High brightness inorganic LEDs have been utilized effectively for signage application using the edgelighting technique. In this thesis. the inorganic LED-based edgelit signage using transparent acrylic has been evaluated. We determine that the edgelighting technique, although superior in efficiency to other available techniques, suffers from intrinsic limitations, particularly in terms of illumination uniformity. The illumination uniformity can be improved by external means such as a diamond grating. In order to quantitatively establish this, the illumination uniformity of the LED-based signage with and without the diamond grating is examined. The results show a considerable improvement in the illumination uniformity when a diamond grating is used. However, the high cost of the diamond grating and the transparent acrylic amplify the overall cost of signage using LEDs. Therefore, a distributed light source, which can eliminate the use of the diamond grating. is determined to be more suitable for signage application. Organic Light-Emitting diode (OLED), which is a distributed light source, emerges as a possible contender. The second part of our research focuses on the application of OLEDs for signage. We examine two OLED modules from different manufacturers for our evaluation. The first module is a prototype module obtained from the National Research Council (NRC) and the second module is a commercially available OLED from RiT Display Corporation. We present novel design techniques that can be used to implement signage based on OLEDs. A prototype tiled OLED display using commercially available OLEDs is designed and tested. Our investigation suggests that good light uniformity in signage panels can be achieved using OLED modules in the form of tiles. This proves that OLEDs are superior to conventional light-emitting diodes as light sources for signage in terms of illumination uniformity. However, we determine that the currently available OLEDs have a lower light-conversion efficiency in addition to higher costs when compared with conventional LEDs. Though the individual OLEDs cost more than LEDs. signage panels based on OLEDs can be made cheaper by avoiding the use of acrylic sheet and diamond grating. Moreover, the light weight of OLEDs and the fact that OLEDs are diffused sources (rather than point sources like LEDs) add an additional advantage. Also. OLEDs have the potential to be built inexpensively on flexible substrates by using the roll-to-roll technique. This makes OLEDs superior to conventional LEDs in large-area signage applications.

This Thesis examines the operation and dynamic performance of a single-stage, single-switch power factor corrector, S4 PFC, with an integrated magnetic device, IM. Also detailed isthe development and analysis of a high power light emitting diode, HP LED, power factorcorrection converter and proposed voltage regulation band control approach.The S4 PFC consists of a cascaded discontinuous current mode, DCM, boost stage anda continuous current mode, CCM, forward converter. The S4 PFC achieves a high powerfactor, low input current harmonics and a regulated voltage output, utilising a singleMOSFET. A steady-state analysis of the S4 PFC with the IM is performed, identifying theoperating boundary conditions for the DCM power factor correction stage and the CCMoutput voltage regulation stage. Integrated magnetic analysis focuses on understanding theperformance, operation and generated flux paths within the IM core, ensuring the device doesnot affect the normal operation of the converter power stage. A design method for the S4 PFCwith IM component is developed along with a cost analysis of this approach. Analysis predictsthe performance of the S4 PFC and the IM, and the theoretical work is validated by MATLABand SABER simulations and measurements of a 180 W prototype converter.It is not only the development of new topological approaches that drives theadvancement of power electronic techniques. The recent emergence of HP LEDs has led to aflurry of new application areas for these devices. A DCM buck-boost converter performs thepower factor correction and energy storage, and a cascaded boundary conduction current modebuck converter regulates the current through the LED arrays. To match the useful operatinglifetime of the HP LEDs, electrolytic capacitors are not used in the PFC converter. Analysisexamines the operation and dynamic characteristics of a PFC converter with low capacitiveenergy storage capacity and its implications on the control method. A modified regulationband control approach is proposed to ensure a high power factor, low input current harmonicsand output voltage regulation of the PFC stage. Small signal analysis describes the dynamicperformance of the PFC converter, Circle Criterion is used to determine the loop stability.Theoretical work is validated by SABER and MATLAB simulations and measurements of a180 W prototype street luminaire.

The molecular design, synthesis and characterization of a series of ligands and the corresponding novel iridium(III) or platinum(II) complexes are discussed in this thesis. Their photophysical and electrochemical properties, the applications in organic light-emitting diodes (OLEDs), dye-sensitized solar cells (DSSCs), aggregation induced emission (AIE) and time-resolved infrared (TRIR) study are also investigated. Chapter 1 generates a brief overview of the background, principle, and development of OLEDs, DSSCs, AIE materials and the involvement of the TRIR technique. Chapter 2 describes the synthesis, spectroscopic, photophysical and electrochemical characterization of a series of cationic iridium(III) complexes. Strong electron-withdrawing carboxylic acid substituted bipyridyl was involved in the ligand system and the intra-ligand charge transfer character of diphenylamino containing ligand further shift the dominant absorption band to the lower energy region. Some of them were applied for DSSC device fabrication. Chapter 3 presents the synthesis, spectroscopic, photophysical and electrochemical characterization as well as OLED application of a group of cyclometalated iridium(III) complexes by using 2-substituted 9-benzylcarbazolyl, 9-phenylcarbazolyl or 2-methyl-7-phenylcarbazolyl groups as the ligands. They show significant bathochromatic shift from those using 3-substituted ligands. And this can be explained by the fact that more electron density is located at 2-position of carbazole moiety and make them suitable candidates for deep red OLED application. Chapter 4 delivers the synthesis, spectroscopic, photophysical and electrochemical characterization of a series of platinum(II) acetylide complexes for AIE study. All of the complexes contain [4-(1,2,2-triphenylethenyl)phenyl]ethynyl ligand, which is designed from AIE active building block tetraphenylamine (TPE). Some of these metal complexes show AIE behavior. Chapter 5 outlines the synthetic methodology and characterization of another series of cyclometalated iridium(III) and platinum(II) complexes, containing TPE or carbazole units. It is very interesting to find out that there is hardly any emission in all of the TPE-containing cyclometalated complexes, nor any signs of AIE behavior. Meanwhile, for carbazole-containing platinum(II) complexes, remarable AIE results could be generated, which is believed to be important for further organometallic AIE active material development. Chapter 6 describes the synthetic methodology and characterization of a series of symmetric or asymmetric platinum(II) acetylides. Some of them were further applied for TRIR analysis to generate detailed experimental information of the electron transitions during excitation. The results demonstrate that both localized and delocalized metal ligand orbital mixing could be generated according to the variations in electronegativity of the ligand system. Chapter 7 and 8 present the concluding remarks and summarize the experimental details of all of the previous chapters.

Tomographic Particle Image Velocimetry Using Colored Shadow Imaging by Meshal K Alarfaj, Master of Science King Abdullah University of Science & Technology, 2015 Tomographic Particle image velocimetry (PIV) is a recent PIV method capable of reconstructing the full 3D velocity field of complex flows, within a 3-D volume. For nearly the last decade, it has become the most powerful tool for study of turbulent velocity fields and promises great advancements in the study of fluid mechanics. Among the early published studies, a good number of researches have suggested enhancements and optimizations of different aspects of this technique to improve the effectiveness. One major aspect, which is the core of the present work, is related to reducing the cost of the Tomographic PIV setup. In this thesis, we attempt to reduce this cost by using an experimental setup exploiting 4 commercial digital still cameras in combination with low-cost Light emitting diodes (LEDs). We use two different colors to distinguish the two light pulses. By using colored shadows with red and green LEDs, we can identify the particle locations within the measurement volume, at the two different times, thereby allowing calculation of the velocities. The present work tests this technique on the flows patterns of a jet ejected from a tube in a water tank. Results from the images processing are presented and challenges discussed.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第22486号 / 農博第2390号 / 新制||農||1075(附属図書館) / 学位論文||R2||N5266(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 髙野 俊幸, 教授 和田 昌久, 教授 河本 晴雄 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

This thesis deals with synthesis and characterization of newoligothiophenes and derivatives thereof, for use as organicsemiconductors in optical and electronic applications, such asfield-effect transistors and light-emitting diodes. Much workis devoted to the development of new synthetic strategies forinteresting building blocks, to beused for synthesizing suchmaterials. One series of regio-defined oligothiophenes, up tothe octamer, has been prepared and evaluated. Photoluminescencequantum efficiencies of these were 22-31 % in solution, butdropped to 2-5 % in the solid state. Another project deals withthe development of oligothiophenes with in-chain chirality.These may find use in polarized lightemitting diodes. Finally,two oligothienyl-substituted porphyrins have been synthesizedand are currently evaluated for use in light-emitting diodesand possibly in solar cells. / NR 20140805

Research efforts towards realizing electrochemically-stable organic semiconductors have been a focus of the organic light-emitting diode (OLED) industry for decades. This is especially true for the discovery of blue-light emitting materials and compounds with optical band gaps greater than 2.8 eV as these materials undergo rapid degradation resulting in poor operational lifetimes. Benzo[1,2-d:4,5-d']bis(oxazole)s and benzo[1,2-d:4,5-d']bis(oxazole)s (BBOs) are useful building blocks that generate highly fluorescent materials with robust thermal and photo-oxidative stabilities and optical band gaps >2.8 eV. Previously, the Jeffries-EL group has synthesized and studied polymeric BBO systems for OLED application, which achieved sky-blue electroluminescence (EL) with external quantum efficiencies (EQEs) of approximately 1.1 %. However, these systems are plagued with broad electroluminescence due to their polydispersity and have yet to achieve power efficiencies >10 lm/W. Small molecule BBO-based emitters (SM-BBOs) are advantageous due to their discrete size, uniform pi-electron delocalization, and high purity. To date, SM-BBOs have realized deep blue EL with good color purity and EQEs approaching 3%. However, the number of possible structural variants are vast, but known examples of these systems are limited, thus more work is required to increase our understanding of these systems to develop SM-BBOs-based OLEDs with higher efficiencies for commercial utility. Herein, several classes of SM-BBOs bearing various aryl substituents are computationally and experimentally studied to understand fundamental optical and electronic properties. This data is used to determine the structure-property relationships between SM-BBO systems and to design functional microelectronic OLEDs. The collected experimental data is used by our computational teams to improve our predictive strategies and refine synthetic efforts. As such, several SM-BBOs were achieved which produced near-UV and deep-blue EL while combinations of these products were used to obtain the first prototype white OLEDs with temperature tunability using SM-BBO emissive materials. / 2022-09-07T00:00:00Z

With the progression towards lighter but larger-display self-sustainable mobile devices, device efficiency becomes increasingly important, owing to the higher power display consumption but at the same time more limitation on the size and volume of energy storage. In this thesis, selected aspects regarding to efficiency of three types of optoelectronic devices, indoor photovoltaics (IPVs), perovskite thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs) have been investigated. IPVs can make off-grid devices self-sustainable by harvesting ambient light energy. Its weak irradiance necessitates high-efficiency IPVs to generate sufficient power. Our work addresses the need of knowing the limit of the device parameters for correct evaluation and understanding the efficiency loss for developing clinical tactics. We delivered a general scheme for evaluating the limiting efficiency and the corresponding device parameters of IPVs under various lights, illuminance and material bandgap. In contrast to the AM1.5G conditions, a maximum power conversion efficiency (PCE) of 51-57 % can be achieved under the optimal bandgap of 1.82-1.96 eV. We also propose using the second thickness peak of interference instead of the first as a better optimal absorber thickness after identifying the finite absorption as the major source of efficiency loss. The work provides insights for device evaluation and material design for efficient IPV devices. The novel hybrid organic-inorganic perovskites have gained enormous research interest for its various excellent optoelectronic properties such as high mobility. TFT as an alternative application to the majorly focused photovoltaics is realized in this work. There are few reports on perovskite TFTs due to wetting issues. By employing polymethacrylates with ester groups and aromatic substituents which provide polar and cation-π interactions with the Pb2+ ions, quality films could be fabricated with large crystals and high electron mobility in TFTs. We further improved the performance by resolving interfacial mixing between the perovskite and the polymer using the crosslinkable SU-8, achieving the highest mobility of 1.05 cm2 V−1 s−1. Subsequently, we cured the grain boundaries using methylamine solvent vapor annealing, suppressing the TFT subthreshold swing. The work provides a map for the improvement of perovskite TFTs. It has been revealed that molecular orientations of the emitters in OLEDs with the transition dipole moment lying in plane enhances light outcoupling efficiency. Multiple experimental techniques are needed to provide complementary orientation information and their physical origin. Here, we propose using TFT to probe the orientation of the phosphorescent emitters. Homoleptic fac-Ir(ppy)3 and heteroleptic trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) were deposited on polystyrene (PS) and SiO2 substrates. Compared to the PS surface inducing isotropic orientation as the control, trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) possessed decreased carrier mobilities on SiO2. With the study of initial film growth, we infer that preferred orientation induced by the polar SiO2 surface led to an increase in energetic disorder in the well-stacked trans-Ir(ppy)2(acac) and hopping distance in the amorphous trans-Ir(ppy)2(tmd). The highly symmetric fac-Ir(ppy)3 remained its isotropic orientation despite the dipolar interaction. Surprisingly, the TFT technique gives much higher sensitivity to surface-induced orientation, and thus may potentially serve as a unique electrical probe for molecular orientation.

With the progression towards lighter but larger-display self-sustainable mobile devices, device efficiency becomes increasingly important, owing to the higher power display consumption but at the same time more limitation on the size and volume of energy storage. In this thesis, selected aspects regarding to efficiency of three types of optoelectronic devices, indoor photovoltaics (IPVs), perovskite thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs) have been investigated. IPVs can make off-grid devices self-sustainable by harvesting ambient light energy. Its weak irradiance necessitates high-efficiency IPVs to generate sufficient power. Our work addresses the need of knowing the limit of the device parameters for correct evaluation and understanding the efficiency loss for developing clinical tactics. We delivered a general scheme for evaluating the limiting efficiency and the corresponding device parameters of IPVs under various lights, illuminance and material bandgap. In contrast to the AM1.5G conditions, a maximum power conversion efficiency (PCE) of 51-57 % can be achieved under the optimal bandgap of 1.82-1.96 eV. We also propose using the second thickness peak of interference instead of the first as a better optimal absorber thickness after identifying the finite absorption as the major source of efficiency loss. The work provides insights for device evaluation and material design for efficient IPV devices. The novel hybrid organic-inorganic perovskites have gained enormous research interest for its various excellent optoelectronic properties such as high mobility. TFT as an alternative application to the majorly focused photovoltaics is realized in this work. There are few reports on perovskite TFTs due to wetting issues. By employing polymethacrylates with ester groups and aromatic substituents which provide polar and cation-π interactions with the Pb2+ ions, quality films could be fabricated with large crystals and high electron mobility in TFTs. We further improved the performance by resolving interfacial mixing between the perovskite and the polymer using the crosslinkable SU-8, achieving the highest mobility of 1.05 cm2 V−1 s−1. Subsequently, we cured the grain boundaries using methylamine solvent vapor annealing, suppressing the TFT subthreshold swing. The work provides a map for the improvement of perovskite TFTs. It has been revealed that molecular orientations of the emitters in OLEDs with the transition dipole moment lying in plane enhances light outcoupling efficiency. Multiple experimental techniques are needed to provide complementary orientation information and their physical origin. Here, we propose using TFT to probe the orientation of the phosphorescent emitters. Homoleptic fac-Ir(ppy)3 and heteroleptic trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) were deposited on polystyrene (PS) and SiO2 substrates. Compared to the PS surface inducing isotropic orientation as the control, trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) possessed decreased carrier mobilities on SiO2. With the study of initial film growth, we infer that preferred orientation induced by the polar SiO2 surface led to an increase in energetic disorder in the well-stacked trans-Ir(ppy)2(acac) and hopping distance in the amorphous trans-Ir(ppy)2(tmd). The highly symmetric fac-Ir(ppy)3 remained its isotropic orientation despite the dipolar interaction. Surprisingly, the TFT technique gives much higher sensitivity to surface-induced orientation, and thus may potentially serve as a unique electrical probe for molecular orientation.

Developing etching of GaN material system is the key to device fabrications. In this thesis, we report on the fabrication of high throughput lift-off of InGaN/GaN based micro-membrane light emitting diode (LED) from sapphire substrate using UV-assisted photoelectroless chemical (PEsC) etching. Unlike existing bandgap selective etching based on unconventional sacrificial layer, the current hydrofluoric acid based wet etching process enables the selective etching of undoped GaN layer already incorporated in standard commercial LED structures, thus attaining the leverage on high performance device design, and facile wet process technology. The lift-off micro-membrane LED showed 16% alleviated quantum efficiency droop under 200 mA/cm2 current injection, demonstrating the advantage of LED epitaxy exfoliation from the lattice-mismatched sapphire substrate. The origin of the performance improvement was investigated based on non-destructive characterization methods. Photoluminescence (PL) characterization showed a 7nm peak emission wavelength shift in the micro-membrane LED compared to the GaN-on-Sapphire LED. The Raman spectroscopy measurements correlate well with the PL observation that a 0.86 GPa relaxed compressive biaxial strain was achieved after the lift-off process. The micro-membrane LED technology enables further heterogeneous integration for forming pixelated red, green, blue (RGB) display on flexible and transparent substrate. The development of discrete and membrane LEDs using nano-fiber paper as the current spreading layer was also explored for such integration.