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Dissertations / Theses on the topic 'Light emitting'
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Chen, Chih-Lei. "Processing light-emitting dendrimers for organic light-emitting diodes." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.489420.
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Light-emitting dendrimers with iridium(III) complex cores have given rise to some of the simplest and most efficient organic light-emitting diodes. However, whilst monochrome devices can be prepared there is currently no method for the patterning of the dendrimer films to give rise to pixelated colour displays. The main aim of this project was to develop methodology for the patterning of dendrimer films. In particular, dendrimers are designed that have an oxetane surface group that can be crosslinked to form patterns by a photo-generated acid.
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O, Yin Wan. "White light organic light emitting device." HKBU Institutional Repository, 2008. http://repository.hkbu.edu.hk/etd_ra/907.
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Schwab, Tobias. "Top-Emitting OLEDs." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-157992.
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In the last decades, investigations of organic light-emitting diodes (OLEDs) have tackled several key challenges of this lighting technology and have brought the electron to photon conversion efficiency close to unity. However, currently only 20% to 30% of the photons can typically be extracted from OLED structures, as total internal reflection traps the major amount of the generated light inside the devices.
This work focuses on the optimization of the optical properties of top-emitting OLEDs, in which the emission is directed away from the substrate. In this case, opaque materials, e.g. a metal foil or a display backplane can be used as substrate as well. Even though top-emitting OLEDs are often preferred for applications such as displays, two main challenges remain: the application of light extraction structures and the deposition of highly transparent materials as top electrode, without harming the organic layers below. Both issues are addressed in this work.
First, top-emitting OLEDs are deposited on top of periodically corrugated light outcoupling structures, in order to extract internally trapped light modes by Bragg scattering and to investigate the basic scattering mechanisms in these devices. It is shown for the first time that the electrical performance is maintained in corrugated top-emitting OLEDs deposited on top of light extraction structures. Furthermore, as no adverse effects to the internal quantum efficiency have been observed, the additional emission from previously trapped light modes directly increases the device efficiency. It has been proven that the spectral emission of corrugated OLEDs is determined by the interference of all light modes inside the air light-cone, including the observation of destructive interference and anti-crossing phenomena. The formation of a coherently coupled mode pair of the initial radiative cavity mode and a Bragg scattered mode has been first observed, when grating structures with an aspect ratio > 0.2 are applied. There, the radiative cavity mode partially vanishes. The observation and analysis of such new emission phenomena in corrugated top-emitting OLEDs has been essential in obtaining a detailed insight on fundamental scattering processes as well as for the optimization and control of the spectral emission by light extraction structures.
Second, the adverse impact of using only moderately transparent silver electrodes in white top-emitting OLEDs has been compensated improving the metal film morphology, as the organic materials often prevent a replacement by state-of-the-art electrodes, like Indium-tin-oxide (ITO). A high surface energy Au wetting layer, also in combination with MoO3, deposited underneath the Ag leads to smooth, homogeneous, and closed films. This allows to decrease the silver thickness from the state-of-the-art 15 nm to 3 nm, which has the advantage of increasing the transmittance significantly while maintaining a high conductivity. Thereby, a transmittance comparable to the ITO benchmark has been reached in the wavelength regime of the emitters. White top-emitting OLEDs using the wetting layer electrodes outperform state-of-the art top-emitting devices with neat Ag top electrodes, by improving the angular colorstability, the color rendering, and the device efficiency, further reaching sightly improved characteristics compared to references with ITO bottom electrode. The enormous potential of wetting layer metal electrodes in improving the performance of OLEDs has been further validated in inverted top-emitting devices, which are preferred for display applications, as well as transparent OLEDs, in which the brittle ITO electrode is replaced by a wetting layer electrode.
Combining both concepts, wetting layer electrodes and light extraction structures, allows for the optimization of the grating-OLED system. The impact of destructive mode interference has been reduced and thus the efficiency increased by a decrease of the top electrode thickness, which would have not been achieved without a wetting layer. The optimization of corrugated white top-emitting OLEDs with a top electrode of only 2 nm gold and 7 nm silver on top of a grating with depth of 150 nm and period of 0.8 µm have yielded a reliable device performance and increased efficiency by a factor of 1.85 compared to a planar reference (5.0% to 9.1% EQE at 1000 cd/m2). This enhancement is comparable to common light extraction structures, such as half-sphere lenses or microlens foils, which are typically restricted to bottom-emitting devices. Overall, the deposition of top-emitting OLEDs on top of light extraction structures finally allow for an efficient extraction of internally trapped light modes from these devices, while maintaining a high device yield.
Finally, the investigations have resulted in a significant efficiency improvement of top-emitting OLEDs and the compensation of drawbacks (optimization of the white light emission and the extraction of internal light modes) in comparison to the bottom-emitting devices. The investigated concepts are beneficial for OLEDs in general, since the replacement of the brittle ITO electrodes and the fabrication of roll-to-roll processing compatible light extraction structures are also desirable for bottom-emitting, or transparent OLEDs.
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Choi, Wai Kit. "Organic light-emitting diodes." HKBU Institutional Repository, 1999. http://repository.hkbu.edu.hk/etd_ra/190.
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Stevenson, Stuart G. "Dendrimer light-emitting diodes." Thesis, St Andrews, 2008. http://hdl.handle.net/10023/581.
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Liu, Jiang. "Light-Emitting Electrochemical Transistors." Doctoral thesis, Linköpings universitet, Fysik och elektroteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-104925.
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Since the discovery of conductive polymers in 1977, the implementation of organic conjugated materials in electronic applications has been of great interest in both industry and academia. The goal of organic electronics is to realize large-area, inexpensive and mechanically-flexible electronic applications. Organic light emitting diodes (OLEDs), as the first commercial product made from organic conjugated polymers, have successfully demonstrated that organic electronics can make possible a new generation of modern electronics. However, OLEDs are highly sensitive to materials selection and requires a complicated fabrication process. As a result, OLEDs are expensive to fabricate and are not suitable for low-cost printing or roll-to-roll process. This thesis studies an alternative to OLEDs: light-emitting electrochemical cells (LECs). The active materials in an LEC consist of a conjugated light-emitting polymer (LEP) and an electrolyte. Taking advantage of electrochemical doping of the LEP, an LEC features an in-situ formed emissive organic p-n junction which is easy to fabricate. We aim to control the electrochemical doping profile by employing a “gate” terminal on top of a conventional LEC, forming a lightemitting electrochemical transistor (LECT). We developed three generations of LECTs, in which the position of the light-emitting profile can be modified by the voltage applied at the gate electrode, as well as the geometry of the gate materials. Thus, one can use this structure to achieve a centered light-emitting zone to maximize the power-conversion efficiency. Alternatively, LECTs can be used for information display in a highly integrated system, as it combines the simultaneous modulation of photons and electrons. In addition, we use multiple LECs to construct reconfigurable circuits, based on the reversible electrochemical doping. We demonstrate an LEC-array where several different circuits can be created by forming diodes with different polarity at different locations. The thereby formed circuitry can be erased and turned into circuitry with other functionality. For example, the diodes of a digital AND gate can be re-programmed to form an analogue voltage limiter. These reprogrammable circuits are promising for fully-printed and large-area reconfigurable circuits with facile fabrication.
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Najafabadi, Ehsan. "Stacked inverted top-emitting white organic light-emitting diodes." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52990.
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The majority of research on Organic Light-Emitting Diodes (OLEDs) has focused on a top-cathode, conventional bottom-emitting architecture. Yet bottom-cathode, inverted top-emitting OLEDs offer some advantages from an applications point of view. In this thesis, the development of high performance green electroluminescent inverted top-emitting diodes is first presented. The challenges in producing an inverted structure are discussed and the advantages of high efficiency inverted top-emitting OLEDs are provided. Next, the transition to a stacked architecture with separate orange and blue emitting layers is demonstrated, allowing for white emission. The pros and cons of the existing device structure is described, with an eye to future developments and proposed follow-up research.
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Rosenow, Thomas. "White Organic Light Emitting Diodes." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-67342.
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Die vorliegende Arbeit beschäftigt sich mit drei Ansätzen der hocheffizienten Erzeugung von weißem Licht mit organischen Leuchtdioden (OLEDs) auf der Basis kleiner Moleküle.
Ein Ansatz kombiniert die Emission eines fluoreszenten und zweier phosphoreszenter Emitter in einer einzelnen Emissionsschicht. Da das Triplettniveau des verwendeten Blauemitters niedriger ist als die Triplettniveaus der phosphoreszenten Emitter, werden die Konzentrationen der Emitter so gewählt, dass ein Exzitonenübertrag zwischen ihnen unterbunden wird. Die strahlungslose Rekombination von Tripletts auf dem fluoreszenten Blauemitter begrenzt die Effizienz dieses Ansatzes, jedoch besticht die resultierende weiße OLED durch eine bemerkenswerte Farbstabilität.
Der zweite Ansatz basiert auf dem “Triplet Harvesting” Konzept. Ansonsten ungenutzte Triplett Exzitonen werden von einem fluoreszenten Blauemitter auf phosphoreszente Emitter übertragen, wodurch interne Quanteneffizienzen bis zu 100 % möglich sind. Der zur Verfügung stehende Blauemitter 4P-NPD erlaubt aufgrund seines niedrigen Triplettniveaus nicht den Triplett übertrag auf einen grünen Emitter. Daher wird das “Triplet Harvesting” auf zwei unterschiedliche phosphoreszente Emitter, anhand des gelben Emitters Ir(dhfpy)2acac und des roten Emitters Ir(MDQ)2acac untersucht. Es wird gezeigt, dass beide phosphoreszente Emitter indirekt durch Exzitonendiffusion angeregt werden und nicht durch direkte Rekombination von Ladungsträgern auf den Emittermolekülen. Eine genaue Justage der Anregungsverteilung zwischen den phosphoreszenten Emittern ist durch Schichtdickenvariation in der Größenordnung üblicher Schichtdicken möglich. Spätere Produktionsanlagen brauchen daher keinen speziellen Genauigkeitsanforderungen gerecht zu werden.
Der dritte und zugleich erfolgreichste Ansatz beruht auf einer Weiterentwicklung des zweiten Ansatzes. Er besteht zunächst darin den Tripletttransfer auf den Übertrag von einem fluoreszenten blauen auf einen phosphoreszenten roten Emitter zu beschränken. Die sich ergebende spektrale Lücke wird durch direktes Prozessieren einer unabhängigen voll phosphoreszenten OLED auf diese erste OLED gefüllt. Verbunden sind beide OLEDs durch eine ladungsträgererzeugende Schicht, in welcher durch das angelegte Feld Elektron/Loch-Paare getrennt werden. Dieser Aufbau entspricht elektrisch der Reihenschaltung zweier OLEDs, welche im Rahmen dieser Arbeit individuell untersucht und optimiert werden. Dabei ergibt sich, dass die Kombination von zwei verschiedenen phosphoreszenten Emittern in einer gemeinsamen Matrix die Ladungsträgerbalance in der Emissionszone sowie die Quanteneffizienz der vollphosphoreszenten OLED stark verbessert. Als Ergebnis steht eine hocheffiziente weiße OLED, welche durch die ausgewogene Emission von vier verschiedenen Emittern farbstabiles Licht mit warm weißen Farbkoordinaten (x, y) = (0.462, 0.429) und ausgezeichneten Farbwiedergabeeigenschaften (CRI = 80.1) erzeugt. Dabei sind die mit diesem Ansatz erreichten Lichtausbeuten (hv = 90.5 lm/W) mit denen von voll phosphoreszenten OLEDs vergleichbar.
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Thomschke, Michael. "Inverted Organic Light Emitting Diodes." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-106255.
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This study focuses on the investigation of the key parameters that determine the optical and electrical characteristics of inverted top-emitting organic light emitting diodes (OLED). A co-deposition of small molecules in vacuum is used to establish electrically doped films that are applied in n-i-p layered devices. The knowledge about the functionality of each layer and parameter is important to develop efficient strategies to reach outstanding device performances.
In the first part, the thin film optics of top-emitting OLEDs are investigated, focusing on light extraction via cavity tuning, external outcoupling layers (capping layer), and the application of microlens films. Optical simulations are performed to determine the layer configuration with the maximum light extraction efficiency for monochrome phosphorescent devices. The peak efficiency is found at 35%, while varying the thickness of the charge transport layers, the
semitransparent anode, and the capping layer simultaneously. Measurements of the spatial light distribution validate, that the capping layer influences the spectral width and the resonance wavelength of the extracted cavity mode, especially for TM polarization. Further, laminated microlens films are applied to benefit from strong microcavity effects in stacked OLEDs by spatial mixing of external and to some extend internal light modes. These findings are used to demonstrate white top-emitting OLEDs on opaque substrates showing power conversion efficiencies up to 30 lm/W and a color rendering index of 93, respectively.
In the second part, the charge carrier management of n-i-p layered diodes is investigated as it strongly deviates from that of the p-i-n layered counterparts. The influence of the bottom cathode material and the electron transport layer is found to be negligible in terms of driving voltage, which means that the assumption of an ohmic bottom contact is valid. The hole transport and the charge carrier injection at the anode is much more sensitive to the evaporation sequence, especially when using hole transport materials with a glass transition
temperature below 100°C. As a consequence, thermal annealing of fabricated inverted OLEDs is found to drastically improve the device electronics, resulting in lower driving voltages and an increased internal efficiency. The annealing effect on charge transport comes from a reduced charge accumulation due to an altered film morphology of the transport layers, which is proven for electrons and for holes independently. The thermal treatment can further lead to a device degradation. Finally, the thickness and the material of the blocking layers which usually control the charge confinement inside the OLED are found to influence the recombination much more effectively in inverted OLEDs compared to non-inverted ones.
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Leirset, Erlend. "Photonic crystal light emitting diode." Thesis, Norwegian University of Science and Technology, Department of Electronics and Telecommunications, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-10014.
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This master's thesis describe electromagnetic simulations of a gallium antimonide (GaSb) light emitting diode, LED. A problem for such devices is that most of the generated light is reflected from the surface due to total internal reflection, and is therefore prevented from coupling out of the semiconductor material. Etching out a 2D photonic crystal grating on the LED surface would put aside the absolute rule of total internal reflection, and could therefore be used to increase the total transmission. The simulation method which was developed was supposed to find geometry parameters for the photonic crystal to optimize the light extraction. A set of plane waves were therefore simulated using FDTD to build an equivalent to the Fresnel equations for the photonic crystal surface. From that the total transmittance and radiation patterns for the simulated geometries were calculated. The results indicated an increase in the transmission properties of up to 70% using a square grating of holes where the holes have a radius of 0.5µm, the hole depth is 0.4µm, and the grating constant is 1µm. A hexagonal grating of holes and a square grating of isotropically etched holes were also simulated, and featured improvements on the same scale, but with different dimensions for the holes. The simulations were computationally very demanding, and the simulation structure therefore had to be highly trimmed to limit the calculation time to reasonable values. This might have reduced the accuracy of the results. Especially the optimum grating constant, and the value of the optimum improvement itself is believed to be somewhat inaccurate.
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Gray, Jonathan William. "Resonant cavity light emitting diodes." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399518.
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Hemingway, Leon Robert. "Dendrimers for light emitting diodes." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325840.
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Liu, Yee-Chen. "Polymer blend light-emitting diodes." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610709.
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Guan, Nan. "Nitride nanowire light-emitting diode." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS372/document.
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Les nanofils nitrures présentent des propriétés optoélectroniques extraordinaires et sont considérés comme des matériaux prometteurs pour des diodes électroluminescentes (LEDs), grâce à leur haute qualité cristalline, leurs surfaces non-polaires, leur bonne flexibilité mécanique, leur rapport d’aspect élevé, etc.Cette thèse adresse la croissance, la fabrication, les caractérisations optiques et électriques et la simulation optique des dispositifs à base de nanofils nitrures, avec un accent particulier sur les LEDs à nanofils.Premièrement, cette thèse présente la croissance par épitaxie en phase vapeur aux organométalliques de nanofils nitrures cœur-coquille auto-assemblés contenant des puits quantiques InGaN/GaN sur les facettes plan m avec différentes concentrations d’In. Puis est décrite la fabrication de LEDs utilisant ces nanofils suivant deux différentes stratégies d’intégration (intégrations planaires et verticales).L’intégration planaire est basée sur des nanofils uniques dispersés horizontalement. J’ai proposé une plateforme photonique intégrée composée d’une LED à nanofil, d’un guide d’onde optimisé et d’un photodétecteur à nanofil. J’ai également développé un système d’alignement des nanofils.L’intégration verticale a pour objectif la réalisation de LEDs flexibles reposant sur une assemblée de nanofils verticaux encapsulées dans des polymères. Je montre que ceci permet la fabrication de LEDs flexibles monochromatiques, bi-couleurs ou blanches.Les nanofils épitaxiés sur des matériaux 2D par épitaxie de van de Waals sont faciles à décoller de leur substrat natif. Avec cette motivation, dans la dernière partie de cette thèse, j’ai étudié la croissance organisée des nanofils GaN sur du graphène micro et nano-structuré utilisant l’épitaxie par jets moléculairesNitride nanowires exhibit outstanding opto-electronic and mechanical properties and are considered as promising materials for light-emitting diodes (LEDs), thanks to their high crystalline quality, non-polar facets, good mechanical flexibility, high aspect ratio, etc.This Ph.D. thesis addresses the growth, the device fabrication, the optical and electrical characterizations and the optical simulations of III-nitride NW devices, with a special emphasis on the LED applications.First, this thesis presents the growth of m-plane InGaN/GaN quantum wells with different In concentrations in self-assembled core-shell nanowires by metal-organic chemical vapor deposition. Then, by using these nanowires, LED devices based on two different integration strategies (namely, in-plane and vertical integration) are demonstrated.The in-plane integration is based on the horizontally dispersed single nanowires. I have proposed a basic integrated photonic platform consisting of a nanowire LED, an optimized waveguide and a nanowire photodetector. I have also developed a nanowire alignment system using dielectrophoresis.The vertical integration targets the fabrication of flexible LEDs based on vertical nanowire arrays embedded in polymer membranes. Flexible monochromatic, bi-color, white LEDs have been demonstrated. Their thermal properties have been analyzed.The nanowires grown on 2D materials by van der Waals epitaxy are easy to be lifted-off from their native substrate, which should facilitate the fabrication of flexible nanowire devices. With this motivation, in the last part of this thesis, I have investigated the selective area growth of GaN NWs on micro- and nano- scale graphene by molecular beam epitaxy
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Lau, Kwok Hing Connie. "Stacked organic light emitting diode." HKBU Institutional Repository, 2008. http://repository.hkbu.edu.hk/etd_ra/916.
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Wang, Yan. "Highly flexible top-emitting phosphorescent organic light emitting diodes (OLEDs)." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/50921.
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Organic Light Emitting Diodes (OLEDs) have become attractive for flat panel display industry, with applications ranging from mobile phone screens to TVs. They have several advantages over inorganic LEDs such as high contrast ratio, wide viewing angle, faster response time, scalable large area processing and most importantly mechanical flexibility. OLEDs on flexible substrates can endure certain level of mechanical deformation such as bending, rolling or folding without disruption of the performance. The current demonstrated flexibility for OLEDs is up to a few centimeters or millimeters bending radius, depending on the materials, substrates and device structures. More flexible OLEDs with bending radius of curvature on the order of microns will be needed for applications in wearable, roll-up, or foldable displays and bezel-free screens and flexible signage systems.
This thesis presents the design, fabrication and characterization of highly flexible and foldable top-emitting OLEDs made on 50 micron thick polyimide (PI) plastic substrates, which can achieve approximately 200 microns bending radius of curvature (folding) without visible damage or impact on emission brightness and uniformity. To the best of our knowledge these are the most flexible phosphorescent OLEDs and first foldable OLEDs ever reported. We believe such flexibility is the benefit of the mechanical stability and low film thickness of the PI substrate. The surface roughness of PI had been the major limitation of its application as OLED substrates, and in this thesis a special side-angle evaporation method is proposed to improve the step coverage of deposited thin films of materials on PI without the requirement of buffer layers. The same method is also proved to be applicable for fabricating OLEDs on much rougher substrates such as Scotch tapes, and fiberglass and transparency sheets. The OLEDs fabricated on above substrates are also presented and characterized.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
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Ferreira, Ricardo Xavier da Graça. "Gallium nitride light-emitting diode enabled visible light communications." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=28805.
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This thesis focuses on the development, measurement and application of novel micrometre-sized light emitting diodes (micro-LEDs) based on Gallium Nitride (GaN) for visible light communications (VLC) in both free-space and guided wave configurations. The goal is to set benchmarks for LED-based wireless optical communications. An overview of the field integrating research, industry and standards is presented. A top-down approach is taken with application requirements driving development of new micro-LEDs with simultaneously increased optical power and modulation bandwidth. This was achieved by mitigating two limitations, namely current crowding and mutual device heating. Two novel techniques were developed to access pixel performance: spatially-resolved mapping of modulation bandwidth and spectral characteristics, and thermal imaging. On this basis, broad-area LEDs were used to understand the independent benefits, providing insight for the design of novel micro-LEDs. Circular segmented micro-LEDs emitting at 450nm achieved modulation bandwidths in excess of 800MHz, the highest reported for LEDs, while maintaining optical power above 2mW. In data transmission using systems with 1.8GHz bandwidth,the devices achieved 8Gbps in free-space and guided-wave operation at wavelengths of 400nm, 450nm and 520nm. Ring and half-ring micro-LEDs introduced here have shown modulation bandwidths that scale with the increase of active area and consequently optical power. Bandwidths in excess of of 600MHz were achieved at optical powers over 5mW. In data transmission using a system limited to 1GHz bandwidth, these devices achieved 7Gbps in free-space operation.
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Fang, Fang. "Investigation of green light emitting diodes." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610094.
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譚祐怡 and Yau-yee Tam. "Dual use of visible light-emitting diodes." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31223436.
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Tam, Yau-yee. "Dual use of visible light-emitting diodes /." Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21949001.
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Taylor, Richard Martin. "Approaches to blue light emitting polymers." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343367.
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Webster, Graham R. "Advanced polymers for light emitting diodes." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393551.
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Liedtke, Alicia. "Liquid crystals for light emitting diodes." Thesis, University of Hull, 2009. http://hydra.hull.ac.uk/resources/hull:2429.
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In this work a series of new semiconducting liquid crystals (LCs), which are applicable for organic light emitting diodes (OLEDs), were investigated. Semiempirical calculations were carried out on monomers and anti-cofacial dimers built from our molecules, representing molecules in solution and thin film respectively. Compared to the monomer a doubling of the oscillator strength in the dimer was found for longitudinal offsets larger than 20 A. Smaller shifts showed a forbidden absorption transition from ground to the lowest excited state. Assuming that the absorption transition is equivalent to the emissive transition, this might explain the reduced optical quantum efficiency observed for all of our materials in the solid state. OLEDs made from blends of three different blue/green emitters with a red component showed white light emission with voltage independent CIE coordinates close to the ideal white. With polarised microscopy nematic phases frozen in a glassy state at room temperature were observed for all blends. Thus the blends were homogeneous and no phase separation occurred. This is important for homogeneous white emission and the alignment of the LCs due to a rubbed alignment layer below. Polarised white electroluminescence with an average polarisation ratio of 8:1 was shown from an OLED made with a blend deposited onto an alignment layer. Polarised background light for LC displays is desirable as this minimises the losses at the polarisers in the display and thus increases its brightness or lowers the power consumption. The low efficiency of the red emitter however limited the OLED performance. Surface relief gratings (SRGs) with periods of a few hundred nm and a maximum depth of 66 nm and periods in the nm-range with a depth of 140 nm were spontaneously induced on our films. They were formed through molecular mass transport from the dark to bright regions during crosslinking by irradiation with a sinusoidal light pattern created by a phase mask. The anisotropic properties of LCs are shown to enhance transport. SRGs were formed at room temperature and an elevated sample temperature of 65deg. They are suitable feedback structures for optically pumped organic lasers and can also be employed to enhance the outcoupling of OLEDs.
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Visweswaran, Bhadri. "Encapsulation of organic light emitting diodes." Thesis, Princeton University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3665325.
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Organic Light Emitting Diodes (OLEDs) are extremely attractive candidates for flexible display and lighting panels due to their high contrast ratio, light weight and flexible nature. However, the materials in an OLED get oxidized by extremely small quantities of atmospheric moisture and oxygen. To obtain a flexible OLED device, a flexible thin-film barrier encapsulation with low permeability for water is necessary.
Water permeates through a thin-film barrier by 4 modes: microcracks, contaminant particles, along interfaces, and through the bulk of the material. We have developed a flexible barrier film made by Plasma Enhanced Chemical Vapor Deposition (PECVD) that is devoid of any microcracks. In this work we have systematically reduced the permeation from the other three modes to come up with a barrier film design for an operating lifetime of over 10 years.
To provide quantitative feedback during barrier material development, techniques for measuring low diffusion coefficient and solubility of water in a barrier material have been developed. The mechanism of water diffusion in the barrier has been identified. From the measurements, we have created a model for predicting the operating lifetime from accelerated tests when the lifetime is limited by bulk diffusion.
To prevent the particle induced water permeation, we have encapsulated artificial particles and have studied their cross section. A three layer thin-film that can coat a particle at thicknesses smaller than the particle diameter is identified. It is demonstrated to protect a bottom emission OLED device that was contaminated with standard sized glass beads.
The photoresist and the organic layers below the barrier film causes sideways permeation that can reduce the lifetime set by permeation through the bulk of the barrier. To prevent the sideways permeation, an impermeable inorganic grid made of the same barrier material is designed. The reduction in sideways permeation due to the impermeable inorganic grid is demonstrated in an encapsulated OLED.
In this work, we have dealt with three permeation mechanisms and shown solution to each of them. These steps give us reliable flexible encapsulation that has a lifetime of greater than 10 years.
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Weaver, Michael Stuart. "Electroluminescence from organic light emitting diodes." Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265610.
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Fehrman, Stephen A. "Passivation of polymer light-emitting diodes." Click here to view, 2009. http://digitalcommons.calpoly.edu/eesp/19/.
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Thesis (B.S.)--California Polytechnic State University, 2009.Project advisor: David Braun. Title from PDF title page; viewed on Jan. 28, 2010. Includes bibliographical references. Also available on microfiche.
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Dinh, Vincent Vinh. "Degradation in organic light emitting devices /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2003. http://uclibs.org/PID/11984.
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Blades, Christopher David James. "Simulation of organic light emitting devices." Thesis, University of Bath, 2000. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760747.
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Gray, Dodd (Dodd J. ). "Thermal pumping of light-emitting diodes." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/76963.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 129-135).
The work presented here is a study of thermally enhanced injection in light-emitting diodes (LEDs). This effect, which we refer to as "thermal pumping", results from Peltier energy exchange from the lattice to charge carriers when current is injected into an LED. For an applied voltage V such that qV < (hw), where q is the electron charge and (hw) is the average emitted photon energy, thermal pumping can greatly enhance the wall plug efficiency of an LED. Thermal pumping can even give rise to LED wall plug efficiency greater than one, which corresponds to electroluminescent cooling of the diode lattice. Thermal pumping and electroluminescent cooling will be studied through numerical modeling and experiment. Our results include the first ever experimental demonstration of electroluminescent cooling in an LED. Finally we use the intuition gained from the study of thermal pumping to design an LED for maximized optical power output with 100% wall plug efficiency.
by Dodd Gray.
M.Eng.
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Lupton, John Mark. "Nanoengineering of organic light-emitting diodes." Thesis, Durham University, 2000. http://etheses.dur.ac.uk/1597/.
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Squire, E. K. "Light emitting microstructures in porous silicon." Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285287.
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Hood, Sean. "Light emitting diode color rendition properties." Kansas State University, 2013. http://hdl.handle.net/2097/15647.
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Master of ScienceDepartment of Architectural Engineering and Construction Science
Fred Hasler
This paper discusses the color rendition capabilities of light emitting diodes (LEDs) and their relationship with the current standard for color rendition quality. The current standard for judging light source color rendering properties, known as the color rendering index (CRI), has come under heavy scrutiny in recent years with the introduction of LED in commercial lighting applications. LEDs, depending on construction type, have highly structured spectral distributions which do not scale well under the color rendering index; moreover, CRI for LEDs has become disjointed with the subjective measurement of human color preference. Unfortunately, given the multidimensional nature of color, an all-encompassing scale with a single rated value for color rendition capabilities of a light source has proven difficult to establish. An analysis on the human visual system is first discussed, establishing how the visual system first detects color in the eye and subsequently encodes that color information through a color-opponent process, formulating conscious color appearance. The formation of color appearance leads into a discussion on human color vision and the creation of three dimensional color space, which is subsequently used for the measurement of color fidelity (CRI) of consumer light sources. An overview of how LED lamps create light and color is then discussed, showing that the highly structured spectral distribution of LED lamps is often the cause of discrepancy within the CRI system. Existing alternatives to the CRI system are then compared and contrasted to each other, and the existing CRI system. A final color preference study was conducted where four LED lamps where compared to a reference lamp of equal correlated color temperature. Observers were asked to rate the various test lamps against the reference lamp in terms of vividness, naturalness, overall preference, and individual color preference. It was found that no significant difference was found between the first three dimensions measured but significant trend lines existed for the preference of individual colors when illuminated by either LED lamps or the reference source. Recommendations are then made for how the lighting industry could move forward in terms of color metrics.
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Galata, Sotiria. "Sulphur doped silicon light emitting diodes." Thesis, University of Surrey, 2005. http://epubs.surrey.ac.uk/842933/.
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In this thesis light emission from sulphur related impurity in silicon has been reported. Although, sulphur related luminescence from silicon has been stated since the 1980's, no room temperature luminescence has been achieved and no compatible devices that can be integrated to the silicon technology have been invented. Photoluminescence and electroluminescence experiments were made on a set of samples implanted with only with sulphur at doses ranging from 1011-1014 S cm-2 at 30 keV, annealed at 1000 °C or 1100 °C for 10 s and on another set of samples implanted with sulphur as above and further implanted with boron at 1015 B cm-2 at 30 keV, further annealed at 950 °C for 1 min. The experiments revealed two major emissions at 1129.5 nm (1.0997 eV) which is due to the Si TO phonon assisted transition and at 1363 nm (0.9097 eV) which is due to sulphur related impurities. Variable temperature experiments were done at both PL and EL experiments. From the EL variable temperature measurements, it was observed that the two main lines were shifting towards longer wavelengths with the increase of temperature. Sulphur emission was present at room temperature with low intensity compared to the silicon emission which was more dominant at room temperature. Of great interest was the effect of power on silicon and sulphur emission. It has revealed a sublinear and a superlinear behaviour for the sulphur and silicon integrated intensity respectively with the increase of the injection condition, which can be attributed to the saturation of sulphur related levels responsible for the 1.33 nm emission at the high excitation levels. A model of the diffusion of sulphur concentration after the annealing treatments was presented, introducing the two cases of perfect reflection and perfect loss from the samples surfaces. Finally a model explaining our PL and EL power dependence experiments was provided which showed that there are two major radiative routes via the silicon and the sulphur that take place, which are competing at each other along with a non-radiative route coming from the sulphur related level. Our model describes the trends in our experimental data well. Finally, the energy related to the sulphur peak quenching was calculated to be 32.2 +/-1.4 meV.
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Siddiqui, Saiful Anam. "Erbium doped silicon light emitting diodes." Thesis, University of Surrey, 2003. http://epubs.surrey.ac.uk/843408/.
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Erbium, a rare earth element, has been shown to exhibit characteristic luminescence at 1.54mum due to its internal 4f transition from the first excited state (4pi3/2) to the ground state (4pi5/2). As this emission wavelength falls inside the maximum transmission window of silicon based optical fibers, erbium doped silicon might lead to the opportunity of silicon based optoelectronics. The introduction of erbium in silicon allows excitation through electron-hole recombination and subsequent radiative emission from the rare earth centers. The works reported here describe the structural, electrical and optical properties of crystalline silicon codoped with erbium and boron by ion implantation technique. Four sets of samples, co-implanted with erbium and boron at different Er dose, implantation energy and at different conditions, were prepared. Post-implantation annealing has been performed to recover the implantation damage to an acceptable value and to activate the dopant atoms optically and electrically. PL and EL measurements have been performed in the temperature range between 80K to room temperature. The sample with the lowest erbium concentration and energy gives the best PL and EL results. The observed emission peaks in both PL and EL measurements were at around 1.129mum, ~1.303mum, 1.50mum and 1.597mum at 80K. At higher temperatures, a broader peak at around 1.50mum with long tail towards the both end of wavelength has been observed. The peak at 1.129mum corresponding to the Si band edge emission, the reason for the peaks at around l.303mum has not been identified while the remaining two peaks correspond the Er3+ emission. Virtually no temperature quenching of Er luminescence is observed in some samples rather room temperature intensity is higher than that at 80K. The improvement of the temperature quenching effect on Er luminescence at room temperature has been attained in our results, which is significant improvement in comparison to the result found in the literature. The structural properties were studied by TEM in both cross-sectional and plan view configurations. TEM analyses showed dislocation loops and other defects of random size and distribution from the surface to 600nm below the surface. Er precipitates defects were also seen in the sample doped with Er comparatively at higher dose (1x1015Er/cm2) and energy (1.0 MeV). No detectable room temperature PL and EL signals were observed from the sample implanted at higher doses and energies.
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Huang, Qiang. "High efficiency top-emitting organic light-emitting diodes: design and fabrication." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1193677683674-43826.
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This thesis focuses mainly on the techniques to achieve high-performance top-emitting OLEDs, regarding device efficiency and lifetime for both non-inverted and inverted structures. It is thus organized as follows: In Chapter 2, the basic physics of organic semiconductor materials are reviewed, including the electronic properties of organic semiconductor materials, molecular excitations and their electronic transitions etc., which are believed to be critical for understanding of the work. Then, the general device physics of OLEDs are reviewed in detail, which includes almost every important electrical and optical process involved in the device. Finally, techniques and methods used to improve the device performance are summarized, which includes electrical doping of charge carrier transport layers. In Chapter 3, all organic materials, experimental techniques, and characterization methods used in this study are briefly described. In the following Chapter 4, techniques that are used for device optimization of non-inverted top-emitting OLEDs are discussed. Also, the mechanism of light outcoupling enhancement by a capping layer is discussed there. In the last part of Chapter 4, the influence of the optical device structure on the intrinsic quantum yield of the emitters is studied. Chapter 5 is focused on inverted top-emitting OLEDs, which are believed to be better applicable with current mainstream n-type amorphous silicon thin film transistor (TFT) technology. In this Chapter, the organic/metal and metal/organic interfaces are investigated in detail and their influence on device performance is discussed. In Chapter 6, the degradation of top-emitting OLEDs is studied, with a focus on the influence of electrode material and electrode thickness on the lifetime of top-emitting devices.
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Chanyawadee, Soontorn. "Resonant energy transfer in light harvesting and light emitting applications." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/72508/.
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The performance of light emitting and light harvesting devices is improved by utilising resonant energy transfer. In lighting applications, the emission energy of a semiconductor heterostructure and the absorption of organic dyes or colloidal quantum dots (QDs) are engineered so that the excitations in the semiconductor heterostructure can be transferred to the light emitters by means of resonant energy transfer. The emitters subsequently emit colour-tunable light ranging from the visible to the near-infrared. As a result, a twofold enhancement of QD emission is demonstrated in a hybrid QD/semiconductor heterostructure. In light harvesting applications, a hybrid structure of colloidal QDs and a quantum well (QW) p-i-n heterostructure is investigated. After highly absorbing QDs absorb photons, the excitations are efficiently transferred to a QW p-i-n heterostructure via resonant energy transfer. The generated electron-hole pairs in the heterostructure are subsequently separated by the built-in electric held and collected by the corresponding electrodes. In order to increase the energy transfer rate, the donor-acceptor separation distance is minimised by fabricating channel structures on the heterostructure surface penetrating its active layers. Consequently, a sixfold enhancement of photocurrent conversion efficiency is demonstrated. Photocurrent of the hybrid structure is further improved by replacing the QW heterostructure with a bulk p-i-n heterostructure which has higher carrier transport efficiency. Hence, the photocurrent of the hybrid bulk heterostructure is about two orders of magnitude higher than that of the hybrid QW heterostructure. The proposed hybrid structures offer efficient light harvesting devices where high absorption of the colloidal QDs is utilised and their low charge transfer is overcome.
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Chang, Mau-Shang, and 張貿翔. "Top-emitting Polymer Light-emitting Diodes." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/67891518469301255707.
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碩士國立成功大學
微電子工程研究所碩博士班
94
Recently, polymer light-emitting diodes (PLEDs) have been significantly fabricated with top-emitting architecture. The emission intensity enhancement and narrowing electroluminescence (EL) spectrum can be attributed to microcavity effects. In this thesis, a top-emitting structure was Glass/ITO/Ag(120nm)/PEDOT:PSS(40nm)/DB-PPV/Ca(10nm)/Ag, and then the device emitted light through the cathode side Ca/Ag. The polymer emissive layer was DB-PPV (2,3-dibutoxy 1,4-poly(phenylene vinylene)), which was sandwiched between two metal electrodes. One electrode was the bottom reflective anode, which was the surface modified silver film, and the other one was the top semitransparent double-layer cathode Ca/Ag. Finally, the emitting light emitted from the semitransparent cathode under forward bias. By changing the thickness of polymer emissive layer in the microcavity structure and the thickness of Ag in the double-layer cathode, narrower EL spectrum and enhancement of emission intensity was obtained simultaneously. By way of appropriately tuned the thickness of polymer emissive layer and concentration, we general found that the maximum luminance efficiency in the concentration of 0.6% with spin speed of 2000rpm (65nm) and 0.7% with spin speed of 4000rpm (58nm), respectively. This was because most of the recombination or emission zone was closer to the antinode, and the normal direction luminance efficiency increased by a factor of 1.13 ~ 1.65 (2.22 to 3.25cd/A) for 0.6% and 1.01 ~ 1.79 (1.68 to 2.99cd/A) for 0.7%, respectively. Besides, the EL peak wavelength of device with a single emissive layer has a wide variation in the spectral range, from 522 to 622nm, due to the different thickness of DB-PPV. Consequently, tuned the emitting color from original yellowish green (λD=560nm) to saturated green (λD=527nm) and yellow orange (λD=582nm). The full width at half maximum (FWHM) of original EL spectra could be reduced from about 70nm to 20nm.
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CHANG, TUN-MIN, and 張敦岷. "Light-Extraction Enhancement of Light Emitting Diodes andOrganic Light Emitting Diodes by Photonic Crystal Structures." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/30191578760954676719.
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碩士國立臺灣大學
光電工程學研究所
95
In this thesis, a flexible and efficient method to calculate light extraction efficiency of light-emitting device is developed. This method is primarily based on finite-difference time-domain ( FDTD) method aided with Fourier analysis to obtain the intensity of the target frequency. Energy through all angles or positions is summed up to evaluate total extraction efficiency. LEDs ( light emitting diodes) and OLEDs ( organic light emitting diodes) might become one of the primary components in displays and lighting. However, both suffer low light extraction efficiency. Considering this issue, this thesis focuses on LED and OLED simulation. Photonic crystal is applied to LED and OLED for light extraction efficiency improvement. Numerous parameters are scanned within parameter bounds to evaluate the best case and the relationship between light extraction efficiency and each individual parameter, enabling us to understand effects of various parameters and design considerations. We define structure without photonic crystals an ”original structure.” The thesis starts with ordinary rectangular structure. Furthermore, triangular, semi-circle and circle structures are also taken into consideration. Finally, simulation results indicate that rectangular structure in LED offers an optimal improvement at three times of the light extraction efficiency compared with original structure, while rectangular structure combined with flat plate in OLED offers an optimal improvement of thirty percent in light extraction efficiency compared with original structure.
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Su, Po-Kun, and 蘇伯昆. "The Synthesis of Light-Emitting Copolymers and Fabrication of Light-Emitting Diodes." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/62324554798695243913.
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碩士國立臺北科技大學
有機高分子研究所
90
We present synthesis and characterization of copolymers. In this study, copolymers of poly (2,3-diphenyl-5-hexyl-1,4-phenylenevinylene)(DP6-PPV) and poly [2-methoxy- 5-(2’ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) have been synthesized via a modified Gilch route involving the use of an acidic additive such as 4-tert-butylbenzyl chloride. As a result of this modified polymerization route, gelation can be minimized and the resulting copolymers were well soluble in common organic solvent, such as THF, toluene and chloroform etc. Blue-green to orange-red emission of copolymers was achieved by the different feeding ratio of two monomers.
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胡峻瑋. "Synthesis of White-Light-Emitting Molecules for White Organic Light-Emitting Diodes." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/9f27q9.
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碩士逢甲大學
化學工程學系
103
Two white-light-emitting small molecules, 1 and 2, were synthesized and fully characterized. Compounds 1 and 2 undergo an excited-stateintramolecular proton transfer (ESIPT) reaction, resulting in a tautomer that is in equilibrium with the normal species, exhibiting a dual emission that covers almost all of the visible spectrum and consequently generates white light. Moreover, the geometric structures and rontier molecular orbitals for 1 in the ground and the first singlet excited state were fully rationalized by density functional theory (DFT) and time-dependent DFT calculations.
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Hsieh, Chun-Yu, and 謝濬宇. "Candle Light-Style Organic Light Emitting Diode." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/50845307637013042446.
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Lee, Kuen-da, and 李昆達. "Study of bicycle traffic lights with Light Emitting Diode." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/71754099906579035008.
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劉漢康. "Synthesis and Characterization of Light-Emitting Polymers and Applications in Organic Light-Emitting Diode." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/27894329868350761490.
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Gau, Huan-Jie, and 高煥捷. "Blue Phosphorescent Organic Light-Emitting Diode and Alternating Driven Current Organic Light-Emitting Diode." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/r2we9f.
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碩士元智大學
光電工程學系
104
In this thesis, the first part is disclosed a series of novel host materials combining hole-transporting moiety, Carbazole, and electron-transporting moieties Triazole and Pyridine, as bipolar host to fabricate high efficiency blue phosphorescence organic light-emitting diode (OLED) with the blue phosphorescent emitting dopant, FIrpic. Second part is the development of an alternating current (AC)-driven organic light emitting diodes (OLED). We co-depositied these materials to modulate their energy level. We designed a symmetrical device structure, to achieve the lit-on OLED at positive and negative half-cycle stage in AC driven. In the chapter I, we introduced the OLED relatives, including history, principle, recent development of OLED in materials and device. Chapter II described the experimental detail to fabricate the OLED devices and some know-how. Chapter III results and discussion, we characterized four novel host materials by, measuring of the absorption spectrum, highest occupied electronic energy levels (HOMO), lowest electronic unfilled full energy level (LUMO), and photoexited fluorescence spectrum. They were employed to host material of emitting layer (EML) of blue OLEDs. Varying the dopant concentration, and the thickness of electron-transporting layer to achieve electron-hole balance for high efficiency blue OLED. Furthermore, we also investigated the main recombination zone of EML using partial doped dopant at distinct EML position. Chapter IV introduced a method using a partial mixed host as a part of EML, combining o-DiCbzBz with various electron-transporting hosts, such as BTBP, DPPS, and TmPyPB. Varying the layer thickness of partial mixed host in EML, the main recombination zone was enlarged and the carrier balance could be achieved because we obtained a great improvement in the device efficiency. Chapter V demonstrated an alternating current (AC)-driven organic light emitting diodes (OLED) by modifying the carrier injection layer. The purpose was to fabricate a direct AC-driven OLED with any dielectric layer. The last Chapter VI was the thesis conclusions.
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Chen, Pin-cheng, and 陳品承. "Investigation of Surface Plasma Enhance Light Emitting Efficiency of Nano-silicon Light Emitting Device." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/88146896019770403461.
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碩士國立成功大學
微電子工程研究所碩博士班
97
In this thesis, we elucidated the development and basic theory of surface plasmon. In the experiment, we deposited the different thickness of silver nanoparticles on the nano-silicon light emitting devices to enhance light extraction efficiency by using localized surface plasmon resonance (LSPR). Silver nanoparticles arrayed layers were fabricated by e-gun and annealing processes. The size and geometry of particles can be controlled by the three conditions, such as a deposited film thickness, annealing temperature and time. These are important factors to determine the efficiency, because a LSPR depends on both of the size and density of particles. Then we measured the electroluminescence (EL) spectra of nano-silicon light emitting devices with silver nanoparticles. We found that the luminescence efficiency enhancement was more apparent when the silver nanoparticles layer were closer to active layer of nano-silicon light emitting devices. From all the results, we can find out that the surface plasmon effect related with light emitters was depended on the parameters of the added structures. If these structures can be well designed, we will have a chance to improve the luminescence efficiency of nano-silicon light emitting devices.
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Pan, Shin-you, and 潘信友. "The study of top-emitting organic light-emitting diodes." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/30847092806231287032.
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碩士義守大學
電子工程學系碩士班
93
Inverted top–emitting organic light emitting diodes (OLEDs) employing an aluminum coated glass substrate directly as a cathode and a semitransparent top Au thin film as an anode have been proposed. Light emits from the anode. The characteristics of Au thin film are very easily scraped by any external factor. This effect reduces the carrier injection ability. Therefore, aluminum is covered on the Au thin film to promote carrier injection and avoid being scraped. The maximum efficiency has been improved from 0.4cd/A up to 2.4cd/A. The interface between cathode and Alq3 is not smooth enough in the inverted structure. Aluminum thin film is used as a buffer layer to smooth the interface. The structure is Glass / Al(2000Å) / LiF(7Å) / Al(10Å) / Alq3(600Å) / NPB(400Å) / m-MTDATA(200Å) / Au(200Å) / Al(200Å). This structure has decreased the turn-on voltage from 12V to 8V and its maximum efficiency is up to 3cd/A.
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吳日中. "Organic Light-Emitting Diode Based Artificial Dusk-Light." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/31730494468755683827.
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Lin, Ching-Liang, and 林京亮. "Light Enhancement of Thin-GaN Light Emitting Diodes." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/51951559488289706667.
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博士國立中央大學
化學工程與材料工程研究所
96
GaN-based materials have leaped to a brand new stage in the past two decades. The single crystalline and direct band-gap GaN film can be grown on the sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The wavelength of the emitting light from GaN ranges from ultra-violate (UV) to blue light region by doping various indium content. Nowadays, the material of the blue light emitting diodes is based on the GaN material. Pumping phosphors or other wavelength converter by blue light, the white light can be generated. Hence, the GaN material is the key material for white solid-state lighting. For the solid-state lighting applications, the GaN-based LED operates under a high electric power. Under such a high operation power, the heat dissipation is a critical issue. The sapphire substrate of the conventional LED has a poor thermal conduction. Also, the degradation of the electric and optical property would be very serious due to the high operation temperature. Therefore, in this study, the thin-GaN LED device is produced by the wafer bonding process and the laser lift-off process, which are used to transfer GaN thin film from the sapphire substrate to a better thermal conductive Si substrate. Owing to the better thermal dissipation, the thin-GaN LED structure is a very promising candidate for developing high-power GaN LED. Two main topics of the studied thin-GaN LED structure in this work: (1) Design a suitable p-GaN contacts and reflector for thin-GaN LED structure. (2) Increase the light extraction efficiency of thin-GaN LED. In thin-GaN LED process, the wafer bonding process is necessary and it is a high temperature and high pressure process. Furthermore, the Si substrate is a non-transparent material for the blue light region. So, the p-type GaN contact should consist of an ohmic contact layer and a reflector as well. It is very important to develop a high thermally stable p-GaN contact. In this study, the Ni/Au/Ni/Al p-GaN contacts and Ni/Ag(Al) p-GaN contacts are investigated. These two thermally stable p-GaN contacts can reduce the degradation of the specific contact resistance and the reflection upon the thermal process. The specific contact resistance of the Ni/Au/Ni/Al p-GaN contact keeps on the order of 10-2 Ω-cm2 after 500 ℃ annealing. The reflectance of the Ni/Au/Ni/Al metal scheme is 60 % after 500 ℃ annealing. This high thermally stable Ni/Au/Ni/Al p-GaN contact is very suitable for the thin-GaN LED structure. Another critical issue is the low light extraction efficiency due to large refraction index difference between GaN and air. The light emitted from the active layer in GaN is significantly trapped in the GaN epi-layer, and a serious total internal reflection occurs. In this study, the aluminum oxide and silicon oxide honeycomb structure are produced on the n-GaN emitting surface by poly-styrene spheres template and sol-gel method. The aluminum oxide and silicon oxide honeycomb structures capping on the n-GaN surface can increase the external quantum efficiency by 35 % and 19 %, respectively. The mechanism of increasing light out-put by the oxide honeycomb structure would be discussed.
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Ho, Pei-Chen, and 賀培誠. "Light extraction analysis of light-emitting diodes array." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/94323868021292534601.
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碩士元智大學
光電工程研究所
99
In this study, we build the optical model for GaN LED to study light extraction efficiency of LEDs based on the simulation with Monte Carlo ray tracing. According to this model, we change the LED-to-LED spacing of 3 × 3 LEDs array to analyze the light extraction efficiency with or without silicon. We analyze the light extraction efficiency for GaN LEDs array with different type of LED and LED-to-LED spacing. Finally, we compare the experiment with simulation results, and present the optimum enhancement of light extraction efficiency with different silicon shape parameters in each type of GaN LED.
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Peng, Sheng-yang, and 彭聖揚. "Multifunctional white light emitting diode." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/79934244374666129071.
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碩士國立臺灣科技大學
光電工程研究所
100
The objective of this thesis to increase the functionality of white light emitting diode (WLED) use the multi-chips structure, modified omni-directional reflector (ODR) and TiO2 photocatalyst to package the WLED which has functionality of the tunable color garmut and air purification. The modified ODR has been improved according to the previous research, which property is that when light incident angle is 40°, the wavelength of 380 nm of transmittance is 40%. Because TiO2 photocatalyst have to be under the UV light emitting and TiO2 photocatalyst can be used to do air purification, we spray the TiO2 photocatalyst on the back side of the modified ODR to fabricate the compound element, and packaged with UV-excited white LED, where TiO2 can be work over the emitting angle of 40°. To packaged WLED with compound element and controlled the composition and concentration of phosphors blend layer by means of Taguchi Method. When TiO2 photocatalyst layers is 3 layers and WLED is at a constant driving current of 20 mA, the color coordinate for light source made was (0.3319, 0.3324), the color correlated temperature (CCT) was 5518 K, the color rendering index (CRI) was 94, the angle distribution of properties of WLED is uniformity, and it could work for degradation of methylene blue. This study proposed a purple light chip (λpeak = 410 nm) and a blue light chip (λpeak = 465 nm) combined with the above structure of UV-excited WLED, and we can achieve a multifunctional WLED which can be color tunable and for air purification by controlling the concentration of phosphor and driving current. Specifically, the color coordinate for light source made was (0.3332, 0.3357), the CCT was 5461 K and CRI was 83. Finally, we changed the chips of a multifunctional WLED for high power chips, and fabricated the WLED lamp to do the experiment of degradation of ammonia concentration. The result showed the multifunctional WLED can really work for air purification. The UV light chips and blue light chips were applied driving current at 20 mA or 100 mA, and it worked for 5 hrs, the degradation rate of ammonia concentration were 42.5 % or 64.3 %.