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Deyu, Getnet Kacha. "Defect Modulation Doping for Transparent Conducting Oxide Materials." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAI071.
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Le dopage des matériaux semi-conducteurs est une partie fondamentale de la technologie moderne. Les oxydes conducteurs transparents (TCO) constituent une famille de semi-conducteurs, qui sont optiquement transparents et électriquement conducteurs. La conductivité électrique élevée est généralement obtenue grâce à un dopage associant des impuretés de substitution hétérovalentes comme dans In2O3 dopé au Sn (ITO), SnO2 dopé au fluor (FTO) et ZnO dopé à l'Al (AZO). Cependant, ces approches classiques ont dans de nombreux cas atteint leurs limites tant en ce qui concerne la densité de porteurs de charge atteignable, que pour la valeur de la mobilité des porteurs de charge. Le dopage par modulation est un mécanisme qui exploite l'alignement de la bande d'énergie à une interface entre deux matériaux pour induire une densité de porteurs de charges libres dans l’un d’entre eux ; un tel mécanisme a permis de montrer dans certains cas que la limitation liée à la mobilité pouvait ainsi était évitée. Cependant, la limite de densité de porteuse ne peut pas être levée par cette approche, du fait de l'alignement des limites de dopage par défauts intrinsèques. Le but de ce travail était de mettre en œuvre cette nouvelle stratégie de dopage pour les TCO. La stratégie repose sur l’utilisation de large bande interdite pour doper la surface des couches de TCO, ce qui résulte à un piégeage du niveau de Fermi pour la phase dopante et à un positionnement du niveau de Fermi en dehors de la limite de dopage dans les TCO. La méthode est testée en utilisant un TCO comme In2O3 non dopé, In2O3 dopé au Sn et SnO2 phase hôte et Al2O3 et SiO2-x en tant que phase de dopant gap à large bandeThe doping of semiconductor materials is a fundamental part of modern technology.Transparent conducting oxides (TCOs) are a group of semiconductors, which holds the features of being transparent and electrically conductive. The high electrical conductivity is usually obtained by typical doping with heterovalent substitutional impurities like in Sn-doped In2O3 (ITO), fluorine-doped SnO2 (FTO) and Al-doped ZnO (AZO). However, these classical approaches have in many cases reached their limits both in regard to achievable charge carrier density, as well as mobility. Modulation doping, a mechanism that exploits the energy band alignment at an interface between two materials to induce free charge carriers in one of them, has been shown to avoid the mobility limitation. However, the carrier density limit cannot be lifted by this approach, as the alignment of doping limits by intrinsic defects. The goal of this work was to implement the novel doping strategy for TCO materials. The strategy relies on using of defective wide band gap materials to dope the surface of the TCO layers, which results Fermi level pinning at the dopant phase and Fermi level positions outside the doping limit in the TCOs. The approach is tested by using undoped In2O3, Sn-doped In2O3 and SnO2 as TCO host phase and Al2O3 and SiO2−x as wide band gap dopant phase
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O'Neil, David H. "Materials chemistry and physics of the transparent conducting oxides." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670028.
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Campion, Michael J. (Michael John). "Understanding the oxidation and reduction process in transparent conducting oxides." Thesis, Massachusetts Institute of Technology, 2018. https://hdl.handle.net/1721.1/121604.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 133-141).
Transparent conductors play important roles in many optoelectronic devices such as LEDs, thin film solar cells, and smart windows through their ability to efficiently transport both photons and electrons. Simultaneous requirements of a wide band gap, high free carrier concentration, and high electron mobility limits the selection of available transparent conductor materials. Further improvements in the optical and electrical properties, along with improvements in processing tolerance, are highly desirable for this material class. One key limitation of current transparent conducting oxides is their response to oxidation, which can cause severe decreases to the conductivity of the material through ionic compensation. Materials with slow oxygen kinetics or resistance to the formation of compensating ionic defects could lead to more flexible operating and processing conditions for applications requiring transparent conductors.
The properties of transparent conducting oxides, Al-doped ZnO and La-doped BaSnO₃, were examined through a variety of methods with a focus on the impact of processing on the free carrier concentration, electron transport, and optical properties. Al-doped ZnO was examined as a well-known alternative to indium tin oxide (ITO) that has been shown to be limited by relatively narrow processing conditions and large variances in reported properties. BaSnO₃ is a comparatively new material in the field of transparent conductors, attractive mainly due to its exceptionally high electron mobility for an oxide. Little is currently known about the nature of defects and processing on the optical and electrical properties of this material, but this information will be important to understand before implementing this material in practical devices.
For these materials, I examined the roles of oxygen stoichiometry and point defect formation in impacting properties and stability under both processing conditions and harsh operating conditions and explored the limitations and opportunities provided by these transparent conducting oxide systems. Al-doped ZnO thin films were produced by pulsed laser deposition under a variety of oxygen conditions demonstrating the strong dependence of free electron concentration and mobility on the oxidation state of the material. The free carrier absorption in the infrared photon range was measured and modeled and found to agree well with theory assuming ionized impurity scattering as the limiting electron scattering mechanism. These effects were understood through the framework of the formation of compensating zinc vacancies under oxidizing conditions, leading to decreases in the free electron concentration.
Atom probe tomography was applied to Al-doped ZnO thin films deposited on Si substrates, demonstrating an effective accumulation of Al near the ZnO/Si interface, but with no detected precipitation or agglomeration in the x-y plane of the film, even for heavily doped films. This was surprising due to the high concentration of Al-dopant in the material, exceeding the thermodynamic solubility limit of bulk ZnO. An accumulation of Al-dopant was observed at the ZnO/Si interface under multiple conditions, with the oxygen atmosphere during deposition and nature of the Si substrate affecting the degree of accumulation. Because transparent conductors are typically used to transfer charge through interfaces, understanding the nature and implications of this observed accumulation effect could be essential to understanding device performance.
La-doped and undoped BaSnO₃ thin films and bulk samples were tested for their electrical conductivity in-situ under various temperatures and oxygen partial pressures. In the undoped case, a p-type to n-type transition was observed at lower temperatures with decreasing oxygen partial pressure, with the behavior correlated to the formation and annihilation of oxygen and cation vacancies. Under donor-doping, a measurable, but weak n-type dependence of conductivity was demonstrated, pointing to a surprisingly weak role played by cation vacancy charge compensation over the measured temperature ranges. Compared to other similar oxide systems, compensation by cation vacancies would normally be expected to be strong under oxidizing conditions.
This is a key advantage for La-doped BaSnO₃ as a high temperature oxygen stable material compared to other competing materials that are more susceptible to conductivity degradation due to ionic compensation of the donor dopant under oxidizing conditions. This was directly demonstrated in the testing of the conductivity response of La-doped BaSnO₃ thin films that maintained high conductivity under a large range of oxygen and temperature conditions. Oxygen diffusion in the material was estimated from conductivity relaxation and further explored with oxygen tracer diffusion studies. These studies revealed an activation energy of 2 eV for the oxygen diffusion process, as well as a depth dependent diffusivity leading to depressed oxygen diffusivities near the surface. Study of epitaxial and polycrystalline thin films of La-doped BaSnO₃ revealed a difference in the rate of oxidation response of the conductivity.
Epitaxial thin films exhibited a weak power law dependence on temperature while polycrystalline thin films under oxidizing conditions exhibited an activation energy of 0.36 eV. This effect was attributed to the formation of narrow space charge regions at the grain boundaries under oxidizing conditions. Simultaneous measurements of the infrared transmission and electrical conductivity of thin films were performed as a means of correlating infrared transmission with conductivity at high temperatures under various controlled atmospheres. These two measurements were found to be strongly correlated and were demonstrated to be connected to the formation and annihilation of free carriers in the thin films. A novel measurement technique was explored in which the conductance response was measured across a substrate during pulsed laser deposition of Al-doped ZnO.
The measured conductance profile as a function of time was correlated to the expected growth regimes typical of an island growth mode, and the thickness dependence of resistivity was directly observed. Additional information about the growth conditions was obtained through conductance relaxation after single pulses, performed under different growth chamber atmospheres.
by Michael J. Campion.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering
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Colucci, Renan [UNESP]. "Desenvolvimento de um compósito contendo polímero condutor (PEDOT:PSS) e material ORMOSIL (GPTMS) com aplicação na fabricação de dispositivos eletroluminescentes." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/141509.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Atualmente é possível fabricar dispositivos eletroluminescentes (EL) utilizando como material ativo uma dispersão de um pó eletroluminescente inorgânico em uma matriz polimérica condutora. Entretanto, esses materiais são quimicamente instáveis, o que impede a deposição de alguns materiais solúveis sobre eles, como por exemplo, eletrodos de tinta prata. Para solucionar este problema, desenvolvemos uma matriz condutora e quimicamente estável formada pelo polímero condutor poli(3,4-etileno dioxitiofeno):poliestireno sulfonado (PEDOT:PSS) e pelo material sílica-orgânico 3-glicidoxipropil trimetilsilano (GPTMS). Foram produzidos compósitos de PEDOT:PSS/GPTMS com diversas concentrações de PEDOT:PSS, com os quais foram produzidos filmes uniformes, insolúveis e com condutividade elétrica entre 2 S/cm e 400 S/cm. A dependência da condutividade elétrica destes materiais em função da temperatura e da concentração de PEDOT:PSS foi descrita pelo modelo de transporte de cargas variable range hopping (VRH-3D). Adicionando-se o material eletroluminescente (EL) inorgânico silicato de zinco dopado com manganês (Zn2SiO4:Mn) à matriz condutora de PEDOT:PSS/GPTMS foi obtido um compósito para a produção de dispositivos EL. Depositando-se este compósito EL sobre substratos de vidro contendo eletrodos transparentes de óxido de estanho e índio, foram obtidos dispositivos EL com tensão de operação de 30 V e eficiência luminosa de 1,3 cd/A. Além disso, a transmitância óptica e a resistência de folha de filmes do compósito condutor (PEDOT:PSS/GPTMS) foram avaliadas, demonstrando que este material apresenta propriedades compatíveis com a aplicação como eletrodo transparente. Por fim, foram produzidos dispositivos EL utilizando o compósito condutor PEDOT:PSS/GPTMS como eletrodos e o compósito EL PEDOT:PSS/GPTMS/ Zn2SiO4:Mn como material ativo. Com este experimento, foi demonstrada a possibilidade de fabricar dispositivos EL por rota líquida, onde o compósito PEDOT:PSS/GPTMS foi utilizado tanto para a fabricação dos eletrodos como para a produção do material ativo do dispositivo.
It is possible to fabricate light-emitting (LE) devices with LE composites as active material. These light-emitting composites are produced with a LE inorganic powder dispersed into a conducting polymer matrix. However, these composites are chemically unstable, limiting the deposition of soluble materials over it. To overcome this problem we developed a high-stability conductive matrix comprising the conductive polymer poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and the organic-silicate 3-glycidyloxypropyl)trimethoxysilane (GPTMS). Composites PEDOT:PSS/GPTMS with diverse weight concentrations of PEDOT:PSS were produced and used to fabricate high-stability films with electrical conductivity from 2 S/cm up to 400 S/cm. The charge transport in these conductive composites were studied as function of the temperature, as well as of the PEDOT:PSS concentration, and described by the 3D variable range hopping model. A light-emitting composite was produced adding to this conductive composite the inorganic electroluminescent powder Mn-doped zinc silicate (Zn2SiO4:Mn). Light-emitting devices, with turn-on voltage of 30 V and luminous efficacy of 1.3 cd/A, were produced with a coating of the developed LE composite done over glass substrates containing indium tin oxide transparent electrodes. Additionally, the optical transmittance and sheet resistance of films produced with the conductive composite PEDOT:PSS/GPTMS were evaluated showing that this material is suitable to fabricate transparent electrodes. Finally, were produced light-emitting devices employing the conductive composite PEDOT:PSS/GPTMS as electrodes and the light-emitting composite PEDOT:PSS/GPTMS/ Zn2SiO4:Mn as active material. This experiment has shown the fabrication of solution-processed light-emitting devices using the composite PEDOT:PSS/GPTMS as transparent electrode and as component of the active material.
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Kainikkara, Vatakketath Rithwik. "Investigation of the Transparent Conducting Oxide (TCO) material used in CIGS thin film solar cell in Midsummer AB." Thesis, Uppsala universitet, Institutionen för elektroteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-423109.
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Deyu, Getnet Kacha [Verfasser], Andreas [Akademischer Betreuer] Klein, and Lambert [Akademischer Betreuer] Alff. "Defect Modulation Doping for Transparent Conducting Oxide Materials / Getnet Kacha Deyu ; Andreas Klein, Lambert Alff." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2020. http://d-nb.info/1205070095/34.
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Amooali, Khosroabadi Akram. "Optical and Electrical Properties of Composite Nanostructured Materials." Diss., The University of Arizona, 2014. http://hdl.handle.net/10150/333480.
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A novel lithographic fabrication method is used to fabricate nanopillars arrays of anisotropic Ag and TCO electrodes. Optical and electrical properties of the electrodes including bandgap, free carrier concentration, resistivity and surface plasmon frequency of different electrodes can be tuned by adjusting the dimensions and geometry of the pillars. Given the ability to tune the nonlocal responses of the plasmonic field enhancements, we attempt to determine the nature of the effective refractive index profile within the visible wavelength region for multi-layer hybrid nanostructures. Knowledge of the effective optical constants of the obtained structure is critical for various applications. nanopillars of TCO\Ag core shell structures have been successfully fabricated. The Maxwell-Garnett mixing law has been used to determine the optical constants of the nanostructure based on spectroscopic ellipsometry measurements. Simulated reflection spectra indicate a down shift in the Brewster angle of the pillars resulting from the reduction in the effective refractive index of the nanostructure. Two plasmonic resonances were observed, with one in the visible region and the other in the IR region. Plasmon hybridization model is used to describe the behavior of metal and metal oxide core shell nanostructured electrodes. Different charge density distributions around the pillars determine the plasma frequency which depends on the core and surrounding media dielectric constants. Finite Difference Time Domain (FDTD) simulation of different structures agree well with experiment and help us to understand electric field behavior at different structures with different geometries and dielectric constants. Plasmonic Ag nanopillar arrays are effective substrates for surface enhanced Raman spectroscopy (SERS). An enhancement factor up to 6 orders of magnitude is obtained. Monolayers of C60 is deposited on the Ag nanopillars and the interface of C60/Ag is studied which is important in optoelectronic devices. Electron delocalization between C60 and Ag is confirmed.
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Martin, Alexis. "Conception et étude d'antennes actives optiquement transparentes : de la VHF jusqu'au millimétrique." Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S126/document.
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Avec le développement de l’internet des objets et l’augmentation des applications sans fil, les antennes sont de plus en plus présentes au quotidien. Cependant, l’implantation de ces antennes est un challenge tant d’un point de vue technologique (intégration des antennes dans les dispositifs), que psychologique (acceptabilité des antennes par le grand public). Dans ce contexte, le développement d’antennes optiquement transparentes permet non seulement leur implantation sur de nouvelles surfaces (vitrages d’immeubles, écrans de smartphones ...), mais promeut aussi leur acceptabilité par le grand public grâce à leur faible impact visuel. Ce travail présente la conception, la fabrication et la caractérisation d’antennes actives optiquement transparentes. Le matériau transparent et conducteur utilisé est un maillage métallique à pas micrométrique développé spécifiquement, alliant conductivité électrique et transparence optique élevées. Dans ce cadre, un premier prototype d’antenne transparente et miniature en bande FM utilisant un transistor MESFET de dimensions sub-millimétriques a été réalisé. Des antennes agiles en fréquence en bande X (~10 GHz) couplées, soit à une diode varicap localisée (agilité ~10%), soit à un matériau ferroélectrique (agilité ~2%), ont été développées et étudiées. Une antenne passive transparente a été conçue en bande V (~60 GHz). Enfin, une transition optique (1540 nm) / hyperfréquence (1,4 GHz) a été réalisée et caractérisée, basée sur la transmission optique d’un faisceau laser au travers du matériau constitutif de l’antenne. Pour l’ensemble des prototypes réalisés, une transparence optique supérieure à 80% dans le domaine du visible associée à une résistance par carré inférieure à 0,1 ohm/sq ont été utiliséesWithin the development of the Internet of Things (IoT) and the increase of the wireless communications, antennas are even more present on everyday life. However, antenna implementation is a real challenge, from a technological point of view (antenna integration into the devices) and from a psychological point of view (acceptability by the general public). Within this framework, the development of optically transparent antennas on new surfaces (glass windows, smartphone screens . . . ) is of great interest to improve the network coverage and to assist the general public in acceptability thanks to the low visual impact of such printed antennas. The present work deals with the design, the fabrication and the characterization of optically transparent and active antennas. The transparent and conducting material used is a micrometric mesh metal film specifically developed, associating high electrical conductivity and high optical transparency. A first optically transparent and miniature FM antenna based on a MESFET transistor with micrometric size has been designed and fabricated. Frequency agile antennas operating in X-band (~10 GHz), based on a beam-lead varactor (agility ~10%) and on a ferroelectric material agility ~2%), have been developed and characterized. An optically transparent and passive antenna has been studied in V-band (~60 GHz). At last, optics (1540 nm) / microwave (1.4 GHz) transition has been performed based on the transmission of a laser beam through the transparent antenna. For all prototypes, an optical transparency level higher than 80% coupled with a sheet resistance value lower than 0.1 ohm/sq have been used
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Wang, Haihang. "PAOFLOW-Aided Computational Materials Design." Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1609102/.
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Functional materials are essential to human welfare and to provide foundations for emerging industries. As an alternative route to experimental materials discovery, computational materials designs are playing an increasingly significant role in the whole discovery process. In this work, we use an in-house developed python utility: PAOFLOW, which generates finite basis Hamiltonians from the projection of first principles plane-wave pseudopotential wavefunctions on pseudo atomic orbitals(PAO) for post-process calculation on various properties such as the band structures, density of states, complex dielectric constants, diffusive and anomalous spin and charge transport coefficients. In particular, we calculated the dielectric function of Sr-, Pb-, and Bi-substituted BaSnO3 over wide concentration ranges. Together with some high-throughput experimental study, our result indicates the importance of considering the mixed-valence nature and clustering effects upon substitution of BaSnO3 with Pb and Bi. We also studied two prototype ferroelectric rashba semiconductors, GeTe and SnTe, and found the spin Hall conductivity(SHC) can be large either in ferroelectric or paraelectric structure phase. Upon doping, the polar displacements in GeTe can be sustained up to a critical hole concentration while the tiny distortions in SnTe vanish at a minimal level of doping. Moreover, we investigated the sensitivity of two dimensional group-IV monochalcogenides to external strain and doping, which reveal for the first time giant intrinsic SHC in these materials, providing a new route for the design of highly tunable spintronics devices based on two-dimensional materials.
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Gayam, Sudhakar R. "High resistivity zinc stannate as a buffer layer in cds/cdte solar cells." [Tampa, Fla.] : University of South Florida, 2005. http://purl.fcla.edu/fcla/etd/SFE0001061.
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Read, Daniel Charles. "Novel transparent conducting polymers." Thesis, University of Newcastle Upon Tyne, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357118.
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Wei, Shijun. "Flame-made Nb-doped TiO2 Thin Films for Application in Transparent Conductive Oxides." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1447071519.
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Mei, Jun S. B. Massachusetts Institute of Technology. "Photoluminescence quenching of organic thin films by transparent conductive oxides." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35059.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.Includes bibliographical references (p. 83-86).
One fundamental challenge in designing organic light-emitting diodes is luminescence quenching near an electrode. In this work, we investigate the underlying mechanism behind luminescence quenching by measuring the reduction in Alq3 photoluminescence due to SnO02. Using an analytical model and a Monte Carlo simulation for exciton dynamics in amorphous organic solids, we find that the exciton diffusion length in bulk Alq3 is in the range of 70--80 A. We also find that for SnO2 films deposited without oxygen in the sputtering ambient, resonant energy transfer from Alq3 to SnO2 is the dominant quenching mechanism. By varying the oxygen content in the Ar/C)2 sputtering gas mixture, we find that the energy transfer distance decreases from 10--25 A for 0% 02 to less than 2 A for 10% 02. Our experimental results suggest that because excess oxygen reduces oxygen vacancies and defect electronic states in SnO2, it leads to a smaller spectral overlap between the emission of Alq3 and the absorption of SnO2, thereby shortening the energy transfer distance and reducing the quenching capability of SnO2.
by Jun Mei.
S.B.
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Zhu, Zhaozhao, and Zhaozhao Zhu. "Emerging Materials for Transparent Conductive Electrodes and Their Applications in Photovoltaics." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/623062.
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Clean and affordable energy, especially solar energy, is becoming more and more important as our annual total energy consumption keeps rising. However, to make solar energy more affordable and accessible, the cost for fabrication, transportation and assembly of all components need to be reduced. As a crucial component for solar cells, transparent conductive electrode (TCE) can determine the cost and performance. A light weight, easy-to-fabricate and cost-effective new generation TCE is thus needed. While indium-doped tin oxide (ITO) has been the most widely used material for commercial applications as TCEs, its cost has gone up due to the limited global supply of indium. This is not only due to the scarcity of the element itself, but also the massive production of various opto-electronic devices such as TVs, smartphones and tablets. In order to reduce the cost for fabricating large area solar cells, substitute materials for ITO should be developed. These materials should have similar optical transmittance in the visible wavelength range, as well as similar electrical conductivity (sheet resistance) to ITO. This work starts with synthesizing ITO-replacing nano-materials, such as copper nanowires (CuNWs), derivative zinc oxide (ZnO) thin films, reduced graphene oxide (rGO) and so on. Further, we applied various deposition techniques, including spin-coating, spray-coating, Mayer-rod coating, filtration and transferring, to coat transparent substrates with these materials in order to fabricate TCEs. We characterize these materials and analyze their electrical/optical properties as TCEs. Additionally, these fabricated single-material-based TCEs were tested in various lab conditions, and their shortcomings (instability, rigidity, etc.) were highlighted. In order to address these issues, we hybridized the different materials to combine their strengths and compared the properties to single-material based TCEs. The multiple hybridized TCEs have comparable optical/electrical metrics to ITO. The doped-ZnO TCEs exhibit high optical transmittance over 90% in the visible range and low sheet resistance under 200Ω/sq. For CuNW-based composite electrodes, ~ 85% optical transmittance and ~ 25Ω/sq were observed. Meanwhile, the hybridization of materials adds additional features such as flexibility or resistance to corrosion. Finally, as a proof of concept, the CuNW-based composite TCEs were tested in dye-sensitized solar cells (DSSCs), showing similar performance to ITO based samples.
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Gillispie, Meagen Anne. "Metal oxide-based transparent conducting oxides." [Ames, Iowa : Iowa State University], 2006.
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Axelsson, Mathias. "Transparent conductive oxides deposited by magnetron sputtering: synthesis and characterization." Thesis, Uppsala universitet, Fasta tillståndets elektronik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-390150.
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The thesis has dealt with transparent conducting oxide (TCO) materials, with a focus on Al:ZnO and with studies on Sn:In2O3 and ZnO. TCOs are a material group that is used for its properties of being conductive and at the same time transparent. In solar cells, a top layer of TCO is often used to allow light to transmit into the cell and then conduct the resulting current. A set of growth parameters was chosen and optimized through a literature study and experiments. The depositied thin films were characterized by optical and electrical characterization methods. Rf-magnetron-sputtering was used as the deposition method, where the influence of O2, argon and substrate temperature were the parameters to be studied. As a part of the characterization a model for spectroscopic ellipsometry on Al:ZnO was made, enabling faster measurement of transport properties. The main parameter affecting the TCO properties was found to be oxygen flow and the optimum flow value for each material has been determined. Substrate heating did not show any significant improvement on the resistivity of Al:ZnO with a minimum value of ~5.0*10-4 Ωcm while no heating resulted in a value of ~6.0*10-4 Ωcm. These values are comparable to the state-of-the-art from the literature. As a demonstration of application, the developed AZO and ZnO were applied to CIGS solar cells and these were compared to a reference. The newly developed AZO and ZnO was comparable to the reference but a lower mean fill factor indicates that improvements can be made.
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Kim, Joung Youn Ellie. "Nanostructured transparent conducting oxides via blockcopolymer patterning." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245293.
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The aim of this thesis was to develop a new class of TCO material in thin film form, one featuring a mesoporous structure with a 20-40nm length scale. The microphaseseparation of block copolymer was exploited for patterning the TCO materials into this nanostructure. As portable electronics become more widespread and integrated into daily life, and impending energy shortages drive progress towards more efficient and economical photovoltaic technologies, the development of fabrication routes to nanostructured TCO has become a subject of study for many. This thesis concentrates on the development of zinc oxide (ZnO) based materials. One of the more common TCOs, ZnO has many potential applications in piezoelectric devices, organic (and dye-sensitised) photovoltaics, gas sensors, and so on. Unfortunately, nanostructured ZnO has been particularly difficult to realise, due to its rapid crystallisation into wurtzite crystals. Therefore, much of this works focus lies in bypassing the widely recognised problems of creating such a nanostructured material, and its processing into a thin film form useful for many applications. The first chapter of this work reviews the main principles of transparent conducting oxides, trends in past research, and current directions of inquiry. Chapter 2 presents the basic underlying principles of block copolymer self-assembly, and discusses its application to the creation of mesoporous metal oxides. Broadly speaking, there are two different ways to do so either as a sacrificial template, or as a structure guiding agent. Both uses of BCP are demonstrated throughout this work. Chapter 3 describes the experimental methods used in this study, including approaches to film processing as well as characterization techniques. In Chapter 4, a reliable and controllable route to preparing 3D bicontinuous polymeric template is presented, which employs phase separation of block copolymer. Using the templates developed in Chapter 4, two fabrication routes to ZnO based materials are presented in Chapter 5 and 6. In Chapter 5, atomic layer deposition was utilised to realise 3D structures of ZnO with 20-40 nm length scale, exploiting its ability to conformally deposit one layer at a time. These structures include an extremely periodic gyroid structure, as well as a bicontinuous wormlike morphology. This mesoporous ZnO was processed into thin film form, and its use was demonstrated in an inverted P3HT-ZnO hybrid solar cell. In Chapter 6, a solution impregnation approach was explored, using sol gel of a recently developed amorphous TCO material, In-Ga-ZnO. Various thin film processing techniques were explored to arrive at the optimum fabrication route to 3D mesoporous In-Ga-ZnO. Upon electrical and optical characterisation, this material revealed excellent transparency and electrical conductivity even in mesoporous form, exhibiting great potential for use as a transparent electrode. Chapter 7 presents a different approach to the previous chapters, where block copolymer was used not as a template, but as a structure guiding agent to fabricate 3D nanostructured ZnO. Due to its simplicity and elegance, this bottom-up coassembly method has been utilised and well-established for other metal oxide systems, but hardly applied to zinc oxide successfully. The issues of rapid crystallisation were bypassed by first synthesising ZnO nano crystals, and incorporating them into the BCP nano-architecture. Finally, Chapter 8, concludes this work by summarising the re- sults and insights gained, and by presenting some preliminary results for possible future work.
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Reiter, Fernando. "Carbon based nanomaterials as transparent conductive electrodes." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41070.
Full textAbstract:
Optically transparent carbon based nanomaterials including graphene and carbon nanotubes(CNTs) are promising candidates as transparent conductive electrodes due to their high electrical conductivity coupled with high optical transparency, can be flexed several times with minimal deterioration in their electronic properties, and do not require costly high vacuum processing conditions.
CNTs are easily solution processed through the use of surfactants sodium dodecyl sulfate(SDS) and sodium cholate(SC). Allowing CNTs to be deposited onto transparent substrates through vacuum filtration, ultrasonic spray coating, dip coating, spin coating, and inkjet printing. However, surfactants are electrically insulating, limit chemical doping, and increase optical absorption thereby decreasing overall performance of electrodes. Surfactants can be removed through nitric acid treatment and annealing in an inert environment (e.g. argon).
In this thesis, the impact of surfactant removal on electrode performance was investigated. Nitric acid treatment has been shown to p-dope CNTs and remove the surfactant SDS. However, nitric acid p-doping is naturally dedoped with exposure to air, does not completely remove the surfactant SC, and has been shown to damage CNTs by creating defect sites. Annealing at temperatures up to 1000°C is advantageous in that it removes insulating surfactants. However, annealing may also remove surface functional groups that dope CNTs. Therefore, there are competing effects when annealing CNT electrodes. The impacts on electrode performance were investigated through the use of conductive-tip atomic force microscopy, sheet resistance, and transmittance measurements.
In this thesis, the potential of graphene CNT composite electrodes as high performing transparent electrodes was investigated. As-made and annealed graphene oxide CNT composites electrodes were studied. Finally, a chemical vapor deposition grown graphene CNT composite electrode was also studied.
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Book, Martin. "Magnetron sputtering of highly transparent p-conductive NiO thin films." Thesis, Uppsala universitet, Solcellsteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-423322.
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P-type transparent conductors are needed for a wide range of applicationssuch as solar cells and electrochromic smart windows. Solar power is animportant form of energy in today’s society as the threat of global warmingpushes the world towards fossil free energy. Hence a lot of solar cell typeshave been developed, among them tandem cells which are to different typesof solar cells stacked on top of each other. If one of the cells is based ona perovskite, a transparent p-type thin film electrode is needed as a holeconductor and electron blocking layer between the two cells. Nickel oxide(NiO) is a good candidate for this application as it has desired propertiessuch as good hole conduction, a high band gap and a matching work functionto the perovskite. The transmittance of as deposited NiO films by reactivemagnetron sputtered is limited so post deposition annealing is used to increasethe transmittance. This is not possible in this solar cell application as parts ofthe solar cell stack is temperature sensitive.Electrochromic smart windows contain a layer that can change its opticalproperties with the application of a voltage. Such windows are used inbuildings to increase energy efficiency and they contain an electrochromicdevice where NiO is used as an electrode as it has electrochromic properties,but just like with the solar cells, the transmittance of NiO is limited. Thisstudy investigates whether it is possible to make as deposited NiO by reactivemagnetron sputtering transparent, eliminating the need for post depositionannealing. Such a deposition process was found using different sputtermachines with the process point on the edge between metal and oxide modein terms of oxygen flow. This resulted in highly transparent and highlyresistive NiO films with a much higher deposition rate than in oxide mode.
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Shih, Grace Hwei-Pyng. "Nanostructure and Optoelectronic Phenomena in Germanium-Transparent Conductive Oxide (Ge:TCO) Composites." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/228175.
Full textAbstract:
Nanostructured composites are attracting intense interest for electronic and optoelectronic device applications, specifically as active elements in thin film photovoltaic (PV) device architectures. These systems implement fundamentally different concepts of enhancing energy conversion efficiencies compared to those seen in current commercial devices. This is possible through considerable flexibility in the manipulation of device-relevant properties through control of the interplay between the nanostructure and the optoelectronic response. In the present work, inorganic nanocomposites of semiconductor Ge embedded in transparent conductive indium tin oxide (ITO) as well as Ge in zinc oxide (ZnO) were produced by a single step RF-magnetron sputter deposition process.It is shown that, by controlling the design of the nanocomposites as well as heat treatment conditions, decreases in the physical dimensions of Ge nanophase size provided an effective tuning of the optical absorption and charge transport properties. This effect of changes in the optical properties of nanophase semiconductors with respect to size is known as the quantum confinement effect. Variation in the embedding matrix material between ITO and ZnO with corresponding characterization of optoelectronic properties exhibit notable differences in the presence and evolution of an interfacial oxide within these composites. Further studies of interfacial structures were performed using depth-profiling XPS and Raman spectroscopy, while study of the corresponding electronic effects were performed using room temperature and temperature-dependent Hall Effect. Optical absorption was noted to shift to higher onset energies upon heat treatment with a decrease in the observed Ge domain size, indicating quantum confinement effects within these systems. This contrasts to previous investigations that have involved the introduction of nanoscale Ge into insulating, amorphous oxides. Comparison of these different matrix chemistries highlights the overarching role of interfacial structures on quantum-size characteristics. The opportunity to tune the spectral response of these PV materials, via control of semiconductor phase assembly in the nanocomposite, directly impacts the potential for the use of these materials as sensitizing elements for enhanced solar cell conversion efficiency.
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Liu, Yujing. "Nanostructured transparent conducting oxide electrodes through nanoparticle assembly." Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-149076.
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Slocombe, Daniel. "The electrical properties of transparent conducting oxide composites." Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/42932/.
Full textAbstract:
The principal aim of this thesis is the investigation of the electrical properties of conducting pigments provided by Merck KGaA. These pigments are generally micron-sized mica particles coated with a transparent conducting oxide (TCO) and are conventionally dispersed in a polymer matrix at varying volume fractions to form composite structures. To measure the electrical properties of composites and powder materials is not easy since one cannot simply attach terminals as in the measurement of bulk materials. We therefore turn to high frequency techniques, which are capable of measuring composites and powders of conducting particles, but are also capable of measuring non-conducting particles. This thesis therefore has three main themes; 1) the development and use of high frequency measurement techniques for the application to Merck pigments, 2) the investigation of the fundamental electrical properties of TCOs, and 3) the study of the complex electrical behaviour of composites.
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Isherwood, Patrick J. M. "Development of transparent conducting oxides for photovoltaic applications." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/18886.
Full textAbstract:
Metal oxides are a very important class of materials with a wide range of photovoltaic applications. Transparent conducting oxides (TCOs) are the primary front contact materials used in thin film solar cells. Identification of methods for reducing the resistivity of these materials would have significant benefits. Development of p-type TCOs would provide alternative back contact materials and could enable further development of technologies such as bifacial, window and multijunction cells. A series of studies into these areas is presented in this work. Aluminium doped zinc oxide (AZO) is a well-known n-type TCO consisting entirely of Earth-abundant materials. Targets were manufactured from AZO powder, which was synthesised using a patented emulsion detonation process developed by Innovnano S.A. All films showed good optical transmission. Resistivity was found to decrease with both increasing time and temperature up to 300 degree C. Temperatures above 300 degree C were found to be detrimental to film formation, with increasing amounts of damage to the crystal structure and consequent increases in the resistivity. The effect of alloying molybdenum oxide with molybdenum nitride through reactive sputtering in a mixed oxygen-nitrogen atmosphere was investigated. All alloys were found to show p-type behaviour. Resistivity was found to improve with increased nitrogen content, in contrast to optical transmission, which reduced. A selection of compositions were deposited onto CdTe cells as back contacts. These cells showed an increase in efficiency with increasing nitrogen content. Work function was found to increase with increasing oxygen content, but all work functions were low. Resistivity was shown to correlate strongly with efficiency, caused by a corresponding increase in cell voltage. This implies that to form an ohmic contact on CdTe with p-type materials, work function may be less important than resistivity. The copper oxides are p-type, but uses are limited by the narrow band gaps. Cupric oxide was chosen for investigation and for alloying with other oxides with the aim of increasing the band gap. It was found that temperature and deposition environment have significant impacts on sputtered cupric oxide (CuO) films, with low temperatures and high oxygen environments producing the lowest resistivities. Extrinsic sodium doping was found to reduce the resistivity by up to four orders of magnitude. High oxygen content sodium-doped films were found to have carrier concentrations two orders of magnitude higher than that of indium tin oxide.
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Poller, Benjamin [Verfasser]. "Untersuchungen zur Darstellung von Transparent Conducting Oxides / Benjamin Poller." Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2012. http://d-nb.info/1031334726/34.
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Attygalle, Dinesh. "Electrochemical Deposition of Transparent Conducting Oxides for Photovoltaic Applications." Connect to full text in OhioLINK ETD Center, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1229464154.
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Potter, D. "Zinc-based thin films for transparent conducting oxide applications." Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10041886/.
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This thesis describes the synthesis of zinc-based transparent conducting oxide (TCO) thin films, as sustainable alternatives to commercial TCOs. There are two main aims to this work. The first is the discovery of suitable TCO materials, which involves finding the optimum optoelectronic properties for applications in photovoltaic devices. The second aim is investigating the scale up of aerosol assisted chemical vapour deposition (AACVD), which is the technique used to deposit the majority of the films in this work. The films deposited in this work were characterised by X-ray diffraction (XRD) to find the crystal structures, X-ray photoelectron spectroscopy (XPS) to find the elemental compositions, scanning electron microscopy (SEM) to analyse the surface morphologies, UV/vis spectroscopy to find the optical properties, and by Hall effect measurements to find the electrical properties. Aluminium, gallium, indium, silicon, and fluorine have been examined as dopants for ZnO, in various combinations, and at different concentrations. The films were generally found to have high transparency, and electrical properties that approached those of industrial TCO materials. The merits of the films are particularly promising, when considering the relative ease through which the films were synthesised. Additionally, the effect of varying the solvent used to make up the precursor solution is investigated. The deposition of ZnSb2O6 thin films via spin coating is also discussed. This thesis also details an investigation into the scale-up of AACVD. An aerosol transport study was performed, whereby the aerosol was transported prior to deposition. It was found that a considerable amount of aerosol was condensing within the tubing, prior to reaching the reactor. Additionally, increasing the film growth rates was investigated by depositing FTO films using high concentrations in the precursor solution. Growth rates of approximately 2 μm min-1 were achieved, making the use of AACVD for commercial applications significantly more feasible.
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Sam, Francis Laurent Maxime. "Nanometric metal grids as transparent conducting electrodes for OLEDs." Thesis, University of Surrey, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.665498.
Full textAbstract:
Organic light emitting diodes are polymer-based devices which promise higher efficiency and lower cost than other lighting devices, and will enable new applications which were not previously possible. An important component of OLEDs is the transparent conducting electrode (TCE), which is commonly indium tin oxide (ITO). It has a low sheet resistance (15 OD) and a high transmission (87 % on average in the visible wavelength range). However, it is also brittle, expensive and has issues from indium and oxygen migration into the polymer layers of the OLED. There are many alternatives that have been proposed to ITO, one of which is a nanometre thin metal grid. It has been shown to be flexible and if a cheap metal is used, then it can be a low cost solution. The sheet resistance can reach very low levels (e.g. 1 OD), and the transmission can be above 90 %. In this thesis, a thorough study is undertaken to investigate how the grid TCE affects the OLED. The grid TCE was optimised using a computer simulation. Then OLEDs were fabricated on them and characterised to investigate how their performance varies as the grid thickness increases. Surprisingly, it was concluded that the best TeE does not make the best OLED. Several possible reasons for this were considered. Grids with different line spacings were also tested and it was found that if the line spacing was too large, the light emission would not be uniform. To overcome this problem, small spacing grids or hybrid grid TCEs consisting of the metal grid and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) PHIOOO, or regioregular poly(3-hexythiophene) (P3HT) wrapped single-wall carbon nanotubes, were used. The OLEDs fabricated on the hybrid grid OLEDs had a luminance as high as the ITO OLED. These results demonstrated the feasibility of thin metal grids as an alternative for ITO, and will lead to better grid TCE design and optimisation for use in OLEDs.
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Vai, Alex T. "Performance limitations in practical transparent conducting oxide thin films." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:b217b317-5b36-4c9f-b1e5-b21fc65ff07b.
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Zinc oxide (ZnO) has long been advanced as a low cost, earth-abundant transparent conducting oxide (TCO) with potential as a replacement for high-performance, but costly, indium oxide (In2O3) based materials in a wide range of technological applications. However, despite decades of research and development efforts, ZnO-based materials have still failed to displace the incumbents in any large-scale applications. Given the compelling materials cost advantages of ZnO, it is almost certain that its poor adoption is due to deficits in its technical performance. This thesis aims to fulfill the need for systematic, fundamental work to identify and examine the factors that limit TCO performance, and in particular, those that limit ZnO relative to In2O3. Using spray pyrolysis as the primary deposition method, many different series of ZnO and In2O3 films have been prepared and examined using a range of chemical, structural, and optoelectronic characterization techniques. After essential background information on the basic physics and chemistry of TCOs, as well as a detailed discussion of the chosen deposition and characterization methods, three main classes of performance limitations will be covered: 1) those related to the intrinsic properties of electronic transport in crystalline TCO domains, 2) those arising in the course of impurity doping, and 3) those occurring due to grain boundary effects and the polycrystalline nature of thin film TCO samples. Taken together, these results will show that preparing ZnO-based TCOs with performance approaching that of the best In2O3-based materials, while very likely to be technically possible, will almost certainly involve overcoming significant engineering and process development challenges that, importantly, are not required to make high quality In2O3. Ultimately, whether ZnO will ever find significant, real-world use as a TCO will depend on whether the deep differences between ZnO and In2O3 performance limits that will be highlighted and examined in this thesis can be bridged in a practical and cost-effective manner.
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Lemire, Heather M. "Degradation of Transparent Conductive Oxides: Mechanistic Insights and Interfacial Engineering." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1386325661.
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Zhang, Kelvin Hongliang. "Structural and electronic investigations of In₂O₃ nanostructures and thin films grown by molecular beam epitaxy." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:de125918-b36f-47cc-b72d-2f3a27a96488.
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Transparent conducting oxides (TCOs) combine optical transparency in the visible region with a high electrical conductivity. In2O3 doped with Sn (widely, but somewhat misleadingly, known as indium tin oxide or ITO) is at present the most important TCO, with applications in liquid crystal displays, touch screen displays, organic photovoltaics and other optoelectronic devices. Surprisingly, many of its fundamental properties have been the subject of controversy or have until recently remained unknown, including even the nature and magnitude of the bandgap. The technological importance of the material and the renewed interest in its basic physics prompted the research described in this thesis. This thesis aims (i) to establish conditions for the growth of high-quality In2O3 nanostructures and thin films by oxygen plasma assisted molecular beam epitaxy and (ii) to conduct comprehensive investigations on both the surface physics of this material and its structural and electronic properties. It was demonstrated that highly ordered In2O3 nanoislands, nanorods and thin films can be grown epitaxially on (100), (110) and (111) oriented Y-stabilized ZrO2 substrates respectively. The mismatch with this substrate is -1.7%, with the epilayer under tensile strain. On the basis of ab initio density functional theory calculations, it was concluded that the striking influence of substrate orientation on the distinctive growth modes was linked to the fact that the surface energy for the (111) surface is much lower than for either polar (100) or non-polar (110) surfaces. The growth of In2O3(111) thin films was further explored on Y-ZrO2(111) substrates by optimizing the growth temperature and film thickness. Very thin In2O3 epilayers (35 nm) grew pseudomorphically under high tensile strain, caused by the 1.7% lattice mismatch with the substrate. The strain was gradually relaxed with increasing film thickness. High-quality films with a low carrier concentration (5.0 1017 cm-3) and high mobility (73 cm2V-1s-1) were obtained in the thickest films (420 nm) after strain relaxation. The bandgap of the thinnest In2O3 films was around 0.1 eV smaller than that of the bulk material, due to reduction of bonding-antibonding interactions associated with lattice expansion. The high-quality surfaces of the (111) films allowed us to investigate various aspects of the surface structural and electronic properties. The atomic structure of In2O3 (111) surface was determined using a combination of scanning tunnelling microscopy, analysis of intensity/voltage curves in low energy electron diffraction and first-principles ab initio calculations. The (111) termination has an essentially bulk terminated (1 × 1) surface structure, with minor relaxations normal to the surface. Good agreement was found between the experimental surface structure and that derived from ab initio density functional theory calculations. This work emphasises the benefits of a multi-technique approach to determination of surface structure. The electronic properties of In2O3(111) surfaces were probed by synchrotron-based photoemission spectroscopy using photons with energies ranging from the ultraviolet (6 eV) to the hard X-ray regime (6000 eV) to excite the spectra. It has been shown that In2O3 is a highly covalent material, with significant hybridization between O and In orbitals in both the valence and the conduction bands. A pronounced electron accumulation layer presents itself at the surfaces of undoped In2O3 films with very low carrier concentrations, which results from the fact the charge neutrality level of In2O3 lies well above the conduction band minimum. The pronounced electron accumulation associated with a downward band bending in the near surface region creates a confining potential well, which causes the electrons in the conduction band become quantized into two subband states, as observed by angle resolved photoemission spectra (ARPES) Fermi surface mapping. The accumulation of high density of electrons near to the surface region was found to shrink the surface band gap through many body interactions. Finally epitaxial growth of In2O3 thin films on α-Al2O3(0001) substrates was investigated. Both the stable body centred cubic phase and the metastable hexagonal corundum In2O3 phase can be stabilized as epitaxial thin films, despite large mismatches with the substrate. The growth mode involves matching small but different integral multiples of lattice planes of the In2O3 and the substrate in a domain matching epitaxial growth mode.
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Alexandre-Vedrine, Jose. "Electromechanical analysis of transparent conducting substrates for flexible display applications /." View online version; access limited to Brown University users, 2005. http://wwwlib.umi.com/dissertations/fullcit/3174688.
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Dekkers, Jan Matthijn. "Transparent conducting oxides on polymeric substrates by pulsed laser deposition." Enschede : University of Twente [Host], 2007. http://doc.utwente.nl/57879.
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Wang, Dongxin. "Preparation and characterisation of transparent conducting oxides and thin films." Thesis, Loughborough University, 2010. https://dspace.lboro.ac.uk/2134/7042.
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Transparent conducting oxide (TCOs) thin films, including non-stoichiometric tin doped indium oxide (ITO) and aluminium doped zinc oxide (AZO), have found considerable applications in various displays, solar cells, and electrochromic devices, due to their unique combination of high electrical conductivity and optical transparency. TCO thin films are normally fabricated by sputtering, thermal vapour deposition and sol-gel method. Among them, sol-gel processing, which was employed in this project, is no doubt the simplest and cheapest processing method, The main objectives of this project were to produce indium tin oxides (ITO) and zinc aluminium oxides (AZO) nanoparticles with controlled particle size and morphology and to fabricate TCO thin films with high optical transmittance and electrical conductivity. In this research, hydrothermal method was used to synthesise ITO and AZO nanoparticles. Tin oxides, zinc oxides, ITO and AZO particles with the particle size ranging from 10 nm to several micrometers and different morphologies were synthesised through controlling the starting salts, alkaline solvents and hydrothermal treatment conditions. ITO and AZO thin films were fabricated via sol-gel technique through dip coating method. The effects of the starting salts, alkaline solvents, surfactant additives and coating and calcination conditions on the formation of thin films were investigated. XRD, TEM, FEG-SEM, DSC-TGA, UV-Vis spectrometer and four-point probe resistance meter were used to characterise the crystallinity, particle size, morphology, optical transmittance and sheet resistance of the particles and thin films. Crack-free thin films with high optical transmittance (>80% at 550 nm) and low sheet resistances (2.11 kΩ for ITO and 26.4 kΩ for AZO) were obtained in optimised processing conditions.
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Waugh, M. R. "The synthesis, characterisation and application of transparent conducting thin films." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1317817/.
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Transparent conducting thin films of metal oxides, doped metal oxides, and carbon nanotubes (CNTs), have been produced using various deposition techniques, including: Aerosol Assisted Chemical Vapour Deposition (AACVD), Atmospheric Pressure Chemical Vapour Deposition (APCVD), and Spray Coating. The resultant thin films were tested for their performance in a number of applications, including: Low emissivity (‘Low-E’) glazing, photovoltaic electrode materials, gas sensing and photocatalysis. AACVD was shown as a viable, and attractive, deposition technique for the synthesis of tin oxide, and doped tin oxide thin films, which allows for controllable doping levels, crystallinity, and surface structure. The tailoring of these physical attributes allows for enhanced performance of the functional properties of the films, whereby, a lower growth temperature produced highly transparent, highly conductive coatings with a low haze value for ‘Low-E’ applications, whereas, higher growth temperatures produced the high electrical conductivity, transparency, and light scattering properties required for high performance electrodes in thin film photovoltaics. In addition, a dual coating methodology was developed using both AACVD, and APCVD, to grow tin oxide thin films in a rapid timescale, but with modified surface structures showing changes to the short range waviness, kurtosis, and the surface area. Growth of carbon nanotubes, using CVD, was investigated over a range of metal catalysts, with varying Pauling electronegativity values, and over a range of temperature, methane, and hydrogen conditions. A growth mechanism has been postulated, whereby, the electronegativity of the metal catalyst, and the solubility and diffusion of the carbon through that catalyst, affects the type and properties of the carbon structure produced. To the authors knowledge, this is the first reported growth of MWCNTs using a chromium solo-metal catalyst, and the first reported growth of the unique ‘carbon nanofibres’ which were produced using gold and silver metal catalysts. Functionalisation of SWCNTs using a microwave reflux process was shown to yield sulphonate and sulphone modified nanotubes, which are highly soluble in water and able to undergo spray coating to produce carbon nanotube, nanonet transparent conducting thin films. The functionalisation process was shown to be reversible upon heating of the modified nanotubes. AACVD has been deemed unable to produced doped zinc oxide transparent conducting films. However, undoped zinc oxide films were produced. They displayed a high photocatalytic action in the degredation of stearic acid, and a UV light induced superhydrophilicity. The modification and deposition techniques, established throughout this work, were utilised to form transparent, hybrid, metal oxide-CNT coatings, for gas sensing. The hybrid materials displayed enhanced response times to combustible target gases, which has been attributed to the catalytic effects of the exposed carbon nanotube surfaces; and to the spillover of adsorbed oxygen from the active nanotubes to the metal oxide surface.
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Zhu, Zhaozhao, Trent Mankowski, Ali Sehpar Shikoh, Farid Touati, Mohieddine A. Benammar, Masud Mansuripur, and Charles M. Falco. "Ultra-high aspect ratio copper nanowires as transparent conductive electrodes for dye sensitized solar cells." SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622550.
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We report the synthesis of ultra-high aspect ratio copper nanowires (CuNW) and fabrication of CuNW-based transparent conductive electrodes (TCE) with high optical transmittance (> 80%) and excellent sheet resistance (R-s < 30 Omega/sq). These CuNW TCEs are subsequently hybridized with aluminum-doped zinc oxide (AZO) thin-film coatings, or platinum thinfilm coatings, or nickel thin-film coatings. Our hybrid transparent electrodes can replace indium tin oxide (ITO) films in dye-sensitized solar cells (DSSCs) as either anodes or cathodes. We highlight the challenges of integrating bare CuNWs into DSSCs, and demonstrate that hybridization renders the solar cell integrations feasible. The CuNW/AZO-based DSSCs have reasonably good open-circuit voltage (V-oc = 720 mV) and short-circuit current-density (J(sc) = 0.96 mA/cm(2)), which are comparable to what is obtained with an ITO-based DSSC fabricated with a similar process. Our CuNW-Ni based DSSCs exhibit a good open-circuit voltage (V-oc = 782 mV) and a decent short-circuit current (J(sc) = 3.96 mA/cm2), with roughly 1.5% optical-to-electrical conversion efficiency.
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Park, Hyesung Ph D. Massachusetts Institute of Technology. "Application of CVD graphene in organic photovoltaics as transparent conducting electrodes." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/84386.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 184-191).
Graphene, a hexagonal arrangement of carbon atoms forming a one-atom thick planar sheet, has gained much attention due to its remarkable physical properties. Apart from the micromechanical cleavage of highly ordered pyrolytic graphite (HOPG), several alternate methods have been explored to achieve reliable and repeatable synthesis of large-area graphene sheets. Among these, the chemical vapor deposition (CVD) process has been demonstrated as an efficient way of producing continuous, large area graphene films and the synthesis of graphene sheets up to 30-inch has been reported. Similar to graphene research, solar cells based on organic materials have also drawn significant attention as a possible candidate for the generation of clean electricity over conventional inorganic photovoltaics due to the interesting properties of organic semiconductors such as high absorption coefficients, light weight and flexibility, and potentially low-cost, high throughput fabrication processes. Transparent conducting electrodes (TCE) are widely used in organic photovoltaics, and metal oxides such as indium tin oxide (ITO) have been commonly used as window electrodes. Usually used as thin films, these materials require low sheet resistance (Rsh) with high transparency (T). Currently the dominant material used in the industry standard is ITO. However, these materials are not ideal options for organic photovoltaic applications due to several reasons: (1) non-uniform absorption across the visible to near infrared region; (2) chemical instability; (3) metal oxide electrodes easily fracture under large bending, and they are not suitable for flexible solar cell applications; (4) limited availability of indium on the earth leading to increasing costs with time. Therefore, the need for alternative/replacement materials for ITO is ever increasing and ideally need to be developed with the following characteristics: low-cost, mechanically robust, transparent, electrically conductive, and ultimately should demonstrate comparable or better performance compared to ITO-based photovoltaic devices. With superior flexibility and good electrical conductivity, as well as abundance of source material (carbon) at lower costs compared to ITO, in this thesis, we propose that the CVD graphene can be a suitable candidate material as TCE in organic photovoltaic applications, satisfying the aforementioned requirements.
by Hyesung Park.
Ph.D.
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Deyu, Getnet Kacha. "Defect Modulation Doping for Transparent Conducting Oxide Materials." Phd thesis, 2020. https://tuprints.ulb.tu-darmstadt.de/9700/1/Getnet%20Kacha%20Deyu-Ph.D.%20Thesis.pdf.
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The doping of semiconductor materials is a fundamental part of modern technology.
Transparent conducting oxides (TCOs) are a group of semiconductors, which holds the
features of being transparent and electrically conductive. The high electrical conductivity
is usually obtained by typical doping with heterovalent substitutional impurities like in
Sn-doped In2O3 (ITO), fluorine-doped SnO2 (FTO) and Al-doped ZnO (AZO). However,
these classical approaches have in many cases reached their limits both in regard to
achievable charge carrier density, as well as mobility. Modulation doping, a mechanism
that exploits the energy band alignment at an interface between two materials to induce
free charge carriers in one of them, has been shown to avoid the mobility limitation.
However, the carrier density limit cannot be lifted by this approach, as the alignment of
doping limits by intrinsic defects. The goal of this work was to implement the novel
doping strategy for TCO materials. The strategy relies on using of defective wide band
gap materials to dope the surface of the TCO layers, which results Fermi level pinning
at the dopant phase and Fermi level positions outside the doping limit in the TCOs.
The approach is tested by using undoped In2O3, Sn-doped In2O3 and SnO2 as TCO
host phase and Al2O3 and SiO2−x as wide band gap dopant phase.
The study was divided into two parts by the approaches followed experimentally. The
first part deals with a physical approach, in which sputtered TCOs are used as a host
materials and covered with dopant layers. To test the versatility of the approach the
second part deals with a chemical approach, in which SnO2 based nanocomposite films
produced in spray pyrolysis deposition.
In the physical approach, ITO/ALD-Al2O3, In2O3/ALD-Al2O3, and In2O3/sputtered
SiO2−x thin film systems were exploited. The study was conducted mostly by photoelectron
spectroscopy and Hall effect measurements. ITO films prepared in different
conditions showed an increase of conductivity after ALD-Al2O3 deposition at 200 °C.
This was mostly due to an increase in carrier concentrations. However, Al2O3 deposition
also resulted in a chemical reduction of ITO. The diffusivity of compensating oxygen interstitial (Oi) defects at 200 °C is sufficiently screen the high Fermi level induced by Al2O3, which disable the use of defect modulation doping at this temperature. The
results indicate that achieving higher carrier concentration in ITO thin films requires
a control of the oxygen pressure in combination with low-temperature ALD process.
Undoped In2O3 films also showed an increase of conductivity upon deposition of upto
10-cycles of ALD-Al2O3. These increases indicate the occurrence of defect modulation
doping. However, in order to improve the interface properties and firmly prove the
modulation doping effect, more detailed studies required on the doped interfaces. The
approach was further examined by depositing reactively sputtered SiO2−x dopant phase
from Si target on the top of In2O3 films. The resulting conductivity of In2O3/sputtered
SiO2−x do not show enhancement of electrical properties. This is due to the implantation
of oxygen species during SiO2 deposition on the surface of In2O3, which counteract the
defect modulation doping by reducing concentration of oxygen vacancies (VO) in In2O3.
Therefore, further studies on the deposition conditions of the dopant phase is still vital
to see enhanced electrical properties.
In the chemical approach two different routes were followed: embedding nanoparticles
in TCO host matrix and formation of demixed composite films. In the first route,
Al2O3 and TiO2 nanoparticles (NPs) were chosen as dopant phases and were deposited
together with SnO2 TCO precursors. Different characterization of the produced films
do not confirm the presence nanoparticles into tin oxide films. Therefore to realise
modulation effect further optimization deposition conditions and sample preparation
techniques are needed. For the second route, mixture of SnCl4 ·5(H2O) and Al(acac)3
precursor solutions in different composition are used to produce SnO2/Al2O3 demixed
composite films. Different physicochemical studies shows that under the deposition
conditions followed during this study Al3+ preferably substitute Sn4+ than forming
another Al2O3 separated phase. Al was acting as an acceptor doping on SnO2 films.
Therefore, enhanced conductivity was not observed on the probed samples. For this
route further optimization of deposition condition is clearly required.
The results of this dissertation are relevant for the usage of TCOs in the emerging field
of oxide thin film electronics in particular in field where the surface to bulk ratio is much
higher than in conventional films, as the approach is near surface phenomena. However,
further utilization of both the processing conditions and material selection are vital.
38
"Nanoporous Conducting Materials." Doctoral diss., 2012. http://hdl.handle.net/2286/R.I.15115.
Full textAbstract:
abstract: Nanoporous electrically conducting materials can be prepared with high specific pore volumes and surface areas which make them well-suited for a wide variety of technologies including separation, catalysis and owing to their conductivity, energy related applications like solar cells, batteries and capacitors. General synthetic methods for nanoporous conducting materials that exhibit fine property control as well as facility and efficiency in their implementation continue to be highly sought after. Here, general methods for the synthesis of nanoporous conducting materials and their characterization are presented. Antimony-doped tin oxide (ATO), a transparent conducting oxide (TCO), and nanoporous conducting carbon can be prepared through the step-wise synthesis of interpenetrating inorganic/organic networks using well-established sol-gel methodology. The one-pot method produces an inorganic gel first that encompasses a solution of organic precursors. The surface of the inorganic gel subsequently catalyzes the formation of an organic gel network that interpenetrates throughout the inorganic gel network. These mutually supporting gel networks strengthen one another and allow for the use of evaporative drying methods and heat treatments that would usually destroy the porosity of an unsupported gel network. The composite gel is then selectively treated to either remove the organic network to provide a porous inorganic network, as is the case for antimony-doped tin oxide, or the inorganic network can be removed to generate a porous carbon material. The method exhibits flexibility in that the pore structure of the final porous material can be modified through the variation of the synthetic conditions. Additionally, porous carbons of hierarchical pore size distributions can be prepared by using wet alumina gel as a template dispersion medium and as a template itself. Alumina gels exhibit thixotropy, which is the ability of a solid to be sheared to a liquid state and upon removal of the shear force, return to a solid gel state. Alumina gels were prepared and blended with monomer solutions and sacrificial template particles to produce wet gel composites. These composites could then be treated to remove the alumina and template particles to generate hierarchically porous carbon.Dissertation/Thesis
Ph.D. Chemistry 2012
39
"Enhanced Carrier Mobility in Hydrogenated and Amorphous Transparent Conducting Oxides." Doctoral diss., 2020. http://hdl.handle.net/2286/R.I.57380.
Full textAbstract:
abstract: The origins of carrier mobility (μe) were thoroughly investigated in hydrogenated indium oxide (IO:H) and zinc-tin oxide (ZTO) transparent conducting oxide (TCO) thin films. A carrier transport model was developed for IO:H which studied the effects of ionized impurity scattering, polar optical phonon scattering, and grain boundary scattering. Ionized impurity scattering dominated at temperatures below ~240 K. A reduction in scattering charge Z from +2 to +1 as atomic %H increased from ~3 atomic %H to ~5 atomic %H allowed μe to attain >100 cm^2/Vs at ~5 atomic %H.
In highly hydrogenated IO:H, ne significantly decreased as temperature increased from 5 K to 140 K. To probe this unusual behavior, samples were illuminated, then ne, surface work function (WF), and spatially resolved microscopic current mapping were measured and tracked. Large increases in ne and corresponding decreases in WF were observed---these both exhibited slow reversions toward pre-illumination values over 6-12 days. A hydrogen-related defect was proposed as source of the photoexcitation, while a lattice defect diffusion mechanism causes the extended decay. Both arise from an under-coordination of the In.
An enhancement of μe was observed with increasing amorphous fraction in IO:H. An increase in population of corner- and edge-sharing polyhedra consisting of metal cations and oxygen anions is thought to be the origin. This indicates some measure of medium-range order in the amorphous structure, and gives rise to a general principle dictating μe in TCOs---even amorphous TCOs. Testing this principle resulted in observing an enhancement of μe up to 35 cm^2/Vs in amorphous ZTO (a-ZTO), one of the highest reported a-ZTO μe values (at ne > 10^19 cm^-3) to date. These results highlight the role of local distortions and cation coordination in determining the microscopic origins of carrier generation and transport. In addition, the strong likelihood of under-coordination of one cation species leading to high carrier concentrations is proposed. This diverges from the historical indictment of oxygen vacancies controlling carrier population in crystalline oxides, which by definition cannot occur in amorphous systems, and provides a framework to discuss key structural descriptors in these disordered phase materials.Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2020
40
Peng, Yen-chun, and 彭彥鈞. "Zinc Oxide as Transparent Conductive Material from First Principles Analysis." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/32145363935128155397.
Full textAbstract:
碩士明志科技大學
材料工程研究所
100
In this work, the properties of electrical and optical in ZnO and GZO (Ga-doped ZnO)will be studied from first-principle. In GGA+Ud+Up method, The calculated band gap and lattice parameter of pure ZnO are 3.37 eV and 3.258 Å , which are good with the experiments. The calculated band structures of substitutional and interstitial Ga-doped ZnO show that the interstitial Ga atom will be generated deep level in band gap, which will significantly decrease the transmittance in the visible light region. Comparing with the pure ZnO, transmittance decrease from 89.2% to 59.0(Gai(oct) ) or 66.1%(Gai(tet) ). When the doping concentration from 1.4 to 25.0 at%, the optical band gap are increased with impurities states of CBM. However, the occupied states is displayed delocalization at 12.5 at% doping concentration. In contrast, the concentration of 25.0 at% will be become localized state, which show that the free carries mobility are decrease. The optical propurties show that the average transmittance are maintained more than 90% when doping concentration from 1.4 to 6.2 at%. However, the high doping concentration will strongly reduce transmittance because of large carries absorption.The research of GZO with nature defects found that the VZn and Oi easy to form at O-rich condition. And the contribution of acceptor levels which kill Ga donors. Although all the band gap narrowing(3.0 and 2.88 eV) and maintained high ransmittance, but the larger energy barrier cannot excited free electrons form valence band to conduction band. In addition, the analysis of PDOS show that the states of localized O-2p will be decreased free carries mobility.
41
"Zinc Oxide Transparent Thin Films For Optoelectronics." Doctoral diss., 2010. http://hdl.handle.net/2286/R.I.8636.
Full textAbstract:
abstract: The object of this body of work is to study the properties and suitability of zinc oxide thin films with a view to engineering them for optoelectronics applications, making them a cheap and effective alternative to indium tin oxide (ITO), the most used transparent conducting oxides in the industry. Initially, a study was undertaken to examine the behavior of silver contacts to ZnO and ITO during thermal processing, a step frequently used in materials processing in optoelectronics. The second study involved an attempt to improve the conductivity of ZnO films by inserting a thin copper layer between two ZnO layers. The Hall resistivity of the films was as low as 6.9×10-5 -cm with a carrier concentration of 1.2×1022 cm-3 at the optimum copper layer thickness. The physics of conduction in the films has been examined. In order to improve the average visible transmittance, we replaced the copper layer with gold. The films were then found to undergo a seven orders of magnitude drop in effective resistivity from 200 -cm to 5.2×10-5 -cm The films have an average transmittance between 75% and 85% depending upon the gold thickness, and a peak transmittance of up to 93%. The best Haacke figure of merit was 15.1×10-3 . Finally, to test the multilayer transparent electrodes on a device, ZnO/Au/ZnO (ZAZ) electrodes were evaluated as transparent electrodes for organic light-emitting devices (OLEDs). The electrodes exhibited substantially enhanced conductivity (about 8×10-5 -cm) over conventional indium tin oxide (ITO) electrodes (about 3.2×10-5 -cm). OLEDs fabricated with the ZAZ electrodes showed reduced leakage compared to control OLEDs on ITO and reduced ohmic losses at high current densities. At a luminance of 25000 cd/m2, the lum/W efficiency of the ZAZ electrode based device improved by 5% compared to the device on ITO. A normalized intensity graph of the colour output from the green OLEDs shows that ZAZ electrodes allow for a broader spectral output in the green wavelength region of peak photopic sensitivity compared to ITO. The results have implications for electrode choice in display technology.Dissertation/Thesis
Ph.D. Materials Science and Engineering 2010
42
"Resistivity and Optical Transmittance Simulation on Metal Embedded Transparent Conducting Oxide Thin Films." Master's thesis, 2012. http://hdl.handle.net/2286/R.I.14668.
Full textAbstract:
abstract: This work focuses on simulation of electrical resistivity and optical behaviors of thin films, where an Ag or Au thin layer is embedded in zinc oxide. Enhanced conductivity and transparency were earlier achieved with multilayer structured transparent conducting oxide (TCO) sandwich layer with metal (TCO/metal/TCO). Sputtering pattern of metal layer is simulated to obtain the morphology, covered area fraction, and the percolation strength. The resistivity as a function of the metal layer thickness fits the modeled trend of covered area fraction beyond the percolation threshold. This result not only presents the robustness of the simulation, but also demonstrates the influence of metal morphology in multilayer structure. Effective medium coefficients are defined from the coverage and percolation strength to obtain simulated optical transmittance which matches experimental observation. The coherence of resistivity and optical transmittance validates the simulation of the sputtered pattern and the incorporation of percolation theory in the model.Dissertation/Thesis
M.S. Materials Science and Engineering 2012
43
Nam, Nguyen Giang, and 阮江南. "Development of ZnO:Ga Transparent Conducting Oxide Thin Films through Metalorganic Chemical Vapor Deposition using various Zn and Ga Source Materials." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/13434547698757893589.
Full textAbstract:
博士國立臺灣科技大學
化學工程系
101
The Ga doped-ZnO (GZO) thin film has been demonstrated to have low resistivity and high transparency in the visible spectral range and that is considered as one of the most promising transparent conducting oxide (TCO) for the next generation of transparent electrode materials. There is still much to be explored and understood about main factor that significantly affect to the properties as well as the cost of GZO film growth process before it can be commercially realized. Most notably, the influence of the type of source materials have surprisingly been received less attention, even though the type of sources actually play critically role not only the quality but also the cost of thin films. In this dissertation, we have developed of GZO TCO thin films through metalorganic chemical vapor deposition (MOCVD) using various Zn source materials. We also explored the methodology to increase the light diffuse transmittance through controlling the preferred orientation of polycrystalline GZO films by MOCVD technique using diethyl zinc (DEZn) as the Zn and trimethylgallium (TMG) as a Ga precursor. We prepared Ga-doped ZnO (GZO) films with qualified opto-electric properties through chemical vapor deposition of an inexpensive solution of DEZn in n-hexane (ca. 17 wt.%). The GZO films exhibited low resistivity (3.61 ?e 10–4 Ω cm) and high transmittance (85%) in the visible range. Interestingly, post-annealing treatment of the GZO films under N2 at 525 °C for just 10 min increased the number of carbon-interstitial oxygen defects (CZn+2Oi)〃, which played the role of acceptors and enhanced the film properties significantly. This approach potentially allows the fabrication of inexpensive transparent conducting oxides for use in solar cells. Moreover, we also explored the methodology to increase the light diffuse transmittance through controlling the preferred orientation of polycrystalline GZO films grown by the low-pressure chemical vapor deposition (LPCVD) technique. X-ray diffraction measurement indicated that major growth direction was (002) plane and secondary electron microscopy showed that column-like granule structure with planar surface was formed. By depositing a low temperature ZnO layer to serve as a template for high temperature GZO film growth, the main preferred orientation of the GZO films was manipulated to (110) plane and the film surface to the pyramid-like structure. Through this two-step growth, the light diffuse transmittance of the film with a GZO (800 nm)/ZnO (766 nm) combination exhibited 13% increase at 420 nm wavelength due to the preservation of the pyramidal surface morphology.
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Neves, Nuno Miguel Pinto. "Al-doped ZnO ceramic sputtering targets based on nanocrystalline powders produced by emulsion detonation synthesis – deposition and application as a transparent conductive oxide material." Doctoral thesis, 2015. http://hdl.handle.net/10362/16474.
Full textAbstract:
Transparent conducting oxides (TCOs) have been largely used in the optoelectronic industry due to their singular combination of low electrical resistivity and high optical transmittance. They are usually deposited by magnetron sputtering systems being applied in several devices, specifically thin film solar cells (TFSCs). Sputtering targets are crucial components of the sputtering process, with many of the sputtered films properties dependent on the targets characteristics.
The present thesis focuses on the development of high quality conductive Al-doped ZnO (AZO) ceramic sputtering targets based on nanostructured powders produced by emulsion detonation synthesis method (EDSM), and their application as a TCO. In this sense, the influence of several processing parameters was investigated from the targets raw-materials synthesis to the application of sputtered films in optoelectronic devices.
The optimized manufactured AZO targets present a final density above 99 % with controlled grain size, an homogeneous microstructure with a well dispersed ZnAl2O4 spinel phase, and electrical resistivities of ~4 × 10-4 Ωcm independently on the Al-doping level among 0.5 and 2.0 wt. % Al2O3. Sintering conditions proved to have a great influence on the properties of the targets and their performance as a sputtering target. It was demonstrated that both deposition process and final properties of the films are related with the targets characteristics, which in turn depends on the initial powder properties.
In parallel, the influence of several deposition parameters in the film´s properties sputtered from these targets was investigated. The sputtered AZO TCOs showed electrical properties at room temperature that are superior to simple oxides and comparable to a reference TCO – indium tin oxide (ITO), namely low electrical resistivity of 5.45 × 10-4 Ωcm, high carrier mobility (29.4 cm2V-1s-1), and high charge carrier concentration (3.97 × 1020 cm-3), and also average transmittance in the visible region > 80 %. These superior properties allowed their successful application in different optoelectronic devices.
45
Liao, Yen-chao, and 廖彥超. "Study on the current distribution of GaN light emitting diodes with and without current blocking layer and different transparent-conductive-layer material and thicknesses." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/e9fg5j.
Full textAbstract:
碩士國立臺灣科技大學
電子工程系
99
To produce higher light-output power by improving non-uniform current distribution of GaN light emitting diodes (LED) has been one of the major endeavors in LED industry. When a sapphire substrate is used as a LED substrate, p-type and n-type electrodes should be located on the same side of the chip because the sapphire substrate does not conduct electricity. As a result, the current tends to crowd as it flows laterally from p-type electrode to n-type electrode, which affects light quantum efficiency. From Hall measurement, we know p-GaN sheet resistance is much larger than n-GaN and ITO transparent conductive layer(TCL), so the current flow is divided between n-type GaN layer and the ITO transparent conductive layer. In this study, the researcher used current blocking layer(CBL) and different TCL material and thicknesses to produce light-emitting diodes. And by changing the current distribution, the light output power was changed. The researcher measured and compared I-V and L-I curves of various devices and recorded their illumination distribution to characterize their current spreading lengths and the effects. Before adding p-pad electrode, we clearly observed the effect of current blocking layer, the light output power compared to LED without CBL was improved by 25%. In addition, by increasing the thickness or decreasing the resistivity of transparent conductive layer, the sheet resistance became smaller and thus the current spreading length was increased, the contact resistance was reduced, and the illumination area was increased.
46
"Investigation of the Evolution of Conduction Mechanism in Metal on Transparent Conductive Oxides Thin Film System." Master's thesis, 2012. http://hdl.handle.net/2286/R.I.14949.
Full textAbstract:
abstract: This thesis discusses the evolution of conduction mechanism in the silver (Ag) on zinc oxide (ZnO) thin film system with respect to the Ag morphology. As a plausible substitute for indium tin oxide (ITO), TCO/Metal/TCO (TMT) structure has received a lot of attentions as a prospective ITO substitute due to its low resistivity and desirable transmittance. However, the detailed conduction mechanism is not fully understood. In an attempt to investigate the conduction mechanism of the ZnO/Ag/ZnO thin film system with respect to the Ag microstructure, the top ZnO layer is removed, which offers a better view of Ag morphology by using scanning electron microscopy (SEM). With 2 nm thick Ag layer, it is seen that the Ag forms discrete islands with small islands size (r), but large separation (s); also the effective resistivity of the system is extremely high. This regime is designated as dielectric zone. In this regime, thermionic emission and activated tunneling conduction mechanisms are considered. Based on simulations, when "s" was beyond 6 nm, thermionic emission dominates; with "s" less than 6 nm, activated tunneling is the dominating mechanism. As the Ag thickness increases, the individual islands coalesce and Ag clusters are formed. At certain Ag thickness, there are one or several Ag clusters that percolate the ZnO film, and the effective resistivity of the system exhibits a tremendous drop simultaneously, because the conducting electrons do not need to overcome huge ZnO barrier to transport. This is recognized as percolation zone. As the Ag thickness grows, Ag film becomes more continuous and there are no individual islands left on the surface. The effective resistivity decreases and is comparable to the characteristics of metallic materials, so this regime is categorized as metallic zone. The simulation of the Ag thin film resistivity is performed in terms of Ag thickness, and the experimental data fits the simulation well, which supports the proposed models. Hall measurement and four point probe measurement are carried out to characterize the electrical properties of the thin film system.Dissertation/Thesis
M.S. Materials Science and Engineering 2012
47
Huang, Yuan-Li, and 黃元利. "Preparation and characterization of carbon materials based transparent conductive film." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/46757357981635152687.
Full textAbstract:
博士國立清華大學
化學工程學系
100
The objectives of this research are the preparation and characterization of transparent conductive films (TCFs) by utilizing Multi-walled carbon nanotubes and graphene. There are five parts in this dissertation. The first part of this dissertation discusses the optically transparent and electrically conductive thin films composed of multi-walled carbon nanotube (MWCNT) reinforced polymethyl methacrylate/acrylic acid (PMMA/AA) which were fabricated using a wire coating technique. Poly(acrylic acid) controls the dispersibility of MWCNT in aqueous mixtures and retains the well-dispersion of MWCNT in the polymer matrix after solidification resulted from extended polymer chains by adjusting the pH value. It causes the lower surface electrical resistance at the same MWCNT content. The second part of this dissertation used Poly (acrylic acid) and Poly (N-vinyl pyrrolidone) as adhesion promoters to improve MWCNT coating significantly. The cross-linked polymer resulted in a better bond between the MWCNTs and substrates. The surface electrical resistance showed significantly lower than that of the original sheet after nitric acid (HNO3) treatment. The lower electrical resistance of PVP/PAA-g-MWCNT conductive films on the PET substrate was due to more complete conductive paths with the cross-linked polymer. Such the electrical resistance was enhanced from 8.83x104Ω/□ to 2.65x103Ω/□ with 0.90mg/cm2 PVP/PAA-g-MWCNT content deposited on the PET after acid treatment. The third part examines the intercalation reaction of graphite oxide (GO) with poly (acryl amide)/poly (acrylic acid) (PMA) as a method to control the spacing between GOs. The intercalated polymer chains of poly (acrylic acid) between GNSs efficiently inhibit GNS aggregation and restacking. The PMA grafted GNS (NE-PMA-GNS) composite films show the lowest sheet resistance of 2.11×102 Ω□-1, which is one order of magnitude less than that without grafting polymer (NE-GNS, 1.86×103 Ω□-1). The fourth part developes a simple method to assemble graphite oxide (GO) densely onto the electrospun (ES) Nylon 66 nanofibrous membranes, used as a guide for the deposition of graphene nanosheets (GNS) conductive networks for preparing the TCFs. The main advantage of this technique by comparison with previous methods is that graphene does not form a uniform coating, but a percolated conductive network is existed, when guided by Nylon 66 nanofiber templates. A low surface coverage of the transparent substrate by GNS resulted in high transmittance. The resulting PVP-GO material could adsorb well on Nylon 66 nanofibers due to stronger hydrogen bond. The TCF optical transmittance was improved after thermal annealing at 350°C above the Nylon 66 melting point. A fused film, obtained after electrospinning Nylon 66 solution for 120 s, and immersing in 0.050 wt% PVP-GO solution, exhibiting a surface resistance of 8.6 × 103 Ω/□, while maintaining 88% light transmittance. The fifth part demonstrates a simple method of integrating hybrid thin films consisted of graphene nanosheets (GNS) and silver nanoparticles (AgNps) via in situ chemical reduction (AgNps-GNS) for preparing the TCFs. In order to obtain conductive films without compromising much on transmittance, the polyurethane (PU) nanofibers were introduced as guides to build the two-dimensional conductive networks of AgNps-GNS. By taking the advantage of the flexible mechanical property of GNS and great conductivity of AgNps, the potential application of hybrid AgNps-GNS as a highly flexible and transparent conductive thin film was demonstrated. A fused film, obtained after electrospinning PU solution for 120 s, and immersing in 0.05 wt% AgNps-GNS (5:1) solution, exhibits a surface resistance of 150 Ω/□, while maintaining 85 % light transmittance.
48
Chu, Yu Hsuan, and 朱佑軒. "Utilize co-precipitation method to prepare transparent conductive titanium-doped indium oxide materials and preparation of RF-Sputtered transparent conductive thin films." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/85177379373660598611.
Full textAbstract:
碩士長庚大學
化工與材料工程學系
100
The objective of this research are to prepare powders of titanium-doped zinc oxide (ITiO) by co-precipitation method, to produce ITiO targets through ceramic processing using these powders, and to deposit transparent conducting ITiOthin films by RF magnetron sputtering. In addition, the effects of the amount of titanium dopant in the ITiO targets as well as other sputtering parameters on the structural, electrical and optical properties. Finally, we are going to utilize ITiO thin films on CIGS solar cell element, and the impacts of ITiO materials on photoelectric effect are also investigated. From the experimental results, we found that the properties of the ITiO materials were sensitive to the conditions in the co-precipitation process. Polycrystalline ITiO powders were synthesized by calcining the precursors co-precipitated at pH=7 the processes of filtering, washing and drying. ITiO targets with relative density 95.54% and electrical resistivity 3.4×〖10〗^(-4) Ωcm were obtained by sintering the ITiO green bodies made from these ITiO powders through the processes of granulation, dry pressing andde-waxing. The optical transmittance and electrical resistivityof the ITiO thin films deposited using 1wt% titanium containing targets at the conditions of substrate temperature 250oC, working pressure 3×〖10〗^(-3)torr, working gas flow rate, and sputtering power 80W were 72.95% and around 2.72×〖10〗^(-4) Ωcm Eventually, CIGS sloar cell element was deposited using 2wt% titanium containing targets at the conditions of substrate temperature 150oC, working pressure 3×〖10〗^(-3)torr, working gas flow rate, and sputtering power 80W. Then, the efficiencyη=8.323% which iscrried out by photovoltaic conversion instrument .
49
Lin, Yin-Chih, and 林盈志. "Preparation and Characterization of Transparent Conducting Oxide." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/24784789539743148298.
Full textAbstract:
碩士國立清華大學
物理學系
95
Transparent Conducting thin film is a remarkable thin film, it has application of solar cell and TFT-LCD. Indium Tin oxide is a important material of TCO. In the experiment,We choose new coating method-Pulse Arc deposition (PAD). It generates ultrahigh current desity to improve the quality of thin film at room temperature. Beside, We find the best coating condition by different bias and different target component. And use Four Point Probe,Hall measurement,AFM,SEM,XRD and spectrometer to measure it . We try to account of optical and electric properties , and drew conclustion from experimental data.
50
陳安琪. "The study of multilayer transparent conducting films." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/47795891022673918975.
Full textAbstract:
碩士輔仁大學
物理學系
91
ITO/Ag/ITO,TiO2/Ag/ITO multilayer and ITO single layers were prepared by RF-magnetron sputtering with different oxygen concentrations of the sputtering atmosphere during the ITO deposition. The multilayer showed a high optical transmittance and good electrical conductivity. With a 19nm intermediate silver layer an ITO/Ag/ITO sheet resistance of 4Ω/□ and a high optical transmittance of 95% at 502nm was achieved. With a 19nm intermediate silver layer an TiO2/Ag/ITO sheet resistance of 5.8Ω/□ and a high optical transmittance of 93% at 568nm was achieved. It could satisfy the requirement for the flat panel display.