work, zinc isopropyl xanthate (Zn(Xt)2) was used as catalyst for the copolymerisation of PO and CS2 into high copolymer. However, the product can be fractionated into high and low molecular weight components. High molecular weight copolymer was rubbery products, but low molecular weight copolymers were oily products containing cyclic dithiocarbonates. Copolymers were characterized by elemental, end group analysis, DSC, TGA, GPC, Light Scattering, UV, IR, NMR spectroscopy, polarized microscopy and refractometry.
Copolymerization process was zeroth order with respect to monomers, and its non-terminated but suffered from several types of transfer reactions. As a result of transfer reactions S-(C=S)-S, O-(C=S)-O, O-(C=O)-O groups in the backbone of copolymer and SH groups at the chain terminals and cyclic dithiocarbonates are formed. Apart from SH groups, OH and double bonds were found and their amounts were
determined at the chain terminals. Copolymers with high mole fractions of PO units (F1) in the copolymer are crystallized in the shape of Malta’
s Cross. Melting points of products were obtained from DSC. The F1 values are calculated from elemental analysis as well as zeroth order rate constants and from melting point of the crystals. All three results were in close agreement and changed between 0.9 &
#8211
0.7. However, these ratios depend on reaction conditions (temperature, catalyst and monomer concentrations, time and dielectric constant of reaction medium). A mechanism for coordination-copolymerization on the basis of above observation was proposed.
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Taylor, Cameron S. "Characterisation of engineered nanoparticles and their interaction with natural biological and non-biological material." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:03810528-de65-4094-907c-8c0d4e0386c8.
Full textAbstract:
Form, mobility, toxicity and the eventual fate of engineered nanomaterials in environmental ecosystems are currently not well defined and are needed to improve risk assessment and legislation. The present study subjected uncoated zinc oxide (ZnO) nanoparticles (30nm and 200nm) and coated silver (Ag) nanoparticles (Paraffin: 3-8nm and citrate/PVP: 50nm) to different ionic strength media and different types of algal/bacterial extracellular-polymeric species (EPS) at long (6 months) and short (2 weeks) timescales. Changes in particle size distribution and stability were examined using a multi-method approach. Sample concentration and sample polydispersity are important factors when selecting techniques. Uncoated ZnO nanoparticles aggregated heavily in water at high concentrations (1000mg/L). However silver nanoparticles (1-10mg/L) remained stable at all ionic strengths and EPS in this study due to the steric component of their coatings. Nano-toxicological experiments involving cyanobacteria S.leopoliensis and green algae C.reinhardtii showed size-dependent toxicity from coated nanosilver particles. Smaller nanoparticles (3-8nm) showed greater dissolution over 72h and greater toxicity to both species than 50nm particles indicating silver ions are an important toxicity mechanism. Nanoparticle coatings were likely important in controlling dissolution levels. Cell viability and production of reactive oxygen species (ROS) were shown to be important mechanisms of toxicity to phycological species. Species specific effects were noted for both silver nanoparticles. EPS from S.leopoliensis were noted to remove ionic silver from suspension and different types of C.reinhardtii EPS were produced when particles underwent different levels of toxic stress indicating that EPS could both affect particle toxicity and be affected by it. This work has demonstrated that coated nanoparticles could remain stable under various ionic strengths and with exposure to algal organic matter for timescales up to 6 months. This could result in adverse effects to aquatic organisms were they to reach environmental systems and is of concern to nanomaterial risk assessors.
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Li, Chin-Chia, and 李晉嘉. "The investigation of Sn-doped zinc oxide in inverted polymer solar cells." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/97682093159763367139.
Full textAbstract:
碩士國立東華大學
光電工程學系
104
In this study, we focus on the inverted organic solar cells. The structure of the inverted device is based on ITO/Al-doped ZnO (AZO) or Sn-doped ZnO (SZO)/ P3HT:ICBA/MoO3/Ag. The content is divided into three parts. First, according to the measurements of J-V curve, external quantum efficiency, dark current to find out the optimum doping ratio of ZnO doped with tin (Sn) of SZO . . Second part is the comparisons of devices characteristics, thin films transmission, contact angle and surface morphology. We found that the devices with SZO as the electron transport layer has the best device performance (PCE=5.75%) than the others. Based on the results of lifetime measurement, the device with SZO also has the highest stability than the others. Moreover, we also found that the best doping ratio of SZO is 1.5% (atomic weight). Finally, the influence of with and without a PEIE layer were investigated, including the discussion of devices characteristics and lifetime. Moreover, for the measurements of contact angle, the AZO and SZO surface with a PEIE layer on top becomes hydrophilic, which benefits the subsequent spin-coating process.
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陳昱全. "Gallium-doped zinc oxide thin films applied to polymer light-emitting diodes." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/86819737815649122188.
Full textAbstract:
碩士國立嘉義大學
電子物理學系研究所
99
In this experiment, the GZO films on glass substrate were prepared by pulsed laser deposition at various substrate temperatures. Conducting atomic force microscopy and scanning surface potential microscopy were adopted to study the nanoscale surface electrical properties of GZO films. When the substrate temperature was approximately set to 250℃, the conductive region of GZO surface is about 95% and average work function is about 4.72eV. After applying it into the polymer light-emitting diodes (PLEDs) as an anode material, the electroluminescent efficiency is better than that of the standard PLEDs which is based on a commcial indium tin oxide substrate. This result demonstrates that the quality of GZO film is enough to become a mainstream window material for PLEDs.
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Fishburn, James R. "Local structure determination in the amorphous polymer electrolyte: Poly(propylene oxide)-zinc bromide." 1996. https://scholarworks.umass.edu/dissertations/AAI9619386.
Full textAbstract:
Polymer electrolytes are neutral polymers that are complexed with salts. They may show promise for use in energy storage devices. However, the conductivity in polymer electrolytes is several orders of magnitude low for use in this application. A major hindrance to improving the conductivity is a lack of understanding of the conduction mechanism. The local structure in the amorphous polymer electrolyte, poly(propylene oxide)-zinc bromide ( (PPO) $\sb{\rm x}$ZnBr$\sb2$), was investigated to obtain a microscopic snapshot of the ionic structure in the conducting amorphous phase. This would provide insight into the conduction mechanism through elucidation of polymer-ion and ion-ion interactions. A combination of differential anomalous x-ray scattering (DAS) and extended x-ray absorption fine structure (EXAFS) were used to determine the structure around the Zn and Br ions in (PPO) $\sb{\rm x}$ZnSr$\sb2$, where x = 6,16. On average, two bromines and two oxygens were coordinated with each Zn. This represented a mixture of species described by the formula ZnBr$\sb{\rm 4-Y}$(O)$\sb{\rm Y}\sp{\rm Y-2}$, of which the majority were the tetrahedral species Zn(O)$\sb4\sp{2+}$ and ZnBr$\sb4\sp{2-}.$ The nature of the ionic groups implied that the conductivity in (PPO) $\sb{\rm x}$ZnBr$\sb2$ would not be high enough to be useful for many applications. This work was also important for the novel application of DAS for investigating polymer electrolytes. The accuracy of DAS in calculating coordination numbers was increased. Two approximations were tested for a weighting factor used when calculating coordination numbers from the peak areas in the differential Radial Distribution Functions (dRDF). A k-peak approximation was more accurate than a k-averaged approximation. Finally, Quasi-Elastic Neutron Scattering (QENS) was used to study the local motions of the polymer chains and to correlate them to the structure determined by DAS and EXAFS. Only preliminary results were obtained and a more complete analysis is needed before any conclusions about the chain motions can be made.
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Agrawal, Nikhil. "Zinc oxide/polymer : fullerene based inverted organic solar cells fabrication, monolithic up-scaling and transparent anti-soil coatings." Thesis, 2018. http://eprint.iitd.ac.in:80//handle/2074/8028.
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Lu, Guangqiang [Verfasser]. "From polymer precursors to metal oxides : preparation and characterization of zinc oxide and ZnO-based mixed metal oxide nanoparticles / vorgelegt von Guangqiang Lu." 2007. http://d-nb.info/982679408/34.
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Jia-RongSyu and 許家榮. "Surface Modification of Zinc Oxide as Electron Injection Layer in Inverted Polymer Light Emitting Diode." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/66394579717561612659.
Full textAbstract:
碩士國立成功大學
化學工程學系碩博士班
98
In this thesis, we suggest two methods for modifying energy levels of zinc oxide (ZnO) conduction band as the electron injection layers in inverted polymer light emitting diode (PLED). First of all, self-assemble monolayer (SAM) is grafted onto ZnO substrate to reduce the barrier between emissive layer (EL) and ZnO. In the next, we use the quaternary ammonium salts (quats) to modify the surface of zinc oxide to improve electron injection ability. The following is the detail of two parts: In the first part, SAM is successfully grafted the surface of ZnO using hydrolysis to reduce the electron injection barrier. Besides, the effect of ZnO crystallinity using annealing process on electron injection ability is further studied. When increasing annealing temperature of zinc oxide, the intensity of crystallinity as well as grain size increases, which results in enhancement of electron mobility. On the contrary, the decrease of hydroxide groups on ZnO surface inhibits SAM formation, which obstructs the establishment of dipole moment. The optimization of annealing temperature can be debated by considering both effects. In the secondary section, the ZnO substrates are modified by various quats and further assembled in inverted PLED. The device performance shows a dramatic enhancement after quats modification. By UPS analysis and Fowler-Nordheim model calculation, electron injection barrier between EL and ZnO is indeed decreased. Besides, the effect of length of alkyl chain on electron injection ability is studied.
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Liao, Yung-Hsin, and 廖永信. "Studying Photoelectric Characteristics of Fully Transparent Polymer Light Emitting Diodes Using Zinc Oxide Thin Film as Gas Barrier." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/65682999754736610159.
Full textAbstract:
碩士長庚大學
光電工程研究所
96
In this thesis, we used the structure of ITO/PEDOT/PF/LiF/Ag/IZO to fabricate the fully transparent PLED devices. The encapsulation technology is critical for OLEDs and PLEDs. A major reason for the degradation of OLEDs and PLEDs due to moisture or oxygen ingress is the formation of non-emissive dark spots. So, the PLEDs need the additional passivetion layer to protect itself. However, a single inorganic thin film is not sufficiently dense to protect the OLEDs and PLEDs from permeation by moisture and oxygen and the performance of a single barrier layer is order of magnitude short of the requirements for OLEDs. Thus, a multilayered passivation composed of inorganic/inorganic or inorganic/polymer coating layers has been developed .We used the advantages of ZnO thin film such as high transparent in the visible light region and blocking ultraviolet combines the UV-cured epoxy resin to fully transparent PLEDs. The ZnO/UV-cured epoxy resin passivation layer can effectively protect PLEDs such a passivated device exhibited similar electrical behavior to a glass-encapsulated device. This result indicated that the fabrication process for forming the passivation layer did not influence the performance of the device. The lifetime of both devices was almost equal (about 100 hours), and no dark spots were formed in the optical images of electroluminescence over time. Moreover, another encapsulation method that the Al2O3/HfO2/Al2O3…HfO2 stacked multi-layers deposited onto the ZnO barrier layer by ALD put in use to the PLEDs encapsulation. The lifetime can improve 50 times (about 85 hours) comparing the PLEDs without passivation layer.
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Lin, Jeng-Bang, and 林政邦. "Effect of Gallium doping on zinc oxide thin films grown by pulsed laser deposition for polymer light-emitting devices." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/71605079309851437179.
Full textAbstract:
碩士吳鳳科技大學
光機電暨材料研究所
101
Transparent conducting Gallium-doped zinc oxide (GZO) thin films have been deposited on glass substrates by pulsed laser deposition. The structural, electrical and optical properties of these films were investigated as a function of Ga-doping amount (0–5 wt.%) in the target. Films were deposited at a substrate temperature of 200 °C in 20.0 m-Torr of oxygen pressure. The properties of GZO thin films such as optical band gap, electricitivity, microstructures and transmission were strongly affected by Ga-doping amount. It was observed that 3.0 wt.% of Ga is the optimum doping amount in the target to achieve the minimum film resistivity and the maximum film transmission. For the ~200 nm thick GZO film deposited using a ZnO target with a Ga content of 3.0 wt.%, the electrical resistivity , concentration and mobility were 2.91x10-4 Ω-cm , 2.0x1021 cm-3 and 10.59 cm2/vs, respectively. The average transmission of GZO thin films in the visible range (400–700 nm) was 90 %. These GZO films grown by PLD were used as transparent anodes to fabricate the polymer light-emitting diode (PLEDs). The device performance was measured in the GZO/PEDOT/PFO/LiF/Ca/Al diode and a luminance of 93 cd/m2 was observed with applied voltage of 10.5V. The intensity of electroluminescence was increased by nearly 1.4 time compared with the PLED, which is based on an un-doped ZnO glass substrate.
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S, ASHOK KUMAR, and ASHOK KUMAR S. "Electrochemical Preparation and Characterization of Chemically Modified Electrodes Based on Zinc Oxide, Polymer and Protein for Chemical and Biosensing Applications." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/65spe6.
Full textAbstract:
博士國立臺北科技大學
生物科技研究所
97
Chapter II-Abstract Electrochemical co-deposition of ZnO and MB hybrid films were carried out onto glassy carbon, gold and ITO electrodes and their electrochemical properties were investigated using CV. The surface morphology and deposition kinetics of MB/ZnO hybrid films were studied by means of SEM, AFM and EQCM techniques, respectively. The MB/ZnO/GCE acted as a sensor and displayed an excellent specific electrocatalytic response to the oxidation of NADH. The linear response range between 50 – 300 μM NADH concentration at pH 6.9 was observed with a detection limit of 10 μM (S/N=3). The electrode was stable during the time it was used for the full study (about 1 month) without a notable decrease in current. Indeed, DA, AA, AP and UA did not show any interference during the detection of NADH at this modified electrode. Chapter III-Abstract Thin TBO and ZnO hybrid films have been grown on GCE and ITO electrodes by using CV. The SEM images revealed spherical and beads-like shape of highly oriented TBO/ZnO hybrid films. The EDS results declared that the films composed mainly of Zn and O. Moreover, TBO/ZnO hybrid films modified electrode is electrochemically active, dye molecules were not easily leached out from the ZnO matrix and the hybrid films can be considered as sensor for amperometric determination of NADH at 0.0 V. A linear correlation between electrocatalytic current and NADH concentration was found to be in the range between 25 and 100 μM in 0.1 M phosphate buffer solution. Chapter IV-Abstract The ZnO and FAD molecules were deposited onto the GCE, gold and ITO by using CV from the bath solution containing aqueous 0.1M Zn(NO3)2, 0.1M NaNO3 and 1×10-4 M FAD. It was called as ZnO/FAD modified electrodes. Second type of modified electrode was prepared by electropolymerization method. Electrochemical polymerization of FAD was carried out from the acidic solution containing 1×10-4 M FAD monomers onto electrode surfaces. This poly(FAD) modified electrode yields a new redox couple in addition to monomer redox couple. The electrochemical and electrocatalytic properties of ZnO/FAD and poly(FAD) modified electrodes are investigated. In addition, the EQCM technique has been employed to follow the deposition process of both kind of modified. The electrocatalytic activity of poly(FAD) modified electrode towards the reduction of H2O2, oxidation of DA and AA has also been explored. The important electrocatalytic properties of poly(FAD) modified electrode was observed for simultaneous separation of DA and AA in (pH 6.0) buffer solution. Chapter V-Abstract Electrochemical synthesis and characterization of PABS films doped with flavins (FAD, FMN, RF) were investigated. In this study, the conducting polymer, PABS served as a matrix during the electropolymerization to synthesize PABS/flavin composite films. The synthetic, morphological and electrochemical properties of PABS/flavin films and PABS films were compared. Characterization was performed by CV, AFM, SEM and UV–vis spectroscopy. UV–vis spectroscopy confirmed the presence of flavins within composite films. PABS/FAD composite modified GCE (PABS/FAD/GCE) is used to electrochemically detect NADH and NAD+. PABS/FAD/GCE showed excellent electrocatalytic activity for the oxidation of NADH and for the reduction of NAD+. At optimum conditions, the sensor has a fast response to NADH and a good linear response to NADH in the range from 10 to 300 μM. Chapter VI-Abstract The electrocatalytic ability of the modified electrodes for the reduction of dioxygen to hydrogen peroxide was investigated by using CV and chronocoulometry techniques at PABS modified GCE. The electrochemical reduction of O2 has been studied in pH 7.0 buffer solution by using PABS modified glassy carbon rotating ring disk electrode (RRDE). The PABS-modified GCE (GCE/PABS) showed excellent electrocatalytic activity for O2 and H2O2 reduction reactions. The RRDE data indicated that the reduction of O2 on GCE/PABS electrodes proceed by a two-electron (n=2) pathway in aqueous buffer solution (pH 7.0). In addition, PABS/GCE was successfully utilized as an enzyme-less amperometric sensor for the detection of H2O2 in the range from 50 – 550 µM with detection limit of (S/N) 10 µM. Chapter VII-Abstract We have investigated electrochemical polymerization of 4-amino-1-1'-azobenzene-3,4'disulfonic acid (AY) was carried out onto the surface of GCE and ITO from acidic solution containing AY monomers. The redox response of the poly(AY) film on the GCE showed a couple of redox peak in 0.1 M sulfuric acid solution and the pH dependent peak potential was -58 mV/pH which was close to the Nernst behavior. The poly(AY) film-coated GCE (GCE/PAY) exhibited excellent electrocatalytic activity towards the oxidations of DA in 0.1M PBS (pH 7.0. However, in contrast to other polymer modified electrode, due to the strong negatively charged back bone of poly(AY) film modified electrode highly repelled the important interference of DA such as AA, UA and NADH in 0.1 M PBS (pH 7.0). This behavior makes the GCE/PAY for selective detection of DA in the presence of higher concentrations of AA, UA and NADH. Using differential pulse volatmmetry the calibration curves for DA were obtained over the range of 1 – 100 μM with good selectivity and sensitivity. Chapter VIII-Abstract Anodic polymerization of the azo dye DB71 on GCE in 0.1 M H2SO4 acidic medium was found to yield thin and stable polymeric films. The poly(DB71) films were electroactive in wide pH range (1 - 13). One pair of symmetrical redox peaks at a formal redox potential, E0’ = -0.02 V vs. Ag/AgCl (pH 7.0) was observed with a Nernstian slope -0.058 V, is attributed to a 1:1 proton + electron involving polymer redox reactions at the modified electrode. SEM, AFM and EIS measurements were used for surface studies of polymer modified electrode. Poly(DB71) modified GCE showed excellent electrocatalytic activity towards ascorbic acid in neutral buffer solution. Using amperometric method, linear range (1×10-6 M to 2×10-3 M), dynamic range (1×10-6 M to 0.01 M) and detection limit (1×10-6 M, S/N=3) were estimated for measurement of ascorbic acid in pH 7.0 buffer solution. Major interferences such as DA and UA were tested at this modified electrode and found that selective detection of AA could be achieved. Chapter IX-Abstract The adsorption processes and electrochemical behavior of 4-NA and 2-NA adsorbed onto GCE have been investigated in aqueous 0.1M HNO3 electrolyte solutions using CV. 4NA and 2-NA adsorbs onto GCE surfaces and upon potential cycling between 0.5 and -0.55 V is transformed into the ArHA which exhibits a well-behaved pH dependent redox couple centered at 0.32V (pH 1.5). This modified electrode can be readily used as an immobilization matrix to entrap proteins and enzymes. In our studies, Mb was chosen as a model protein for investigation. A pair of well-defined reversible redox peaks for Mb(Fe(III)–Fe(II)) was obtained at the Mb/ArHA modified GCE (Mb/ArHA/GCE) by direct electron transfer between the protein and the GCE. E0’, Γ and ks were calculated as -0.317 V, 4.15±0.5×10-11 mol/cm2 and 51±5 s-1, respectively. Dramatically enhanced biocatalytic activity was exemplified at the Mb/ArHA/GCE for the reduction of H2O2, TCA and O2.
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Huang, Yi-Jiun, and 黃義鈞. "Doping Zinc Oxide with Molybdenum or Tungsten Disulfide Nanosheets as Electron Transport Layers for Polymer with Fullerene or Small Molecule Photovoltaics." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/c7z7k5.
Full textAbstract:
博士國立交通大學
材料科學與工程學系所
107
In organic photovoltaic (OPV) devices, more effective transfer of dissociated electrons and holes from the active layer to the respective electrodes will result in higher fill factors (FF) and short-circuit current densities (Jsc) and, thus, enhanced power conversion efficiencies (PCE). The PCE of OPVs is affected not only by active layer but also transport layer. In my study, I specialize in developing the electron transport layer (ETL) by doping two-dimensional (2D) transition-metal dichalcogenide (TMD) materials for OPV devices. In the first part study, we incorporated molybdenum disulfide (MoS2) nanosheets into sol–gel processing of zinc oxide (ZnO) to form ZnO:MoS2 composites for use as ETLs in inverted polymer solar cells featuring a binary bulk heterojunction active layer. We could effectively tune the energy band of the ZnO:MoS2 composite film from 4.45 to 4.22eV by varying the content of MoS2 up to 0.5 wt%, such that the composite was suitable for use in bulk heterojunction photovoltaic devices based on poly[bis(5-(2-ethylhexyl)thien-2-yl)benzodithiophene–alt–(4-(2-ethylhexyl)-3-fluorothienothiophene)-2-carboxylate-2,6-diyl)] (PTB7-TH):phenyl-C71-butryric acid methyl ester (PC71BM). In particular, the PCE of the PTB7-TH:PC71BM (1:1.5, w/w) device incorporating the ZnO:MoS2 (0.5 wt%) composite layer as the ETL was 10.1%, up from 8.8% for the corresponding device featuring ZnO alone as the ETL—a relative increase of 15%. Incorporating a small amount of MoS2 nanosheets into the ETL altered the morphology of the ETL and resulted in enhanced current densities, fill factors, and PCEs for the devices. We used ultraviolet photoelectron spectroscopy (UPS), synchrotron grazing-incidence wide-/small-angle X-ray scattering (GIWAXS/GISAXS), atomic force microscopy (AFM), and transmission electron microscopy (TEM) to characterize the energy band structures, internal structures, surface roughness, and morphologies, respectively, of the ZnO:MoS2 composite films. For the second part study, a new universal ETL that involves doping hydrogen-plasma treated tungsten disulfide (WS2) nanosheets into ZnO for polymer/fullerene or small molecule OPVs was prepared. A hydrogen-plasma treatment was used to alter the structures of WS2 nanosheets such that the W6+ content was converted into W4+; then ZnO:WS2 nanosheets composites were prepared to form ETLs. The energy band of the ZnO:WS2 films could be tuned from 5.15 to 4.60 eV by varying the concentration of the WS2 nanosheets up to 0.5 wt%. It was found that ZnO:WS2 ETLs exhibited superior charge transport properties than those of the pristine ZnO layer because of the structure changes, as determined from the X-ray scattering characterizations. OPVs incorporating active layers of PTB7-TH/PC71BM and PTB7-TH/IDIC blends exhibited their power conversion efficiencies of 10.3% and 6.7%, respectively, with the incorporation of 0.3 wt% of the WS2 nanosheets, up from 8.9% and 5.4% for the corresponding devices featuring pristine ZnO—relative increases of 16% and 24%, respectively. This study demonstrates the effectiveness of hydrogen-plasma treatment for altering the surface structures of 2D TMD nanosheets, and paves a way for the composite ETLs for use in OPVs.
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Chen, Hsiu-Cheng, and 陳修成. "Solution-processed Zinc Oxide/Polyethyleneimine Nanocomposites as an Electron Transport Layer in Conjugated Polymer/Fullerene and a Block Copolymer Blended in Small Molecule/Fullerene Bulk Heterojunction Organic Photovoltaics." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/85778872994071744571.
Full textAbstract:
博士國立交通大學
材料科學與工程學系所
104
Bulk heterojunction organic solar cells (OSCs) based on blends of conjugated polymers or small molecules and fullerene derivatives have been extensively studied over the past few years because of their inexpensive, flexibility, renewability, and large-area processing. In traditional OSCs devices, the indium-tin oxide (ITO) appears as transparent anode normally, and poly(3,4-ethylenedioxythioph ene):poly(styrene-sulfonate) (PEDOT:PSS) is often used as anode interfacial layer to modify the morphology of ITO, further the work function of anode and ensure Ohmic contact. However, the acidic PEDOT:PSS may rust the ITO anode and cause the diffusion of indium into the active layer and such that the degradation of OSCs performance. Therefore, an inverted architecture can avoid the negative influence of PEDOT:PSS on the ITO surface and increase the absorption and stability of the OSC devices. In the first part study, we employed polyethyleneimine-doped sol–gel-processed zinc oxide composites (ZnO:PEI) as efficient electron transport layers (ETL) for facilitating electron extraction in inverted polymer solar cells. Using ultraviolet photoelectron spectroscopy, synchrotron grazing-incidence small-angle X-ray scattering and transmission electron microscopy, we observed that ZnO:PEI composite films’ energy bands could be tuned considerably by varying the content of PEI up to 7wt%—the conduction band ranged from 4.32 to 4.0 eV—and the structural order of ZnO in the ZnO:PEI thin films would be enhanced to align perpendicular to the ITO electrode, particularly at 7 wt% PEI, facilitating electron transport vertically. We then prepared two types of bulk heterojunction systems—based on poly(3-hexylthiophene) (P3HT):phenyl-C61-butryric acid methyl ester (PC61BM) and benzo[1,2-b:4,5-b´]dithiophene-thiophene-2,1,3-benzooxadiazole (PBDTTBO):phenyl -C71-butryric acid methyl ester (PC71BM)—that incorporated the ZnO:PEI composite layers. When using a composite of ZnO:PEI (93:7, w/w) as the ETL, the power conversion efficiency (PCE) of the P3HT:PC61BM (1:1, w/w) device improved to 4.6% from a value of 3.7% for the corresponding device that incorporated pristine ZnO as the ETL—a relative increase of 24%. For the PBDTTBO:PC71BM (1:2, w/w) device featuring the same amount of PEI blended in the ETL, the PCE improved to 8.7% from a value of 7.3% for the corresponding device that featured pure ZnO as its ETL—a relative increase of 20%. Accordingly, ZnO:PEI composites can be effective ETLs within organic photovoltaics. Then for the second part study, we took advantage of the different polarities of the blocks of a low-molecular-wieght diblock copolymer polystyrene-b- poly(ethylene oxide) (PS-b-PEO) that interact differentially with small molecules and fullerenes to tune the extent of the phase separation in the solution-processed small-molecule bulk-heterojunction (SMBHJ) solar cells. We incorporated small amounts of a nanostructured PS-b-PEO to solar cells’ active layers featuring p-DTS(FBTTh2)2 and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) for optimizing morphology and thus enhancing devices’ power conversion efficiency. For understanding the effect of PS-b-PEO on devices’ performances, we used synchrotron grazing-incidence wide-angle X-ray scattering, atomic force microscopy (AFM) and transmission electron microscopy (TEM) to probe and to decipher the morphologies of the resulting SMBHJ thin films. Without undergoing any annealing process, a device with an active layer of p-DTS(FBTTh2)2:PC71BM (1.5:1, w:w) that incorporated 0.5 wt % of PS-b-PEO and was processed with 1,8-diiodooctanesolvent additive displayed a power conversion efficiency (PCE) of 7.3%, a relative increase of 2.5 times as compared to the PCE of 2.1% for the control device featuring only p-DTS(FBTTh2)2 and PC71BM. Thus, incorporating this nanostructured block copolymer in the active layer allowed effective tuning of the small molecule active layer morphology and resulted in enhanced device efficiency.
33
Yuvaraj, D. "Studies On The Growth And Characterization Of II-VI Semiconductor Nanostructures By Evaporation Methods." Thesis, 2009. https://etd.iisc.ac.in/handle/2005/1037.
Full textAbstract:
In recent years, there has been growing interests on II-VI semiconductor nanostructures, which are suitable for applications in electronics and optoelectronic devices such as solar cells, UV lasers, sensors, light emitting diodes and field emission displays. II-VI semiconductor nanostructures with different morphologies such as wires, belts, rods, tubes, needles, springs, tetrapods, plates, hierarchical structures and so on, have been widely grown by vapor transport methods. However the process conditions used for the growth of nanostructures still remains incompatible for device fabrication. The realization of practical nanoscale devices using nanostructured film depends mainly on the availability of low cost and lower processing temperatures to manufacture high purity nanostructures on a variety of substrates including glass and polymer.
In this thesis work, studies have been made on the growth and characterization of II-VI semiconductor nanostructures prepared at room temperature, under high vacuum, without employing catalysts or templates.
(i) ZnO nanostructured films with different morphology such as flowers, needles and shrubs were deposited at room temperature on glass and polymer substrates by plasma assisted reactive process. (ii) Zn/ZnO core/shell nanowires were grown on Si substrates under optimized oxygen partial pressure. Annealing of this core shell nanowire in high vacuum resulted in the formation of ZnO nanocanals. (iii) ZnS and ZnSe nano and microstructures were grown on Si substrates under high vacuum by thermal evaporation. The morphology, structural, optical properties and composition of these nano and microstructures were investigated by XRD, SEM, TEM, Raman, PL and XPS. The growth mechanism behind the formation of the different nanostructures has been explained on the basis of vapour-solid (VS) mechanism.
34
Yuvaraj, D. "Studies On The Growth And Characterization Of II-VI Semiconductor Nanostructures By Evaporation Methods." Thesis, 2009. http://hdl.handle.net/2005/1037.
Full textAbstract:
In recent years, there has been growing interests on II-VI semiconductor nanostructures, which are suitable for applications in electronics and optoelectronic devices such as solar cells, UV lasers, sensors, light emitting diodes and field emission displays. II-VI semiconductor nanostructures with different morphologies such as wires, belts, rods, tubes, needles, springs, tetrapods, plates, hierarchical structures and so on, have been widely grown by vapor transport methods. However the process conditions used for the growth of nanostructures still remains incompatible for device fabrication. The realization of practical nanoscale devices using nanostructured film depends mainly on the availability of low cost and lower processing temperatures to manufacture high purity nanostructures on a variety of substrates including glass and polymer.
In this thesis work, studies have been made on the growth and characterization of II-VI semiconductor nanostructures prepared at room temperature, under high vacuum, without employing catalysts or templates.
(i) ZnO nanostructured films with different morphology such as flowers, needles and shrubs were deposited at room temperature on glass and polymer substrates by plasma assisted reactive process. (ii) Zn/ZnO core/shell nanowires were grown on Si substrates under optimized oxygen partial pressure. Annealing of this core shell nanowire in high vacuum resulted in the formation of ZnO nanocanals. (iii) ZnS and ZnSe nano and microstructures were grown on Si substrates under high vacuum by thermal evaporation. The morphology, structural, optical properties and composition of these nano and microstructures were investigated by XRD, SEM, TEM, Raman, PL and XPS. The growth mechanism behind the formation of the different nanostructures has been explained on the basis of vapour-solid (VS) mechanism.
35
Tang, Chun-Fang, and 董春芳. "Preparation, Characterization and Their Electrocatalytic Properties of osmiumhexacyanoferrate/silicomolybdate, Nano-TiO2/Poly 4-amino-1-1''- azobenzene-3, 4''-disulfonic acid(acid yellow 9), and zinc oxide/polymer core-shell microparticles hybrid film mod." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/h6r5rq.
Full textAbstract:
碩士國立臺北科技大學
化學工程研究所
95
Polynuclear mixed-valent osmium hexacyanoferrate/silicomolybdate have been prepared using repetitive cyclic voltammetry. The osmium/hexacyanoferrate/silicomolybdate films have been prepared using repetitive cyclic voltammetry. The cyclic voltammograms recorded for the deposition of the mixed-valent osmium/hexacyanoferrate/silicomolybdate hybrid films directly from the mixing of os3+, Fe(CN)63-and SiMo12O4-40 ions from the acidic aqueous solutions. The polynuclear mixed-valent osmium hexacyanoferrate/silicomolybdate films exhibited four redox couples. The scanning electron microscopy has been used to study the surface morphology of above films. Electrocatalytic reactions of dopamine, ascorbic acid, epinephrine, norepinephrine, and IO3- were carried out using the mixed-valent osmium/hexacyanoferrate/silicomolybdate films. Electrochemical polymerization of 4-amino-1-1''-azobenzene-3,4''-disulfonic acid (acid yellow 9 dye (AY)) was carried out onto the surface of nano-TiO2 modified glassy carbon (GC) electrode from acidic solution containing AY monomers. A nano-TiO2/poly(AY) modified GC electrode (nano-TiO2/PAY/GC) was characterized by cyclic voltammetry (CV). The redox response of the nano-TiO2/PAY/GC electrode showed a pH dependent redox peak potential was -54 mV/pH which was close to the Nernst behavior. The nano-TiO2/PAY/GC electrode exhibited excellent electrocatalytic activity towards the oxidations of dopamine (DA) and acetaminophen (AP) in 0.1M phosphate buffer solution (pH 7.0). Increased the anodic peak current three times higher for DA and six times higher for AP than bare GC electrode and reduced the considerable over potential. Electrocataltyic activity, electrode stability and antifouling properties of nano-TiO2/PAY/GC was compared with poly(AY) coated GC electrode. It was observed that in the presence of nano-TiO2 the stability, antifouling properties and self-life of modified electrode were improved than poly(AY)/GC modified electrode. However, in contrast to other polymer modified electrode, due to the strong negatively charged back bone of poly(AY) highly neglected the important interference such as ascorbic acid (AA), uric acid (UA) and reduced form of nicotinamide adenine dinucleotide (NADH) in 0.1M phosphate buffer solution (pH 7.0) and did not showed any response for oxidation of these interferences. This behavior makes the PAY/GC for simultaneous detection of DA and AP in the presence of higher concentrations AA, UA and NADH. Rotatable ring disk electrode (RRDE) was used for study electrode kinetics. Using differential pulse volatmmetry the calibration curves for DA and AP were obtained over the range of 1 – 120 μM with good selectivity and sensitivity. The proposed method provides a simple method for selective detection of DA and AP. Electrochemically initiated polymerization of serotonin (SN) onto zinc oxide (ZnO) coated glassy carbon and indium tin oxide coated electrodes were carried out from its monomer solution. This method results ZnO/polymer(serotonin) core-shell microparticels on electrodes surface. Surface characterizations of ZnO/polymer(serotonin) microparticles were performed by using atomic force microscope and scanning electron microscope. Finally the electrochemical properties of ZnO/polymer(serotonin) microparticles coated electrode were tested by using cyclic voltammetry. In addition, ZnO/polymer(serotonin) microparticles coated electrode is successfully applied to use for simultaneous detection of dopamine, ascorbic acid and uric acid in physiologically relevant condition.
36
Chitara, Basant. "Properties And Applications Of Semiconductor And Layered Nanomaterials." Thesis, 2012. https://etd.iisc.ac.in/handle/2005/2288.
Full textAbstract:
This thesis deals with the research work carried out on the properties and applications such as GaN nanoparticles, Graphene etc.
Chapter 1 of the thesis gives introduction to nanomaterials and various aspects of the thesis. Chapter 2 of the thesis describes the synthesis of GaN nanocrystals and their use as white light sources and as room temperature gas sensors. It also discusses negative differential resistance above room temperature exhibited by GaN. Electroluminescence from GaN-polymer heterojunction forms the last section of this chapter. Chapter 3 demonstrates the role of defect concentration on the photodetecting properties of ZnO nanorods with different defects prepared at different temperatures. Chapter 4 presents remarkable infrared and ultraviolet photodetector properties of reduced graphene oxide and graphene nanoribbons. Chapter 5 presents the infrared detecting properties of graphene-like few-layer MoS2.
The summary of the thesis is given at the end of the thesis.
37
Chitara, Basant. "Properties And Applications Of Semiconductor And Layered Nanomaterials." Thesis, 2012. http://hdl.handle.net/2005/2288.
Full textAbstract:
This thesis deals with the research work carried out on the properties and applications such as GaN nanoparticles, Graphene etc.
Chapter 1 of the thesis gives introduction to nanomaterials and various aspects of the thesis. Chapter 2 of the thesis describes the synthesis of GaN nanocrystals and their use as white light sources and as room temperature gas sensors. It also discusses negative differential resistance above room temperature exhibited by GaN. Electroluminescence from GaN-polymer heterojunction forms the last section of this chapter. Chapter 3 demonstrates the role of defect concentration on the photodetecting properties of ZnO nanorods with different defects prepared at different temperatures. Chapter 4 presents remarkable infrared and ultraviolet photodetector properties of reduced graphene oxide and graphene nanoribbons. Chapter 5 presents the infrared detecting properties of graphene-like few-layer MoS2.
The summary of the thesis is given at the end of the thesis.
38
Ivaturi, Sameera. "Electron Filed Emission Studies of Nanostructured Carbon Materials." Thesis, 2012. http://etd.iisc.ac.in/handle/2005/3251.
Full textAbstract:
Field emission is the emission of electrons from a solid under an intense electric field, of the order of 109 V/m. Emission occurs by the quantum mechanical tunneling of electrons through a potential barrier to vacuum. Field emission sources offer several attractive features such as instantaneous response to field variation, resistance to temperature fluctuation and radiation, a high degree of focusing ability in electron optics, good on/off ratio, ballistic transport, and a nonlinear current-voltage relationship.
Carbon nanotubes (CNTs) are potential candidates as field emitters since they possess high aspect ratio and are chemically inert to poisoning, and physically inert to sputtering during field emission. They can carry a very high current density and do not suffer field-induced tip sharpening like metallic tips. In addition, the CNT field emitters have the advantage of charge transport through 1D channels and electron emission at the sharp tips due to large enhancement. But the injection of electrons from the back contact remains a technical challenge which requires binding of CNT emitters to metallic substrate. Also, detachment of the CNT from the substrate tends to occur with time. The electrically conducting mixtures of CNTs and polymer can provide an alternative route to address these issues in the field emission of CNTs. The composites can be casted on any substrate in desired shape and the polymer matrix provides necessary support.
The research work reported in this thesis includes the preparation of high quality multiwall carbon nanotubes (MWCNTs), MWCNT-polystyrene (PS) composites, and experimental investigation on field emission properties of MWCNT¬PS composites in two different configurations. Electrical conductivity and percolation threshold of the MWCNT-PS composites are also investigated to ensure their high quality prior to the field emission studies. The study has been further extended to reduced graphene oxide (rGO) coated on polymer substrate. The main results obtained in present work are briefly summarized below.
This thesis contains eight chapters.
Chapter 1 provides an overview of basics of field emission, and the potential of CNT and CNT-polymer composites as field emitters.
Chapter 2 deals with the concise introduction of various structural characterization tools and experimental techniques employed in this study.
Chapter 3 describes the synthesis of MWCNTs and characterization by using electron microscopy and Raman spectroscopy.
MWCNTs are synthesized by chemical vapor deposition (CVD) of toluene [(C6H5) CH3] and ferrocene [(C5H5)2 Fe] mixture at 980 °C. Here toluene acts as carbon source material and ferrocene provides catalytic iron (Fe) particles. The MWCNT formation is based on the thermal decomposition of the precursor mixture. Scanning electron microscopy (SEM) characterization shows that the MWCNTs are closely packed and quite aligned in one direction. The average length of MWCNTs is about 200 μm and outer diameter lies in the range of 50-80 nm. The high quality of as-prepared MWCNT sample is confirmed by Raman spectroscopy. The as-grown MWCNTs are encapsulated with catalytic Fe nanoparticles, revealed by transmission electron microscopy. The Fe nanoparticles trapped within the MWCNT serve as fantastic system for studying the magnetic properties. Three types of MWCNT samples filled with Fe nanoparticles of different aspect ratio (~10, 5 and 2) are synthesized by varying the amount of ferrocene in the precursor material, and their magnetic properties are investigated. Enhanced values of coercivity (Hc) are observed for all samples, Hc being maximum (~2.6 kOe) at 10 K. The enhancement in Hc values is attributed to the strong shape anisotropy of Fe nanoparticles and significant dipolar interactions between Fe nanoparticles.
Chapter 4 deals with the field emission studies of MWCNT-PS composites in the parallel configuration.
By incorporating as-prepared MWCNTs in PS matrix in a specific ratio, composites with varying loading from 0.01-0.45 weight (wt.) fraction are prepared using solution mixing and casting. High degree of dispersion of MWCNTs in PS matrix without employing any surfactant is achieved by ultrasonication. Low percolation threshold (~0.0025 wt. fraction) in the MWCNT-PS composites ensures the good connectivity of filler in the fabricated samples. Field emission of MWCNT¬PS composites is studied in two different configurations: along the top surface of the film (parallel configuration) and along the cross section of the sample (perpendicular configuration). In this chapter field emission results of the MWCNT-PS composites in parallel configuration are presented. The effect of charge transport in limiting the field emission of MWCNT-PS composite is discussed. Field emission results of MWCNT-PS composites in parallel configuration indicate that the emission performance can be maximized at moderate wt. fraction of MWCNT (0.15). The obtained current densities are ~10 µA/cm2 in the parallel configuration.
Chapter 5 presents the study of field emission characteristics of MWCNT¬PS composites of various wt. fractions in the perpendicular configuration. Till date most studies using nanotube composites tend to have the nanotubes lying in two dimensional plane, perpendicular to the applied electric field. In the perpendicular configuration, the nanotubes are nearly aligned parallel to the direction of the applied electric field which results in high field enhancement, and electron emission at lower applied fields.
SEM micrographs in cross-sectional view reveal that MWCNTs are homogeneously distributed across the thickness and the density of protruding tubes can be scaled with wt. fraction of the composite film. Field emission from composites has been observed to vary considerably with density of MWCNTs in the polymer matrix. High emission current density of 100 mA/cm2 is achieved at a field of 2.2 V/µm for 0.15 wt. fraction. The field emission is observed to follow the Fowler– Nordheim tunneling mechanism, however, electrostatic screening plays a role in limiting the current density at higher wt. fractions.
Chapter 6 highlights the field emission response of rGO coated on a flexible PS film.
Field emission of rGO coated PS film along the cross section of the sample is studied in addition to the top film surface of the film. The effect of geometry on the improved field emission efficiency of rGO coated polymer film is demonstrated. The emission characteristics are analyzed by Fowler–Nordheim tunneling for field emission. Low turn-on field (~0.6 V/µm) and high emission current (~200 mA/cm2) in the perpendicular configuration ensure that rGO can be a potential field emitter.
Furthermore, stability and repeatability of the field emission characteristics are also presented.
Chapter 7 deals with the synthesis, characterization, and field emission of two different kinds of hybrid materials: (1) MWCNT coated with zinc oxide (ZnO) nanoparticles (2) ZnO/graphitic carbon (g-C) core-shell nanowires. The field emission from the bucky paper is improved by anchoring ZnO nanoparticles on the surface of MWCNT. A shift in turn on field from 3.5 V/µm (bucky paper) to 1.0 V/µm is observed by increasing the ZnO nanoparticle loading on the surface of MWCNT with an increase in enhancement factor from 1921 to 4894.
Field emission properties of a new type of field emitter ZnO/g-C core-shell nanowires are also presented in this chapter. ZnO/g-C core/shell nanowires are synthesized by CVD of zinc acetate at 1300 °C. Overcoming the problems of ZnO nanowire field emitters, which in general possess high turn on fields and low current densities, the core-shell nanowires exhibit excellent field emission performance with low turn on field of 2.75 V/µm and high current density of 1 mA/cm2.
Chapter 8 presents a brief summary of the important results and future perspectives of the work reported in the thesis.
39
Ivaturi, Sameera. "Electron Filed Emission Studies of Nanostructured Carbon Materials." Thesis, 2012. http://hdl.handle.net/2005/3251.
Full textAbstract:
Field emission is the emission of electrons from a solid under an intense electric field, of the order of 109 V/m. Emission occurs by the quantum mechanical tunneling of electrons through a potential barrier to vacuum. Field emission sources offer several attractive features such as instantaneous response to field variation, resistance to temperature fluctuation and radiation, a high degree of focusing ability in electron optics, good on/off ratio, ballistic transport, and a nonlinear current-voltage relationship.
Carbon nanotubes (CNTs) are potential candidates as field emitters since they possess high aspect ratio and are chemically inert to poisoning, and physically inert to sputtering during field emission. They can carry a very high current density and do not suffer field-induced tip sharpening like metallic tips. In addition, the CNT field emitters have the advantage of charge transport through 1D channels and electron emission at the sharp tips due to large enhancement. But the injection of electrons from the back contact remains a technical challenge which requires binding of CNT emitters to metallic substrate. Also, detachment of the CNT from the substrate tends to occur with time. The electrically conducting mixtures of CNTs and polymer can provide an alternative route to address these issues in the field emission of CNTs. The composites can be casted on any substrate in desired shape and the polymer matrix provides necessary support.
The research work reported in this thesis includes the preparation of high quality multiwall carbon nanotubes (MWCNTs), MWCNT-polystyrene (PS) composites, and experimental investigation on field emission properties of MWCNT¬PS composites in two different configurations. Electrical conductivity and percolation threshold of the MWCNT-PS composites are also investigated to ensure their high quality prior to the field emission studies. The study has been further extended to reduced graphene oxide (rGO) coated on polymer substrate. The main results obtained in present work are briefly summarized below.
This thesis contains eight chapters.
Chapter 1 provides an overview of basics of field emission, and the potential of CNT and CNT-polymer composites as field emitters.
Chapter 2 deals with the concise introduction of various structural characterization tools and experimental techniques employed in this study.
Chapter 3 describes the synthesis of MWCNTs and characterization by using electron microscopy and Raman spectroscopy.
MWCNTs are synthesized by chemical vapor deposition (CVD) of toluene [(C6H5) CH3] and ferrocene [(C5H5)2 Fe] mixture at 980 °C. Here toluene acts as carbon source material and ferrocene provides catalytic iron (Fe) particles. The MWCNT formation is based on the thermal decomposition of the precursor mixture. Scanning electron microscopy (SEM) characterization shows that the MWCNTs are closely packed and quite aligned in one direction. The average length of MWCNTs is about 200 μm and outer diameter lies in the range of 50-80 nm. The high quality of as-prepared MWCNT sample is confirmed by Raman spectroscopy. The as-grown MWCNTs are encapsulated with catalytic Fe nanoparticles, revealed by transmission electron microscopy. The Fe nanoparticles trapped within the MWCNT serve as fantastic system for studying the magnetic properties. Three types of MWCNT samples filled with Fe nanoparticles of different aspect ratio (~10, 5 and 2) are synthesized by varying the amount of ferrocene in the precursor material, and their magnetic properties are investigated. Enhanced values of coercivity (Hc) are observed for all samples, Hc being maximum (~2.6 kOe) at 10 K. The enhancement in Hc values is attributed to the strong shape anisotropy of Fe nanoparticles and significant dipolar interactions between Fe nanoparticles.
Chapter 4 deals with the field emission studies of MWCNT-PS composites in the parallel configuration.
By incorporating as-prepared MWCNTs in PS matrix in a specific ratio, composites with varying loading from 0.01-0.45 weight (wt.) fraction are prepared using solution mixing and casting. High degree of dispersion of MWCNTs in PS matrix without employing any surfactant is achieved by ultrasonication. Low percolation threshold (~0.0025 wt. fraction) in the MWCNT-PS composites ensures the good connectivity of filler in the fabricated samples. Field emission of MWCNT¬PS composites is studied in two different configurations: along the top surface of the film (parallel configuration) and along the cross section of the sample (perpendicular configuration). In this chapter field emission results of the MWCNT-PS composites in parallel configuration are presented. The effect of charge transport in limiting the field emission of MWCNT-PS composite is discussed. Field emission results of MWCNT-PS composites in parallel configuration indicate that the emission performance can be maximized at moderate wt. fraction of MWCNT (0.15). The obtained current densities are ~10 µA/cm2 in the parallel configuration.
Chapter 5 presents the study of field emission characteristics of MWCNT¬PS composites of various wt. fractions in the perpendicular configuration. Till date most studies using nanotube composites tend to have the nanotubes lying in two dimensional plane, perpendicular to the applied electric field. In the perpendicular configuration, the nanotubes are nearly aligned parallel to the direction of the applied electric field which results in high field enhancement, and electron emission at lower applied fields.
SEM micrographs in cross-sectional view reveal that MWCNTs are homogeneously distributed across the thickness and the density of protruding tubes can be scaled with wt. fraction of the composite film. Field emission from composites has been observed to vary considerably with density of MWCNTs in the polymer matrix. High emission current density of 100 mA/cm2 is achieved at a field of 2.2 V/µm for 0.15 wt. fraction. The field emission is observed to follow the Fowler– Nordheim tunneling mechanism, however, electrostatic screening plays a role in limiting the current density at higher wt. fractions.
Chapter 6 highlights the field emission response of rGO coated on a flexible PS film.
Field emission of rGO coated PS film along the cross section of the sample is studied in addition to the top film surface of the film. The effect of geometry on the improved field emission efficiency of rGO coated polymer film is demonstrated. The emission characteristics are analyzed by Fowler–Nordheim tunneling for field emission. Low turn-on field (~0.6 V/µm) and high emission current (~200 mA/cm2) in the perpendicular configuration ensure that rGO can be a potential field emitter.
Furthermore, stability and repeatability of the field emission characteristics are also presented.
Chapter 7 deals with the synthesis, characterization, and field emission of two different kinds of hybrid materials: (1) MWCNT coated with zinc oxide (ZnO) nanoparticles (2) ZnO/graphitic carbon (g-C) core-shell nanowires. The field emission from the bucky paper is improved by anchoring ZnO nanoparticles on the surface of MWCNT. A shift in turn on field from 3.5 V/µm (bucky paper) to 1.0 V/µm is observed by increasing the ZnO nanoparticle loading on the surface of MWCNT with an increase in enhancement factor from 1921 to 4894.
Field emission properties of a new type of field emitter ZnO/g-C core-shell nanowires are also presented in this chapter. ZnO/g-C core/shell nanowires are synthesized by CVD of zinc acetate at 1300 °C. Overcoming the problems of ZnO nanowire field emitters, which in general possess high turn on fields and low current densities, the core-shell nanowires exhibit excellent field emission performance with low turn on field of 2.75 V/µm and high current density of 1 mA/cm2.
Chapter 8 presents a brief summary of the important results and future perspectives of the work reported in the thesis.