Organic light-emitting diodes (OLEDs) have drawn much attention in the last two decades. In recent years, the power efficiency of OLEDs has been increased to exceed the efficiency of fluorescent light bulbs. However, such high-efficiency devices are typically based on small molecules that have to be evaporated in vacuum. A much higher fabrication throughput and therefore lowered costs are expected if high-efficiency OLEDs were processed from solution. This thesis shows how solution-processed electrophosphorescent multilayer OLEDs can be achieved by starting with an evaporated three-layer device structure and replacing layer by layer with a solution-processed layer. First, the hole-transport layer was replaced by a polymer and high efficiencies were observed when using a hole-transport polymer with a high ionization potential and a low hole mobility. Then, the emissive layer was replaced by a copolymer consisting of hole-transport groups and emissive complexes in its side-chains. OLEDs with four different colors are shown where the orange devices showed the highest efficiency. The orange copolymer was further optimized by making changes to the chemical nature of the polymer, such as different molecular weight, different concentrations of the emissive complex and different linkers between the side-chains and the polymer backbone. Finally, a three-layer solution-processed OLED was fabricated by crosslinking the hole-transport and the emissive layer, and by spin-coating an electron-transport polymer on top. Moreover, using the photocrosslinking properties of the emissive layer, solution-processed multilayer OLEDs of two different colors were patterned using photolithography to fabricate a white-light source with a tunable emission spectrum. Furthermore, with more and more organic semiconductors being integrated into the circuitry of commercial products, good electrical models are needed for a circuit design with predictive capabilities. Therefore, a model for the example of an organic single-layer diode is introduced in the last chapter of this thesis. The model has been implemented into SPICE and consists of an equivalent circuit that is mostly based on intrinsic material properties, which can be measured in independent experiments. The model has been tested on four different organic materials, and good agreement between model and experimental results is shown.

The use of photonic crystals for light extraction from light-emitting diodes (LEDs) gives the possibility to shape the farfield emission pattern. This is of particular interest for étendue-limited LED applications that require a more directional farfield than state- of-the-art Lambertian emitters. However, the application of a photonic crystal in a LED results in directional emission only if the photonic crystal and the distribution of guided modes in the LED are tuned correctly. In this thesis, red- and blue-emitting thin-film PhC-LEDs in the AlGaInP and InGaN material systems were modelled, designed, fabricated and characterized. The first experimental results show that light extraction with photonic crystals from AlGaInP thin-film LEDs several microns thick is neither directional nor more efficient than state-of-the-art LEDs with a rough surface structure. Directional light extraction for AlGaInP PhC-LEDs is for the first time demonstrated in much thinner devices where the photonic crystal light extraction of guided modes is combined with the resonant-cavity effect. In an attempt to approach the ideal PhC-LED, strong photonic crystal farfield shaping is demonstrated in InGaN thin-film LEDs of sub-micron thickness. Analysis of their spectral farfields unexpectedly shows that high order diffraction contributes significantly to the light extraction efficiency if the mode absorption is sufficiently low. It is also demonstrated that directional photonic crystal light extraction is possible in InGaN thin-film LEDs several microns thick. The directionality stems from the modulation of the spontaneous emission caused by the proximity of the active region to the bottom mirror. Two new concepts for enhanced light extraction and high directionality are presented: Photonic crystals with two dominating lattice constants are found to outperform conventional photonic crystal LEDs. An alternative approach is the dielectric PhC-LED - FDTD simulations show that the high extraction efficiency of LEDs with surface roughness is combined with the higher directionality of photonic crystal light extraction.

<p>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.</p>

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In the past decade, GaN-based nitrides have had a considerable impact in solid state lighting and high speed high power devices. InGaN-based LEDs have been widely used for all types of displays in TVs, computers, cell phones, etc. More and more high power LEDs have also been introduced in general lighting market. Once widely used, such LEDs could lead to the decrease of worldwide electrical consumption for lighting by more than 50% and reduce total electricity consumption by > 10%. However, there are still challenges for current state-of-the art InGaN-based LEDs, including ‘efficiency droop’ issues that cause output power quenching at high current injection levels (> 100 A/cm2). In this dissertation, approaches were investigated to address the major issues related to state-of-the-art nitride LEDs, in particular related to (1) efficiency droop investigations on m-plane and c-plane LEDs: enhanced matrix elements in m-plane LEDs and smaller hole effective mass favors the hole transport across the active region so that m-plane LEDs exhibit 30% higher quantum efficiency and negligible efficiency droop at high injection levels compared to c-plane counterparts; (2) engineering of InGaN active layers for achieving high quantum efficiency and minimal efficiency droop: lower and thinner InGaN barrier enhance hole transport as well as improves the quantum efficiencies at injection levels; (3) double-heterostructure (DH) active regions: various thicknesses were also investigated in order to understand the electron and hole recombination mechanism. We also present that using multi-thin DH active regions is a superior approach to enhance the quantum efficiency compared with simply increasing the single DH thickness or the number of quantum wells (QWs, 2 nm-thick) in multi-QW (MQW) LED structures due to the better material quality and higher density of states. Additionally, increased thickness of stair-case electron injectors (SEIs) has been demonstrated to greatly mitigate electron overflow without sacrificing material quality of the active regions. Finally, approaches to enhance light extraction efficiency including using Ga doped ZnO as the p-GaN contact layer to improve light extraction as well as current spreading was introduced.

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by Yeung Mei Ki. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 122-127). / Text in English; abstracts in English and Chinese. / by Yeung Mei Ki. / Abstract --- p.i / 論文摘要 --- p.iii / Acknowledgements --- p.iv / Table of Contents --- p.v / List of Figures --- p.viii / List of Tables --- p.xi / Abbreviations --- p.xii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Polymer light emitting devides --- p.1 / Chapter 1.1.1 --- Development history of PLEDs --- p.3 / Chapter 1.1.2 --- Basic structure of the PLEDs --- p.4 / Chapter 1.1.3 --- Operation principle of the PLEDs --- p.7 / Chapter 1.1.4 --- Electroluminescent (EL) polymers --- p.9 / Chapter 1.2 --- Research motivation and aim of study --- p.11 / Chapter 1.3 --- Thesis outline --- p.16 / Chapter Chapter 2 --- Instrumentation / Chapter 2.1 --- Thermal analysis --- p.18 / Chapter 2.1.1 --- Thermogravimetry (TG) --- p.19 / Chapter 2.1.2 --- Differential scanning calorimetry (DSC) --- p.22 / Chapter 2.2 --- Spectroscopic analysis --- p.27 / Chapter 2.2.1 --- Fourier transform infrared spectroscopy (FTIR) --- p.27 / Chapter 2.2.2 --- X-ray photoelectron spectroscopy (XPS) --- p.32 / Chapter 2.2.3 --- Photoluminescence spectroscopy (PL) --- p.36 / Chapter Chapter 3 --- Experimental metods to charaterize the elimination of / Chapter 3.1 --- Introduction --- p.41 / Chapter 3.2 --- Synthesis of the PPV precursor polymer --- p.43 / Chapter 3.3 --- Average molecular weight of the PPV precursor --- p.46 / Chapter 3.4 --- Thermal elimination of the precursor polymer --- p.48 / Chapter 3.5 --- Thermal stability of the PPV precursor polymer --- p.50 / Chapter 3.5.1 --- Sample preparation --- p.50 / Chapter 3.5.2 --- Experimental --- p.51 / Chapter 3.5.3 --- Results and discussion --- p.52 / Chapter 3.6 --- Structural changes of the precursor polymer during elimination --- p.57 / Chapter 3.6.1 --- Sample preparation --- p.57 / Chapter 3.6.2 --- Experimental --- p.58 / Chapter 3.6.3 --- Results and discussion --- p.58 / Chapter 3.7 --- Chemical composition of the precursor polymer upon elimination --- p.67 / Chapter 3.7.1 --- Sample preparation --- p.67 / Chapter 3.7.2 --- Experimental --- p.67 / Chapter 3.7.3 --- Results and discussion --- p.68 / Chapter 3.8 --- Effect of the conjugation length of the polymer on photoluminescence --- p.74 / Chapter 3.8.1 --- Sample preparation --- p.76 / Chapter 3.8.2 --- Experimental --- p.78 / Chapter 3.8.3 --- Results and discussion --- p.79 / Chapter 3.9 --- Conclusions --- p.89 / Chapter Chapter 4 --- Experimental methods to characterize the water absorption by PEDOT:PSS / Chapter 4.1 --- Introduction --- p.90 / Chapter 4.2 --- Determination of the water content of PEDOT:PSS at different relative humidity using TG --- p.93 / Chapter 4.2.1 --- Experimental --- p.94 / Chapter 4.2.2 --- Results and discussion --- p.96 / Chapter 4.3 --- Determination of bounded water content of PEDOT:PSS at different RH by DSC --- p.98 / Chapter 4.3.1 --- Experimental --- p.98 / Chapter 4.3.2 --- Results and discussion --- p.100 / Chapter 4.4 --- Determination of bounded water content of PEDOT:PSS at different RH by FTIR --- p.108 / Chapter 4.4.1 --- Experimental --- p.109 / Chapter 4.4.2 --- Results and discussion --- p.112 / Chapter 4.5 --- Conclusions --- p.118 / Chapter Chapter 5 --- Conclusions --- p.120 / References --- p.122

O auto sombreamento das folhas posicionadas nas porções inferiores do dossel de plantas pode limitar a produtividade em cultivos tutorados. Assim, a produtividade do tomateiro pode ser aumentada por meio da suplementação luminosa posicionada no interior do dossel, técnica conhecida como interlighting. O sistema de condução do tomateiro também interfere na distribuição da radiação solar, além de afetar os tratos culturais, a competição intra e entre plantas e a relação entre as partes vegetativas e reprodutivas. Desta forma, o objetivo deste trabalho foi avaliar a influência do sistema de condução de minitomate cultivar \'Sweet Grape\' em diferentes números de hastes por planta (duas, três e quatro hastes) e da suplementação luminosa com módulos de LED na produtividade e qualidade dos frutos, na eficiência do uso de água e nutrientes, além da morfologia das plantas e fatores relacionados ao manejo cultural, em ambiente protegido nas condições climáticas do sudeste brasileiro. Ao longo do ciclo de cultivo foram avaliados os seguintes parâmetros: volume irrigado, pH, condutividade elétrica, porcentagem e volume da solução drenada pelos vasos. As colheitas foram realizadas semanalmente, a partir de 90 dias após o transplante. Os frutos colhidos foram classificados, contados e pesados para a obtenção do número e massa de frutos grandes, médios, pequenos, comercial, não comercial e total. Amostras de frutos e tecidos foliares foram coletadas em cinco períodos e avaliadas quanto ao teor de sólidos solúveis, pH, acidez titulável e concentração de ácido ascórbico nos frutos e teor de nutrientes nas folhas. Além disso, ao final do ciclo cultural, foram realizadas as medições dos seguintes parâmetros morfológicos nas plantas: comprimento de hastes, número de cachos normais e bifurcados por hastes e diâmetro apical, mediano e basal das hastes. A suplementação luminosa apresentou aumento no número e na massa de frutos grandes e médios, elevando a produtividade total em 12%. Plantas com duas e três hastes apresentaram maior acúmulo de massa total de frutos, porém plantas com três hastes apresentaram maior massa de frutos não comerciais, com redução na massa de frutos comerciais. A maior eficiência no uso de água e nutrientes foi alcançada em plantas cultivadas com duas hastes. Plantas com quatro hastes demandaram mais solução nutritiva comparada às plantas com duas e três hastes. Esta maior demanda de solução, acarretou em aumento da condutividade elétrica da solução drenada. Plantas com quatro hastes apresentaram maiores teores de sólidos solúveis nos frutos. A suplementação luminosa também resultou em aumento do teor de sólidos solúveis e ligeiro aumento no teor de ácido ascórbico nos frutos. A suplementação luminosa favoreceu o acúmulo de nitrogênio, fósforo e potássio nas folhas do tomateiro. Desta forma, conclui-se que a suplementação luminosa é uma estratégia de manejo tecnicamente viável nas condições climática estudada. O sistema de condução de haste afeta a produtividade e qualidade dos frutos do tomateiro. Plantas com duas hastes além de apresentar maior produtividade de frutos comerciais, mostrou-se a estratégia mais eficiente no uso da água e nutrientes. / The auto shading of leaves located within lower part of plant canopy can limit productivity of the tutored crops. Therefore, tomato productivity can be enhanced through supplementation of light positioned within the canopy using a technique known as interlighting. In addition, management system also affects the distribution of solar radiation, cultural practices as well as intra and between plants competition, which changes the relationship between vegetative and reproductive parts. The objective of this study was to evaluate the influence of different numbers of stems per plant (two, three and four stems) and light supplementation with LED modules in productivity and quality of the fruit of cherry tomato cv. \"Sweet Grape\". Furthermore, it was quantified the efficient use of water and nutrients, plant morphology and factors related to cultural management. The experiment was conducted in a greenhouse located in Piracicaba, southeastern Brazil, using a randomized block design with four replications. Throughout crop cycle were evaluated the following parameters: Irrigated water volume, pH, electrical conductivity, percentage and volume of drained solution. Fruit samples were collected weekly from 90 days after transplantation of tomato seedlings. The harvested fruits were sorted, counted and weighed to obtain number and weight of large, medium, small, commercial, non-commercial and total fruits. Fruit samples and leaf tissues were collected in five periods for quantifying soluble solids, pH, titratable acidity and concentration of ascorbic acid in fruit and nutrient content in the leaves. Furthermore, in the end of the crop cycle, measurements of the following plant morphological parameters were performed: length stems, number of normal and bisected by stems clusters and apical, middle and basal diameter of the stems. Our findings showed that light supplementation induced higher number and mass of large and medium commercial fruit, increasing total productivity by 12%. Two- and three-stem plants had higher total mass accumulation of fruit, but three-stem plants had greater mass of non-commercial fruit, with a reduction in the mass of commercial fruits. The more efficient use of water and nutrients was achieved by two-stem plants. Four-stem plants demanded more nutrient solution compared to two- and three-stem plants, resulting in an increased electrical conductivity of the drained nutrient solution. Four-stem plants had higher soluble solids in the fruit. The light supplementation also resulted in an increase of soluble solids and a slight increase in the ascorbic acid content in fruits. The light supplementation favored the accumulation of nitrogen, phosphorus and potassium within tomato leaves. We concluded that the light supplementation is a technically feasible management strategy in the climatic conditions studied. The management system affects the productivity and quality of cherry tomato fruits. Two stem plants had higher productivity of commercial fruits, as well as it proved to be the most effective strategy in the use of water and nutrients.

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