Spelling suggestions: "subject:"light emitting diode"" "subject:"might emitting diode""
41 |
Synthesis Of Novel Blue-emitting Poly(arylene ether)s with Application to Light Emitting DiodesChang, Ming-sian 19 July 2012 (has links)
In this thesis, a novel blue Poly (arylene ether) s polymer was prepared for the organic polymer light emitting diodes which was composed of the main material anthracene difluoro monomer derivatives, and object material of triphenylamine with the extension structure similar to the literature seen BD-1 asymmetric derivatives, as the hole transport material of carbazole of the diol derivatives. In general, Anthracene derivatives and BD-1, often seen in the literature as the host, guest blue polymer doping, the main use to Forster energy transfer to transfer energy to the guest, so it has good luminous efficiency. Anthracene, flat Good, easy to crystallization during evaporation, resulting in leakage generated; and the deposition of the multilayer structure will hinder charge injection to the emitting layer. From the angle of the molecular design of this study. (1) Use of the CF bond and Carbazole increase the steric hindrance of the polymer chain and change by fluoride compounds of the highest occupied molecular orbital - lowest unoccupied molecular orbital energy level. (2) The hole transport layer to import into the emitting layer. The two monomers Anthracene derivatives fluoride monomer the Carbazole of diol derivatives via nucleophilic polycondensation synthesis of a novel in proper proportion, Blue polymer.
Component parts, the Blue poly aromatic ether polymer doped with a small amount of blue light-emitting guest as a component layer of the component structure: ITO / PEDOT: PSS / emitting layer / LiF / Al light-emitting layer can make use of spin coating of solvent process, and its advantage is the convenience of the process and a large area. The undoped guest before the Blue polymer production the PLED starting voltage can be reduced to 4.5 V, and maximum brightness 7 466 cd/m2, efficiency as high as 4.2 cd / A. C.I.E. coordinates of (0.15,0.08), very close to the official regulations of the NTSC Blue coordinates (0.14,0.08). When doped with 3% of the guest, the starting voltage can be reduced to 4.5 V, maximum brightness of 12104 cd/m2 and efficiency as high as 5.79 cd/A.
|
42 |
Temperature and Thermal Stress Distributions on High Power Phosphor Doped Glass LED ModulesHuang, Pin-che 18 July 2012 (has links)
The temperature and thermal stress distributions and variations of the high power LED module were studied in this work. The thermal-elastic-plastic 3D finite element models of MSC.marc software package are employed to simulate these performances for the high power LED module. Two high power white light LED module designs are investigated¡G one is the traditional phosphorescent silicone with blue LED module and the other is a phosphor glass lens with blue LED module. The distributions of temperature and thermal stress of in these two operating LED modules are compared and discussed. The effects of different packaging parameters¡Ge.g. bonding materials, substrate materials, lens materials on the temperature and thermal stress have also been studied in this work. The simulated results reveal that the serious thermal crack may occur for these two designs if the power of single die is over 10 watt. The simulated results also indicate that an attached fin cooler may improve these thermal crack disadvantaged significantly. The effect of fin design parameters on the peak temperature reduction has studied. A feasible fin design for the high power LED module has also been proposed.
|
43 |
The Effectiveness Analysis and Strategy of Energy-efficient Lighting in Developing a Low Carbon City ¡V A Case on Electro-Magnetic Induction LampsHu, Cheng-Hsiung 04 September 2012 (has links)
The background and motivation of this study are based on: (1) Energy saving and
carbon emission reduction are the rising issues gaining more awareness and efforts
worldwide. (2) Taiwan plans to build ¡§low-carbon cities¡¨ in order to implement the
policy of greenhouse gas reduction. (3) The most direct and practical way to reduce
carbon emissions is by saving energy. (4) Everyone has to use illumination sources.
(5) ¡§Electro-Magnetic Induction Lamps¡¨ is a useful tool to achieve the goal of energy
saving and carbon emission reduction. Thus the topic of this study is ¡§The
Effectiveness Analysis and Strategy of Energy-efficient Lighting in Developing a
Low Carbon City ¡V A Case on Electro-Magnetic Induction Lamps¡¨.
The objectives of this study are:
1. To analyze the characteristics of ¡§Electro-Magnetic Induction Lamps¡¨ and their
conformity with local and overseas energy-efficient lighting policies.
2. To analyze the effectiveness of lighting economics of the case companies before and
after their adoption of ¡§Electro-Magnetic Induction Lamps¡¨.
3. To explore the possible obstacles and their solutions for lighting industry
development of ¡§Electro-Magnetic Induction Lamps¡¨ in the public sectors¡¦ strategies
to develop low-carbon cities in Taiwan.
The main issues of this study are about energy-efficient lighting policies and the
economical effectiveness of ¡§Electro-Magnetic Induction Lamps¡¨, which belong to
policy research on energy-saving equipment and the lighting industry. Therefore
three research methods: Literature Review, Case Study, and In-depth Interview were
adopted to collect, compare, and analyze the data.
The conclusions of this study are:
1. The characteristics of ¡§Electro-Magnetic Induction Lamps¡¨ are in conformance with
energy-efficient lighting policies in Taiwan.
2. To provide the analysis result of the case companies¡¦ economic benefits after its
adoption of ¡§Electro-Magnetic Induction Lamps¡¨.
3. To indicate the possible Dilemma of the lighting industry development of
¡§Electro-Magnetic Induction Lamps¡¨ and the energy-efficient lighting policies for
the strategies to develop low-carbon cities in Taiwan.
According to above research outcomes, three suggestions have been further proposed:
1. Users must change their concepts and habits of lighting usage in order to cultivate
good energy-saving habits.
2. Users must select appropriate illumination sources according to their needs in order
to achieve most effectiveness of lighting economics.
3. According to the needs of appropriate illumination sources, the government should
promote and subsidize the development and use of ¡§Electro-Magnetic Induction
Lamps¡¨.
|
44 |
Package of Homojunction of Fully Conjugated Heterocyclic Aromatic Rigid-rod Polymer Light Emitting DiodesLiao, Hung-chi 20 July 2004 (has links)
The focus of this study is mono-layer polymer light emitting diode (PLED). The emitting layer is poly-p-phenylenebenzobisoxazole (PBO). PBO is a fully conjugated heterocyclic aromatic rigid-rod polymer. Anode is indium-tin-oxide (ITO). Cathode is aluminum (Al). We used UV epoxy resin to package PLED devices, then measured current-voltage response, electroluminescence (EL) emission, and device lifetime.
We demonstrate that the packaged mono-layer PBO LED reduced its demise from water and oxygen. Device lifetime increased from 1 hour to several hundred hours. At a larger bias voltage or current, emission intensity and device efficiency became higher. But decay rate increased leading to shortened device lifetime. Device temperature appeared linearly with current density. A red shift of the EL emission was observed. The £fmax. of emission spectra moved from 534 nm (initial) to 582 nm (after 100 hrs).
After thermal annealing at 120¢J for ten hours, threshold voltage increased from 5 V to 12 V, current density decreased to several 10 mA/cm2, luminous intensity improved several ten times to 10-2 cd/m2, emission color changed from yellow-green to orange, luminous efficiency improved from 10-7 to 10-4 cd/A, but device lifetime declined to less than 20 hrs.
|
45 |
Enhancement of Coupling Efficiency of Plastic Optical Fibers with Different End ShapesChang, Kuang-yao 15 July 2006 (has links)
The fiber-optics communication device with a plastic optical fiber (POF) has become a technology of increasing interests. The attenuation of commercial available POF has been improved to tens of decibels per kilometer. Due to its flexibility and high alignment efficiency, it has been widely used in many areas.
In this study, different end shapes of POF have been proposed to increase the coupling efficiency of a POF from a surface emitting LED. Both the experiments and a ray tracing simulation are performed to investigate the coupling scheme. Experimental results also illustrate the feasibility of using ray tracing model in POF end shapes design.
The effect of ball fiber lens on coupling efficiency is studied first. Lens material is EPO-TEK 353ND two parts epoxy. The result indicates that the ball fiber lens can improve the coupling efficiency significantly. A more impact end shape modified from the ball fiber lens is proposed in this study, i.e. a thin tip-rounded fiber lens. Numerical and experimental results show the tip can work as good as a ball fiber lens does. A reflection-styled end shape has also been proposed in this thesis, i.e. a taper-ended POF. In this design, the taper edge serves as a reflector to bend the rays incident on it by total internal reflection. The maximum efficiency achieves a great improvement from the previous design.
Further study on the various fiber types with different sizes and numerical apertures have also been studied by the ray tracing model.
|
46 |
Photovoltaic Cells and Light Emitting Diodes of Fully Conjugated Rigid-rod PolymerTsai, Jung-lung 24 July 2006 (has links)
Polymer photovoltaic cell (PV cell) utilizes a polymer to absorb photons for generating excitons. When excitons are separated into electrons and holes, the device has the photovoltaic effect. Polymer light emitting diode (PLED) injects electrons and holes respectively from cathode and anode into a polymer emission layer. Some of the electrons and the holes would recombine to induce light emission.
This research used a heterocyclic aromatic rigid-rod polymer poly-p-phenylene- benzobisoxazole (PBO) as the opto-electronic layer, and a conducting material of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) as the hole transport layer. PV cells were fabricated using indium-tin-oxide (ITO) as anode and aluminium as cathode. Same layer arrangement was applied for PLEDs. These two kinds of devices were measured for electrical and optical response.
It was evidenced that the addition of PEDOT:PSS layer facilitated the separation of excitons into electrons and holes at the PBO/PEDOT:PSS interface. Insertion of a LiF layer between PBO layer and Al cathode reduced their energy band gap and facilitated charge transport leading to an enhanced efficiency for PV cells and PLEDs.
Thickness variations were found on spun PBO layer. According to emission intensity, we knew that the PBO layer quality was significant for electroluminescence. Introduction of a PEDOT:PSS layer improved the interface between ITO and PBO. The thickness of PEDOT:PSS layer depended on the ITO surface roughness. With a PEDOT:PSS layer, the opto-electronic efficiency of PV cell and PLED was improved.
|
47 |
Light Emitting Diodes and Photovoltaic Cells of Fully Conjugated Heterocyclic Aromatic Rigid-rod Polymers Doped with Multi-wall Carbon NanotubeHuang, Jen-Wei 01 November 2006 (has links)
Poly-p-phenylenebenzobisoxazole (PBO) and carbon nanotube (CNT) contain fully conjugated rod like backbone entailing excellent mechanical properties, thermo -oxidative stability and solvent resistance. Rigid-rod PBO is commonly processed by dissolving in methanesulfonic acid or Lewis acid. A CNT of multi-wall carbon nanotube (MWNT) was dissolved in a Lewis acid solution of PBO for dispersion, and then spun for thin film. MWNT concentration in the films was from zero up to 5 wt. %. Compared to that of pure PBO film, all PBO/MWNT composite films retained same but enhanced UV-Vis absorption peaks, according to MWNT concentration, showing that PBO and MWNT did not have overlapping electron orbitals affecting their energy gaps.
The composite films were excited at 325 nm using a He-Cd laser for photoluminescence (PL) emission. All PL spectra had maximum intensity at 540 nm indicative of yellow-green light emission. The composite films were fabricated as light emitting diodes using indium-tin-oxide/glass as substrate and anode, as well as vacuum evaporated Al as cathode for respectively hole and electron injectors. In these light emitting devices, MWNT doped PBO would decrease threshold voltage for about 2 V. Up to 0.1 wt. % of MWNT, the device emission current was increased two orders of magnitude than those of the devices without MWNT. Further increase of MWNT caused a successive decrease in electroluminescence emission intensity attributed to a quench effect from aggregations of MWNTs.
UV epoxy resin was applied to package the mono-layer and bilayer PBO light emitting devices. The UV epoxy resin had some gas release during encapsulation. The devices were packaged with vacuum and without vacuum encapsulation. It was demonstrated that the device encapsulation reduced its demise from water and oxygen. The vacuum encapsulation could remove gaseous volatile of the device to inhibit oxygen and moisture to prolong device lifetime. The main degradation of light emitting device was the oxidization of cathode. The interactions between nitrogen of PBO and H2O caused the formation of hydrogen bonding at room temperature.
Oxygen and moisture diffused into PBO polymer and were suspected to form mid-gap state for the polymer. The mid energy band disappeared upon heat treatment before encapsulation. A device under a higher bias voltage was found to have a shorter lifetime, but a larger EL emission intensity. The EL emission intensity was not a constant under a constant current bias. The vacuum encapsulated device had two or twenty times lifetime than, respectively, the device encapsulation without vacuum evacuation or in ambient conditions.
The sandwich structure of ITO/PBO/Al had no observable photovoltaic effect due to insufficient exciton separation into electrons and holes. Poly(2,3-dihydro thieno-1,4-dioxin):polystyrenesulfonate (PEDOT:PSS), a hole transferring medium, was spun into a thin-film between PBO and indium-tin-oxide to facilitate photovoltaic (PV) effect by forming a donor-acceptor interlayer to separate and to transport photoinduced charges. Optimum PBO thickness for the PV heterojunctions was about 71 nm at which the hole transferring PEDOT:PSS generated the maximum short circuit current (Isc) at a thickness of 115 nm. By using a layer of lithium fluoride (LiF) as an electron transferring layer adhering to Al cathode, the most open circuit voltage (Voc) and the maximum short circuit current (Isc) were achieved with a LiF thickness of 1-2 nm due to possible electric dipole effect leading to an increase of Voc from 0.7 V to 0.92 V and of Isc from about 0.1
|
48 |
Electrode Modifications of Molecular Light Emitting DiodesCheng, Han-Yuan 09 June 2003 (has links)
Molecular light emitting diode, including organic light emitting diode (OLED) and polymer light emitting diode (PLED), is commonly consist of one or several molecular layer(s) sandwiched between an anode and a cathode. When electrons and holes are injected respectively from cathode and anode into the molecular layer by a bias voltage, these two types of carriers migrate towards each other and a fraction of them recombine to form light emission.
The focus of this study is electrode modifications of molecular light emitting diode. The electrode modifications include using a low work function cathode material, a high work function anode material or inserting a very thin electrode modifier between molecular layer and electrode for enhancing the electron or the hole injection efficiency leading to higher electroluminescence emission and/or lower threshold voltage.
Low work function metal, Mg, could effectively reduce the electron injection barrier between molecular layer and cathode leading to better emission brightness and threshold voltage. A monolayer rigid-rod poly-p-phenylenebenzobisthiazole (PBT) or poly-p-phenylenebenzobis- oxazole (PBO) PLED with Mg cathode demonstrated a low threshold voltage of 3 V. Besides, a very thin layer of LiF (or Al2O3) inserted between molecular layer and Al cathode was applied to enhance the electron injection efficiency leading to a stronger electroluminescence intensity and a low threshold voltage of 2.8 V.
On anode modification, a thin PBO layer was inserted between molecular layer and the indium-tin-oxide (ITO) substrate for improving the electroluminescence emission brightness and the threshold voltage. The PBO modified anode could effectively enhance the electro- luminescence intensity and lower the threshold voltage to 1 V~ 3 V on several mono- or multi-layer molecular light emitting diodes. Besides, a novel ITO substrate cleaning method via acid treatment was applied for increasing the work function of ITO to effectively enhance the hole injection efficiency.
|
49 |
Effects of Layer Thickness on Electroluminescence of Fully Conjugated Rigid-rod Polymer Light Emitting DiodesTseng, Hua-wei 12 July 2008 (has links)
A heterocyclic aromatic rigid-rod polymer poly-p-phenylene-benzobisoxazole (PBO) was applied as the opto-electronic layer¡Fand a conducting material of poly(3,4-ethylenedioxythio-phene):poly(4-styrenesulfonic acid) (PEDOT: PSS) was used as the hole transport layer. Aluminum (Al) and indium tin oxide (ITO) were served as device cathode and anode¡Arespectively, fabricated into a bi-layer structure of ITO/PEDOT:PSS/PBO/Al for electrical and luminescence responses.
This research demonstrated an increase of current density and a decrease of threshold voltage with a decrease of PBO layer thickness from 90 nm to 27 nm to facilitate electron tunneling and electron-hole recombination. With a lower spin coating speed, polymer chain would aggregate and inter-penetrate resulted in red-shift of electroluminescence (EL) emission spectrum. Furthermore, micro-cavity effect might influence EL spectrum by varying layer thickness. Modulation of PBO layer thickness led to tunable EL emission color.
It was also demonstrated that an increase of current density and a slightly decrease of threshold voltage with a PEDOT:PSS film thickness changing from 96 nm to 17 nm at a constant PBO layer thickness of 90 nm. Micro-cavity effect thus influenced EL emission for a tunable emission color.
Photolithography was applied to obtain ITO substrate of grating depth of periodic variation and then coated with a PEDOT:PSS leading to a grated PEDOT:PSS layer of periodic thickness. This led to ITO/PEDOT:PSS/PBO/Al device showing broadened EL emission spectra.
|
50 |
Fabrication of aspherical micro-lens using modified LIGA processLee, Wan-chi 26 August 2009 (has links)
This study utilizes a modified LIGA process to fabricate a high aspect ratio aspherical micro lens array, which improves low light output of OLED due to its intrinsic total internal reflection.
Presently typical OLED extraction efficiency is not high. How to increase OLED extraction efficiency is a valuable topic to discuss. This study analyzes related parameters that influence the formation of micro lenses, for example, the influence of variation of diametric dimension, dry etching parameters and electroforming rate. The experimental results indicate that the tolerance of dimensional variation of the diameter is about 5% during the thermal reflow and dry etching stage. The oxygen content and the photoresist surface during dry etching influence the result. A high electroforming rate is helpful for covering the surface defects on photoresist. An undercut caused by dry etching will discontinue the initial electroformed layers. A apherical microens array can raise the luminance to a maximum of 15 times higher.
|
Page generated in 0.1101 seconds