High Efficiency and Wide Color Gamut Liquid Crystal Displays

Liquid crystal display (LCD) has become ubiquitous and indispensable in our daily life. Recently, it faces strong competition from organic light emitting diode (OLED). In order to maintain a strong leader position, LCD camp has an urgent need to enrich the color performance and reduce the power consumption. This dissertation focuses on solving these two emerging and important challenges. In the first part of the dissertation we investigate the quantum dot (QD) technology to improve the both the color gamut and the light efficiency of LCD. QD emits saturated color and grants LCD the capability to reproduce color vivid images. Moreover, the QD emission spectrum can be custom designed to match to transmission band of color filters. To fully take advantage of QD\u27s unique features, we propose a systematic modelling of the LCD backlight and optimize the QD spectrum to simultaneously maximize the color gamut and light efficiency. Moreover, QD enhanced LCD demonstrates several advantages: excellent ambient contrast, negligible color shift and controllable white point. Besides three primary LCD, We also present a spatiotemporal four-primary QD enhanced LCD. The LCD\u27s color is generated partially from time domain and partially from spatial domain. As a result, this LCD mode offers 1.5× increment in spatial resolution, 2× brightness enhancement, slightly larger color gamut and mitigated LC response requirement (~4ms). It can be employed in the commercial TV to meet the challenging Energy star 6 regulation. Besides conventional LCD, we also extend the QD applications to liquid displays and smart lighting devices. The second part of this dissertation focuses on improving the LCD light efficiency. Conventional LCD system has fairly low light efficiency (4%~7%) since polarizers and color filters absorb 50% and 67% of the incoming light respectively. We propose two approaches to reduce the light loss within polarizers and color filters. The first method is a polarization preserving backlight system. It can be combined with linearly polarized light source to boost the LCD efficiency. Moreover, this polarization preserving backlight offers high polarization efficiency (~77.8%), 2.4× on-axis luminance enhancement, and no need for extra optics films. The second approach is a LCD backlight system with simultaneous color/polarization recycling. We design a novel polarizing color filter with high transmittance ( \u3e 90%), low absorption loss (~3.3%), high extinction ratio (\u3e10,000:1) and large angular tolerance (up to ±50˚). This polarizing color filter can be used in LCD system to introduce the color/polarization recycling and accordingly boost LCD efficiency by ~3 times. These two approaches open new gateway for ultra-low power LCDs. In the final session of this dissertation, we demonstrate a low power and color vivid reflective liquid crystal on silicon (LCOS) display with low viscosity liquid crystal mixture. Compared with commercial LC material, the new LC mixture offers ~4X faster response at 20oC and ~8X faster response at -20°C. This fast response LC material enables the field-sequential-color (FSC) driving for power saving. It also leads to several attractive advantages: submillisecond response time at room temperature, vivid color even at -20oC, high brightness, excellent ambient contrast ratio, and suppressed color breakup. With this material improvement, LCOS display can be promising for the emerging wearable display market

Using flat phosphor layer in dual-layer remote phosphor configuration to improve luminous efficacy

The phosphor layer shape and components distances are the subjects proposed to advance the quality of WLEDs in this article. The two distances, between phosphor layers (d1) and between the phosphor layer and the LED chip (d2) in Flat dual-remote phosphor (FDRP) and Concave dual-remote phosphor (CDRP) were examined by experiments to determine their impacts on WLEDs lighting performances. The results suggest that FDRP is a better option than CDRP for lighting performance. In each respective structure, the distances influence the lighting capacity and color output whenever they fluctuate. Therefore, to effectively control and study this phenomenon, the correlated color temperature is maintained at 8500 K, and the concentration of phosphor material is altered while the distances are changing. When d1 and d2 are at the starting value of 0, the recorded lumen output and chromatic performance of lighting devices are the lowest and begin to increase as d1 and d2 expand. Bigger d1 and d2 mean bigger scattering area and better chromatic light integration, which leads to higher color quality. Detailed results present that optimal values of d1 or d2 for the highest lumen output of 1020 lm are 0.08 mm or 0.63 mm, respectively. Meanwhile the lowest color deviation is accomplished with d1=0.64 mm or d2=1.35 mm

Quantum dot polymer composite materials for light management in optoelectronic devices

This dissertation will highlight a path to achieve high conversion efficiency of optoelectronic devices, including photovoltaic concentrators and LED display modules. Semiconductor nanocrystals, also known as quantum dots (QDs), serve as the pivotal luminescent materials in these devices. A quantum dots encapsulation method was developed here to homogeneously disperse QDs in a transparent polymer matrix, enabling high optical quality devices and thorough investigation of light material interactions. A luminescent solar concentrator (LSC) typically consists of a luminophore embedded in a polymer sheet with a high-performance solar cell attached at the side. In such a device, sunlight is absorbed in a luminophore, emitted into the waveguide modes of the polymer sheet, and directed to a photovoltaic cell where it is absorbed and converted to electricity. Since the area of the polymer sheet is greater than the area of the photovoltaic cell, concentration of the solar photon flux is achieved. Approaching high concentration ratio will require a luminophore with large Stokes Shift, high quantum yield, minimal overlap between absorption and emission, and a narrow emission spectrum. We have examined the performance of LSCs utilizing CdSe/CdS core-shell QDs, with significantly reduced absorption-emission overlap and long propagation distances in the waveguide. Furthermore, a distributed Bragg reflector dramatically mitigates the negative impact of scattering in the waveguide, allowing efficient photon collection and concentration ratio. White-light LED is achieved by using a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light. However, tradition yellow phosphors suffer from low color rendering index due to the broad emission spectrum of the phosphors. QDs have been proposed as better candidate than traditional yellow phosphors due to their narrow and tunable emission spectrum, and wide absorption spectrum in the UV-blue spectrum range. We have fabricated QD-polymer thin films as color conversion layers on blue LED via different methods, including spin-coating, drop casting and electrohydrodynamic jet printing. The polymer surface has been incorporated with nano-sized features to create photonic crystal structure. Up to 8 times QD excitation and emission enhancement have been demonstrated. We have also designed and fabricated QD-polymer based concentrating cavity on blue LED that acts both as color conversion layer and light concentrator. Distributed Bragg reflector and sputtered silver have been used as reflectors surrounding QD-polymer thin film. The exterior of the concentrator cavity was coated with black absorber to suppress light reflection, and a small aperture in the center allows concentrated photons to exit. High power conversion efficiency and high ambient contrast have been achieved in module devices

디스플레이 및 이미징 시스템으로의 응용을 위한 3D 프린팅 기반 맞춤형 광학 요소의 개발

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2021. 2. 홍용택.일반적으로 제조 공정은 절삭 방식과 적층 방식으로 구분된다. 이 중에서 적층 방식 공정은 저비용 및 단시간으로 복잡한 형태의 구조를 만들 수 있어서 이에 대한 연구와 개발이 꾸준히 진행되어왔다. 특히 3D 프린팅은 적층 방식 공정 중에서 가장 대표적인 방법으로, 기계 부품 및 생체 기관 제조 등의 분야에서는 이미 상용화가 진행되고 있다. 하지만 전자 소자 및 광학 요소 분야에서의 3D 프린팅의 활용은 여전히 연구 개발 또는 시제품 제작 단계에 머무르고 있다. 특히 마이크로 렌즈, 컬러 필터 등이 3D 프린팅으로 응용할 수 있는 가장 가능성 있는 광학 요소로서 디스플레이 및 이미징 시스템에 널리 사용될 것으로 예상되지만 여전히 상용화를 위한 연구가 진행 중이다. 또한 3D 프린팅을 이용한 광학 요소의 제작은 소재, 길이 스케일, 형상 및 응용 방안 등에서도 제한이 많은 상황이다. 따라서 이러한 문제를 극복하기 위해서는 디스플레이 및 이미징 시스템에서의 3D 프린팅 된 광학 요소의 유용성을 확장해야 하며, 다음과 같이 세 가지 측면에서 향상된 성능을 달성해야 한다. 첫째, 다양한 방식의 3D 프린팅 방법을 통해 마이크로미터에서 센티미터까지 광범위의 길이 스케일을 가지는 구조물의 제작이 가능해야 한다. 둘째, 임의의 곡면, 계층적 구조 등 복잡한 형상의 구조물을 쉽게 제작할 수 있어야 한다. 셋째, 단단한 소재 대신 탄성체와 같은 소프트 소재를 이용하여 광학적인 기능을 용이하게 조절할 수 있어야 한다. 이와 같은 동기를 바탕으로 본 학위 논문에서는 디스플레이 및 이미징 시스템으로의 응용을 위한 3D 프린팅 기반 맞춤형 광학 요소의 개발에 대한 내용을 보고한다. 3D 프린팅 기반 광학 요소를 매크로 스케일, 마이크로 스케일 그리고 매크로 및 마이크로 스케일이 혼합된 계층적 구조 등 세 가지 유형으로 분류하고 각각에 대한 응용 분야를 제시한다. 매크로 스케일의 광학 요소로는 가장 기본적인 요소인 렌즈와 거울을 선택한다. 렌즈는 공압식 디스펜싱 방법을 이용하여 실린드리컬 쌍 형태로 제작되었으며, 심리스 모듈러 평판식 디스플레이의 구현을 위해 적용된다. 또한 용융 적층 방식의 3D 프린팅으로 만들어진 몰드를 이용하여 거울을 제작하고, 이를 이용하여 심리스 모듈러 커브드 엣지 디스플레이를 구현한다. 이와 같이 모듈러 디스플레이의 이음새 부분에 3D 프린팅으로 제작된 렌즈 또는 거울을 부착하는 방식으로 화면을 심리스로 확장하는 기술을 제시하고, 다양한 형태의 디스플레이에 적용할 수 있는 가능성을 보여준다. 마이크로 스케일의 광학 요소로는 발광 다이오드에서 색 변환과 광 추출 기능을 동시에 나타내는 색 변환 마이크로 렌즈를 선택한다. 양자 점/광 경화성 고분자 복합체의 전기수력학적 프린팅을 통해 양자 점이 내장된 다양한 형태의 색 변환 마이크로 렌즈를 제작하며, 이를 청색 마이크로 발광 다이오드 어레이의 발광부 상에 적용하여 풀 컬러 마이크로 발광 다이오드 디스플레이로의 응용 가능성을 제시한다. 마지막으로 매크로 및 마이크로 스케일이 혼합된 계층적 구조의 광학 요소로서 디스펜싱 및 건식 러빙 과정의 조합으로 제작된 겹눈 형태를 모사한 렌즈 구조를 제시한다. 반구 형태의 매크로 렌즈를 디스펜싱으로 형성하고, 매크로 렌즈의 곡면 상에 단층의 마이크로 입자의 배열을 얻기 위해 건식 러빙 공정을 진행한다. 이러한 방식으로 형성된 계층적 구조가 소프트한 소재로 복제되어서 신축성을 가지는 겹눈 형태 모사 구조가 완성된다. 마이크로 렌즈 어레이는 매크로 렌즈의 표면을 따라 형성되고 리지드 아일랜드로 역할을 하여, 전체 계층적 구조에 기계적 변형이 가해져 매크로 렌즈의 모양이 변형되어도 마이크로 렌즈는 형상과 해상도, 초점 거리 등의 광학적 특성을 유지할 수 있다. 본 학위 논문은 3D 프린팅을 이용하여 다양한 형태와 스케일의 광학 요소를 제작하고 디스플레이 및 이미징 시스템으로의 여러 응용을 보여줌으로서 앞으로의 새로운 연구 및 개발 방향성을 제시하는 것을 주요 목적으로 한다. 3D 프린팅 설비의 단가가 낮아지고 정밀도 및 해상도가 높아지는 추세에 따라, 광학 요소를 쉽게 만들고 응용할 수 있는 맞춤형 광학 또는 스스로 구현하는 광학 분야가 변형 가능하고 멀티 스케일의 광학계로 점차 확대될 것으로 예상된다. 궁극적으로는 차세대 디스플레이 및 이미징 시스템에 필요한 광학 요소를 위한 기술의 저변을 넓히고, 이를 산업 전반에 응용할 수 있는 기반을 마련하고자 한다.Generally, the manufacturing process is divided into the subtractive (top-down) type and additive type (bottom-up). Among them, the additive manufacturing process has attracted a lot of attention because it can manufacture products with complex shapes in a low-cost and short-time process. In particular, three-dimensional (3D) printing is a representative method, which has already been commercialized in the field of mechanical components and biomedical organ. However, it remains in the research and development step in the field of electronic devices and optical components. Especially, although 3D printed optical components including microlens and color filter are expected to be widely used in display and imaging systems, it is still under investigation for commercialized products, and there are limitations in terms of materials, length scale, shape, and practical applications of components. Therefore, to overcome these issues, it is required for investigating and expanding the potential usefulness for 3D printed optical components in display and imaging systems to achieve better performance, productivity, and usability in three aspects. First, it should be possible to manufacture structures with a wide range of length scales from micrometer to centimeter through various 3D printing methods. Second, complex shapes such as free-from curved surfaces and hierarchical structures should be easily fabricated. Third, it is necessary to add functionality by manufacturing structures in which tunable functions are introduced using soft materials like an elastomer. Based on the above motivations, 3D printing-based customized optical components for display and imaging system applications are introduced in this dissertation. 3D printed optical components are classified into three types and their applications are showed to verify the scalability of 3D printing: macro-scale, microscale, and hierarchical macro/micro-scale. As macro-scale printed optical components, lens and mirror which are the most basic optical components are selected. The lens is fabricated by a pneumatic-type dispensing method with the form of a cylindrical pair and adopted for demonstration of seamless modular flat panel display. Besides, a seamless modular curved-edge display is also demonstrated with a mirror, which is fabricated from fused deposition modeling (FDM)-type 3D printed mold. By simply attaching a printed lens or mirror onto the seam of the modular display, it is possible to secure seamless screen expansion technology with the various form factor of the display panel. In the case of micro-scale printed optical components, the color-convertible microlens is chosen, which act as a color converter and light extractor simultaneously in a light-emitting diode (LED). By electrohydrodynamic (EHD) printing of quantum dot (QD)/photocurable polymer composite, QD-embedded hemispherical lens shape structures with various sizes are fabricated by adjusting printing conditions. Furthermore, it is applied to a blue micro-LED array for full-color micro-LED display applications. Finally, a tunable bio-inspired compound (BIC) eyes structure with a combination of dispensing and a dry-phase rubbing process is suggested as a hierarchical macro/micro-scale printed optical components. A hemispherical macrolens is formed by the dispensing method, followed by a dry-phase rubbing process for arranging micro particles in monolayer onto the curved surface of the macrolens. This hierarchical structure is replicated in soft materials, which have intrinsic stretchability. Microlens array is formed on the surface of the macrolens and acts as a rigid island, thereby maintaining lens shape, resolution, and focal length even though the mechanical strain is applied to overall hierarchical structures and the shape of the macrolens is changed. The primary purposes of this dissertation are to introduce new concepts of the enabling technologies for 3D printed optical components and to shed new light on them. Optical components can be easily made as 3D printing equipment becomes cheaper and more precise, so the field of Consumer optics or Do it yourself (DIY) optics will be gradually expanded on deformable and multi-scale optics. It is expected that this dissertation can contribute to providing a guideline for utilizing and customizing 3D printed optical components in next-generation display and imaging system applications.Chapter 1. Introduction 1 1.1. Manufacturing Process 1 1.2. Additive Manufacturing 4 1.3. Printed Optical Components 8 1.4. Motivation and Organization of Dissertation 11 Chapter 2. Macro-scale Printed Optical Components 15 2.1. Introduction 15 2.2. Seamless Modular Flat Display with Printed Lens 20 2.2.1. Main Concept 20 2.2.2. Experimental Section 23 2.2.3. Results and Discussion 26 2.3. Seamless Modular Curved-edge Display with Printed Mirror 32 2.3.1. Main Concept 32 2.3.2. Experimental Section 33 2.3.3. Results and Discussion 36 2.4. Conclusion 46 Chapter 3. Micro-scale Printed Optical Components 47 3.1. Introduction 47 3.2. Full-color Micro-LED Array with Printed Color-convertible Microlens 52 3.2.1. Main Concept 52 3.2.2. Experimental Section 54 3.2.3. Results and Discussion 57 3.3. Conclusion 65 Chapter 4. Hierarchical Macro/Micro-scale Printed Optical Components 66 4.1. Introduction 66 4.2. Tunable Bio-inspired Compound Eye with Printing and Dry-phase Rubbing Process 69 4.2.1. Main Concept 69 4.2.2. Experimental Section 71 4.2.3. Results and Discussion 73 4.3. Conclusion 79 Chapter 5. Conclusion 80 5.1. Summary 80 5.2. Limitations and Suggestions for Future Researches 83 References 88 Abstract in Korean (국문 초록) 107Docto

Spectrum management for high efficiency photonic devices

Spectrum management holds great promise for high-performance photonics devices. Optical elements that split, up- or down-convert the available light to a specified spectrum can result in higher efficiencies in various devices such as photovoltaic cells, photodetectors, and electronic displays. In this thesis, the method of spectrum splitting to efficiently utilize the full spectrum of sunlight in converting from solar energy to electricity was demonstrated. Multi-junction solar cells are already efficient, but further gains are possible by splitting the solar spectrum laterally, rather than vertically, onto electrically isolated cells. A textured thin film was used to diffract two spectral bands to laterally displaced regions in the far field. The optimized optical element having multi-level textures was fabricated using 3D direct laser writing on photoresist. The fabricated samples were optically characterized and potential modifications to achieve even higher efficiencies were pointed out. Further, this thesis demonstrated a new display architecture that can alleviate problems associated with liquid crystal display (LCD) devices: substantial losses in optical intensity due to employed color filters and low ambient contrast ratio because of reflection of external light from the front surface. A luminescent film having quantum dots was placed inside an enclosed microcavity. The design for a high-contrast and high efficiency display comprised an enclosed cavity having a front wall and a back wall, where the front wall comprised a pinhole opening for emission of light from the cavity and the back wall was configured to transmit light into the cavity. The outer surface of the front wall was made to absorb substantially all optical wavelengths of externally incident light so as to appear black. The inner surface of the front wall and sidewalls were highly reflective to promote photon recycling within the cavity and light emission through the pinhole opening. Finally, although the single pixel demonstration served to optimize the optics within the cavity and study the physics of the proposed architecture, a micrometer sized pixel array was proposed since the current portable electronics industry demands displays with large pixel arrays, where each pixel is on the order of micrometers in size. An individually addressable micropixel array was proposed and fabricated using standard microfabrication techniques that can be integrated into commercial displays

A psychophysical investigation of global illumination algorithms used in augmented reality

Global illumination rendering algorithms are capable of producing images that are visually realistic. However, this typically comes at a large computational expense. The overarching goal of this research was to compare different rendering solutions in order to understand why some yield better results when applied to rendering synthetic objects into real photographs. As rendered images are ultimately viewed by human observers, it was logical to use psychophysics to investigate these differences. A psychophysical experiment was conducted judging the composite images for accuracy to the original photograph. In addition, iCAM, an image color appearance model, was used to calculate image differences for the same set of images. In general it was determined that any full global illumination is better than direct illumination solutions only. Also, it was discovered that the full rendering with all of its artifacts is not necessarily an indicator of judged accuracy for the final composite image. Finally, initial results show promise in using iCAM to predict a relationship similar to the psychophysics, which could eventually be used in-the-rendering-loop to achieve photo-realism

Lifetime and Efficiency of Blue Phosphorescent Organic-Light Emitting Diodes

Organic light-emitting diodes (OLEDs) are poised to realize high performance for innovative display and lighting applications in the future. However, the development of suitable blue OLEDs remains a challenge which has impeded the progress of large-scale OLED commercialization for more than a decade. Blue devices are critical components for red-green-blue displays and white lighting, but to date suffer from short operational lifetimes as well as a lack of efficient deep blue emitting materials. This thesis aims at understanding the physical background of these issues and providing potential solutions. OLEDs produce photons via radiative recombination of electron-hole bound pairs, called excitons. Fluorescent OLEDs depend on emission from the singlet excitons achieving an electron-to-light conversion, or internal quantum efficiency (IQE), from 25% up to 62.5%. On the other hand, phosphorescent OLEDs (PHOLEDs) exploit the emission from triplet excitons, attaining nearly 100% IQE. In OLED-based products, red and green PHOLEDs are universally used due to their high efficiency and long operational lifetime, while fluorescent OLEDs are still used for the blue emitting component despite their low performance. Thus, the development of long-lived and high efficiency blue PHOLEDs is a key to the success of the technology. In the first part of this thesis, we investigate the nonradiative loss mechanism dominant in deep blue emitting phosphorescent materials. We identify the metal-centered ligand-field states (3MC states) as a major source of efficiency loss and a probability of thermal population to these states increases with the emission energy of the emitter. Thus, we develop tris-cyclometalated Iridium (III) complexes using N-heterocyclic carbene (NHC) ligands that render the energy of the 3MC states inaccessibly high while keeping a wide energy gap for deep blue emission. The NHC-ligand based Ir(III) complex can thereby minimize the nonradiative loss and achieve high IQE in deep blue. In PHOLEDs, the NHC-Ir(III) complexes are used as the emitters, as well as hole transporting and electron blocking components. This multiple use enables a very high brightness operation of deep blue PHOLEDs, potentially suitable for demanding display applications. In the second part of this thesis, we focus on understanding and solving the short lifetime of blue PHOLEDs. We identify the intrinsic mechanism of the device degradation is the bimolecular annihilation between the excited states in the emission layer (EML) that generates the energetically “hot” excited state. If such a hot excited state dissipates its energy on the EML molecule, the resulting chemical bond dissociation and its products permanently deteriorate device performance. The frequency of this failure process increases with the energy of the excited state, particularly severe in blue PHOLEDs compared to red and green emitting devices. Thus, we propose two solutions to this problem: (i) reducing the probability of the bimolecular annihilation via distributing the excited state density and (ii) bypassing the dissociative reaction via thermalizing the hot excited states on the ancillary dopant in the PHOLED EML. The stability of the blue PHOLED employing both strategies is cumulatively improved and a theory is proposed to explain such lifetime enhancement.PHDElectrical & Computer Eng PhDUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/136937/1/jsanglee_1.pd

DEVELOPMENT OF IONIC CONDUCTIVE CELLULOSE MAT BY SOLUTION BLOW SPINNING AND LASER-INDUCED GRAPHENE FROM PINEAPPLE NANOCELLULOSE FOR USE IN FLEXIBLE ELECTRONIC DEVICES

In the face of environmental issues and aiming at electronic devices of rapid production at low cost, this doctoral thesis proposed two new and innovative approaches to obtain substrates, dielectrics, and electrodes from a single biopolymer: cellulose. In a first moment, a simple approach to produce low-cost flexible ionic conductive cellulose mats (ICCMs) using solution blow spinning (SB-Spinning) is reported. The electrochemical properties of the ICCMs were adjusted through infiltration with alkali hydroxides (LiOH, NaOH, or KOH), which enabled of ICCMs application as dielectric and substrate in oxide-based field effect transistors (FETs) and pencil-drawn resistorloaded inverters. The FETs showed good electrical performance under operating voltage <2.5 V, which was strictly associated with the type of alkali ion incorporated, presenting satisfactory performance for the ICCM infiltrated with K+ ion. The inverters with K+ ions also presented good dynamic performance, with a gain close to 2. Regarding the cellulose-based electrodes, a second innovative approach is reported to synthetize laser-induced graphene (LIG) structures from carboxymethyl cellulose (CMC)-based ink containing LIG obtained from cellulose nanocrystals (CNCs) extracted from pineapple leaf fibers (PALFs). To prove this concept, zinc oxide ultraviolet (ZnO UV) sensors were designed varying the amount of LIG from CNCs. Sensor obtained from LIG written directly on paper substrate were also performed. The ZnO UV sensors designed with CMC-based ink showed responsivity 40-fold higher than that of paper direct-written LIG, as well as excellent electrical performance under flexion. These findings may open new promising possibilities for low-consumption wearable electronics, allowing the use of concepts such as the "Internet of Things" and opening the possibility of generating 100% organic cellulose-produced electronic devices.Frente às questões ambientais e visando dispositivos eletrônicos de rápida produção e baixo custo, este projeto de pesquisa de doutorado propôs duas abordagens inovadoras para a obtenção de substratos, materiais dielétricos e eletrodos a partir de um único biopolímero: a celulose. Em um primeiro momento relata-se uma abordagem simples para produzir mantas condutoras iônicas de celulose (ICCM) flexíveis aplicando fiação por sopro em solução (SB-Spinning) seguido da infiltração com hidróxidos alcalinos (LiOH, NaOH ou KOH), permitindo sua aplicação como dielétrico e substrato em transistores e inversores com resistor desenhado a lápis. Os transistores exibiram um bom desempenho sob tensão de operação abaixo de 2,5 V, apresentando desempenho satisfatório para as mantas infiltradas com K+, além do inversor apresentar um ganho próximo de dois. Visando também eletrodos oriundos da celulose, este projeto relatou uma abordagem inovadora para sintetizar grafeno induzido por laser (LIG) a partir de tinta à base de carboximetilcelulose (CMC) contendo LIG obtido de nanocristais de celulose (CNCs) do abacaxi. Como prova de conceito, sensores de ZnO UV foram projetados variando a quantidade de LIG dos CNCs na tinta a base de CMC, assim como sensores obtidos por escrita direta de LIG em substrato de papel. Os sensores de ZnO UV flexíveis formulados com tinta apresentaram responsividade 40 vezes maior que os sensores contendo LIG direto do papel. Essas descobertas podem inaugurar uma nova Era na geração de eletrônicos vestíveis de baixo consumo, permitindo conceitos como "Internet das Coisas", e abrindo a possibilidade de dispositivos 100% orgânicos oriundos da celulose

The Optical Outcoupling of Organic Light Emitting Diodes

OLEDs have seen a strong growth in development in recent years, however up to 80% of emitted light may be lost within the OLED stack and in the substrate layers. This thesis investigates the effects of the layer stack on the OLED properties and also studies a number of approaches to substrate structuring and treatment in order to couple light from the devices