2,175 research outputs found

    Intrinsically stretchable and transparent thin-film transistors based on printable silver nanowires, carbon nanotubes and an elastomeric dielectric.

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    Thin-film field-effect transistor is a fundamental component behind various mordern electronics. The development of stretchable electronics poses fundamental challenges in developing new electronic materials for stretchable thin-film transistors that are mechanically compliant and solution processable. Here we report the fabrication of transparent thin-film transistors that behave like an elastomer film. The entire fabrication is carried out by solution-based techniques, and the resulting devices exhibit a mobility of โˆผ30โ€‰cm(2)โ€‰V(-1)โ€‰s(-1), on/off ratio of 10(3)-10(4), switching current >100โ€‰ฮผA, transconductance >50โ€‰ฮผS and relative low operating voltages. The devices can be stretched by up to 50% strain and subjected to 500 cycles of repeated stretching to 20% strain without significant loss in electrical property. The thin-film transistors are also used to drive organic light-emitting diodes. The approach and results represent an important progress toward the development of stretchable active-matrix displays

    High-Contrast OLEDs with High-Efficiency

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    Peer reviewed: YesNRC publication: Ye

    The theoretical study of passive and active optical devices via planewave based transfer (scattering) matrix method and other approaches

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    In this thesis, we theoretically study the electromagnetic wave propagation in several passive and active optical components and devices including 2-D photonic crystals, straight and curved waveguides, organic light emitting diodes (OLEDs), and etc. Several optical designs are also presented like organic photovoltaic (OPV) cells and solar concentrators. The first part of the thesis focuses on theoretical investigation. First, the plane-wave-based transfer (scattering) matrix method (TMM) is briefly described with a short review of photonic crystals and other numerical methods to study them (Chapter 1 and 2). Next TMM, the numerical method itself is investigated in details and developed in advance to deal with more complex optical systems. In chapter 3, TMM is extended in curvilinear coordinates to study curved nanoribbon waveguides. The problem of a curved structure is transformed into an equivalent one of a straight structure with spatially dependent tensors of dielectric constant and magnetic permeability. In chapter 4, a new set of localized basis orbitals are introduced to locally represent electromagnetic field in photonic crystals as alternative to planewave basis. The second part of the thesis focuses on the design of optical devices. First, two examples of TMM applications are given. The first example is the design of metal grating structures as replacements of ITO to enhance the optical absorption in OPV cells (chapter 6). The second one is the design of the same structure as above to enhance the light extraction of OLEDs (chapter 7). Next, two design examples by ray tracing method are given, including applying a microlens array to enhance the light extraction of OLEDs (chapter 5) and an all-angle wide-wavelength design of solar concentrator (chapter 8). In summary, this dissertation has extended TMM which makes it capable of treating complex optical systems. Several optical designs by TMM and ray tracing method are also given as a full complement of this work

    Optical Simulation and Optimization of Light Extraction Efficiency for Organic Light Emitting Diodes

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    abstract: Current organic light emitting diodes (OLEDs) suffer from the low light extraction efficiency. In this thesis, novel OLED structures including photonic crystal, Fabry-Perot resonance cavity and hyperbolic metamaterials were numerically simulated and theoretically investigated. Finite-difference time-domain (FDTD) method was employed to numerically simulate the light extraction efficiency of various 3D OLED structures. With photonic crystal structures, a maximum of 30% extraction efficiency is achieved. A higher external quantum efficiency of 35% is derived after applying Fabry-Perot resonance cavity into OLEDs. Furthermore, different factors such as material properties, layer thicknesses and dipole polarizations and locations have been studied. Moreover, an upper limit for the light extraction efficiency of 80% is reached theoretically with perfect reflector and single dipole polarization and location. To elucidate the physical mechanism, transfer matrix method is introduced to calculate the spectral-hemispherical reflectance of the multilayer OLED structures. In addition, an attempt of using hyperbolic metamaterial in OLED has been made and resulted in 27% external quantum efficiency, due to the similar mechanism of wave interference as Fabry-Perot structure. The simulation and optimization methods and findings would facilitate the design of next generation, high-efficiency OLED devices.Dissertation/ThesisMasters Thesis Mechanical Engineering 201

    Progress and challenges in commercialization of organic electronics

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    Plant-derived cis-ฮฒ-ocimene as a precursor for biocompatible, transparent, thermally-stable dielectric and encapsulating layers for organic electronics

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    This article presents low-temperature, one-step dry synthesis of optically transparent thermally-stable, biocompatible cis-ฮฒ-ocimene-based thin films for applications as interlayer dielectric and encapsulating layer for flexible electronic devices, e.g. OLEDs. Morphological analysis of thin films shows uniform, very smooth (R q < 1 nm) and defect-free moderately hydrophilic surfaces. The films are optically transparent, with a refractive index of โˆผ1.58 at 600 nm, an optical band gap of โˆผ2.85 eV, and dielectric constant of 3.5-3.6 at 1 kHz. Upon heating, thin films are chemically and optically stable up to at least 200 ยฐC, where thermal stability increases for films manufactured at higher RF power as well as for films deposited away from the plasma glow. Heating of the sample increases the dielectric constant, from 3.7 (25 ยฐC) to 4.7 (120 ยฐC) at 1 kHz for polymer fabricated at 25 W. Polymers are biocompatible with non-adherent THP-1 cells and adherent mouse macrophage cells, including LPS-stimulated macrophages, and maintain their material properties after 48 h of immersion into simulated body fluid. The versatile nature of the films fabricated in this study may be exploited in next-generation consumer electronics and energy technologies

    Photon Generation and Dissipation in Organic Light-Emitting Diodes

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    By using phosphorescent and thermally activated delayed fluorescence emitters, the internal quantum efficiency of organic light-emitting diodes (OLEDs) can now reach 100%. However, a major fraction of generated photons is trapped inside the device, because of the intrinsic multi-layer device structure and the mismatch of refractive indices. This thesis comprises different approaches for the efficiency enhancement of planar OLEDs. In particular, outcoupling strategies to extract trapped photons to obtain highly efficient OLEDs are investigated

    ์œ ๊ธฐ ๋ฐœ๊ด‘ ์†Œ์ž์— ๋Œ€ํ•œ ์ž„ํ”ผ๋˜์Šค ๋ถ„๊ด‘ ๋ถ„์„ ๋ฐฉ๋ฒ•์— ๋Œ€ํ•œ ์—ฐ๊ตฌ

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    ํ•™์œ„๋…ผ๋ฌธ (๋ฐ•์‚ฌ)-- ์„œ์šธ๋Œ€ํ•™๊ต ๋Œ€ํ•™์› : ๊ณต๊ณผ๋Œ€ํ•™ ์ „๊ธฐยท์ •๋ณด๊ณตํ•™๋ถ€, 2019. 2. ํ™์šฉํƒ.In this dissertation, the method of analyzing the characteristics of organic light-emitting diodes using impedance spectroscopy was studied. Generally, the organic light-emitting device has a structure in which organic materials necessary for light emission are thinly laminated between a TCO (Transparent Conductive Oxide) and a metal electrode. Due to chemical vulnerability of organic materials as well as the complexity with their hetero-junction, it is necessary to investigate the characteristics of fabricated an organic light-emitting diodes in a non-destructive manner rather than destructive manner. Classically, a method of measuring a current-voltage curve using a current-voltage meter and measuring a luminescence using luminance meter is used to evaluate the characteristics of the OLEDs. However, in order to investigate details at intrinsic interface state or carrier dynamics of OLEDs, it is require measuring the impedance response under operating condition. Impedance spectroscopy (IS) covers all impedance responses in the frequency range from milli hertz to megahertz, while focusing primarily on capacitance in solid-state electronics. This makes it possible to construct a high-resolution equivalent circuit and analyze each measured impedance. Each impedance is measured by applying ac small signal after determining the dc operating voltage. The dc operating voltage and ac small signal should be strategically chosen to describe the behavior of the device. In Chapter 1, an overview of the Impedance Spectroscopy Analysis is introduced and the background of the impedance measurement method is explained. Then the motivation for applying this impedance analysis method to OLEDs is explained and the methods of analyzing the characteristics of OLEDs through impedance spectroscopy are discussed. Chapter 2 reviews previously reported papers about impedance analysis methods of OLEDs and explains the limitations of these papers. In particular, the contributions of the diffusion capacitance that they underestimate are very important to prevent errors when characterizing of OLEDs. To explained diffusion capacitance the Laux & Hess model is applied. This model can explain the impedance response to the residual current and even demonstrate the negative capacitance phenomenon. The analytical results using the Laux & Hess model[1] were verified to describe the characteristics of the OLEDs during operation and an approximate and fitting process for the analytical method of this model is proposed. In Chapter 3, ITO/a-NPD[N,Nโ€ฒ-Bis(naphthalen-1-yl)-N,Nโ€ฒ-bis(phenyl)-2,2โ€ฒ-dimethylbenzidine]/Alq3[Tris-(8-hydroxyquinolinato)aluminum]/LiF/Al type OLEDs were fabricated and investigated using the improved impedance analysis method proposed in Chapter 2. First, according to the structural (thickness) change, the physical analysis was performed quantitatively by changing the impedance response. The measured impedance at high frequencies represents the interface and buck characteristics in the OLEDs, and the impedance at low frequencies explains the dynamics of carriers in the OLEDs. In addition, the impedance changes due to OLEDs degradation are analyzed. Using the proposed Impedance Spectroscopy Analysis method in this paper, the origin of degradation can be accurately and effectively separated from the state change of the interface and the buck. The results strengthen the existing interpretation of the interface trap effect of HTL/EML and showed that it can be traced with the rate of change of the extracted impedance value. Chapter 4 briefly introduces the program tool for analyzing the OLEDs used in this paper, and attached an appendix for derived the formula. And I will discuss the possibility of applying this Impedance Spectroscopy Analysis to mass products industry in the future.๋ณธ ๋…ผ๋ฌธ์€ ์ž„ํ”ผ๋˜์Šค ๋ถ„๊ด‘๋ฒ•์„ ์ด์šฉํ•œ ์œ ๊ธฐ ๋ฐœ๊ด‘ ๋‹ค์ด์˜ค๋“œ์˜ ํŠน์„ฑ ๋ถ„์„ ๋ฐฉ๋ฒ•์— ๋Œ€ํ•œ ์—ฐ๊ตฌ์ด๋‹ค. ์ผ๋ฐ˜์ ์œผ๋กœ ์œ ๊ธฐ ๋ฐœ๊ด‘ ์†Œ์ž๋Š” TCO (Transparent Conductive Oxide)์™€ ๊ธˆ์† ์ „๊ทน ์‚ฌ์ด์— ๋ฐœ๊ด‘์— ํ•„์š”ํ•œ ์œ ๊ธฐ ๋ฌผ์งˆ์ด ์–‡๊ฒŒ ์ ์ธต ๋œ ๊ตฌ์กฐ๋ฅผ ๊ฐ–๋Š”๋‹ค. ์œ ๊ธฐ ๋ฌผ์งˆ์˜ ํ™”ํ•™์  ์ทจ์•ฝ์„ฑ๊ณผ ํ—คํ…Œ๋กœ ์ ‘ํ•ฉ์˜ ๋ณต์žก์„ฑ์œผ๋กœ ์ธํ•ด ํŒŒ๊ดด์ ์ธ ๋ฐฉ์‹ ๋ณด๋‹ค๋Š” ๋น„ํŒŒ๊ดด ๋ฐฉ์‹์œผ๋กœ ์ œ์กฐ๋œ ์œ ๊ธฐ ๋ฐœ๊ด‘ ๋‹ค์ด์˜ค๋“œ์˜ ํŠน์„ฑ์„ ์กฐ์‚ฌํ•ด์•ผ ํ•œ๋‹ค. ๊ณ ์ „์ ์œผ๋กœ, ์ „๋ฅ˜-์ „์••๊ณ„๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ์ „๋ฅ˜-์ „์•• ๊ณก์„ ์„ ์ธก์ •ํ•˜๊ณ  ํœ˜๋„ ๊ณ„๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ๋ฐœ๊ด‘์„ ์ธก์ •ํ•˜๋Š” ๋ฐฉ๋ฒ•์ด OLEDs์˜ ํŠน์„ฑ์„ ํ‰๊ฐ€ํ•˜๋Š”๋ฐ ์‚ฌ์šฉ๋œ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ OLEDs์˜ ์ธํ„ฐํŽ˜์ด์Šค ์ƒํƒœ ๋˜๋Š” ์บ๋ฆฌ์–ด ๋™์—ญํ•™์— ๋Œ€ํ•œ ์„ธ๋ถ€ ์‚ฌํ•ญ์„ ์กฐ์‚ฌํ•˜๊ธฐ ์œ„ํ•ด์„œ๋Š” ์ž‘๋™ ์กฐ๊ฑด ํ•˜์—์„œ์˜ ์ž„ํ”ผ๋˜์Šค ์‘๋‹ต์„ ์ธก์ •ํ•ด์•ผ ํ•œ๋‹ค ์ผ๋ฐ˜์ ์ธ ๊ณ ์ฒด ๋ฌผ๋ฆฌ์—์„œ์˜ ์ž„ํ”ผ๋˜์Šค ๋ถ„์„ ๋ฐฉ๋ฒ•์€ ์ปคํŒจ์‹œํ„ด์Šค์— ์ฃผ๋กœ ์ดˆ์ ์„ ๋งž์ถ”๊ณ  ์žˆ๋Š” ๋ฐ˜๋ฉด์—, ์ž„ํ”ผ๋˜์Šค ๋ถ„๊ด‘๋ฒ• (IS)์€ miliherz ์—์„œ megaherz์˜ ์ฃผํŒŒ์ˆ˜ ๋ฒ”์œ„์—์„œ ๋ชจ๋“  ์ž„ํ”ผ๋˜์Šค ์‘๋‹ต์„ ๋‹ค๋ฃจ๋Š” ๊ฒƒ์ด ํŠน์ง•์ด๋‹ค. ์ด๋ฅผ ํ†ตํ•ด ๋ถ„ํ•ด๋Šฅ์ด ๋†’์€ ๋“ฑ๊ฐ€ ํšŒ๋กœ๋ฅผ ๊ตฌ์„ฑํ•˜๊ณ  ๊ฐ๊ฐ ์ธก์ • ๋œ ์ž„ํ”ผ๋˜์Šค๋ฅผ ๋ฉด๋ฐ€ํžˆ ๋ถ„์„ ํ•  ์ˆ˜ ์žˆ๋‹ค. ๊ฐ ์ž„ํ”ผ๋˜์Šค๋Š” ์ž‘๋™ ์ง๋ฅ˜ ์ „์••์„ ๊ฒฐ์ •ํ•œ ํ›„ ๊ต๋ฅ˜ ์†Œ์‹ ํ˜ธ๋ฅผ ์ธ๊ฐ€ํ•˜์—ฌ ์ธก์ •๋˜๋Š”๋ฐ, ์ด ์ž‘๋™ ์ง๋ฅ˜ ์ „์••๊ณผ ๊ต๋ฅ˜ ์†Œ์‹ ํ˜ธ๋Š” ์†Œ์ž์˜ ๋™์ž‘์„ ์ ์ ˆํžˆ ์„ค๋ช…ํ•˜๊ธฐ ์œ„ํ•ด ์ „๋žต์ ์œผ๋กœ ์„ ํƒ๋˜์–ด์•ผ ํ•œ๋‹ค. ์ œ 1 ์žฅ์—์„œ๋Š” ์ž„ํ”ผ๋˜์Šค ๋ถ„๊ด‘ ๋ถ„์„์˜ ๊ฐœ์š”๋ฅผ ์†Œ๊ฐœํ•˜๊ณ  ์ž„ํ”ผ๋˜์Šค ์ธก์ • ๋ฐฉ๋ฒ•์˜ ๋ฐฐ๊ฒฝ์„ ์„ค๋ช…ํ•œ๋‹ค. ๊ทธ๋ฆฌ๊ณ  ์ž„ํ”ผ๋˜์Šค ๋ถ„์„ ๋ฐฉ๋ฒ•์„ OLEDs์— ์ ์šฉํ•˜๋ ค๋Š” ๋™๊ธฐ์— ๋Œ€ํ•ด์„œ ์„ค๋ช…ํ•˜๊ณ  ์ž„ํ”ผ๋˜์Šค ๋ถ„๊ด‘ํ•™์„ ํ†ตํ•ด OLEDs์˜ ํŠน์„ฑ์„ ๋ถ„์„ํ•˜๋Š” ๋‹ค์–‘ํ•œ ๋ฐฉ๋ฒ•๋“ค์ด ๋…ผ์˜๋œ๋‹ค. ์ œ 2 ์žฅ์€ OLEDs์˜ ์ž„ํ”ผ๋˜์Šค ๋ถ„์„ ๋ฐฉ๋ฒ•์— ๋Œ€ํ•ด ์ด์ „์— ๋ณด๊ณ ๋œ ๋…ผ๋ฌธ์„ ๊ฒ€ํ† ํ•˜๊ณ  ์ด๋“ค ๋…ผ๋ฌธ์˜ ํ•œ๊ณ„๋ฅผ ์„ค๋ช…ํ•œ๋‹ค. ํŠนํžˆ, ์ด์ „์— ๊ณผ์†Œํ‰๊ฐ€๋œ ํ™•์‚ฐ ์บํŒจ์‹œํ„ด์Šค์˜ ๊ธฐ์—ฌ๋Š” OLEDs์˜ ํŠน์„ฑ์„ ๊ฒฐ์ •ํ•  ๋•Œ ์˜ค๋ฅ˜๋ฅผ ๋ฐฉ์ง€ํ•˜๋Š” ๋ฐ ๋งค์šฐ ์ค‘์š”ํ•˜๋‹ค๋Š” ๊ฒƒ์„ ๋ณด์—ฌ์ค„ ๊ฒƒ์ด๋‹ค. ์ด๋Ÿฌํ•œ ํ™•์‚ฐ ์šฉ๋Ÿ‰์„ ์„ค๋ช…ํ•˜๊ธฐ ์œ„ํ•ด Laux & Hess ๋ชจ๋ธ์ด ์ ์šฉ๋˜์—ˆ๋‹ค. ์ด ๋ชจ๋ธ์€ ์ž”๋ฅ˜ ์ „๋ฅ˜์— ๋Œ€ํ•œ ์ž„ํ”ผ๋˜์Šค ์‘๋‹ต์„ ๋งค์šฐ ์ž˜ ์„ค๋ช… ํ•  ์ˆ˜ ์žˆ๊ณ  ์‹ฌ์ง€์–ด ์Œ์˜ ์ปคํŒจ์‹œํ„ด์Šค ํ˜„์ƒ๋„ ์ž˜ ์„ค๋ช…ํ•ด ์ค€๋‹ค. Laux & Hess ๋ชจ๋ธ์„ ์‚ฌ์šฉํ•œ ๋ถ„์„ ๊ฒฐ๊ณผ๋Š” ์ž‘๋™ ์ค‘์˜ OLEDs์˜ ํŠน์„ฑ์„ ์ž˜ ๋ฌ˜์‚ฌ ํ•˜๊ณ  ์žˆ์Œ์„ ๋ณด์˜€๊ณ  ์ด ๋ชจ๋ธ์˜ ๋ถ„์„ ๋ฐฉ๋ฒ•์„ ์œ„ํ•œ ๊ทผ์‚ฌ ํ”„๋กœ์„ธ์Šค๋ฅผ ์ œ์•ˆํ•˜์˜€๋‹ค. ์ œ 3 ์žฅ์—์„œ๋Š” ITO/a-NPD[N,Nโ€ฒ-Bis(naphthalen-1-yl)-N,Nโ€ฒ-bis(phenyl)-2,2โ€ฒ-dimethylbenzidine]/Alq3[Tris-(8-hydroxyquinolinato)aluminum]/LiF/Al ํ˜• OLED๋ฅผ ์ œ์ž‘ํ•˜์—ฌ ์ œ 2 ์žฅ์—์„œ ์ œ์•ˆ๋œ ๊ฐœ์„ ๋œ ์ž„ํ”ผ๋˜์Šค ๋ถ„์„๋ฒ•์„ ์‚ฌ์šฉํ•˜์—ฌ ์กฐ์‚ฌํ•˜์˜€๋‹ค. ๋จผ์ €, ๊ตฌ์กฐ์ (๋‘๊ป˜) ๋ณ€ํ™”์— ๋”ฐ๋ฅธ ์ž„ํ”ผ๋˜์Šค ์‘๋‹ต์˜ ๋ณ€ํ™”๋ฅผ ์ธก์ •ํ•˜์—ฌ ๋ฌผ๋ฆฌ์ , ์ •๋Ÿ‰์  ํ•ด์„์ด ์ˆ˜ํ–‰๋˜์—ˆ๋‹ค. ๋†’์€ ์ฃผํŒŒ์ˆ˜์—์„œ ์ธก์ •๋œ ์ž„ํ”ผ๋˜์Šค๋Š” OLEDs์˜ ์ธํ„ฐํŽ˜์ด์Šค ๋ฐ ๋ฒ„ํฌ ํŠน์„ฑ์„ ๋‚˜ํƒ€๋‚ด๋ฉฐ ์ €์ฃผํŒŒ์ˆ˜์—์„œ์˜ ์ž„ํ”ผ๋˜์Šค๋Š” OLEDs์˜ ์บ๋ฆฌ์–ด์˜ ๋™์  ์ด๋™์„ ์„ค๋ช…ํ•œ๋‹ค. ๋˜ํ•œ OLEDs์˜ ์—ดํ™”๋กœ ์ธํ•œ ์ž„ํ”ผ๋˜์Šค ๋ณ€ํ™”๋ฅผ ๋ถ„์„ํ•˜์˜€๋‹ค. ๋ณธ ๋…ผ๋ฌธ์—์„œ ์ œ์•ˆ ๋œ Impedance Spectroscopy Analysis ๋ฐฉ๋ฒ•์„ ์‚ฌ์šฉํ•˜๋ฉด, ์—ดํ™”์˜ ์›์ธ์œผ๋กœ์„œ ๊ณ„๋ฉด๊ณผ ๋ฒ„ํฌ์˜ ์ƒํƒœ ๋ณ€ํ™”๊ฐ€ ์ •ํ™•ํ•˜๊ณ  ํšจ๊ณผ์ ์œผ๋กœ ๋ถ„๋ฆฌ ๋  ์ˆ˜ ์žˆ๋‹ค. ๊ฒฐ๊ณผ๋Š” HTL/EML์˜ ์ธํ„ฐํŽ˜์ด์Šค ํŠธ๋žฉ ํšจ๊ณผ์— ๋Œ€ํ•œ ๊ธฐ์กด ํ•ด์„์„ ๊ฐ•ํ™”ํ•˜๋Š” ๊ฒƒ์œผ๋กœ ๋‚˜์™”๊ณ  ์ถ”์ถœ๋œ ์ž„ํ”ผ๋˜์Šค ๊ฐ’์˜ ๋ณ€ํ™”์œจ์„ ์ถ”์  ํ•  ์ˆ˜ ์žˆ์Œ์„ ๋ณด์—ฌ ์ฃผ์—ˆ๋‹ค. 4 ์žฅ ์—์„œ๋Š” ์ด ๋…ผ๋ฌธ์—์„œ ์‚ฌ์šฉ๋œ OLEDs๋ฅผ ๋ถ„์„ํ•˜๊ธฐ ์œ„ํ•œ ํ”„๋กœ๊ทธ๋žจ ๋„๊ตฌ๋ฅผ ๊ฐ„๋žตํ•˜๊ฒŒ ์†Œ๊ฐœํ•˜๊ณ  ์ˆ˜์‹์— ๋Œ€ํ•œ ๋ถ€๋ก์„ ์ฒจ๋ถ€ ํ–ˆ๋‹ค. ๊ทธ๋ฆฌ๊ณ  ํ–ฅํ›„ ์ด ์ž„ํ”ผ๋˜์Šค ๋ถ„๊ด‘ํ•™ ๋ถ„์„์„ ์‚ฐ์—…์— ์ ์šฉ ์‹œํ‚ฌ ๊ฐ€๋Šฅ์„ฑ์— ๋Œ€ํ•ด ๋…ผ์˜ํ•˜๊ณ  ์š”์•ฝํ•˜๋„๋ก ํ•˜๊ฒ ๋‹ค.Abstract i Contents v List of Figures viii List of Tables xiii Chapter 1 Introduction 1 1.1 Motivation 1 1.1.1 History of Organic Light Emitting Diodes 6 1.1.2 OLEDs Hetero Structures 8 1.1.3 OLEDs life time 11 1.2 Materials 15 1.2.1 Alq3 16 1.2.2 HAT-CN 17 1.2.3 ฮฑ-NPB 18 1.2.4 DCM 19 1.3 Equipment & Instrument 20 1.3.1 Thermal Evaporator 20 1.3.2 Impedance Measurement Equipment for OLEDs 23 Chapter 2 Analytic Theory of OLED Impedance Spectroscopy 26 2.1 Problems of Previous Reported Impedance Spectroscopy to extract parameter on OLEDs 28 2.2 Complex Capacitance Concepts for IS 31 2.2.1 ARC 31 2.2.2 ZARC 34 2.2.3 Negative Capacitance 38 2.2.4 Equivalent circuit strategy for OLEDs 43 2.3 Theory 45 2.3.1 Impedance Spectroscopy 45 2.3.2 Small-Signal Model 49 2.3.3 Complex Plane Diagram 51 2.3.4 Equivalent Circuit Modeling 54 2.3.5 Superposition of various Impedance Component 58 2.3.6 Debye relaxation plot( -plot) 60 2.4 How to extract reasonable parameter from impedance spectroscopy 64 Chapter 3 Experiments 71 3.1 Thickness modification OLEDs 72 3.1.1 Analysis of the Interface of the OLEDs 76 3.1.2 Analysis of the Carrier Distribution of OLEDs 78 3.2 Thickness ratio modification 80 3.2.1 Relation between efficiency and M-plot 82 3.3 DCM doping ration Modification 84 3.3.1 Correlation between Current-Voltage-Efficiency and Impedance Response 84 Chapter 4 Discussion 90 4.1 Consideration of Effects of Interface Properties 90 4.2 Consideration of Effects of Bulk properties 92 4.3 Negative Capacitance relation with efficiency analysis 93 4.4 Mobility Measurement Using Impedance analysis 96 Chapter 5 Conclusion 101 Appendix 109 Bibliography 116 Publications 122 ์ดˆ ๋ก 127Docto

    High Efficiency and Wide Color Gamut Liquid Crystal Displays

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    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 1.5ร— increment in spatial resolution, 2ร— 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%), 2.4ร— 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 ยฑ50หš). 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 -20ยฐC. 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

    Physical And Electrical Study Of Aloe Vera Dielectric Layer

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    Commercially available Aloe vera gel and naturally extracted Aloe vera gel were compared and used as dielectric material in organic electronic device. Commercial Aloe vera and extracted natural Aloe vera layers were formed respectively on aluminum coated glass substrate by screen-printing. Both types of Aloe vera layers were dried at room temperature for 24 hours and followed by oven drying in air. The effects of oven drying temperature (30-80oC) and duration (30-60 min), number of stacking Aloe vera layers and distance in between two metal electrodes on commercial Aloe vera layer were studied. The effects of oven drying temperature (30-90oC) and duration (30-180 min) as well as loading of silicon dioxide nanoparticles (SiO2 NPs) on extracted natural Aloe vera layer were investigated. Structural, physical and electrical properties of the commercial and extracted natural Aloe vera samples were examined and compared. Atomic force microscope, scanning electron microscope, and Fourier transform infrared spectroscope were used to identify the differences between those two types of Aloe vera layers that had been dried at different conditions. It was aimed to understand the cross-linking of polysaccharides in the materials as it is an important consideration for electrical application. It found that single layer of oven dried (40ยฐC for 30 min) commercial Aloe vera demonstrated the lowest leakage current density (J) and the J value was not affected by the distance between two metal electrodes. This revealed the electrical uniformity of the dielectric layer
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