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Author: Thomas Sannicolo
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Transparent 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.
Author: Thomas Sannicolo
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Transparent 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.
Author: Mark Greyson Christoforo
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Metal nanowire based transparent electrodes offer a lower cost, mechanically flexible alternative to industry standard transparent conductive oxides without making any optical or electrical performance tradeoffs. My PhD research has been focused on making high performance, fully solution processed transparent electrodes using meshes of randomly oriented, high aspect ratio silver nanowires (AgNWs). In this dissertation, I will cover several aspects of my work in this area. First, I will discuss the use of computer simulations to understand what has historically limited the performance of metal nanowire networks with an eye on understanding the changes that can be made during fabrication and post processing to address these performance limitations and increase overall transparent conductor performance. Secondly, I will cover the deposition and post-processing techniques I have developed to produce the highest performance solution processed transparent electrodes which reach a sheet resistance of 6.3 ohm/s while maintaining 92% visible light transmission, besting the performance metrics of the industry standard transparent conductor, ITO. I will cover the design and operating principals of a custom built deposition tool which uses silver nanowires having diameters 35-90nm and lengths 10-30μm to produce uniform, large area electrodes by a spray deposition method. I will also discuss the use of a laser annealing method to further increase the conductivity of these silver nanowire electrodes. Finally, I will discuss the integration of these high performance transparent conductors into several different types of optoelectronic devices. These devices include organic light emitting diodes with enhanced off-normal transmission, and a semi-transparent perovskite solar cell with 77% peak light transmission and 12.7% power conversion efficiency which is used as the top cell in a four terminal tandem architecture with a CIGS bottom cell giving an 18.6% tandem.
Author: Mélanie Lagrange
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Transparent 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.
Author: Martin Dressel
Publisher: Cambridge University Press
ISBN: 9780521597265
Category : Science
Languages : en
Pages : 490
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Book Description
The authors of this book present a thorough discussion of the optical properties of solids, with a focus on electron states and their response to electrodynamic fields. A review of the fundamental aspects of the propagation of electromagnetic fields, and their interaction with condensed matter, is given. This is followed by a discussion of the optical properties of metals, semiconductors, and collective states of solids such as superconductors. Theoretical concepts, measurement techniques and experimental results are covered in three interrelated sections. Well-established, mature fields are discussed (for example, classical metals and semiconductors) together with modern topics at the focus of current interest. The substantial reference list included will also prove to be a valuable resource for those interested in the electronic properties of solids. The book is intended for use by advanced undergraduate and graduate students, and researchers active in the fields of condensed matter physics, materials science and optical engineering.
Author: Tobias Seewald
Publisher:
ISBN:
Category :
Languages : en
Pages : 45
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Book Description
Author: Hadi Hosseinzadeh khaligh
Publisher:
ISBN:
Category : Electrodes
Languages : en
Pages : 104
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Book Description
Random networks of silver nanowires are a promising option to replace conventional transparent conductive oxides, such as indium tin oxide (ITO), which are expensive, brittle, and require high temperatures and vacuum during deposition. In this work, silver nanowire transparent electrodes are fabricated with similar optoelectronic properties as ITO, while having a more convenient deposition process and being both cheaper and more mechanically flexible. Alongside these benefits, however, are some technical challenges that need to be addressed before nanowire electrodes can be widely used in commercial electronic devices. Firstly, the high surface roughness of the nanowire electrodes can cause issues such shorting when they are integrated into thin-film devices. A simple hot-rolling method was studied to embed the nanowires into the surface of plastic substrates, which reduces both the surface roughness and nanowire adhesion. A second issue with nanowire electrodes is the Joule heating that occurs when they conduct current for long periods of time, as is the case when used in solar cells and light emitting diodes. It is shown that the current density in the nanowires is both much higher and non-uniform than in a continuous film such as ITO. This leads to localized temperatures of 250 °C or more when conducting current levels encountered in organic solar cells and OLEDs. These temperatures accelerate electrode breakdown. A passivation layer of reduced graphene oxide is deposited on the nanowire films to slow their degradation. However, Joule heating still occurs and the electrodes fail due to melting of the plastic substrate. Recommendations for managing these adverse effects are proposed. To expand the application of silver nanowire transparent electrodes, they are integrated into polymer dispersed liquid crystal (PDLC) smart windows for the first time. Not only are the materials and fabrication costs of the nanowire electrodes less than ITO, but the resulting smart windows exhibit superior electro-optical characteristics. In another application, silver nanowires in conjunction with Al-doped ZnO (AZO) are developed as a conformal and transparent electrode to improve the efficiency of 3D solar cells. Lastly, a simple method of growing AgCl nanocubes directly on silver nanowires is introduced, which can have applications in surface enhanced Raman spectroscopy (SERS) and photocatalytic reactions.
Author: Manuela Göbelt
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Volker Bühler
Publisher: Springer Science & Business Media
ISBN: 9783540234128
Category : Medical
Languages : en
Pages : 272
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Book Description
The book describes the properties, analytical methods and the applications of different polyvinylpyrrolidone excipients (povidone, crospovidone, copovidone etc.) for use in pharmaceutical preparations. This group of excipients is one of the most important excipients used in modern technology to produce drugs. The book is intended for all persons working in the research, development and quality control of drugs. It gives a survey of all applications in solid, liquid and semisolid dosage forms including many drug formulation examples and more than 600 references to the literature.
Author: Peiyun Yi
Publisher:
ISBN:
Category : Technology
Languages : en
Pages :
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Book Description
There has been an explosion of interests in using flexible transparent electrodes for next-generation flexible electronics, such as touch panels, flexible lighting, flexible solar cells, and wearable sensors. Silver nanowires (AgNWs) are a promising material for flexible transparent electrodes due to high electrical conductivity, optical transparency and mechanical flexibility. Despite many efforts in this field, the optoelectronic performance of AgNW networks is still not sufficient to replace the present material, indium tin oxide (ITO), due to the high junction resistance. Also, the environmental stability and the mechanical properties need enhancement for future commercialization. Many studies have attempted to overcome such problems by tuning the AgNW synthesis and optimizing the film-forming process. In this chapter, we survey recent progresses of AgNWs in flexible electronics by describing both fabrication and applications of flexible transparent AgNW electrodes. The synthesis of AgNWs and the fabrication of AgNW electrodes will be demonstrated, and the performance enhanced by various methods to suit different applications will be also discussed. Finally, technical challenges and future trends are presented for the application of transparent electrodes in flexible electronics.
Author: Kallum M. Koczkur
Publisher: American Chemical Society
ISBN: 0841299013
Category : Science
Languages : en
Pages : 164
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Book Description
Our society depends heavily on metals. They are ubiquitous construction materials, critical interconnects in integrated circuits, common coinage materials, and more. Excitingly, new uses for metals are emerging with the advent of nanoscience, as metal crystals with nanoscale dimensions can display new and tunable properties. The optical and photothermal properties of metal nanocrystals have led to cancer diagnosis and treatment platforms now in clinical trials, while, at the same time, the ability to tune the surface features of metal nanocrystals is giving rise to designer catalysts that enable more sustainable use of precious resources. These are just two examples of how metal nanocrystals are addressing important social needs.
