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1
Selzer, Franz. "Transparent Electrodes for Organic Solar Cells." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-199652.
Full textAbstract:
The aim of this work was to investigate silver nanowire as well as carbon nanotube networks as transparent conducting electrodes for small molecule organic solar cells.
In the framework of the nanowire investigations, a low-temperature method at less than 80 °C is developed to obtain highly conductive networks directly after the deposition and without post-processing. In detail, specific non-conductive organic materials act as a matrix where the nanowires are embedded in such that a mutual attraction based on capillary forces and hydrophobic interaction is created. This process is mediated by the ethanol contained in the nanowire dispersion and works only for sublayer materials which exhibit hydrophobic and hydrophilic groups at the same time. In contrast to high-temperature processed reference electrodes (210 °C for 90 min) without matrix, a slightly lower sheet resistance of 10.8 Ohm/sq at a transparency of 80.4 % (including substrate) is obtained by using polyvinylpyrrolidone as the sublayer material. In comparison to annealed silver nanowire networks, the novel approach yields a performance enhancement in corresponding organic solar cells which can compete with ITO-based devices.
Furthermore, a novel approach for scalable, highly conductive, and transparent silver nanowire top-electrodes for organic optoelectronic devices is introduced. By utilizing a perfluorinated methacrylate as stabilizer, silver nanowires with high aspect ratio can be transferred into inert solvents which do not dissolve most organic compounds making this modified dispersion compatible with small molecule and polymer-based organic optoelectronic devices. The inert silver nanowire dispersion yields highly performing top-electrodes with a sheet resistance of 10.0 Ohm/sq at 80.0 % transparency (including substrate) directly after low-temperature deposition at 30 °C and without further post-processing. In comparison to similarly prepared reference devices comprising a thin-metal film as transparent top-electrode, reasonable power conversion efficiencies are demonstrated by spray-coating this dispersion directly on simple, air-exposed small molecule-based organic solar cells.
Moreover, a deeper understanding of the percolation behavior of silver nanowire networks has been achieved. Herein, direct measurements of the basic network parameters, including the wire-to-wire junction resistance and the resistance of a single nanowire of pristine and annealed networks have been carried out for the first time. By putting the values into a simulation routine, a good accordance between measurement and simulation is achieved. Thus, an examination of the electrical limit of the nanowire system used in this work can be realized by extrapolating the junction resistance down to zero. The annealed silver nanowires are fairly close to the limit with a theoretical enhancement range of only 20 % (common absolute sheet resistance of approximately 10 Ohm/sq) such that a significant performance improvement is only expected by an enlargement of the nanowire length or by the implementation of new network geometries.
In addition, carbon nanotube networks are investigated as alternative network-type, transparent bottom-electrode for organic small molecule solar cells. For that purpose, cleaning and structuring as well as planarization procedures are developed and optimized which maintain the optoelectronic performance of the carbon nanotube electrodes. Furthermore, a hybrid electrode consisting of silver nanowires covered with carbon nanotubes is fabricated yielding organic solar cells with only 0.47 % power conversion efficiency. In contrast, optimized electrodes comprising only carbon nanotubes show significantly higher efficiency. In comparison to identically prepared ITO devices, comparable or lower power conversion efficiencies of 3.96 % (in p-i-n stack), 4.83 % (in cascade cell) as well as 4.81 % (in p-n-i-p architecture) are demonstrated. For an inverted n-i-p stack design, the highest power conversion efficiency of 5.42 % is achieved.
2
Kinner, Lukas. "Flexible transparent electrodes for optoelectronic devices." Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/22419.
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Transparente Elektroden (TE) sind unverzichtbar in modernen optoelektronischen Bauelementen. Die derzeitig am häufigsten verwendete TE ist Indium Zinn Oxid (ITO). Aufgrund der Nachteile von ITO setzt sich die vorliegende Arbeit mit ITO-Alternativen auseinander. Zwei Ansätze werden in dieser Arbeit untersucht. Der erste Ansatz beruht auf Dielektrikum/Metall/Dielektrikum (DMD) Filmen, im zweites Ansatz werden Silber Nanodrähten (NW) als TE untersucht. Im ersten Ansatz wurden DMD Elektroden auf Glas und Polyethylenterephthalat (PET) fabriziert. Eine Kombination von gesputterten TiOx/Ag/AZO Schichten lieferte die höchste jemals gemessene Transmission und Leitfähigkeit für eine Elektrode auf Glas und PET. Eine durchschnittliche Transmission größer als 85 % (inklusive Substrat) im Bereich von 400-700 nm und einen Schichtwiderstand von unter 6 Ω/sq wurden erreicht. Um die Leistung der TiOx/Ag/AZO Elektrode in einem Bauteil zu überprüfen, wurde sie in einer organischen Licht emittierenden Diode (OLED) implementiert. Die DMD-basierten OLEDs erreichten eine 30 % höhere Strom Effizienz auf Glas und eine 260 % höhere Strom Effizienz auf PET im Unterschied zu den ITO-basierten Bauteilen. Im zweiten Ansatz zur Realisierung flexibler transparenter Elektroden wurden NWs diskutiert. Die Implementierung von Nanodrähten in lösungsprozessierten organischen Licht emittierenden Dioden weißt noch immer zwei große Hürden auf: hohe Rauigkeit der Nanodrahtfilme und Wärmeempfindlichkeit von PET. Um die Rauigkeit zu verkleinern und gleichzeitig die Stabilität zu erhöhen werden zunächst die Nanodrähte in ein UV-härtendes Polymer eingebettet. Es wird eine Transmission von bis zu 80 % (inklusive Substrat) und ein Schichtwiderstand von 13 Ω/sq erreicht. Gleich wie bei den DMD Elektroden wurden auch NW Elektroden in eine OLED implementiert. Die Bauteile zeigten eine größere Flexibilität, Leitfähigkeit und Luminanz als die PET/ITO Referenzen während die selbe Leistungseffizienz erreicht wurde.Transparent electrodes (TEs) are a key element in optoelectronics. TEs assure simultaneous light interaction with the active device layers and efficient charge carrier injection or extraction. The most widely used TE in today’s industry is indium tin oxide (ITO). However, there are downsides to the use of ITO. The scope of this thesis is to discuss alternatives to ITO. Two main approaches are examined in this thesis - one approach is based on using dielectric/metal/dielectric (DMD) films and the other is based on using silver nanowire (NW) films. For the first approach, a combination of sputtered TiOx/Ag/AZO was found to yield the highest transmittance and conductivity ever reported for an electrode on PET with an average transmittance larger than 85 % (including the substrate) in the range 400-700 nm and sheet resistance below 6 Ω/sq. To test the device performance of TiOx/Ag/AZO, DMD electrodes were implemented in organic light emitting diodes (OLEDs). DMD-based devices achieve up to 260 % higher efficacy on PET, as compared to the ITO-based reference devices. As a second approach, NWs were investigated. The implementation of silver nanowires as TEs in solution processed organic light emitting diodes still faces two major challenges: high roughness of nanowire films and heat sensitivity of PET. Therefore, within this thesis, an embedding process with different variations is elaborated to obtain highly conductive and transparent electrodes of NWs on flexible PET substrates. The NWs are embedded into a UV-curable polymer, to reduce the electrode roughness and to enhance its stability. A a transmittance of 80 % (including the substrate) and sheet resistance of 13 Ω/sq is achieved.
3
Reiter, Fernando. "Carbon based nanomaterials as transparent conductive electrodes." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41070.
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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.
4
Schubert, Sylvio. "Transparent top electrodes for organic solar cells." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-162670.
Full textAbstract:
Organic solar cells offer attractive properties for novel applications and continuous advances in material and concept development have led to significant improvements in device performance. To exploit their full potential (roll-to-roll production of flexible and top-illuminated devices, using e.g. opaque metal foil or textile as substrate), highly transparent, conductive, mechanically flexible, and cost-efficient top electrodes are of great importance. The current standard material indium tin oxide (ITO) is rigid, expensive and requires a high energy / high temperature deposition process, limiting ITO (and other transparent conductive oxides) to bottom electrode applications.
This work presents fundamental investigations to understand and control the properties of transparent conductors and documents four different approaches to prepare transparent electrodes on top of efficient small molecule organic solar cells, with the aim to replace ITO. Fullerene C60 layers are investigated as completely carbon-based electrodes. For an optimized doping concentration, sheet resistance and transmittance are improved and efficient solar cells are realized. Since the lateral charge transport is still limited, a combination with a microstructured conductor is suggested.
Pulsed laser deposition allows for the first time a damage-free preparation of gallium doped zinc oxide (ZnO:Ga) layers on top of organic devices by careful optimization of the deposition atmosphere. ZnO:Ga electrodes with a transmittance of Tvis = 82.7 % and sheet resistance Rs = 83 Ohm/sq are obtained. The formation of local shunts due to ZnO:Ga droplets is identified and then prevented by a shadow mask between the target and the sample, enabling solar cells with similar efficiency (2.9 %) compared to a reference device using a state-of-the-art metal top contact.
Another very promising alternative are intrinsically flexible, ultra-thin silver layers. By introducing an oxide interlayer, the adverse interpenetration of silver and organic materials is prevented and the charge extraction from the solar cells is improved. With a second oxide layer on top, the silver electrode is significantly stabilized, leading to an increased solar cell lifetime of 4500 h (factor of 107). Scanning electron micrographs of Ag thin films reveal a poor wetting on organic and oxide substrates, which strongly limits the electrode performance. However, it is significantly improved by a 1 nm thin seed layer. An optimized Au/Ag film reaches Tvis = 78.1 % and Rs = 19 Ohm/sq, superior to ITO.
Finally, silver electrodes blended with calcium show a unique microstructure which enables unusually high transmittance (84.3 % at 27.3 Ohm/sq) even above the expectations from bulk material properties and thin film optics. Such values have not been reached for transparent electrodes on top of organic material so far. Solar cells with a Ca:Ag top electrode achieve an efficiency of 7.2 %, which exceeds the 6.9 % of bottom-illuminated reference cells with conventional ITO electrodes and defines a new world record for top-illuminated organic solar cells. With these electrodes, semi-transparent and large-area devices, as well as devices on opaque and flexible substrates are successfully prepared. In summary, it is shown that ZnO:Ga and thin metal electrodes can replace ITO and fill the lack of high performance top electrodes. Moreover, the introduced concepts are not restricted to specific solar cell architectures or organic compounds but are widely applicable for a variety of organic devices.
5
Song, Yi Ph D. Massachusetts Institute of Technology. "Graphene as transparent electrodes for solar cells." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/112027.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 133-142).
The aim of this thesis is to develop an understanding of the science and engineering in applying chemical vapor deposition (CVD) graphene as the transparent conductor in photovoltaic devices. Transparent conducting oxides currently dominate the transparent conductor market but suffer drawbacks that make them unsuitable certain applications. Graphene is mechanically robust, chemically inert, and has work function that can be tuned by chemical doping, making it a versatile substitute that is compatible many types of devices. We start by demonstrating a scalable method for directly transferring graphene onto a variety of substrates and exploring a doping method that vastly enhances the conductivity of graphene films. These developments improve the attractiveness of CVD graphene for transparent electrode applications. Next, we apply graphene to various types of devices to assess key advantages and challenges. We develop an understanding of the importance of the interface in graphene/silicon Schottky barrier solar cells and apply our understanding to achieve record efficiency in these devices. We also explore graphene/SrTiO₃ Schottky junctions, where the graphene itself is responsible for absorbing visible light and show that these devices can be used as tunable photodetectors. We demonstrate highly-transparent organic solar cells with all-graphene electrode as well as inkjet-printed perovskite solar cells with graphene electrodes. Finally, we use graphene/perovskite Schottky barrier solar cells to gain a better understanding of carrier dynamics in perovskite films.
by Yi Song.
Ph. D.
6
Boscarino, Stefano. "Ultra-thin transparent electrodes for energy applications." Doctoral thesis, Università di Catania, 2015. http://hdl.handle.net/10761/1723.
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Due to the unique feature of being contemporarily optically transparent and electrically conducting, Transparent Conductive Oxides (TCOs) play a fundamental role in many technologies: communications, information, energy, buildings. Up to now, the most diffused material in the TCO s family was indium tin oxide (ITO), especially for large-area applications such as flat panel displays. Recently, the increasing expansion of the display market and, even more, of photovoltaics, are endangered by the scarcity and rising price of indium. This is one of the reasons and a strong motivation for searching alternative transparent electrodes, not necessarily oxides, to replace ITO. Moreover, in order to meet the expectations for the growing demand and lower production costs for photovoltaic and electronic applications, new TCOs, or equivalent materials, must be abundant, not expensive and very thin, so to be suitable for flexible electronics. Among new transparent electrodes candidates, Aluminium-doped zinc oxide (AZO) films and very thin multilayers of AZO/Ag/AZO have emerged as a very promising alternative . In particular, AZO films are Indium-free and show electro-optical properties comparable to ITO films of the same thickness (700-900 nm for industrial applications), especially after thermal annealing at 250 °C. On the other hand, AZO/Ag/AZO multilayer structures, 10 times thinner than ITO or AZO single layers, show very high transparency and low resistivity even at room temperature. Replacing thick TCO layers with thin TCO/Ag/TCO multilayers would produce great benefits in terms of material consumption, cost, toxicity and flexibility (a mandatory point for the development of the electronics on plastic). In this context, it is important the study and understanding of the fundamental properties of these materials, the process conditions and post fabrication treatments to optimize their application to different fields. Transparent conductive materials are known since about 100 years and represent one of the strategic topics for the actual industrial research, but still many fundamental properties and mechanisms need to be clarified and explained. Aim of this work is the fabrication, processing and characterization of ultra-thin AZO and TCO/Ag/TCO transparent electrodes. The study focused on the optimization of structural, optical and electrical properties for application in photovoltaics. The thesis is organized as follows. Chapter 1 introduces TCOs and covers the conventional and non materials history, properties, applications and market. Chapter 2 starts with a comprehensive and detailed study about thick AZO grown by RF magnetron sputtering films on glass substrates, focusing on the influence of sputtering process parameters, i.e. power, temperature substrate, and thermal treatment (during or after the deposition) on the film properties. After the work on thick AZO, we report the modification of optical, electrical and structural properties of very thin films (60 nm) upon ion irradiation with different ion type (O+ or Ar+ ions) and energy (30 and 350 keV) at different ion doses (3, 10, 30E15ions/cm-2), before and after thermal treatments up to 400°C. Chapter 3 treats of very thin TCO/Ag/TCO multilayer structures grown by RF magnetron sputtering. Synthesis and properties of AZO/Ag/AZO multilayers as a function of Ag film thickness, with a fixed AZO thickness (~20 nm), are investigated. Then, we studied multilayers with fixed Ag thickness(~10 nm), but different combinations of AZO and ITO as top and bottom TCO layers. Chapter 4 describes the compatibility of the AZO/Ag/AZO multilayers with one of the most important steps for the implementation in thin film photovoltaic technology: laser scribing. AZO/Ag/AZO multilayers must be able to guarantee the same level of TCO reliability under laser scribing processes. In this study, we used a single nanosecond laser pulse to irradiate AZO/Ag/AZO deposited on glass.
7
Tomita, Yuto. "Alternative transparent electrodes for organic light emitting diodes." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1236711483222-35217.
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Solid state lighting is a new environmentally friendly light source. So far, light emitting diodes (LEDs) and organic LEDs (OLEDs) have been presented as candidates with potentially high efficiency. Recent advances of OLEDs in device architecture, light-out coupling, and materials have ensured high efficiency, exceeding that of incandescent light bulbs. In contrast to conventional point source LEDs, OLEDs distribute light throughout the surface area and are not restricted by their size. Additionally, OLEDs are expected to reach sufficient stability in the near future. The remaining challenge for OLEDs is their cost. New OLED technologies provide cost effective manufacturing methods which could be presented for transparent electrode materials because indium tin oxide (ITO), a widely used material as a transparent electrode for OLEDs, is less than optimal due to its high element price. In this work, alternative transparent electrodes for OLEDs as a replacement of ITO were studied. First, Al doped ZnO (ZnO:Al) which is composed of abundant materials was investigated with DC magnetron sputtering under a wide range of experimental conditions. The optimised ZnO:Al received comparable performance with conventional ITO films, low sheet resistance of 22.8 Ω/sq as well as a high transparency of 93.1 % (average value in the visible range). Various type of p-i-n OLEDs were employed on the structured ZnO:Al using photolithography. Green OLEDs with double emission layers have been archived stable efficiencies even at higher luminance. Also, OLEDs using two fluorescent colour system on ZnO:Al anode showed a purely white emission. It has been found that the OLEDs on ZnO:Al anode has comparable or better device efficiencies and operational lifetime compared to OLEDs on conventional ITO anode. As another alternative electrode, the conductive polymer Baytron®PH510 (PEDOT:PSS) was investigated. Due to a relatively high sheet resistance of PEDOT:PSS, metal grid was designed for large size OLEDs. White OLEDs on PEDOT anode with a size of 5 × 5 cm2 have achieved more than 10 lm/W of power efficiency using a scattering foil. Furthermore, up-scaled devices on 10 × 10 cm2 were also demonstrated. These results showed ZnO:Al and PEDOT are suitable for OLEDs as anode and have high potential as alternative transparent electrode materials.
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Ghosh, Dhriti Sundar. "Ultrathin metal transparent electrodes for the optoelectronics industry." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/285839.
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Transparent electrodes (TEs) are the essential elements of many optoelectronic devices such as solar cells, touch screens, organic LEDs, and LCDs. Consequently demand for TEs is growing very steeply and the market value presently stands at 8 billion USDs. The state-of-art indium tin oxide (ITO) has an excellent trade-off between optical transparency and electrical sheet resistance but suffers from several drawbacks, mainly the increasing cost due to indium shortage, and inadequate flexibility due to poor mechanical ductility.
This thesis presents the development of a new class of TEs based on ultrathin metal films (UTMFs). The work started from understanding the fundamental aspects of UTMF growth and properties, and then focused on different UTMF based geometries, composition, and combination for potential applications in different optoelectronic applications.
Single component ultrathin Ni and Cr films were shown to possess significantly high transparency in the ultraviolet (175–400 nm) and mid-infrared
(2.5–25 μm) regions making them viable TE for devices such as UV photodiodes, and IR pyroelectric detectors. The natural oxidation process, which is a major concern for metal films, has been exploited to achieve stable metallic films by inducing a protective oxide layer.
In another proposed novel design, incorporating an ad hoc conductive grid, the sheet resistance of UTMFs can be reduced by more than two orders of magnitude with negligible loss in transparency, which in turn eliminates the inverse trade-off relationship between optical transparency and electrical conductivity of continuous metal based TEs.
A TE structure based on the ultrathin conductive Cu films with an application specific functionalized capping layer of Ti or Ni layer has been demonstrated. The properties of the TE can be tuned accordingly and show excellent stability against temperature, and oxidation. The suitability of Ag-Cu alloy films as TE as an alternative to ITO has been also investigated. The optical spectrum of such alloy films follows the average optical behavior of single component Cu and Ag layers, thus resulting in a much flatter optical response in the visible region.
UTMFs combined with Al doped ZnO (AZO), which is possible ITO replacement, has also been demonstrated to show the possibility of hybridizing the two technologies. A bilayer Ag/AZO has been developed which can overcome the high reflection of metals and retain their good electrical behavior, while maintaining a minimum total film thickness. In another structure, UTMF capping layer were used to improve the stability of AZO. It was found that an ultrathin oxidized Ni capping layer with a thickness at percolation threshold greatly enhances the stability of AZO layer in harsh environment without affecting the electro-optical propertiesLos electrodos transparentes (TEs) son elementos básicos de muchos dispositivos optoelectrónicos, tales como células solares, pantallas táctiles, LEDs orgánicos i LCDs. En consecuencia, la demanda de éstos TEs está creciendo paulatinamente y con un valor de mercado actual de 8 billones de dólares (USD). El estado del arte del óxido de estaño dopado con Indio (ITO) ofrece un excelente compromiso entre transparencia óptica y resistencia eléctrica de hoja pero también tiene inconvenientes, principalmente de precio debido a la escasez del Indio, así como de una inadecuada flexibilidad debida a una baja ductilidad mecánica. En esta tesis se presenta el desarrollo de una nueva clase de TEs basados en capas ultradelgadas de metales (UTMFs). El trabajo empieza des de la comprensión de los aspectos fundamentales relacionados con el crecimiento de los UTMF y sus propiedades, para luego focalizarse en diferentes geometrías, composición y combinaciones para diferentes aplicaciones potenciales en el campo de la optoelectrónica. Las capas ultradelgadas monocomponentes de Ni y de Cr han mostrado tener significativamente alta transparencia en el rango ultravioleta (175-380nm) y en el Infrarrojo mediano (2.5-25um), haciéndolos, por tanto, TE viables para dispositivos tales como fotodiodos de UV y detectores piroeléctricos del IR. El proceso natural de oxidación, el cual es un problema central para las capas metálicas, ha sido aprovechado para conseguir capas metálicas estables gracias a una capa protectora de óxido. En otro novedoso diseño, gracias a la incorporación ad hoc de una malla conductora, la resistencia eléctrica de hoja de los UTMFs puede ser disminuida hasta dos órdenes de magnitud y con una pérdida de transmisión despreciable, y por lo tanto, elimina el compromiso limitante entre transparencia óptica y conductividad eléctrica de los TE basados en capas metálicas continuas. Una estructura de los TEs, basada en una capa conductora ultradelgada de Cu, la cual puede ser funcionalizada para aplicaciones específicas con capas protectoras de Ti o Ni, ha sido demostrada. Las propiedades del TE pueden ser modificadas bajo control y muestran una excelente estabilidad a la temperatura y la oxidación. La idoneidad de la aleación Ag-Cu como capa alternativa al ITO para los TE ha sido también investigada. El espectro óptico de esta aleación sigue el comportamiento óptico medio de las capas monocomponentes de Ag y Cu, y por lo tanto se obtiene una respuesta óptica mucho mas plana en la región del espectro visible. Los UTMFs en combinación con ZnO dopado con Al (AZO), el cual es una opción factible como sustituto del ITO, ha demostrado la posibilidad de hibridar ambas tecnologías. Una bicapa de Ag/AZO ha sido desarrollada, la cual evita el problema de la alta reflexión de los metales y mantiene a su vez sus buenas propiedades eléctricas con un espesor total de capa mínimo. En otra estructura, la capa protectora de los UTMF ha sido utilizada para mejorar la estabilidad del AZO. Se ha visto que una capa protectora ultra-delgada y oxidada de Ni con un espesor igual a su límite de percolación, mejora notablemente la estabilidad de las capas de AZO, manteniendo sus propiedades electro-ópticas, incluso en condiciones severas
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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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Kinner, Lukas [Verfasser]. "Flexible transparent electrodes for optoelectronic devices / Lukas Kinner." Berlin : Humboldt-Universität zu Berlin, 2021. http://d-nb.info/1228333432/34.
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Tomita, Yuto. "Alternative transparent electrodes for organic light emitting diodes." Doctoral thesis, Technische Universität Dresden, 2008. https://tud.qucosa.de/id/qucosa%3A23806.
Full textAbstract:
Solid state lighting is a new environmentally friendly light source. So far, light emitting diodes (LEDs) and organic LEDs (OLEDs) have been presented as candidates with potentially high efficiency. Recent advances of OLEDs in device architecture, light-out coupling, and materials have ensured high efficiency, exceeding that of incandescent light bulbs. In contrast to conventional point source LEDs, OLEDs distribute light throughout the surface area and are not restricted by their size. Additionally, OLEDs are expected to reach sufficient stability in the near future. The remaining challenge for OLEDs is their cost. New OLED technologies provide cost effective manufacturing methods which could be presented for transparent electrode materials because indium tin oxide (ITO), a widely used material as a transparent electrode for OLEDs, is less than optimal due to its high element price. In this work, alternative transparent electrodes for OLEDs as a replacement of ITO were studied. First, Al doped ZnO (ZnO:Al) which is composed of abundant materials was investigated with DC magnetron sputtering under a wide range of experimental conditions. The optimised ZnO:Al received comparable performance with conventional ITO films, low sheet resistance of 22.8 Ω/sq as well as a high transparency of 93.1 % (average value in the visible range). Various type of p-i-n OLEDs were employed on the structured ZnO:Al using photolithography. Green OLEDs with double emission layers have been archived stable efficiencies even at higher luminance. Also, OLEDs using two fluorescent colour system on ZnO:Al anode showed a purely white emission. It has been found that the OLEDs on ZnO:Al anode has comparable or better device efficiencies and operational lifetime compared to OLEDs on conventional ITO anode. As another alternative electrode, the conductive polymer Baytron®PH510 (PEDOT:PSS) was investigated. Due to a relatively high sheet resistance of PEDOT:PSS, metal grid was designed for large size OLEDs. White OLEDs on PEDOT anode with a size of 5 × 5 cm2 have achieved more than 10 lm/W of power efficiency using a scattering foil. Furthermore, up-scaled devices on 10 × 10 cm2 were also demonstrated. These results showed ZnO:Al and PEDOT are suitable for OLEDs as anode and have high potential as alternative transparent electrode materials.
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He, Tianda. "Electrospun Nanofibers and Their Applications in Transparent Electrodes." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1396876037.
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Habis, Christelle. "Development of ZnO-FTO nanocomposites for the use in transparent conductive thin films." Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0192.
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Cette thèse s'inscrit dans le cadre de développement de couches d'oxyde transparentes avec des techniques à faible cout, basées sur des matériaux non polluants permettant de fonctionnaliser des dispositifs opérationnels efficace, donc à haut rendement pour la production d'énergies renouvelables. Notre choix s'est porté plus particulièrement sur l'étude des couches TCO à base d'étain et dopés au fluor, F :SnO2, dénommées FTO pour « Fluor Tin Oxydes ». Les FTO sont des oxydes à large bande interdite, à l'instar du ZnO, TiO2, Al2O3, purs ou dopés. Ces couches possèdent en principe un facteur de diffusion, défini précédemment, élevé afin d'améliorer le chemin optique et l'absorption. De plus, la texture optique des TCO peut être facilement contrôlée par dépôt de suspensions de nanostructures avant le dépôt de la couche. Généralement, ces nanostructures sont des nanoparticules voire nano-fils de carbone ou nano-fils métalliques (argent, cuivre, …) et plus récemment des nano-fils de TiO2 (présentant l'inconvénient de l'élément titane) ou de ZnO non-dopés qui diminuent, malheureusement la conductivité du fait de l'augmentation de la résistance d'interface avec la concentration des nanoparticules. C'est pourquoi, nous proposons l'étude de couches de FTO, pures et également en présence de nanofibres de ZnO et ZnO:Al par électrofilage à partir d'une solution à base de PVA afin d'avoir une couche nanostructuré ayant des propriétés de transparence et de conductivité électrique améliorées pour être intégrer comme électrodes transparentes dans les cellules photovoltaïques, répondant aux critères performatifs définis ci-dessus. Les croissances des couches seront suivies par des études morphologiques et structurales, en utilisant des techniques de caractérisations disponibles au sein du laboratoire LMOPS et de l'Université de Lorraine ( tel que: MEB, Raman, EDX, DRX, spectroscopie UV-vis, ATG, AFM, profilomètre). Enfin, les propriétés électriques et optiques, en particulier l'absorption et le facteur de Haze, seront aussi largement investies sur les couches sélectionnées présentant les meilleures propriétés structurales et morphologiqueMy thesis work entitled “Development of ZnO-FTO nanocomposites for the use in transparent conductive thin films” is supervised by Professor Michel Aillerie at University of Lorraine. This work was mainly made at the “Laboratoire des Matériaux Optiques, Photoniques et Systèmes” LMOPS in Centrale Supélec, Metz. Although this work forms a whole in the elaboration of transparent conductive oxides, it is divided into two parts. The first part consists on identifying the properties of bulk materials (ZnO and FTO) deposited in the form of thin film. Whereas, the second part is about the elaboration and characterization of Zinc Oxide (ZnO) and Aluminum doped Zinc Oxide (AZO) nanofibers, then associated to FTO thin films to form nanocomposite. The main objective of this work is to make flexible electrodes using low cost and abundant material, but also improving the optical properties and more specifically the haze factor of the nanocomposite layers.Transparent conductive oxides (TCOs) are technologically significant class of materials extensively used in thin film solar cells due to their ability to transmit light and collect charge carriers. In addition to the fundamental qualities of transparency and conductivity, the TCOs are frequently desired to have a certain degree of surface roughness (i.e., texture) in order to effectively scatter transmitted light into the active materials, therefore lengthen the optical path and, as a result, enhance the performance of the cell and light absorption. This thesis focuses on the development of low-cost fabrication techniques for transparent oxide layers using non-polluting materials to enable the functionalization of operational devices with high efficiency for renewable energy production. The choice was made to study tin-based TCO layers doped with fluorine, F:SnO2, known as FTOs for "Fluor Tin Oxides". FTOs are wide band gap oxides, like ZnO, TiO2, Al2O3, pure or doped. In principle, these layers have a high scattering factor, as defined above, in order to improve the optical path and absorption. In addition, the optical texture of TCOs can be easily controlled by depositing suspensions of nanostructures before the film deposition. Generally, these nanostructures are nanoparticles or even carbon nanowires or metallic nanowires (silver, copper, ...) and more recently nanowires of TiO2 (presenting the disadvantage of the titanium element) or of undoped ZnO which unfortunately decrease the conductivity due to the increase of the interface resistance with the concentration of the nanoparticles.Therefore, we propose the study of FTO thin films, pure and also in the presence of ZnO and AZO nanofibers by electrospinning from a PVA-based solution in order to have a nanostructured layer with improved transparency and electrical conductivity properties to be integrated as transparent electrodes in photovoltaic cells, meeting the performance criteria defined above. With the characterization techniques available in the LMOPS laboratory and the University of Lorraine (SEM, Raman, EDX, DRX, UV-vis Spectro, ATG, AFM, profilometer) the growth will be followed by morphological and structural studies of the layers. Finally, electrical and optical properties, in particular absorption and scattering factor, will also be extensively investigated on selected layers with the best structural and morphological properties and the minimum of interface defects when deposited on a PV structure
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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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Bormann, Jan Ludwig. "Transparent Silver Nanowire Bottom Electrodes in Organic Solar Cells." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-216346.
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Organic solar cells (OSCs) is an emerging photovoltaic technology that opens up new application areas where common inorganic techniques are not able to score. Some of those key features are flexibility, light weight, semitransparency, and low cost processing. The current industry-standard for the transparent electrode, indium tin oxide (ITO), cannot provide these properties because it is brittle and expensive. This thesis aims to investigate an alternative type of promising transparent electrode: silver nanowire (AgNW) networks. They exhibit similar or even better optical and electrical performance than ITO down to a sheet resistance of 12 Ohm/sq at 84% transmission (including the glass substrate). Furthermore, AgNWs are more flexible, solution-processable, and more cost-effective than ITO. However, two challenges occur during implementation as bottom electrode in OSCs. First, their inherently high roughness causes devices to shunt. Second, the AgNW network structure exhibits – in contrast to the continuous ITO – µm²-sized voids that have to be bridged electrically by the organic layers. In the first part of this thesis, solution-processed small molecule charge transport layers are investigated. In the case of hole transport layers (HTL), the host BF-DPB and the dopant NDP9 are investigated using tetrahydrofuran as a solvent. It is shown that BF-DPB is already doped by NDP9 in solution via the formation of a hybrid molecule complex. Solution-processed layers exhibit similar conductivities as compared to the reference deposition, which is thermal evaporation in high vacuum. The layers sufficiently smoothen the AgNW electrode such that DCV5T-Me:C60 organic solar cells with an efficiency up to 4.4% are obtained. Moreover, the influence of the square micrometer large network voids is investigated using HTLs of varying conductivity. As a result, a minimum conductivity of 1e−4 S/cm is needed to avoid macroscopic performance losses. Equivalent circuit simulations are performed to confirm these results. As a second planarization method, the AgNWs are buried in an insulating polymer that serves concurrently as flexible and ultrathin substrate. Out of three different polymers tested, the optical adhesive ’NOA63’ gives the best results. The roughness is strongly reduced from 30 nm down to (2 ± 1) nm. Two different OSC types are employed as testing devices with fully-flexible alumina encapsulation against moisture ingress. Maximum power conversion efficiencies of 5.0% and 5.6% are achieved with a fullerene-free cascade layer architecture and a DCV5T-Me:C60 OSC, respectively. To evaluate the applicability of these fully-flexible and encapsulated devices, degradation studies are performed under continuous illumination and a humid climate. Although employing the intrinsically stable DCV5T-Me:C60 stack design, within one day a fast degradation of the fully-flexible solar cells is observed. The degradation is attributed to AgNW electrode failure that results from photo-oxidation and -sulfurization, photo-migration, and electromigration. It is further shown that the cascade organic solar cell lacks intrinsic stability. In summary, efficient, fully-flexible, and encapsulated devices are shown. However, in terms of competitive OSCs, the low stability of AgNW electrodes is a challenge to be taken care of. In current research, this issue needs to be addressed more frequentlyOrganische Solarzellen (OSZ) sind ein junges Forschungsgebiet der Photovoltaik, welches neue Anwendungsgebiete erschließt, für die herkömmliche anorganische Solarzellen nicht einsetzbar sind. Einige der Haupteigenschaften sind Flexibilität, niedriges Gewicht, Teiltransparenz und geringe Herstellungskosten. Indiumzinnoxid (ITO), der aktuelle Industriestandard transparenter Elektrodentechnologie, ist nicht in der Lage, diese Eigenschaften zu gewährleisten. Dies liegt vor allem an der Brüchigkeit von ITO und der begrenzten Verfügbarkeit von Indium, welche mit einem hohen Preis einhergeht. Das Ziel dieser Dissertation ist die Integration einer alternativen und vielversprechenden Elektrodentechnologie: Netzwerke aus Silbernanodrähten (AgNWs). Mit einem Schichtwiderstand von 12 Ohm/sq bei einer Transmission von 84% (inklusive Glassubstrat) besitzen sie ähnliche oder sogar bessere optische und elektrische Eigenschaften als ITO. Des Weiteren sind AgNW-Elektroden flexibler und kostengünstiger als ITO und aus flüssiger Phase prozessierbar. Es gibt allerdings zwei Herausforderungen, welche die Integration als Grundelektrode in OSZ erschweren. Zum einen sind AgNW-Netzwerke sehr rauh, sodass organische Bauteile kurzgeschlossen werden. Zum anderen weisen AgNW-Elektroden, im Gegensatz zu einer vollflächigen ITO-Schicht, Lücken zwischen den einzelnen Drähten auf. Diese Lücken müssen von den organischen Schichten der OSZ elektrisch überbrückt werden. Im ersten Teil der Arbeit werden daher flüssigprozessierte Ladungsträgertransportschichten aus kleinen Molekülen untersucht, welche die AgNW-Elektroden glätten und die verhältnismäßig großen Lücken füllen sollen. Im Falle von Lochleitschichten (HTL) wird BF-DPB als Matrix und NDP9 als Dotand in Tetrahydrofuran gelöst und zur Anwendung gebracht. BF-DPB wird dabei schon in Lösung von NDP9 dotiert, wobei sich ein Hybridmolekülkomplex ausbildet. Die Leitfähigkeit der entstehenden Schichten ist ähnlich zu Referenzschichten, die durch thermisches Verdampfen im Hochvakuum hergestellt wurden. Die erhaltenen HTLs glätten die AgNW-Elektroden, sodass DCV5T-Me:C60-Solarzellen mit einer Effizienz von maximal 4.4% hergestellt werden können. Weiterhin wird der Einfluss der quadratmikrometergroßen Löcher auf die makroskopische Effizienz der Solarzelle in Abhängigkeit der HTL Leitfähigkeit untersucht. Um signifikante Effizienzverluste zu verhindern, muss der HTL eine minimale Leitfähigkeit von etwa 1e−4 S/cm aufweisen. Simulationen eines Ersatzschaltkreises bestätigen hierbei die experimentellen Ergebnisse. Im zweiten Teil der Arbeit wird eine Planarisierungsmethode untersucht, in welcher die AgNWs in nichtleitfähigen Polymeren eingebettet werden. Diese Polymere fungieren anschließend als flexibles Substrat. Der optische Kleber ”NOA63” erzielt hierbei die besten Ergebnisse. Die Rauheit der AgNW-Elektroden wird von etwa 30 nm auf 1 bis 3 nm stark reduziert. Anschließend werden diese AgNW-Elektroden in zwei unterschiedlichen OSZ Konfigurationen getestet und mit einer vollflexiblen Schicht aus Aluminiumoxid gegen Wasserdampfpermeation verkapselt. Somit können maximale Effizienzen von 5% mithilfe einer organischen Kaskadenstruktur und 5.6% mit DCV5T-Me:C60 OSZ erreicht werden. Um die Anwendbarkeit dieser vollflexiblen und verkapselten OSZ zu bewerten, werden Alterungsstudien unter konstanter Beleuchtung und feuchtem Klima durchgeführt. Es wird gezeigt, dass die in das Polymer eingebettete AgNW-Elektrode aufgrund von Photooxidation und -schwefelung und Photo- und Elektromigration instabil ist. Dieser Sachverhalt ist für die Anwendung von AgNW-Elektroden in kommerziellen OSZ von großer Bedeutung und wurde in der Forschung bisher nicht ausreichend thematisiert
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Yang, Chaobin. "All-Solution-Processed Transparent Conductive Electrodes with Crackle Templates:." Thesis, Boston College, 2019. http://hdl.handle.net/2345/bc-ir:108648.
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Thesis advisor: Michael J. NaughtonIn this dissertation, I first discuss many different kinds of transparent conductors in Chapter one. In Chapter two, I focus on transparent conductors based on crackle temples. I and my colleagues developed three (one sputter-free and two fully all-solution) methods to fabricate metallic networks as transparent conductors. The first kind of all-solution process is based on crackle photolithography and the resulting silver networks outperform all reported experimental values, including having sheet resistance more than an order of magnitude lower than ITO, yet with comparable transmittance. The second kind of all-solution proceed transparent conductor is obtained by integrating crackle photolithography-based microwires with nanowires and electroplate welding. This combination results in scalable film structures that are flexible, indium-free, vacuum-free, lithographic-facility-free, metallic-mask-free, with small domain size, high optical transmittance, and low sheet resistance (one order of magnitude smaller than conventional nanowire-based transparent conductors)
Thesis (PhD) — Boston College, 2019
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Physics
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Lee, Min-Hsuan. "Solution-processable organic-inorganic hybrid transparent electrode for optoelectronic applications." HKBU Institutional Repository, 2016. https://repository.hkbu.edu.hk/etd_oa/320.
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The aim of this PhD thesis is to undertake a comprehensive research to study the optical, electrical, surface electronic and morphologic properties, formulation and surface modification of solution processable organic-inorganic hybrid transparent electrodes as well as their applications in optoelectronic devices. In this study, MoO3 nanoparticles and graphene oxide (GO) nanosheets were incorporated into the poly(3,4-ethylenedioxythiophene) -poly(styrenesulfonate) (PEDOT:PSS) layer forming a hybrid anode interfacial layer (AIL) and subsequently a hybrid transparent electrode of AIL/silver nanowires (AgNWs), significantly improved charge injection in CdSe/ZnS-based quantum dot-light emitting diodes (QD-LEDs) and charge collection in bulk heterojunction (BHJ) organic solar cells (OSCs). The effect of oxidation behavior and charge transfer between PEDOT and MoO3, as well as PEDOT and GO, on the enhancement in conductivity of hybrid PEDOT:PSS-MoO3 and PEDOT:PSS-GO AILs was investigated systematically. The presence of a PEDOT:PSS-MoO3 AIL promotes a good interfacial contact between the hole transporting layer (HTL) and the solution-processed hybrid transparent electrode for efficient operation of QD-LEDs. This work reveals that the use of the hybrid PEDOT:PSS-MoO3 AIL benefits the performance of QD-LEDs in two ways: (1) to assist in efficient hole injection, thereby improving luminous efficiency of QD-LEDs, and (2) to improve electron-hole current balance and suppression of interfacial defects at the QD/electrode interface. The surface wettability of the PEDOT:PSS-MoO3 AIL was controlled successfully for making a good contact between the HTL and the AgNWs, enabling efficient charge injection or charge collection, and thereby improvement in the device performance. The effect of PEDOT:PSS-GO AIL on the performance of transparent QD-LEDs was also analyzed. The maximum brightness of the transparent QD-LEDs, made with a solution-processed hybrid top transparent electrode of PEDOT:PSS-GO/AgNWs, is 3633 cd/m2 at 15 V, comparable to that of a structurally identical control QD-LED made with an evaporated Ag electrode, with a brightness of 4218 cd/m2 operated under the same condition. The change in the hydrophobicity of the PEDOT:PSS-GO AIL, e.g., from the hydrophobic to hydrophilic characteristics, was observed. The interaction between PEDOT and GO nanosheets induces the transition between benzoid-quinoid structures, contributing to the enhanced charge carrier transport via the PEDOT:PSS-GO AIL. The energy level alignment at the HTL/electrode interface and the excellent electrical conductivity of PEDOT:PSS- GO/AgNWs transparent electrode result in an obvious improvement in the performance of QD-LEDs. Transparent QD-LEDs also demonstrated remarkable efficiency via cathode interfacial engineering. Two cathode interfacial modifications include incorporating (1) a hybrid bathophenanthroline (Bphen):Cs2CO3-based electron transporting buffer layer (EBL) and (2) a conjugate polymer of poly[(9,9-bis(3'-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7- fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN-Br)-based EBL. The approach of n-doping effect in the BPhen:Cs2CO3 EBL not only modifies the surface electronic properties of the ZnO electron transporting layer (ETL) but also improves the electron injection at the QD/cathode interface. The n-doping mechanism in the Bphen:Cs2CO3 EBL was investigated. PFN-Br EBL has also been employed to tune the surface work function of ZnO ETL. It was observed that the ZnO/PFN-Br formed an interfacial dipole at the ETL/QD interface, which is suitable for efficient electron injection in the transparent QD-LEDs. In order to improve electron-hole current balance, a GO/MoO3-based multilayer AIL was adopted facilitating efficient charge transfer through improved energy level alignment at the HTL/hybrid electrode interface. Photoelectron spectroscopy revealed tuned surface work function with reduced interfacial barrier for efficient hole injection in transparent QD-LEDs. In these devices, the cathode and anode interfacial modifications have been optimized and studied. This study was also extended to investigate the effect of the organic-inorganic hybrid electrode on performance enhancement of all solution processable organic solar cells (OSCs). The reduction in series resistance and increase in shunt resistance of solution-processed OSCs originated from improved contact selectivity as well as enhanced charge collection efficiency. These properties are reflected in the significantly improved fill factor and short-circuit photocurrent density for the all solution-processed OSCs. Enhanced charge collection at the BHJ/electrode interfaces and improved process compatibility are mainly responsible for efficiency improvement in the cells. The outcomes of this work would allow further advances in device performance. This research also highlights the need to explore interfacial electronic properties and reduce energetic barrier at BHJ/electrode interfaces in fully solution-processed OSCs through photoelectron spectroscopy measurements. The results of this research demonstrate that the solution processable organic-inorganic hybrid transparent electrode developed in this work is beneficial for application in fully solution-processed optoelectronic devices.
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Chari, Tarun. "Reduced graphene oxide based transparent electrodes for organic electronic devices." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104534.
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This thesis explores the utility of reduced graphene oxide and hybrid reduced graphene oxide/single walled carbon nanotubes as a transparent electrode. Graphene oxide was fabricated using the modified Hummers method, transferred to arbitrary substrates by a vacuum filtration method, and reduced chemically and thermally thus creating thin, large area reduced graphene oxide films. Films were characterized electrically, optically, spectroscopically, and topographically. Raman and X-ray photoelectron spectroscopy techniques were utilized to ensure successful fabrication of reduced graphene oxide. The reduced graphene oxide electrodes exhibit sheet resistances on the order of 10 – 100 kΩ/sq with transparencies between 60 – 90 %. To ameliorate these electronic properties, single walled nanotubes were introduced during the filtration process to separate the graphene oxide nanoplatelets and prevent structural deformation during reduction. This nanotube doping yielded a two-fold decrease in sheet resistance for low nanotube to graphene oxide ratios, but increased sheet resistance for higher nanotube to graphene oxide ratios. Reduced graphene oxide electrodes and nanotube/reduced graphene oxide hybrid electrodes were used in organic light emitting diode and organic solar cell applications. Organic light emitting diodes exhibited current efficiencies of about 1 cd/A and organic solar cells exhibited power conversion efficiencies less than 1 % for both reduced graphene oxide and hybrid electrodes.Cette thèse examine l'utilité de l'oxyde de graphène réduit et de l'hybride oxyde de graphène réduit et nanotubes carbone en fonction d'une utilisation comme électrode transparente. L'oxyde de graphène a été fabriqué par la méthode de Hummers modifié puis a été transféré sur un substrat arbitraire par la méthode de filtration avec suction à vide, et a été réduit chimiquement et thermiquement pour créer des feuilles d'oxyde de graphène réduit qui sont minces et qui couvrent une grande surface. Les feuilles ont été caractérisées par des mesures électriques, optiques, spectroscopiques, et topographiques. Les spectroscopies Raman et par photoélectron induits par rayons-X ont été utilisées pour s'assurer que la fabrication de l'oxyde de graphène reduit a été obtenue. Les électrodes d'oxyde de graphène reduit montrent des résistances de feuille de 10– 100 kΩ/sq avec des transparences entre 60 – 90 %. Pour améliorer ces propriétés, des nanotube de carbone monoparois ont été introduits pendant le processus de filtration pour séparer les nanoplatelets d'oxyde de graphène et pour éviter la déformation structurelle pendant la processus de réduction. Ce dopage de nanotubes a diminué la résistance de feuille par un facteur deux pour des proportion faibles de nanotubes avec l'oxyde de graphène, mais a augmenté la resistance pour les hautes proportions. Les électrodes d'oxyde de graphène reduit et les électrodes hybrides nanotubes/oxyde de graphène reduit ont été utilisées dans des dispositifs optoélectroniques organiques; spécialement des diodes électroluminescentes et des cellules solaires. Les diodes électroluminescentes organiques ont des rendements de courant inferieurs à 1 cd/A et les cellules solaire ont des rendements de puissance inferieurs à 1 % pour les deux types d'életrodes: oxyde de graphène réduit et hybrides.
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Wilkins, Ian. "Multilayer composite AZO / AGZO thin films for transparent conductive electrodes." Thesis, Wilkins, Ian (2016) Multilayer composite AZO / AGZO thin films for transparent conductive electrodes. Honours thesis, Murdoch University, 2016. https://researchrepository.murdoch.edu.au/id/eprint/40056/.
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Transparent electronics are an essential ingredient in many new technologies which are emerging in the 21st century - high efficiency solar cells [1, 2], interactive and transparent displays, energy efficient windows, and photonics for communications and computing [3]. The development of transparent conductors which are abundant, cheap and environmentally friendly, is critical for materials science in developing such applications. Specifically, an important research goal is to find substitutes for indium tin oxide (ITO) - the dominant transparent conductive oxide (TCO) material. ITO is a high performing and robust transparent conductor, but it is made from indium which is scarce, expensive and toxic. Zinc oxides doped with small amounts of aluminium (AZO), are promising candidates for such a substitute but generally don’t perform as well as ITO [3]. Gallium co-doping with aluminium improves AZO performance significantly, but raises similar concerns to ITO, in terms of the scarcity and high cost of gallium.
This project aims to enhance the conductivity of AZO thin films, by adding a thin middle layer, co-doped with Ga (AGZO). The project employed the solution based sol-gel technique for synthesising AZO and AGZO nanoparticles, and then deposited composite multi-layered thin films on glass substrates using a spin coating process. The optical properties, crystal structure and morphology of the films were characterised using UV-vis and FTIR spectroscopy, X-ray diffraction and Field Emission Scanning Electron Microscopy. Composite multilayer films were produced with thickness around 320nm, exhibiting transmittance above 90% across the visible range and resistivity approximately 10 Ωcm.
Results indicate significant improvement in AZO films, resulting from the addition of the co-doped AGZO mid-layer. The enhancement in performance recorded, was 4 similar to that found in uniformly doped AGZO films, except that the composite films contained only 20% of the gallium compared with the AGZO films. Due to the high cost of gallium, this presents the potential for significant reduction in the materials cost for TCO thin films.
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Kim, Yong Hyun. "Alternative Electrodes for Organic Optoelectronic Devices." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-113279.
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This work demonstrates an approach to develop low-cost, semi-transparent, long-term stable, and efficient organic photovoltaic (OPV) cells and organic light-emitting diodes (OLEDs) using various alternative electrodes such as conductive polymers, doped ZnO, and carbon nanotubes. Such electrodes are regarded as good candidates to replace the conventional indium tin oxide (ITO) electrode, which is expensive, brittle, and limiting the manufacturing of low-cost, flexible organic devices. First, we report long-term stable, efficient ITO-free OPV cells and transparent OLEDs based on poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) electrodes by using a solvent post-treatment or a structure optimization. In addition, a high performance internal light out-coupling system for white OLEDs based on PEDOT:PSS-coated metal oxide nanostructures is developed. Next, we demonstrate highly efficient ITO-free OPV cells and OLEDs with optimized ZnO electrodes doped with alternative non-metallic elements. The organic devices based on the optimized ZnO electrodes show significantly improved efficiencies compared to devices with standard ITO. Finally, we report semi-transparent OPV cells with free-standing carbon nanotube sheets as transparent top electrodes. The resulting OPV cells exhibit very low leakage currents with good long-term stability. In addition, the combination of various kinds of bottom and top electrodes for semi-transparent and ITO-free OPV cells is investigated. These results demonstrate that alternative electrodes-based OPV cells and OLEDs have a promising future for practical applications in efficient, low-cost, flexible and semi-transparent device manufacturingDie vorliegende Arbeit demonstriert einen Ansatz zur Verwirklichung von kostengünstigen, semi-transparenten, langzeitstabilen und effizienten Organischen Photovoltaik Zellen (OPV) und Organischen Leuchtdioden (OLEDs) durch die Nutzung innovativer Elektrodensysteme. Dazu werden leitfähige Polymere, dotiertes ZnO und Kohlenstoff-Nanoröhrchen eingesetzt. Diese alternativen Elektrodensysteme sind vielversprechende Kandidaten, um das konventionell genutzte Indium-Zinn-Oxid (ITO), welches aufgrund seines hohen Preises und spröden Materialverhaltens einen stark begrenz Faktor bei der Herstellung von kostengünstigen, flexiblen, organischen Bauelementen darstellt, zu ersetzten. Zunächst werden langzeitstabile, effiziente, ITO-freie Solarzellen und transparente OLEDs auf der Basis von Poly(3,4-ethylene-dioxythiophene):Poly(styrenesulfonate) (PEDOT:PSS) Elektroden beschrieben, welche mit Hilfe einer Lösungsmittel-Nachprozessierung und einer Optimierung der Bauelementstruktur hergestellt wurden. Zusätzlich wurde ein leistungsfähiges, internes Lichtauskopplungs-System für weiße OLEDs, basierend auf PEDOT:PSS-beschichteten Metalloxid-Nanostrukturen, entwickelt. Weiterhin werden hoch effiziente, ITO-freie OPV Zellen und OLEDs vorgestellt, bei denen mit verschiedenen nicht-metallischen Elementen dotierte ZnO Elektroden zur Anwendung kamen. Die optimierten ZnO Elektroden bieten im Vergleich zu unserem Laborstandard ITO eine signifikant verbesserte Effizienz. Abschließend werden semi-transparente OPV Zellen mit freistehenden Kohlenstoff-Nanoröhrchen als transparente Top-Elektrode vorgestellt. Die daraus resultierenden Zellen zeigen sehr niedrige Leckströme und eine zufriedenstellende Stabilität. In diesem Zusammenhang wurde auch verschiedene Kombinationen von Elektrodenmaterialen als Top- und Bottom-Elektrode für semi-transparente, ITO-freie OPV Zellen untersucht. Zusammengefasst bestätigen die Resultate, dass OPV und OLEDs basierend auf alternativen Elektroden vielversprechende Eigenschaften für die praktische Anwendung in der Herstellung von effizienten, kostengünstigen, flexiblen und semi-transparenten Bauelement besitzen
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Sankaran, Bharat. "Immobilization of biological matter using transparent metal electrodes and silicon microstructures." Fairfax, VA : George Mason University, 2007. http://hdl.handle.net/1920/2929.
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Thesis (M.S.)--George Mason University, 2007.Title from PDF t.p. (viewed Jan. 22, 2008). Thesis director: V. Rao Mulpuri. Submitted in partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering. Vita: p. 49. Includes bibliographical references (p. 43-48). Also available in print.
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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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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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Sannicolo, Thomas. "Transparent electrodes based on silver nanowire networks : electrical percolation, physical properties, and applications." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAI073/document.
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L’intérêt pour les électrodes transparentes (TEs) concerne un large spectre de domaines technologiques, tels que les dispositifs optoélectroniques (cellules solaires, LEDs, écrans tactiles), les films chauffants transparents, ou les applications électromagnétiques. Les TEs de nouvelle génération auront à combiner à la fois un très haut niveau de conduction électrique, de transparence optique, mais aussi de flexibilité mécanique. L’oxyde d’Indium dopé Etain (ITO) domine actuellement le marché des matériaux transparents conducteurs (TCMs). Cependant, la rareté de l’Indium, combinée à ses faibles performances en flexion mécaniques et ses coûts de fabrication élevés ont orienté les recherches vers des TCMs alternatifs. Les réseaux percolants de nanofils métalliques, en particulier les nanofils d’argent (AgNWs), se sont imposés comme l’une des alternatives les plus sérieuses à l’ITO, en raison de leurs propriétés physiques très attractives. Ces réseaux interconnectés offrent également la possibilité d’utiliser des méthodes de synthèse en voie chimique et d’impression à bas coût, sur de grandes surfaces. De manière générale, les premières estimations concernant les coûts de fabrication sont inférieures à celles de l’ITO. De plus, grâce au très haut facteur de forme des nanofils et à la nature percolante des réseaux, les besoins en quantité de matières premières nécessaires pour atteindre un haut niveau de performance sont moindres.Ce travail de thèse s’intéresse à l’étude des propriétés physiques fondamentales – inexplorées ou non encore suffisamment étudiées – des réseaux d’AgNWs, afin d’améliorer la robustesse, la fiabilité et la compatibilité de ce type d’électrodes avec les critères de performance industriels. La première partie est consacrée à l’étude des méthodes d’optimisation utilisées pour diminuer au mieux la résistance électrique des électrodes. Les mesures électriques in situ effectuées au court d’un recuit thermique et/ou après traitement chimique fournissent de précieuses informations concernant les mécanismes d’activation au niveau des jonctions entre nanofils. A l’échelle du réseau, notre capacité à distinguer les zones qui participent efficacement à la conduction électrique de celles qui seraient potentiellement inactives est un défi majeur. Pour les réseaux dont la densité en nanofils est proche du seuil de percolation, un processus d’activation discontinu de chemins efficaces de percolation à travers le réseau a pu être mis en évidence. De manière générale, l’influence de plusieurs paramètres (densité du réseau, tension, niveau d’optimisation) sur l’homogénéité et la stabilité électrique et thermique des électrodes a été étudiée, à l’aide de techniques de cartographie électrique et de simulations. A tension élevée, un processus d’emballement thermique conduisant à la formation d’une fissure physique à travers un réseau d’AgNWs soumis à des plateaux de tension croissants a pu être détecté visuellement. Des modèles de simulation via les logiciels Matlab et Comsol ont aussi été construits afin de confirmer, voire anticiper, les phénomènes observés expérimentalement. Par ailleurs, encouragés par la demande croissante pour les dispositifs électroniques portatifs en toute circonstance, des tests préliminaires ont été conduit pour évaluer le comportement des réseaux d’AgNWs sous contrainte d’étirement mécanique lorsqu’ils sont transférés sur des substrats élastiques. Ce travail de thèse a également donné lieu à l’intégration de réseaux d’AgNWs dans des dispositifs. Des études ont été menées afin d’améliorer la stabilité des films chauffants transparents à base d’AgNWs et de mieux appréhender les mécanismes favorisant l’émergence de défauts. L’utilisation des réseaux d’AgNWs pour des applications électromagnétiques (antennes, blindage) a également fait l’objet de tentatives préliminaires dont les résultats sont commentés à la fin du manuscritTransparent electrodes attract intense attention in many technological fields, including optoelectronic devices (solar cells, LEDs, touch screens), transparent film heaters (TFHs) and electromagnetic (EM) applications. New generation transparent electrodes are expected to have three main physical properties: high electrical conductivity, high transparency and mechanical flexibility. The most efficient and widely-used transparent conducting material is currently indium tin oxide (ITO). However the scarcity of indium associated with ITO’s lack of flexibility and the relatively high manufacturing costs have prompted search into alternative materials. With their outstanding physical properties, silver nanowire (AgNW)-based percolating networks appear to be one of the most promising alternatives to ITO. They also have several other advantages, such as solution-based processing, and compatibility with large area deposition techniques. First cost estimates are lower for AgNW based technology compared to current ITO fabrication processes. Unlike ITO, AgNW are indeed directly compatible with solution processes, never requiring vacuum conditions. Moreover, due to very large aspect ratio of the NWs, smaller quantities of raw materials are needed to reach industrial performance criteria.The present thesis aims at investigating important physical assets of AgNW networks – unexplored (or not explored enough) so far – in order to increase the robustness, reliability, and industrial compatibility of such technology. This thesis work investigates first optimization methods to decrease the electrical resistance of AgNW networks. In situ electrical measurements performed during thermal ramp annealing and/or chemical treatments provided useful information regarding the activation process at the NW-NW junctions. At the scale of the entire network, our ability to distinguish NW areas taking part in the electrical conduction from inactive areas is a critical issue. In the case where the network density is close to the percolation threshold, a discontinuous activation process of efficient percolating pathways through the network was evidenced, giving rise to a geometrical quantized percolation phenomenon. More generally, the influence of several parameters (networks density, applied voltage, optimization level) on the electrical and thermal homogeneity and stability of AgNW networks is investigated via a dual approach combining electrical mapping techniques and simulations. A thermal runaway process leading to a vertical crack and associated to electrical failure at high voltage could be visually evidenced via in situ electrical mapping of AgNW networks during voltage plateaus. Moreover many efforts using Matlab and Comsol softwares were devoted to construct reliable models able to fit with experimental results. Due to the increasing demand for portable and wearable electronics, preliminary tests were also conducted to investigate the stretching capability of AgNW networks when transferred to elastomeric substrates. Finally, integrations of AgNW networks in several devices were performed. Specifically, studies were conducted to understand the mechanisms leading to failure in AgNW-based transparent film heaters, and to improve their overall stability. Preliminary investigations of the benefits of incorporating of AgNW networks into electromagnetic devices such as antennas and EM shielding devices are also discussed at the end of the manuscript
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Jackson, Roderick Kinte'. "Development of single wall carbon nanotube transparent conductive electrodes for organic electronics." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/29635.
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Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Graham, Samuel; Committee Member: Garimella, Srinivas; Committee Member: Kippelen, Bernard; Committee Member: Melkote, Shreyes; Committee Member: Ready, Jud. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Morselli, Serena. "Thermally reduced Graphene Oxide: a well promising way to transparent flexible electrodes." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9324/.
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L'elaborato tratta dell'ottimizzazione del processo di riduzione termica dell'ossido di grafene in termini di conduttività e trasmittanza ottica. Definiti gli standard di deposizione tramite spin-coating e riduzione termica, i film prodotti vengono caratterizzati tramite XPS, AFM, UPS, TGA, ne vengono testate la conducibilità, con e senza effetto di gate, e la trasmittanza ottica, ne si misura l'elasticità tramite spettroscopia di forza, tutto al fine di comprendere l'evoluzione del processo termico di riduzione e di individuare i parametri migliori al fine di progredire verso la produzione di elettrodi flessibili e trasparenti a base di grafen ossido ridotto.
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Müller, Vesna. "Mesoporous transparent conducting films of antimony doped tin oxide as nanostructured electrodes." Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-158995.
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Langley, Daniel. "Silver nanowire networks : effects of percolation and thermal annealing on physical properties." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI054/document.
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L'utilisation de matériaux conducteurs transparents (TCM) a rapidement augmenté au cours des deux dernières décennies en raison de la demande croissante liée à l'usage d'appareils électroniques personnels ainsi qu'au développement de cellules solaires à base de couches minces. Jusqu'à présent, le TCM le plus couramment utilisé a été l'oxyde d'indium et d'étain (ITO), mais l'indium est une terre rare dont l'environnement géopolitique lié à son approvisionnement et à sa production est complexe. En outre, la famille des oxydes transparents conducteurs possèdent de médiocres propriétés mécaniques (associée à une fragilité mécanique) et exige souvent pour leur dépôt soit une synthèse à haute température (> 400 ° C) soit des procédés sous vide. Pour ces raisons, la recherche au cours des dernières années a mis l'accent sur la recherche de TCM alternatifs afin de remplacer l'ITO. Cette thèse s'ancre sur une double approche combinant simulations numériques et des expériences pour explorer le dépôt et l'optimisation des réseaux de nanofils d'argent pour une utilisation comme électrode transparente d'une part et d'améliorer la compréhension de leurs propriétés physiques d'autre part. L'approche par simulation concerne la modélisation de la percolation de réseaux de nanofils 2D tandis que la composante expérimentale explore les propriétés électriques et optiques des réseaux de nanofils d'argent et notamment le comportement de la résistance électrique lors de recuits thermiques. Nous présentons dans ce travail la modélisation 2D de la percolation de systèmes initialement composés de bâtonnets parfaits au sein d'un réseau idéal, puis l'étude de l'influence de paramètres tels que: la distribution des longueurs de bâtonnets, des distributions angulaires ou de la courbure de ces bâtonnets. Nous nous sommes aussi intéressés à la divergence de la densité critique nécessaire pour observer la percolation au sein de systèmes de petite taille (vis-à-vis de la longueur des bâtonnets). Par ailleurs un travail préliminaire sur la simulation de l'efficacité de collecte (ou d'injection) de charges par un réseau de nanofils est présenté. Le volet expérimental fournit une analyse de l'influence de la longueur des fils, de leur diamètre, de la densité du réseau et enfin de la méthode de dépôt sur les propriétés optiques et électriques des réseaux de nanofils d'argent. Une étude approfondie de l'effet de recuit thermique sur les propriétés des réseaux a été réalisée qui a révélé plusieurs mécanismes qui sont à l'origine de la diminution initiale de la résistance électrique à relativement basse température puis la divergence de la résistance électrique observée à haute température. Une observation originale a permis de révéler un phénomène de percolation géométrique quantifiée pour les réseaux peu denses qui a été associé à la présence de chemins efficaces de percolation indépendants. Ce travail permet de conclure que les réseaux de nanofils d'argent constituent une solution intéressante pour une utilisation comme électrode transparente en remplacement de l'ITO ; notamment car ils ont des propriétés mécaniques supérieures et peuvent atteindre des propriétés électro-optiques comparables voire même supérieuresThe use of transparent conductive materials (TCMs) has rapidly increased in the last two decades as a result of increasing demand for personal electronic devices and the development of thin film based solar cells. To date the most commonly used TCM is indium tin oxide (ITO), however indium is a rare earth metal with a complex geopolitical environment surrounding its supply and production. Furthermore the oxide family suffers from poor mechanical properties such as brittleness and generally requires either high temperature synthesis (>400°C) or vacuum processes for their deposition. For these reasons, research in recent years has focused on searching for a TCM to replace ITO. This thesis uses a dual approach combining simulations and experiments to explore the fabrication and optimisation of silver nanowire networks for use as a TCM and to improve the understanding of their physical properties. The simulation component focuses on the application of percolation modelling to 2D nanowire networks while the experimental component explores the electrical and optical properties of silver nanowire networks and their electrical behaviour under thermal annealing. We present in this work the modelling of 2D stick percolation systems initially composed of perfect idealised sticks, and then investigate the influence of parameters such as: length distributions, angular distributions or curved nanowires. We address the divergence of the critical density for the onset of percolation observed for small system sizes and introduce some preliminary work on simulating the collection (or injection) efficiency of charges by a nanowire network. The experimental component provides a discussion of the impact of wire length, wire diameter, network density and fabrication technique on the optical and electrical properties of silver nanowire networks. An in-depth study of the effect of thermal annealing on the networks properties was undertaken which revealed several mechanisms that were responsible for the initial reduction of resistance and final loss of conductivity observed. An original observation enables the revelation of geometrical quantized percolation for rather sparse networks. Finally we conclude that silver nanowire networks are an excellent prospect for a TCM to replace ITO, they have superior mechanical properties and can achieve comparable and even superior electro optical properties
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Marikkar, Fathima Saneeha. "Molecular Design of Electrode Surfaces and Interfaces: For Optimized Charge Transfer at Transparent Conducting Oxide Electrodes and Spectroelectrochemical Sensing." Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/193952.
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This dissertation has focused on i) optimizing charge transfer rates at indium-tinoxide (ITO) electrodes, and ii) characterization of the supramolecular structure and properties of ultra thin surface modifier films on modified electrodes for various device applications. Commercial ITO surfaces were modified using conducting polymer thin film architectures with and without various chemical activation procedures. Ferrocene derivatives were used as redox probes, which showed dramatic changes in electron transfer rate as the SA-PANI/PAA layers were added to the ITO surface. Highest rates of electron transfer were observed for DMFc, whose oxidation potential coincides with the potential region where these SA-PANI/PAA films reach their optimal electroactivity. Apparent heterogeneous electron transfer rate constants, kS, measured voltammetrically, were ca.10 x higher for SA-PANI/PAA films on ITO, versus clean ITO substrates. These films also showed linear potentiometric responses with retention of the ITO transparency with the capability to create smoothest films using an aqueous deposition protocol, which proved important in other applications. ITO electrodes were also modified via chemisorption of carboxy functionalized EDOTCA and electropolymerization of PEDOTCA/PEDOT copolymers, when properly optimized for thickness and structure, enhance voltammetrically determined electron transfer rates (kS) to solution probe molecules, such as dimethylferrocene (DMFc). Values of kS ≥ 0.4 cm•sec⁻¹, were determined, approaching rates seen on clean gold surfaces. ITO activation combined with formation of these co-polymer films has the effect of enhancing the electroactive fraction of electrode surface, versus a non-activated, unmodified ITO electrode, which acts as a “blocked” electrode. The electroactivity and spectroelectrochemistry of these films helped to resolve the electron transfer rate mechanism and enabled the construction of models in combination with AFM, XPS, UPS and RAIRS studies. The surface topography, structure, composition, work function and contact angle, also revealed other desirable properties for molecular electronic devices. The carboxylic functionality of the EDOTCA molecule adds more desirable properties compared to normal PEDOT films, such as favoring the deposition of smooth films, increasing the optical contrast, participating in hydrogen-bonding, chemisorption to oxide surface, self-doping and providing a linker for incorporation of different functional groups, new molecules, or nanoparticles. Periodic sub-micron electrode arrays can be created using micro-contact printing and electropolymerization. The sinusoidal modulation of the refractive index of such confined conducting polymer nanostructures or nanoparticle stripes allows efficient visible light diffraction. The modulation of the diffraction efficiency at PANI and PEDOT gratings in the presence of an analytical stimulus such as pH or potential demonstrate the sensing capability at these surfaces. The template stripped gold surfaces that are being developed in our lab demonstrate several advantages over commercially available evaporated gold films especially for nanoscale surface modification.
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Mankowski, Trent, and Trent Mankowski. "Integrating Copper Nanowire Electrodes for Low Temperature Perovskite Photovoltaic Cells." Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/624135.
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Recent advances in third generation photovoltaics, particularly the rapid increase in perovskite power conversion efficiencies, may provide a cheap alternative to silicon solar cells in the near future. A key component to these devices is the transparent front electrode, and in the case of Dye Sensitized Solar Cells, it is the most expensive part. A lightweight, cost-effective, robust, and easy-to-fabricate new generation TCE is required to enable competition with silicon.
Indium Tin Oxide, commonly used in touchscreen devices, Organic Light Emitting Diodes (OLEDs), and thin film photovoltaics, is widely used and commonly referred to as the industry standard. As the global supply of indium decreases and the demand for this TCE increases, a similar alternative TCE is required to accompany the next generation solar cells that promise energy with lighter and significantly cheaper modules. This alternative TCE needs to provide similar sheet resistance and optical transmittance to ITO, while also being mechanically and chemically robust.
The work in this thesis begins with an exploration of several synthesized ITO replacement materials, such as copper nanowires, conductive polymer PEDOT:PSS, zinc oxide thin films, reduced graphene oxide and combinations of the above. A guiding philosophy to this work was prioritizing cheap, easy deposition methods and overall scalability. Shortcomings of these TCEs were investigated and different materials were hybridized to take advantage of each layers strengths for development of an ideal ITO replacement. For CuNW-based composite electrodes, ~85% optical transmittance and ~25 Ω/sq were observed and characterized to understand the underlying mechanisms for optimization.
The second half of this work is an examination of many different perovskite synthesis methods first to achieve highest performance, and then to integrate compatible methods with our CuNW TCEs. Several literature methods investigated were irreproducible, and those that were successful posed difficulties integrating with CuNW-based TCEs. Those shortcomings are discussed, and how future work might skirt the issues revealed here to produce a very low cost, high performance perovskite solar cell.
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Zhang, Di, and 张笛. "Transparent electrode design and interface engineering for high performance organic solar cells." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/202360.
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With the growing needs for energy, photovoltaic solar cells have attracted increasing research interests owing to its potentially renewable, feasible and efficient applications. Compared to its inorganic counterparts, organic solar cell (OSC) is highly desirable due to the low-cost processing, light weight, and the capability of flexible applications. While rapid progress has been made with the conversion efficiency approaching 10%, challenges towards high performance OSCs remain, including further improving device efficiency, fully realizing flexible applications, achieving more feasible large-area solution process and extending the stability of organic device.
Having understood the key technical issues of designing high performance OSCs, we focus our work on (1) introducing flexible graphene transparent electrodes into OSCs as effective anode and cathode; (2) interface engineering of metal oxide carrier transport layers (CTLs) in OSCs through incorporating plasmonic metal nanomaterials ;(3)proposing novel film formation approach for solution-processed CTLs in OSCs in order to improve the film quality and thus device performance.
The detailed work is listed below:
1. Design of transparent graphene electrodes for flexible OSCs
Flexible graphene films are introduced into OSCs as transparent electrodes, which complement the flexibility of organic materials. We demonstrate graphene can function effectively as both the anode and cathode in OSCs:
a) Graphene anode: we propose an interface modification for graphene to function as anode as an alternative to using aconventional polymer CTL. Using the proposed interfacial modification, graphene OSCs show enhanced performance. Further analysis shows that our approach provides favorable energy alignment and improved interfacial contact.
b) Graphene cathode: efficient OSCs using graphene cathode are demonstrated, using a new composite CTL of aluminum-titanium oxide (Al-TiO2).We show that the role of Al is two-fold: improving the wettability as well as reducing the work function of graphene. To facilitate electron extraction, self-assembledTiO2is employed on the Al-covered graphene, which exhibits uniform morphology.
2. Incorporation of plasmonic nanomaterialsinto the metal oxide CTLinOSCs
By incorporating metallic nanoparticles (NPs) into the TiO2CTLin OSCs, we demonstrate the interesting plasmonic-electrical effect which leads to optically induced charge extraction enhancement. While OSCs using TiO2CTL can only operate by ultraviolet (UV)activation, NP-incorporated TiO2enables OSCs to perform efficiently at a plasmonic wavelength far longer than the UV light. In addition, the effciency of OSCs incorporated with NPs is notably enhanced. We attribute the improvement to the charge injection of plasmonically excited electrons from NPs into TiO2.
3. Formation of uniform TiO2CTLfor large area applications using a self-assembly approach
A solution-processed self-assembly method is proposed for forming large-area high-quality CTL films. Owing to the careful control of solvent evaporation, uniform film is formed, leading to enhanced OSC performance. Meanwhile, our method is capable of forming large-area films. This approach can contribute to future low-cost, large-area applications.published_or_final_version
Electrical and Electronic Engineering
Doctoral
Doctor of Philosophy
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Liu, Yujing [Verfasser], and Thomas [Akademischer Betreuer] Bein. "Nanostructured transparent conducting oxide electrodes through nanoparticle assembly / Yujing Liu. Betreuer: Thomas Bein." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2012. http://d-nb.info/102684679X/34.
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Lagrange, Mélanie. "Physical analysis of percolating silver nanowire networks used as transparent electrodes for flexible applications." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI075/document.
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Les électrodes transparentes (ET) sont présentes dans de nombreux dispositifs optoélectroniques. Par exemple, on peut les trouver au sein de cellules solaires, d'écrans tactiles, d'OLEDs ou encore de films chauffants transparents. Les propriétés physiques de ces électrodes influencent l'efficacité de ces dispositifs. Les ET sont fabriquées à partir de matériaux transparents conducteurs (TCM) dont le développement a débuté dans les années 1950 notamment avec les oxydes métalliques. Parmi ces oxydes transparents conducteurs (TCO), l'oxyde d'étain-indium (ITO) est celui le plus communément utilisé dans les cellules solaires et les écrans de télévision ou de smartphones. Cependant, de nouvelles exigences telles qu'une réduction des coûts, la flexibilité et la fabrication à faible température et/ou faible coût, ont orienté les recherches vers de nouveaux TCM, notamment à base de nanostructures. Parmi ces matériaux émergents, les réseaux de nanofils métalliques, en particulier de nanofils d'argent, présentent déjà des propriétés optiques et électriques approchant celles de l'ITO, c'est-à-dire une conductivité électrique et une transparence élevées. Ces deux propriétés sont cependant intrinsèquement liées à la densité de nanofils constituant le réseau, et lorsque la conductivité augmente, la transparence diminue. Des traitements post-dépôt existent et permettent d'augmenter la conductivité électrique des ET sans changer la densité du réseau. Plusieurs de ces méthodes d'optimisation ont été étudiées pendant ce travail de thèse, en particulier le recuit thermique, analysé minutieusement afin de comprendre les différents mécanismes de réduction de la conductivité électrique induits par la température. L'examen des effets thermiques a soulevé la question de l'instabilité des nanofils en température, qui est aussi abordée et discutée dans ce document. Le paramètre clé de la densité de nanofils optimale menant au meilleur compromis entre transparence et conductivité a été recherché pour des nanofils de différentes dimensions. La taille des nanofils a en effet un fort impact sur les propriétés du réseau. Ainsi, les propriétés électriques, dans le cadre de la théorie de la percolation, les propriétés optiques comme la transmittance et le facteur de haze, et même l'instabilité thermique ont été reliées aux dimensions des nanofils ainsi qu'à la densité du réseau en utilisant des modèles physiques simples. En ce qui concerne les applications de ces ET émergentes, des études ont été menées sur l'application des réseaux de nanofils d'argent comme film chauffant transparent, et les résultats sont rapportés à la fin de ce document. Les limitations soulevées par cette application, comme les limites de stabilités électrique et thermique ont aussi été abordées. Pour finir, des études préliminaires menées sur de nouvelles applications comme des antennes transparentes ou le blindage électromagnétique transparent utilisant les nanofils d'argent sont présentéesTransparent electrodes (TE) are used in a variety of optoelectrical devices. Among them, solar cells, flat panel displays, touch screens, OLEDs and transparent heaters can be cited. The physical properties of the TE influence the efficiency of the device as a whole. Such electrodes are fabricated from transparent conducting materials (TCM) that have been undergoing development since the 1950s, initially from metallic oxides. Among these transparent conducting oxides (TCO), indium tin oxide (ITO) is the most commonly used in solar cells, and television or smartphone screens. However requirements such as cost reduction, flexibility and low cost/temperature fabrication techniques have oriented the researches toward emerging TCM, mostly using nanostructures. Among them, metallic nanowire networks, and in particular silver nanowires (AgNW), already present optical and electrical properties approaching those of ITO, i.e. a high electrical conductivity and a high transparency. These two properties are intrinsically linked to the network density, therefore a tradeoff has to be considered knowing that when conductivity increases, transparency decreases. Some post-deposition treatments do exist, allowing an increase of the TE electrical conductivity without changing the network density. Several of these optimization methods have been thoroughly studied during this thesis work, especially thermal annealing. This method have been investigated in details to understand the different thermally-induced mechanisms of conductivity improvement. In addition, the investigation of thermal effects raised the question of thermal instability of the nanowires, which is also addressed and discussed in this document. The key issue of density optimization, allowing the best tradeoff between transparency and conductivity, has been investigated for nanowires with different dimensions. Nanowire size has a strong impact on the network properties. Thus, electrical properties, within the framework of percolation theory, optical properties such as transmittance or haziness, and even thermal instability have been linked to the nanowires' dimensions and the network density by using simple physical models. Regarding the application of these emerging TE, studies were conducted on the application of AgNWs as transparent heaters, and the results are reported at the end of the document. Limitations arising from this application, like thermal and electrical stabilities, have also been addressed. To finish, preliminary studies conducted on new applications such as transparent antennas and transparent electromagnetic shielding using AgNW are presented
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Pirzado, Azhar Ali Ayaz. "Integration of few kayer graphene nanomaterials in organic solar cells as (transparent) conductor electrodes." Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAD016/document.
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Dans cette thèse, des films à base de graphène ont été étudiés comme alternatives viables dans la fabrication d'électrodes transparentes (TCE). Elle met l'accent sur des couches fines de graphène (FLG), sur l'oxyde de graphène réduit (RGO) et leurs hybrides avec des nanotubes de carbone (NTCs) pour être utilisé comme TCE dans les cellule solaires organiques (OSC). Les FLGs et RGO ont été préparés par des méthodes d'exfoliation mécanique ou en phase liquide assistée par micro-ondes. Ces nanomatériaux dilués dans un solvant liquide ont été déposé en couche mince par aérographe. Des caractérisations de transport de charge ont été obtenues grâce à la méthode des 4 pointes. Ces échantillons ont été caractérisés: leur transparence(UV-Visible), leur morphologie et leur topographique (MEB, MET, AFM) ainsi que le travail de sortie (UPS). Pour obtenir des informations sur la qualité structurelle des échantillons, nous avons utilisés les méthodes de spectroscopie XPS, Raman et la photoluminescenceGraphene mate rials have been researched as viable alternatives of transparent conductors electrodes (TCEs) in this thesis. Current study focuses on few layer graphene (FLG), reduced graphene oxide (rGO) and their hybrids with carbon nanotubes (CNTs) for TCE applications inorganic solar cells (OSCs). FLGs and rGOs have been prepared by mechanical and microwave-assisted exfoliation methods. This films of these materials have been produced by hot-spray method. Results of charge transport characterizations by four-point probes, transparency (UV-Vis), measurements, along with morphological (SEM, TEM) and topgraphic (AFM) studies of films have been presented. UPS studies were performed to determine for a work-function. XPS,Raman and Photoluminescence studies have been employed to obtain the information about the structural quality of the samples
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Alomairy, Sultan. "Next generation solar cells using flexible transparent electrodes based on silver nanowires and grapheme." Thesis, University of Surrey, 2015. http://epubs.surrey.ac.uk/807954/.
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Organic photovoltaic (OPV) devices have been developed extensively and optimised due to the use of nanomaterials in their construction. More recently, the demand for such devices to be flexible and mechanically robust has been a major area of research. Presently, Indium Tin Oxide (ITO) is the material that is used almost exclusively for transparent electrode. However, it has several drawbacks such as brittleness, high refractive index and high processing temperature. Furthermore, the price of ITO has been highly volatile due to scarcity of indium resources and the increased consumption of the material. Therefore, cheap, flexible and solution-processed transparent conductors are required for emerging optoelectronic devices with flexible construction which can be promising for wearable or environmentally adaptable devices purposes such as flexible solar cells and displays. Therefore, over the past decade an alternative material has been sought intensively, particularly in the need for producing large area flexible transparent electrodes. Many materials have been investigated but most investigations have focused on carbon nanotube (CNT), graphene flakes and metallic nanowires. Silver nanowires (Ag NWs) networks have been proven to show a high electrical conductivity with high optical transmittance. This special characteristic is desirable in transparent conductive electrodes in optoelectronic applications such as solar cells, light emitting diodes, and touch screen. On the other hand, Polymeric substrates that act as a non-brittle scaffold as well as protective packaging of the OPV are an essential element for such an “All-plastic” device. However, for such applications where the coating should be relatively hard a bottleneck to fabricating large area homogeneous films is associated with the formation of cracks as a result of local mismatches in mechanical properties during film formation. In this work, the fabrication and characterization of flexible transparent electrodes of Ag NWs on flexible substrates by spray deposition technique have been described. Furthermore, a way to enhance the electrical and mechanical properties of the Ag NWs transparent electrodes by incorporating a low density ensemble of graphene on top of the metal electrode networks using the Langmuir-Schafer has been achieved. Interestingly, the electrical conductivity in these hybrid electrodes is stable over relatively large strains during mechanical agitation indicating that such electrodes may have important application in future applications. Finally, producing crack-free monolayer latex over large area has been fabricated and characterised. Therefore, the polymer latex thin film has promising applications as purposes of hard coatings.
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Fahmi, Machda. "Durability and Recoverability of Al-doped ZnO Transparent Electrodes Exposed to a Harsh Environment." Kyoto University, 2020. http://hdl.handle.net/2433/259062.
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Lockwood, Tobias. "Electronic applications of single-walled carbon nanotubes: Electropolymerised transparent electrodes and CNT monolayers on silicon." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=86893.
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The viability of two independent electronic applications of single-walled carbon nanotubes was studied. Firstly, the use of a transparent, conductive, nanotube film as an electrode on which to electrochemically synthesise a thin film of poly(ethylenedioxythiophene). Such an electrode, possessing advantageous properties of both the nanotube and polymer film, should prove useful for numerous organic devices. Polymer-nanotube electrodes were made with HipCO and arc-discharge CNTs, on glass and flexible substrates; showing up to 100 Ω/sq. improvement in sheet resistance over conventional spin-coated films was demonstrated on glass. Preliminary organic LED devices were fabricated and successfully tested. Secondly, covalently bound monolayers of SWNTs on silicon were synthesised with a view to exploring the electronic properties of vertically aligned SWNT arrays. Silicon surfaces with hydroxyl functionality were prepared by a radical reaction with hydroxyl terminated 1-alkenes, which were then ester couple to oxidised carbon nanotubes. The resulting substrates showed bound, but disordered nanotube films.Nous avons étudié deux applications basées sur l'utilisation de nanotubes de carbone. Nous avons tout d'abord réalisé des couches conductives et transparentes de nanotubes servant de substrat pour le dépôt électrochimique d'une couche mince de poly(éthylenedioxythiophene). Une telle électrode, ayant les propriétés des nanotubes ainsi que du polymère, devrait être bénéfique pour divers dispositifs organiques. Les électrodes polymère-nanotubes ont été fabriquées avec les SWNTs HipCO et à l'arc électrique sur du verre et sur du plastique; le gain obtenu rapport aux couches déposées par enduction centrifuge en terme de résistance va jusqu'à 100 Ω/sq. Quelques DEL organiques fonctionnelles ont été fabriquées avec succès en utilisant ces électrodes. Ensuite, nous avons synthétisé des couches auto-assemblées de SWNTs sur du silicium, afin d'étudier les propriétés électriques des SWNTs alignés verticalement. Les surfaces de silicium fonctionnalisées avec des groupes hydroxyles ont été liées aux nanotubes par estérification. Les substrats obtenus ont des nanotubes liés à la surface qui sont désordonnés.
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Göbelt, Manuela [Verfasser], and Erdmann [Gutachter] Spiecker. "Encapsulated silver nanowire networks for novel indium-free transparent electrodes / Manuela Göbelt ; Gutachter: Erdmann Spiecker." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2017. http://d-nb.info/1154594297/34.
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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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Canestraro, Carla Daniele. "Electrical and optical properties of thin film SnO₂ and SnO₂:F : transparent electrodes in organic photovoltiaics /." Stockholm : Materials Science and Engineering (Materialvetenskap), Kungliga Tekniskan högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4832.
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Selzer, Franz Verfasser], Karl [Akademischer Betreuer] [Leo, and Frank [Akademischer Betreuer] Nüesch. "Transparent Electrodes for Organic Solar Cells / Franz Selzer. Betreuer: Karl Leo. Gutachter: Karl Leo ; Frank Nüesch." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://d-nb.info/1095395467/34.
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Papanastasiou, Theodora. "Investigation of silver nanowire networks : physical properties, stability and integration into devices." Thesis, Université Grenoble Alpes, 2020. http://www.theses.fr/2020GRALI083.
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Les électrodes transparentes sont des composants essentiels au sein d’une grande variété de dispositifs, par exemple, chauffants ou liés à l’énergie et l'éclairage. L’oxyde d'indium et d'étain est le matériau le plus utilisé jusqu'à présent. Cependant, en raison de la fragilité et de la rareté de l'indium, un intérêt de recherche intensif a émergé au cours de la dernière décennie pour des matériaux conducteurs transparents (TCM) alternatifs. Les réseaux de nanofils métalliques, et surtout les réseaux de nanofils d'argent (AgNW), semblent être parmi les plus prometteurs, grâce à leurs très bonnes propriétés électriques et optiques, combinées à leurs excellentes performances mécaniques et à leur faible coût de fabrication. Malgré l'optimisation des réseaux AgNW, il reste des défis à relever pour mettre au point une technologie plus mature qui puisse être intégrée avec succès dans les dispositifs. La présente thèse de doctorat se concentre sur la compréhension fondamentale des phénomènes physiques qui ont lieu à l'échelle des nanofils et des réseaux. En combinant les approches expérimentales et de modélisation, l'un des principaux objectifs est de déterminer l'origine de l’instabilité des réseaux AgNW lors de contraintes électriques. Les mesures in situ de la résistance électrique avec une mesure parallèle de la température de surface spatiale par imagerie IR fournissent des informations précieuses pour les mécanismes de dégradation. La simulation de la distribution électrique et du chauffage induit par la puissance permet de mieux comprendre la physique sous-jacente et peut être utilisée pour prédire les performances électriques et de chauffage des réseaux. Sur la base de ces données, un modèle physique a été proposé estimant la durée de vie du réseau, et sa dépendance à la température, au courant électrique et à la densité du réseau AgNW. Un autre paramètre crucial qui est étudié est la présence de défauts et l'impact de la non-homogénéité des réseaux sur la distribution électrique, la dynamique de l’instabilité et la température de surface induite par le chauffage par effet Joule. De plus, la stabilité des réseaux AgNW a été grandement améliorée grâce à l'encapsulation des réseaux par des oxydes transparents et protecteurs développés au LMGP pour le dépôt de couches minces à pression atmosphérique grâce à l’ALD spatiale (AP-SALD). L'AP-SALD est désormais une méthode de dépôt à l'air, peu coûteuse et évolutive, et les composites d'oxydes AgNW qui en résultent conservent une excellente flexibilité. Enfin, l'intégration des réseaux AgNW dans les dispositifs a été étudiée grâce à plusieurs collaborations et projets avec des équipes scientifiques. Les films chauffants transparents (TH) ont été étudiés et intégrés à des dispositifs de laboratoire biomédical sur puce. De plus, nous avons récemment publié un article de synthèse sur les TH, incluant les différentes technologies et la physique liées au chauffage par effet Joule et aux applications associées. Un autre exemple d'intégration étudiée est l'utilisation des AgNW intégrés dans des substrats polymères, comme électrodes étirables pour les générateurs électrostatiques ou piézoélectriques dans les dispositifs de collecte d'énergie. Dans le cadre de projets ANR avec des partenaires de laboratoire et industriels, nous avons étudié l'utilisation des AgNW en émission de champ froide pour des sources de rayons X miniaturisées et comme électrodes transparentes et flexibles pour le photovoltaïque organique. En conclusion, les réseaux AgNW optimisés en termes de propriétés électriques, optiques et mécaniques et leur combinaison avec d'autres films minces transparents ou des matériaux 2D sont très prometteurs, ainsi que l'intérêt industriel croissant pour leur mise en œuvre. Au cours de cette thèse de doctorat, des pistes potentielles pour l'amélioration de la stabilité et de l'intégration dans les dispositifs ont été étudiées, au moyen d'approches expérimentales et de modélisationTransparent electrodes are essential components in a huge variety of energy, lighting and heating devices with indium tin oxide being the most efficient and widely used so far. However, due the brittleness and scarcity of indium, an intensive research interest has emerged the last decade towards alternative transparent conductive materials (TCM). Metallic nanowire networks and especially silver nanowire (AgNW) networks appear to be one of the most promising among them, thanks to their excellent electrical and optical properties combined with their excellent mechanical performance and low cost fabrication. Despite the optimization of AgNW network fabrication methods and properties, there are still challenges to be tackled, in order to build a mature technology that can be successfully integrated into devices. The present PhD thesis focuses on the fundamental understanding of the physical phenomena that take place at both scales of nanowires and networks. Combining both experimental and modelling approaches, one of the main goals focuses on the origin of failure in AgNW networks during electrical stress. In situ measurements of the electrical resistance with a parallel recording of the spatial surface temperature by IR imaging are techniques that provide valuable information for the degradation mechanisms in a AgNW network. The simulation of the electrical distribution and power-induced heating offer a deeper understanding of the underlying physics and can be used to predict the networks electrical and heating performances. Moreover, an experimental study, conducted under simultaneous electrical and thermal stress, was useful for the successful integration of AgNW into devices. Based on these data, a physical model was proposed for the prediction of the time of failure, with its dependence with temperature, electrical current and AgNW network density (i.e. electrical resistance). Another crucial parameter that is investigated during this PhD thesis, is the presence of defects and the impact of networks non-homogeneity on the electrical distribution, the dynamics of failure and the surface temperature induced by Joule heating. Furthermore, the enhancement of the AgNW networks stability was successful with the network encapsulation by transparent, protective oxides developed in LMGP by Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD). The AP-SALD is now an emerging open air, low-cost and scalable deposition method and the resulting AgNW-oxide composites retain an excellent flexibility. Finally, during the present PhD thesis, the integration of AgNW networks in devices was studied in the framework of several collaborations and projects with scientific teams of laboratories in Grenoble and elsewhere. Transparent heaters (TH) are in the core of our research and biomedical lab-on-a-chip devices were thoroughly studied. In addition, the increasing interest of the TCM community to the TH, lead our team to write and publish recently a review-article on the topic, including all different technologies and the physics related to Joule heating and the associated applications. Another example of studied integration is the use of the AgNW embedded in polymer substrates, as stretchable electrodes for electrostatic or piezoelectric generators in energy harvesting devices. In the framework of ANR projects with laboratory and industrial partners, we studied the use of AgNWs in cold field emission for miniaturized X-ray sources and as transparent, flexible electrodes in organic photovoltaic. To conclude, the AgNW networks optimized electrical, optical and mechanical properties and their combination with other transparent thin films or 2D materials are highly promising, as well as the growing industrial interest for their implementation. During this PhD Thesis, potential pathways for the stability enhancement and the improvement of the integration into devices have been traced, by means of both experimental and modelling approaches
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Müller, Vesna [Verfasser], and Thomas [Akademischer Betreuer] Bein. "Mesoporous transparent conducting films of antimony doped tin oxide as nanostructured electrodes / Vesna Müller. Betreuer: Thomas Bein." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2013. http://d-nb.info/1037311531/34.
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Islam, Md Mazharul. "Printed transparent conducting electrodes based on carbon nanotubes (CNTs), reduced graphene oxide (rGO), and a polymer matrix." Thesis, Umeå universitet, Institutionen för fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-156366.
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The main focus of this project was to prepare transparent and conductive electrodes (TCEs). TCEs were made out of multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO), and polyvinylpyrrolidone (PVP). Based on the theoretical aspect, MWCNTs has emerged as a promising nanofiller in the polymer matrix due to its high electrical conductivity. As a nanofiller, MWCNTs were used with a small ratio of rGO with PVP as a polymer matrix in this project to prepare TCEs having low sheet resistance with high transparency. An appropriate amount of PVP has been shown to be a good combination with MWCNTs and rGO in the solvent to keep MWCNTs dispersed for a long time. Carboxyl group (-COOH) functionalized MWCNTs (FMWCNTs) was produced in a controlled oxidative procedure due to enabling good dispersion of FMWCNTs in water and ethanol solvents. In contrast, water dispersible rGO was chemically prepared by using GO and sodium borohydride where GO was produced from graphite by using improved Hummer's method. Drop casting and spray coating methods were applied to fabricate TCEswhere only water was used as the solvent for drop casted TCEs and a mixing ratio of water and ethanol was 70:30 as solvent for spray coated TCEs. It was also determined in this project that the spray coating method was more suitable for preparing TCEs rather than thedrop casting method due to easy fabrication, large area coating possibility, and the smoothness of the coated film surface. The sheet resistance was obtained as 5026 Ω/ ⃣ where the transparency was 65% in the case of the drop casted electrode for the ratio of rGO:FMWCNTs:PVP was 1.2:60:1 with 0.02 mg FMWCNTs. In the case of spray coated electrode at the same ratio of rGO:FMWCNTs:PVP, the sheet resistance was measured as 5961 Ω/ ⃣ where the transparency was 73%. But in the case of 60:1 mass ratio of FMWCNTs:PVP with 0.02 mg FMWCNTs, the sheet resistance was 7729 Ω/ ⃣ and transparency was 77% for spray coated electrode. So, it is clear that the sheet resistance was improved by adding a small mass ratio of rGO with FMWCNTs:PVP.
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Madeira, Alexandra. "Amélioration des performances d'électrodes conductrices et transparentes en modifiant le design de nanofils d'argent." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0107/document.
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Les électrodes transparentes sont les composants indispensables de nombreux dispositifsoptoélectroniques commerciaux (cellules solaires, écrans plats, écrans tactiles ou encorediodes électroluminescentes). Elles sont constituées le plus souvent d’oxyde d’indium etd'étain (ITO). Les électrodes à base d'ITO sont produites par un procédé relativementcoûteux et sont très fragiles à la contrainte mécanique, ce qui limite leur utilisation au seinde dispositifs optoélectroniques flexibles. Des matériaux alternatifs, sans indium, à base deréseaux de nano-fils d’argent, font actuellement l'objet d'un grand nombre de recherches.Ces réseaux à base de nanostructures métalliques ont des propriétés opto-électroniquescomparables voire supérieures à celles de l’ITO. Ils sont adaptables à des substrats flexibleset sont compatibles avec les procédés de dépôt « roll to roll ». L'objectif de cette thèse estd'explorer de nouvelles voies de synthèse et de modification de surface de nanofils d'argentpour développer des électrodes transparentes plus performantes. De nouvelles nanostructuresmétalliques, différentes de celles commercialisées, ont été élaborées : (i) des fils d’argentultra-longs (ii) des fils d’argent présentant une architecture inhabituelle i.e avec desramifications. Des paramètres clés du procédé polyol ont été modifiés pour élaborer les filsà facteur de forme très élevé. Ils ont permis d'accroître les performancesrésistance/transparence des dispositifs conventionnels. Des nano-fils d’argent de forme « Y» ou « V » ont également été synthétisés en soumettant le milieu de croissance à des ultrasons.Ces nanostructures devraient permettre de limiter les problèmes de conduction quiapparaissent, à l'heure actuelle, au niveau des contacts entre les fils dans les dispositifsnanostructurés. Par ailleurs, des réseaux de fils d'argent modifiés en surface avec de l'acide11-mercaptoundecanoïque (MuA) ont été élaborés. Ils constituent une solution trèsintéressante pour améliorer la stabilité chimique des réseaux métalliques. Le MuA limite l'oxydation de surface du métal et permet aux électrodes de conserver leurs transparence etconductivité initialesTransparent electrodes are a necessary component in a number of devices such as solar cells,flat panel displays, touch screens and light emitting diodes. The most commonly usedtransparent conductor, indium tin oxide (ITO), is expensive and brittle, the latter propertymaking it inappropriate for up-and-coming flexible devices. Films consisting of randomnetworks of solution-synthesized silver nanowires have emerged as a promising alternative toITO. They have transparency and conductivity values better than competing new technologies(e.g. carbon nanotubes films, graphene, conductive polymers, etc.) and comparable to ITO.Furthermore, these silver nanowire films are cheap, flexible, and compatible with roll-to-rolldeposition techniques. The main objectives of this PhD work are to improve the properties ofsilver nanowire electrodes and to study and solve issues that are currently hindering their usein commercial devices. Specifically, I studied the important areas of electrode conductivity andstability. To increase the conductivity of nanowire electrodes, two silver nanostructuresdifferent from what is commercially available were synthesized i) ultra-long nanowires and (ii)branched nanowires. Regarding (i), by using 1.2-propanediol as the medium rather than thetypical ethylene glycol in the polyol synthesis process, as well as the molecular weight of PVP,the temperature of the process, or the concentration of silver nitrate, we obtained silvernanowires with an aspect ratio between their lengths and diameters of 1050. Among all theultra-long silver nanowires elaborated in polyol process reported in the literature, they have themaximum length. The synthesis developed is also cheap and the reaction time takes less than2h. Moreover, they have a high yield of 2 mg/ml. Electrodes with a sheet resistance of 5 Ω/Sqfor a transparency of 94% were obtained (with post thermal treatment applied). However, thispost-deposition anneal is shown to have a small influence on the decrease of the sheetresistance. It is thus not required to elaborate electrodes with good performance, which is veryadvantageous for the elaboration of electrodes on plastic substrates. Regarding (ii), “V-like shape” or “Y-like branched” nanowires were elaborated thanks to the input of ultrasonicirradiation during the polyol process. Unfortunately, their length being short (6 μm), theirinterest is limited to enhance the performance of transparent electrodes. In addition, structuralanalyses of both branched and unbranched nanowires revealed the nanostructures notmonocrystalline. Concerning the stabilities issues, the thermal stability of silver nanowireelectrodes coated with graphene was investigated. This coating allows a better homogeneity ofthe heat through the network, decreasing the number of hot spots and thus increasing thelifetime of the electrodes. The corrosion of silver nanowire and the resulting electrode resistanceincrease over time is a severe problem hindering their use in commercial devices. 11-mercaptoundecanoic acid (MuA) was identified as a promising passivation agent of silvernanowires. Lifetime testing showed that the electrode resistance increased more slowly (12%)than any other passivated electrodes reported in the literature. Furthermore, unlike many otherpassivation methods, the MuA molecule itself does not negatively affect the conductivity ortransparency of the electrode and is very inexpensive, all contributing to the commercialviability of the passivation method
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Bessaire, Bastien. "Fabrication et étude de nanomatériaux 1D conducteurs par électrofilage pour leurs propriétés optoélectroniques." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1175/document.
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L'utilisation de matériaux transparents et conducteurs a subi une croissance exponentielle lors de la dernière décennie, puisque faisant partie intégrante de nombreux dispositifs optoélectroniques tels que les écrans tactiles & les cellules solaires. Parmi ces matériaux, l'oxyde d'indium-étain occupe la quasi-totalité du marché puisqu'il associe une conductivité élevée et une transparence supérieure à 90% sous forme de film mince. Cependant, le développement de technologies flexibles pousse à rechercher des alternatives à son utilisation car son cout élevé et sa faible flexibilité le rendent incompatible. Au milieu des alternatives carbonées (graphène et nanotubes), les nanomatériaux métalliques ou les polymères conducteurs se présentent comme des alternatives intéressantes : bas cout et facilité à mettre en forme pour les polymères conducteurs, hautes performances pour les nanofils métalliques. Cette thèse présente la mise en œuvre de ces matériaux alternatifs par la méthode originale d'électrofilage et l'étude de leurs propriétés optoélectroniques. La maitrise des conditions de mise en forme (champ, débit, paramètres environnementaux) et l'optimisation des solutions utilisées (rhéologie, concentration en polymère, co-solvants) nous a permis d'obtenir 2 types de nanostructures : des nanofibres 100% polymériques à base de PEDOT:PSS et des nanofibres composites PVP:Nanofils d'argent. L'étude des propriétés opto-électroniques des réseaux ainsi obtenus a aussi été étudiéeThe use of transparent and conductive materials has been growing exponentially in the last decade as they are part of many optoelectronic devices such as touch screens and solar cells. Among these materials, Indium-Tin Oxide (ITO) is the market reference since it combines a low resistivity and a high transparency up to 90% in the form of thin film. However, the growing in the development of flexible technologies created a real need in alternatives as ITO has poor mechanical properties. Carbon nanotubes and graphene are potential substitutes, but metallic nanowires and conductive polymers have been developed for their high performances and low cost respectively.This thesis presents the implementation of these alternatives by the original method of electrospinning and the study of their optoelectronic properties. The optimization of the experimental setup (field, rate, environmental parameters) and solutions (rheology, polymer concentration, co-solvents) allowed us to obtain 2 different kinds of nanostructures: fully polymeric with PEDOT:PSS and composite with PVP and silver nanowires. The study of the optoelectronic properties of the resulting networks has also been investigated
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Schubert, Sylvio [Verfasser], Lars Akademischer Betreuer] Müller-Meskamp, Karl [Akademischer Betreuer] [Leo, and Marius [Akademischer Betreuer] Grundmann. "Transparent top electrodes for organic solar cells / Sylvio Schubert. Gutachter: Karl Leo ; Marius Grundmann. Betreuer: Lars Müller-Meskamp." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://d-nb.info/1070694789/34.
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Walker, Erin Kate. "Transparent carbon electrodes for spectroelectrochemical studies." Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-08-5954.
Full textAbstract:
This dissertation describes the assessment and use of carbon optically transparent electrodes (C-OTEs) based on pyrolyzed photoresist films (PPFs) as a platform for spectroelectrochemical investigations. C-OTEs are examined for use in UV-Vis spectroelectrochemistry and electrogenerated chemiluminescence and compared to non-transparent glassy carbon (GC) and the conventional transparent electrode indium tin oxide (ITO). Chapter 1 provides a general overview of transparent electrodes, carbon electrodes, and spectroelectrochemistry. Chapter 2 details a UV-Vis spectroelectrochemical investigation of electrogenerated graphitic oxides (EGO) on the surface of the C-OTE in the presence of KCl. X-ray photoelectron spectroscopy and time of flight secondary ion mass spectroscopy are used to determine EGO composition. Several supporting electrolytes are investigated to determine the mechanism of EGO formation. Chapter 3 details experiments to electrochemically access the exciton emission from self-assembled double-walled tubular J-aggregates via electrogenerated chemiluminescence (ECL). Optimization of ECL intensity with respect to the coreactant concentration and the supporting electrolyte pH is performed on opaque glassy carbon electrodes. ECL and fluorescence spectra are compared, and C-OTEs are utilized to determine the source of disagreement between the spectra. Chapter 4 describes the preparation and characterization (i.e. transparency, thickness, sheet resistance, rms roughness, and electroactive surface area) of C-OTEs and explores C-OTEs for general use in ECL under a variety of conditions. Simultaneous cyclic voltammograms and ECL transients are obtained for three thicknesses of PPFs and compared to non-transparent GC and the conventional transparent electrode ITO in both front face and transmission electrode cell geometries. Despite positive potential shifts in oxidation and ECL peaks, attributed to the internal resistance of the PPFs that result from their nanoscale thickness, the PPFs display similar ECL activity to GC, including the low oxidation potential observed for amine coreactants on hydrophobic electrodes. Overall, C-OTEs are promising electrodes for spectroelectrochemical applications because they yield higher ECL than ITO in both oxidative-reductive and reductive-oxidative ECL modes, are more stable in alkaline solutions, display a wide potential window of stability, and have tunable transparency for more efficient detection of light in the transmission cell geometry. Future directions for this research are discussed in Chapter 5, which outlines several approaches to designing and improving spectroelectrochemical sensors.text
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Selzer, Franz. "Transparent Electrodes for Organic Solar Cells." Doctoral thesis, 2015. https://tud.qucosa.de/id/qucosa%3A29318.
Full textAbstract:
The aim of this work was to investigate silver nanowire as well as carbon nanotube networks as transparent conducting electrodes for small molecule organic solar cells.
In the framework of the nanowire investigations, a low-temperature method at less than 80 °C is developed to obtain highly conductive networks directly after the deposition and without post-processing. In detail, specific non-conductive organic materials act as a matrix where the nanowires are embedded in such that a mutual attraction based on capillary forces and hydrophobic interaction is created. This process is mediated by the ethanol contained in the nanowire dispersion and works only for sublayer materials which exhibit hydrophobic and hydrophilic groups at the same time. In contrast to high-temperature processed reference electrodes (210 °C for 90 min) without matrix, a slightly lower sheet resistance of 10.8 Ohm/sq at a transparency of 80.4 % (including substrate) is obtained by using polyvinylpyrrolidone as the sublayer material. In comparison to annealed silver nanowire networks, the novel approach yields a performance enhancement in corresponding organic solar cells which can compete with ITO-based devices.
Furthermore, a novel approach for scalable, highly conductive, and transparent silver nanowire top-electrodes for organic optoelectronic devices is introduced. By utilizing a perfluorinated methacrylate as stabilizer, silver nanowires with high aspect ratio can be transferred into inert solvents which do not dissolve most organic compounds making this modified dispersion compatible with small molecule and polymer-based organic optoelectronic devices. The inert silver nanowire dispersion yields highly performing top-electrodes with a sheet resistance of 10.0 Ohm/sq at 80.0 % transparency (including substrate) directly after low-temperature deposition at 30 °C and without further post-processing. In comparison to similarly prepared reference devices comprising a thin-metal film as transparent top-electrode, reasonable power conversion efficiencies are demonstrated by spray-coating this dispersion directly on simple, air-exposed small molecule-based organic solar cells.
Moreover, a deeper understanding of the percolation behavior of silver nanowire networks has been achieved. Herein, direct measurements of the basic network parameters, including the wire-to-wire junction resistance and the resistance of a single nanowire of pristine and annealed networks have been carried out for the first time. By putting the values into a simulation routine, a good accordance between measurement and simulation is achieved. Thus, an examination of the electrical limit of the nanowire system used in this work can be realized by extrapolating the junction resistance down to zero. The annealed silver nanowires are fairly close to the limit with a theoretical enhancement range of only 20 % (common absolute sheet resistance of approximately 10 Ohm/sq) such that a significant performance improvement is only expected by an enlargement of the nanowire length or by the implementation of new network geometries.
In addition, carbon nanotube networks are investigated as alternative network-type, transparent bottom-electrode for organic small molecule solar cells. For that purpose, cleaning and structuring as well as planarization procedures are developed and optimized which maintain the optoelectronic performance of the carbon nanotube electrodes. Furthermore, a hybrid electrode consisting of silver nanowires covered with carbon nanotubes is fabricated yielding organic solar cells with only 0.47 % power conversion efficiency. In contrast, optimized electrodes comprising only carbon nanotubes show significantly higher efficiency. In comparison to identically prepared ITO devices, comparable or lower power conversion efficiencies of 3.96 % (in p-i-n stack), 4.83 % (in cascade cell) as well as 4.81 % (in p-n-i-p architecture) are demonstrated. For an inverted n-i-p stack design, the highest power conversion efficiency of 5.42 % is achieved.
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Pei-YingHsieh and 謝佩穎. "Silver Coated PMMA Electrospun Webs by Electroless Plating as Transparent Electrodes." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/90432599140382851228.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系碩博士班
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This study develops a novel process for transparent electrodes by electrospinning and electroless plating technique. PMMA nanofibers were first electrospun from the solution containing PMMA and silver precursor CF3COOAg. To obtain uniform webs with high transmittance for further electroless plating, the effect of electrospun parameters on morphology and diameter of nanofibers, including polymer concentration, silver precursor concentration, applied voltage, flow rate, and electrospun time was carefully investigated. After forming PMMA webs, silver nanolayer was coated on the surface of nanofibers by a simple silver mirror reaction. To improve the uniformity of silver coating, PMMA nanofibers encapsulated with silver nanoparticles were synthesized by a heat treatment at 100 oC 12h and acted as nucleation sites for the following electroless plating. Moreover, soluble substrates were adopted to ensure that silver could only be deposited on the nanofibers. The silver coated PMMA webs fabricated in this research has the transmittance of 73.1% and the sheet resistance of 16.7Ω/sq. In addition, this composite webs show only 60.5% changes in resistance after bending for 10,000 times and the sheet resistance rate less than 1.3 during a heat storage test at 150oC ,15hours and 90oC,250 hours. By the results of Figure of Merit, the performance of our transparent electrode was better than the graphene and carbon nanotubes. The most important is that we can prepare our thin film at room temperature and ambient pressure, which will have great development potential in the future