Dissertations / Theses on the topic 'Organic light-emitting materials'
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Chen, Haiying. "Study on materials for organic light-emitting diodes /." View abstract or full-text, 2003. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202003%20CHEN.
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Visweswaran, Bhadri. "Encapsulation of organic light emitting diodes." Thesis, Princeton University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3665325.
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Organic Light Emitting Diodes (OLEDs) are extremely attractive candidates for flexible display and lighting panels due to their high contrast ratio, light weight and flexible nature. However, the materials in an OLED get oxidized by extremely small quantities of atmospheric moisture and oxygen. To obtain a flexible OLED device, a flexible thin-film barrier encapsulation with low permeability for water is necessary.
Water permeates through a thin-film barrier by 4 modes: microcracks, contaminant particles, along interfaces, and through the bulk of the material. We have developed a flexible barrier film made by Plasma Enhanced Chemical Vapor Deposition (PECVD) that is devoid of any microcracks. In this work we have systematically reduced the permeation from the other three modes to come up with a barrier film design for an operating lifetime of over 10 years.
To provide quantitative feedback during barrier material development, techniques for measuring low diffusion coefficient and solubility of water in a barrier material have been developed. The mechanism of water diffusion in the barrier has been identified. From the measurements, we have created a model for predicting the operating lifetime from accelerated tests when the lifetime is limited by bulk diffusion.
To prevent the particle induced water permeation, we have encapsulated artificial particles and have studied their cross section. A three layer thin-film that can coat a particle at thicknesses smaller than the particle diameter is identified. It is demonstrated to protect a bottom emission OLED device that was contaminated with standard sized glass beads.
The photoresist and the organic layers below the barrier film causes sideways permeation that can reduce the lifetime set by permeation through the bulk of the barrier. To prevent the sideways permeation, an impermeable inorganic grid made of the same barrier material is designed. The reduction in sideways permeation due to the impermeable inorganic grid is demonstrated in an encapsulated OLED.
In this work, we have dealt with three permeation mechanisms and shown solution to each of them. These steps give us reliable flexible encapsulation that has a lifetime of greater than 10 years.
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Shaheen, Sean E. "Device physics of organic light-emitting diodes." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/289012.
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This work investigated several aspects of OLED device physics. The mechanisms responsible for the efficiency enhancement typically seen when a dye molecule is doped into the emission layer were examined. By comparing the spectra and efficiencies of single-layer devices for varying dopant concentrations, it was found that both charge transfer and energy transfer from the host molecule to the dye dopant are important processes. The measured efficiencies for photoluminescence and electroluminescence were found to be consistent with a simple model developed to explain the functional dependence on the dopant concentration. Work was also done on the enhancement of electron injection from an aluminum cathode using a thin layer of LiF. A double-layer device with the blue emitter DPVBi showed a factor of 50 enhancement in quantum efficiency upon insertion of a LiF layer. This technique has important practical application since it allows for the use of an environmentally-stable aluminum cathode while retaining high device efficiency. The effect of the ionization potential of the hole transport layer on the efficiency of a double-layer device was also investigated. TPD side-group polymers were used as the hole transport layer. The device efficiency was shown to increase as the ionization potential of the hole transport layer was pushed further from the work-function of ITO. This trend was attributed to an improved balance between the injection rates of holes and electrons. A Monte Carlo simulation of a single-layer device was developed which demonstrated the importance of balanced injection to obtain high efficiency. Drawing upon these results, an optimized OLED was fabricated which exhibited a luminous efficiency of 20 lm/W for green emission. This is one of the highest OLED efficiencies reported as of the date of this writing.
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Vlachos, Panagiotis. "Heterocyclic liquid crystal materials for organic light emitting diodes." Thesis, University of Hull, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396738.
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Flechon, C. "Organic light-emitting diodes based on new promising materials." Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1386057/.
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The present work focuses on the investigation of two types of new materials, phosphorescent and near-infrared, for the fabrication of solution-processible Organic Light-Emitting Diodes (OLEDs). After the introduction of the theoretical background in the first part, the second part concentrates on phosphorescent OLEDs based on copper transition metal complexes. The photophysical properties of the copper complexes, the phosphorescent host and the interlayers were studied before the fabrication of phosphorescent OLEDs. Despite the various colours exhibited by the metal complexes all devices emit white light. The possible formation of an exciplex at the guest/host interface was thus investigated. Finally the influence of the solvent on the morphologies of the films and the performances of the devices were studied. The third part focuses on near-infrared OLEDs obtained by using two different strategies. First by using a near-infrared copolymer emitting at 880 nm and incorporating it in green and red hosts and second by the creation of what is believed to be an exciplex at the interface between a hole injection layer and twisted organic molecules that emit at 515 and 540 nm. In both cases pure infra-red light above 800 nm was achieved.
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Bronstein, Hugo. "Electrophosphorescent materials for use in organic light emitting devices." Thesis, Imperial College London, 2009. http://hdl.handle.net/10044/1/11225.
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Keyworth, Colin William. "Silicon-containing organic conjugated materials for light emitting diodes." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/11192.
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This thesis contains a study of polymer light emitting diodes (PLEDs) for commercial use within blue organic light-emitting diode (OLED) display technologies. The introduction chapter outlines the aims and synthetic strategies / targets employed during the research and gives background information as to the historical development of OLEDs and PLEDs. The first chapter of research involves the synthesis of several alternating co-polymers of dibenzosilole (a previously reported monomer used in light emitting devices), along with the prerequisite monomers. These co-polymers have been fully characterised and their optoelectronic properties evaluated. The energy levels of the co-polymers (HOMO / LUMO) were measured, then compared with each other and used to establish correlations between these values and the use of co-monomers and the polymer backbone linearity. By tuning the energy levels of conjugated polymers, it is possible to alter both the energy of the light emitted (and therefore the colour) and also improve the charge-injection balance within the OLED device, thereby improving lifetimes and performance. This research was primarily concerned with blue light-emission, therefore these energy level studies were conducted with a view to achieving blue light emission with the desired CIE coordinates and luminance. The novel co-polymers were used to fabricate several prototype OLED devices and the performance of these has been evaluated. The second chapter of research contains a study of several novel silicon-containing monomer structures, for incorporation into conjugated PLEDs. The first structure is a disilaanthracene derivative and the attempted synthesis of this monomer is reported. The other two monomers are based on spirosilabifluorene and the syntheses and full characterisations are reported. Attempts at the coupling of these monomers were made, using several different known coupling reactions including Suzuki, Stille and Kumada. The attempted coupling products were simple trimers, using 9,9-dioctylfluorene as a co-monomer. These were to be used in small molecule organic light-emitting diodes (SMOLEDs). The outcomes of these coupling reactions are described.
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Anderson, Michele Lynn 1968. "Characterization of organic/organic' and organic/inorganic heterojunctions and their light-absorbing and light-emitting properties." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/282555.
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Increasing the efficiency and durability of organic light-emitting diodes (OLEDs) has attracted attention recently due to their prospective wide-spread use as flat-panel displays. The performance and efficiency of OLEDs is understood to be critically dependent on the quality of the device heterojunctions, and on matching the ionization potentials (IP) and the electron affinities (EA) of the luminescent material (LM) with those of the hole (HTA) and electron (ETA) transport agents, respectively. The color and bandwidth of OLED emission color is thought to reflect the packing of the molecules in the luminescent layer. Finally, materials stability under OLED operating conditions is a significant concern. LM, HTA, and ETA thin films were grown in ultra-high vacuum using the molecular beam epitaxy technique. Thin film structure was determined in situ using reflection high energy electron diffraction (RHEED) and ex situ using UV-Vis spectroscopy. LM, HTA, and ETA occupied frontier orbitals (IP) were characterized by ultraviolet photoelectron spectroscopy (UPS), and their unoccupied frontier orbitals (EA) estimated from UV-Vis and fluorescence spectroscopies in combination with the UPS results. The stability of the molecules toward vacuum deposition was verified by compositional analysis of thin film X-ray photoelectron spectra. The stability of these materials toward redox processes was evaluated by cyclic voltammetry in nonaqueous media. Electrochemical data provide a more accurate estimation of the EA since the energetics for addition of an electron to a neutral molecule can be probed directly. The energetic barriers to charge injection into each layer of the device has been correlated to OLED turn-on voltage, indicating that these measurements may be used to screen potential combinations of materials for OLEDs. The chemical reversibility of LM voltammetry appears to limit the performance and lifetimes of solid-state OLEDs due to degradation of the organic layers. The role of oxygen as an electron trap in OLEDs has also been verified electrochemically. Finally, a more accurate determination of the offset of the occupied energy levels at the interface between two organic layers has been achieved via in situ monitoring of the UPS spectrum during heterojunction formation.
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Zhang, Lu. "TADF process in blended organic luminescent material." HKBU Institutional Repository, 2016. https://repository.hkbu.edu.hk/etd_oa/340.
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Organic light-emitting diode (OLED) devices have been applied in the fields of display and solid-state lighting. In addition to phosphorescent OLEDs using heavy transition metals, a new approach of harvesting both singlet and triplet excitons generated in the OLED device by using pure organic materials has drawn a lot of attentions in recent years. It is thermally activated delayed fluorescence (TADF) process, which makes it possible to obtain potential 100% internal quantum efficiency (IQE);TADF is a process existing in certain organic materials with small singlet-triplet exchange energy (EST), which is generally observed in the molecules with weak-coupled electron-donating (D) group and electron-accepting (A) group. Individual molecule containing D/A, which is named intramolecular exciplex, or intermolecular exciplex with D/A on separated molecules, can fulfill this requirement. Although at present the intramolecular exciplex attracts considerable research interests, it takes a lot of efforts to design an individual molecule with high fluorescent quantum yield as well as small EST. Intermolecular exciplex, which is achieved by physically blending individual D and A molecules with appropriate selection from present materials, has excellent performance comparable to the phosphorescent emitter.;In this work, we studied the TADF process in an intermolecular exciplex and its application in highly efficient OLED devices. By doping electron-donating material tris(4-carbazoyl-9-ylphenyl)amine (TCTA) with electron-accepting material 2,4,6-tris(3'-(pyridin-3-yl)biphenyl-3-yl)-1,3,5-triazine (Tm3PyBPZ), an exciplex with a green emission around 514 nm was demonstrated. The time-resolved photoluminescence of the exciplex under different temperatures from 12 K to 300 K demonstrated the existence of temperature-dependent delayed fluorescence. By applying this exciplex as the emissive layer, a highly efficient all-fluorescent organic lighting emitting diode with maximum efficiencies of 13.1% and 53.4 lm/W was realized with an extremely low turn-on voltage of only 2.4 V. The efficiencies of the device have outperformed conventional fluorescent OLED devices due to the contribution of triplet excitons. By doping this exciplex with other conventional green or yellow fluorescent dopants, we observed that the performances of these dopants also surpass the limitation of conventional fluorescent OLED (5̃ % external quantum efficiency)
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Perez-Bolivar, Cesar A. "Synthesis and Studies of Materials for Organic Light-Emitting Diodes." Bowling Green State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1272652295.
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Fong, Hon Hang. "Transport and luminance of organic electronic materials." HKBU Institutional Repository, 2004. http://repository.hkbu.edu.hk/etd_ra/612.
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Reig, Canyelles Marta. "Carbazole-Based Materials for Organic Thin-Film Transistors and Organic Light-Emitting Diodes." Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/404560.
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This thesis deals with the preparation and characterization of novel organic semiconductors based on the carbazole heterocycle for electronic and optoelectronic applications, specifically to be studied as active layers in OTFTs and as emitting layers in OLEDs. Carbazole-based materials are recognised for their high thermal stability, high emission efficiencies and excellent hole-transporting properties associated to its electron-donating ability, which make of them promising candidates for OTFTs and OLEDs applications.
OLEDs have been studied extensively due to their promising applications in flat panel displays and solid-state lighting. However, further improvement of power efficiency and colour purity are still required to produce more efficient industrial devices. Thus, the first part of this thesis deals with the preparation of a series of carbazole-based blue emitters for their application as emitting layers in blue and in particular in deep-blue OLEDs. The extension of the π-conjugated carbazole system by preparing bicarbazole and tricarbazole derivatives afforded materials with the sought deep-blue emission properties in the solid state, which were modulated by the insertion of the ethynylene linker. OLED devices exhibited very low turn-on voltages and a maximum luminance as high as 1.4 x 104 cd m–2.
The second part of this thesis is focused on the development of new organic semiconductors with effective charge transport properties. In order to obtain new n-type or ambipolar materials, the hole-transporting behaviour of the electron-donating carbazole moiety was modified by the introduction of electron-withdrawing groups on its structure. As a first approach, the coupling of the carbazole heterocycle with the electron acceptor tris(2,4,6-trichlorophenyl)methyl radical (TTM) yielded ambipolar materials, whose charge-transporting properties were found to be dependent on the substitution patterns of the carbazole core. As a second approach, the introduction of the strong electron-withdrawing tricyanovinyl group on the carbazole core afforded a push-pull system with high electron affinity, resulting in materials with n-type or ambipolar behaviour as determined by TOF and OTFT measurements.
The last part of this thesis is focused on the preparation of a series of p-type carbazole related derivatives, in which the extension of the π-conjugated core was progressively varied in order to study its effect on the charge-transporting properties. Indolo[3,2-b]carbazole and triindole derivatives showed enhanced OTFT device performance with hole mobilities in the range of 10–3 to 0.1 cm2 V–1 s–1. In particular, N-trimethyltriindole exhibits a face-to-face molecular packing with π–π interactions, and an optimal perpendicular molecular disposition to the substrate surface as determined by XRD, that can be related to a more favourable charge transport in the OTFT devices. The introduction of long hexyl chains in the triindole core contributes with additional C–H···π interactions to those of π–π type between the triindole cores, enhancing the degree of molecular order in the thin films as reflected in the determined hole mobility, which was found to be the highest value of all the series with a value of 0.1 cm2 V–1 s–1.
The knowledge of the molecular packing and intermolecular interactions in the organic layers has been proved to be essential to rationalize the charge-transporting properties and it is shown here to be a useful tool to be considered on the design of new organic semiconductors.El desenvolupament de nous semiconductors orgànics amb capacitat de transport de càrrega presenta un gran interès per a la seva aplicació en transistors orgànics de capa prima (OTFTs), díodes emissors de llum orgànics (OLEDs) i cel·les solars orgàniques, entre d’altres. L’objectiu d’aquesta tesi és la preparació i caracterització de nous semiconductors orgànics basats en l’heterocicle carbazole i el seu estudi com a components en OTFTs i en OLEDs. En primer terme, aquesta tesi està centrada en la preparació de nous derivats del carbazole amb propietats luminescents en la zona del blau de l’espectre electromagnètic. En concret, es pretén modular les propietats òptiques del carbazole mitjançant l’extensió de la conjugació del seu nucli aromàtic per introducció de grups donadors d’electrons en la seva estructura, així com per la introducció del triple enllaç com a espaiador entre el nucli carbazole i els grups donadors d’electrons. L’estudi dels materials preparats com a capes emissores en OLEDs ha donat lloc a dispositius amb emissió a la zona del blau que han presentat una elevada luminància de fins a 1.4 x 104 cd m–2. La segona part de la tesi està enfocada en el desenvolupament de nous semiconductors orgànics basats en l’heterocicle carbazole i l’estudi de les seves propietats de transport de càrrega. Per tal de preparar nous semiconductors orgànics de tipus n o ambipolars, es pretén modificar les propietats de transport de forats del nucli carbazole mitjançant la introducció de grups atractors d’electrons en la seva estructura. Per una altra banda, s’ha preparat una sèrie de materials basats en el carbazole en què s’ha variat progressivament l’extensió del seu sistema conjugat, per tal d’obtenir derivats amb propietats de transport de forats efectives. Les propietats de transport de càrrega dels materials preparats s’han avaluat mitjançant la tècnica “time of flight” (TOF) i la preparació i mesura de OTFTs. S’han obtingut alts valors de mobilitat de forats de fins a 0.1 cm2 V–1 s–1 a partir de OTFTs basats en derivats del triindole. Els resultats obtinguts s’han correlacionat amb l’estructura molecular, el tipus d’empaquetament molecular, i amb el grau d’ordre i disposició de les molècules a les capes dels dispositius mitjançant estudis de difracció de raigs X i càlculs teòrics.
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Du, Weiwei. "Development of new organic emissive materials for organic light-emitting diodes and organic laser applications." Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS215.
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Dans ce travail, de nouveaux matériaux émetteurs organiques ont été développés pour des applications dans le domaine des diodes électroluminescentes ou des lasers organiques. Tout d’abord, trois séries de molécules « through space » TADF (Fluorescence retardée activée thermiquement) à base de cœurs cyclophane ont été préparées avec succès. Leurs structures chimiques ont été caractérisées par résonnance magnétique nucléaire (RMN) et spectroscopie de masse haute résolution (HRMS). Leurs propriétés photophysiques ont été étudiées en solution et à l’état solide. Dans ces structures, le transfert de charge intramoléculaire est produit via des interactions intramoléculaires à travers l’espace entre les groupements donneur et accepteur, et leurs études ont révélé que la plupart des dérivés synthétisés présentent un caractère TADF. Les propriétés d’électroluminescence de certains dérivés ont été également étudiées en configuration OLED et des résultats prometteurs ont été mis en évidence. Ensuite, une série de molécules à gain basées sur des structures pi-conjuguées ou tridimensionnelles étendues ont été synthétisées avec succès pour des applications lasers. Leurs structures chimiques ont été caractérisées par résonnance magnétique nucléaire (RMN) et spectroscopie de masse haute résolution (HRMS). De bonnes propriétés de luminescence telles que de hauts rendements quantiques de photoluminescence (PLQY) et de courts temps de vie de fluorescence ont été démontrés en solution et à l’état solide pour la plupart des dérivés. Pour finir, ces matériaux émissifs présentent de bonnes propriétés d’émission spontanée amplifiée (ASE) avec de faibles valeurs de seuil et des dispositifs laser optiquement pompés ont également pu être fabriqués à partir de certains des dérivés de la sérieIn this work, new organic emitting materials were designed for the organic light-emitting diodes (OLED) or laser applications. First, three series of through-space TADF (Thermally Activated Delayed Fluorescence) molecules based on different cyclophane cores have been successfully prepared. Their chemical structures were confirmed by Nuclear Magnetic Resonance (NMR) and high-resolution mass spectrometry (HRMS). The photophysical properties were investigated in solution and solid state. In these systems, the intramolecular charge transfer was produced via intramolecular through-space interactions between the donor and acceptor units, and their study revealed that most of these derivatives exhibit a TADF character. The electroluminescence properties of some derivatives were also investigated in OLED configuration and promising results were evidenced. Second, a new set of soluble gain molecules based on extended π-conjugated or three dimensional (3D) structures have been successfully synthesized for laser applications. Their chemical structures were confirmed by Nuclear Magnetic Resonance (NMR), high-resolution mass spectrometry (HRMS) and elemental analysis. High luminescence properties such as high photoluminescence quantum yields (PLQY) and short fluorescence lifetimes were demonstrated in both solution and solid state for most of the derivatives. Finally, these emitting materials exhibits good amplified spontaneous emission (ASE) properties with low thresholds and optically pumped laser devices were fabricated based on some derivatives of the series
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Gorjanc, Timothy C. "Study of lanthanum-based cathode materials for organic light-emitting devices." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ38751.pdf.
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Lin, Meifang. "Robust organic light emitting device with advanced functional materials and novel device structures." HKBU Institutional Repository, 2008. http://repository.hkbu.edu.hk/etd_ra/939.
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Somasundaram, Sahadev. "Design of low-cost organic light emitting diodes." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/122470/2/__qut.edu.au_Documents_StaffHome_StaffGroupH%24_halla_Desktop_Sahadev_Somasundaram_Thesis.pdf.
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This project focused on reducing the production cost of organic light emitting diodes and organic semiconductors through intuitive engineering design. Included in the thesis is a comprehensive, bottom-up method of design, synthesis, fabrication and analysis of both a set of luminescent materials and semiconductor device structure for use in organic light emitting diodes. The results demonstrate the viability of the method and reveal novel findings about the "thermally activated delayed fluorescence" phenomenon and its application in organic light emitting diodes.
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Chen, Zhao. "Cyclometalated iridium(III) complexes for full-color and near infrered phosphorescent organic light-emitting diodes." HKBU Institutional Repository, 2018. https://repository.hkbu.edu.hk/etd_oa/484.
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Dramatic increase of energy consumption and environmental problems invigorate the development of organic semi-conductive materials to substitute for the conventional inorganic materials in the application of photovoltaic and light-emitting devices. In view of the merits of low driving voltage, high power conversion efficiency, large-area fabrication of thin and light organic films as well as saturated emission, organic light-emitting diodes (OLEDs) have received much more consideration by scientists in the past two decades. And even out of laboratory, the OLEDs are popular among the commercial electronic products for solid-state displays and illumination. Generally, three primary RGB emitters, involving red (R), green (G) and blue (B), are footstones to achieve solid-state displays and illumination because the spectra by compositing RGB emissions match very well with the solar spectrum. Also, the combination of two complementary luminophors, blue and orange or yellow is an alternative approach to simulate the solar spectrum for white light illumination. Except for the full-color light-emitting materials for solid-state displays and illumination, near infrared (NIR) organics are of great importance for applications in information-secured devices, communications, biosensors, and phototherapy. To date, uncountable research works focusing on the emitters for full-color emissions have demonstrated their synthesis, photophysical properties and OLED application, which shows enough efficiency and stability to commercial utility. However, there are still three challenging issues which are needed to be handled urgently. Firstly, the lack of efficient deep blue emitters makes the external quantum efficiency (EQE) of deep blue OLEDs around 10% when the Commission Internationale de l'Éclairage (CIE) coordinates of y is smaller than 0.1. On the one hand it is difficult to achieve the deep blue emitters with extremely broad energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). On the other hand the triplet and frontier energy levels of the host, electron transporting layer (ETL) and hole transporting layer (HTL) in the device are required to well match with that of the emitters. Secondly, high energy in the emissive layer (EML) of deep blue OLEDs may degrade the materials used inside the EML, resulting in their short lifetimes. Thirdly, by comparison with other colors, the investigations of NIR emitters, such as their preparation, property study and device fabrications are sparse.;By harvesting both 25% singlet and 75% triplet excited states, iridium(III) [Ir(III)] complexes have been proven to be one of the best candidates to achieve highly efficient phosphorescent OLEDs (PHOLEDs) for solid-state displays and illumination. Herein, based on Ir(III) complexes, 18 phosphors were synthesized to achieve a widely tunable phosphorescence from deep blue to NIR. In this thesis, their synthesis were fully characterized by NMR spectroscopy, mass spectrometry and X-ray crystallography. Further investigations on the photophysical, electrochemical and thermal properties reveal that these phosphors have the possibility of device fabrication. And rational design of device architectures afford the OLEDs with high efficiencies.;Firstly, N-heterocyclic carbene ligands (CˆC:) were used to elevate the LUMO of phosphors (Ir1-Ir7), resulting in true and deep blue emission spanning from 420 to 450 nm. Secondly, the widely tunable phosphorescence from 470 to 614 nm was accomplished by using polyfluorinated 2-phenylpyridine (CˆN) derivatives as cyclometallated ligands of Ir(III) complexes (Ir10-Ir17). Interestingly, electron-withdrawing trifluoromethyl (CF3) group on the phenyl ring of CˆN-type ligands results in significantly red-shifted emissions of Ir(III) complexes, which distinguishes with the blue-shift effect of fluoride approach. Lastly, by comparison with the reported literature on NIR Ir(III) phosphors with extensive conjugation, the addition of slight conjugation but electron-withdrawing moieties onto the pyridyl ligands is a powerful and convenient avenue to tune the phosphorescence of Ir(III) phosphor into the NIR region, emitting at 729 nm.;Meanwhile, the deepest blue OLED made from Ir1 showed a peak EQE of 7.1% with CIE of (0.16, 0.11). And the best deep blue OLEDs made from Ir7 by using single and double electroluminescent (EL) units gave the highest EQE of 19.0% and 31.5% with CIE coordinates of (0.15, 0.19) and (0.15, 0.22), respectively. Such high efficiencies are comparable to and even better than the currently reported deep blue PHOLEDs. Also, the sky blue, green, yellow, orange, red and NIR PHOLEDs fabricated from Ir10, Ir13, Ir15, Ir16, Ir17 and Ir18 afforded the maximum EQE of 11.2%, 20.1%, 15.4%, 9.9%, 6.8% and 4.0%, respectively. By stacking RGB EML, the white PHOLED (PHWOLED) made by Ir1, Ir13 and Ir17 gave a peak EQE of 16.0% and CIE of (0.36, 0.47).;All in all, this thesis has successfully combined the materials synthesis and devices design to achieve efficient full-color and NIR PHOLEDs which are of great interest for solid-state displays and illumination. These works have a great significance in terms of the improvement of efficiency and stability of deep blue OLEDs as well as simplifying the synthesis methods to prepare highly efficient NIR Ir(III) phosphors.
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Fan, Jia. "Concentration quenching mechanism in doped OLED materials." HKBU Institutional Repository, 2007. http://repository.hkbu.edu.hk/etd_ra/829.
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Hunting, Lindsay (Lindsay E. ). "Components, production processes, and recommendations for future research in organic light emitting diodes." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/58447.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 29).
Organic Light Emitting Diodes (OLEDs) are small, optoelectronic devices that can be used in the production of energy-efficient, high definition displays in cell phones, computers, and televisions. These devices have great potential to replace light emitting diodes (LEDs) completely because they are more environmentally friendly to produce, they are more efficient, and they can create displays much thinner than current LED displays. Moreover, OLEDs allow for the creation of brighter, flexible screens. While these devices have great potential, it has not been realized yet due to cost and difficulty in optimizing production processes. Many companies have been attempting to produce affordable OLED displays for years, but have not been successful due to lack of optimization of production processes. Work should continue to be done in economic optimization of the processes and also optimization of energy efficiency of the devices.
by Lindsay Hunting.
S.B.
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Kwok, Chi-chung. "Functional light-emitting materials of platinum, zinc and boron for organic optoelectronic devices." Click to view the E-thesis via HKUTO, 2005. http://sunzi.lib.hku.hk/hkuto/record/B34617693.
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郭子中 and Chi-chung Kwok. "Functional light-emitting materials of platinum, zinc and boron for organic optoelectronic devices." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B34617693.
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Fisher, Alison Lauren. "A study of light-emitting diodes and transistors based on ambipolar organic materials." Thesis, Durham University, 2014. http://etheses.dur.ac.uk/10626/.
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This thesis is concerned with the incorporation of a range of fluorescent ambipolar materials into Organic Light-Emitting Diodes (OLEDs) and transistors and the characterisation of their optoelectronic properties. Initial studies focused on the incorporation of donor-acceptor compounds based on carbazole-fluorene-oxadiazole in OLEDs. Using this approach, a simple, efficient, deep-blue device was realised, with Commission Internationale de l’Eclairage, CIE (x, y) coordinates (0.16, 0.08), very close to the blue standard of (0.14, 0.08) defined by the National Television System Committee. The devices also exhibited one of the highest efficiencies reported for simple deep-blue OLEDs at 4.71%. Further experiments revealed that the efficiency was dependent on the thin film processing technique used in the device fabrication, with thermally evaporated layers of active materials showing enhanced properties, compared to spin-coated films. The development of OLEDs incorporating structural analogues of the deep-blue emitting carbazole molecule revealed how molecular modification can be used to tune the emission colour of OLEDs, and was found to fit well with the calculated band gap for each molecule. Removing fluorene from the fluorescent materials resulted in a very deep-blue emission, with CIE (x, y) coordinates of (0.16, 0.05), but a simultaneous drop in efficiency. Therefore it was shown that carbazole, not fluorene, was responsible for the deep-blue colour observed during light emission. These experiments revealed that the combination of carbazole separated from oxadiazole (OXD) by the fluorene group is required to achieve high efficiency. Improvement of efficiency through the chemical addition of OXD groups was also explored as an alternative approach to adding an electron transporting OXD7 layer in the device structure. Addition of two OXD groups was found to result in a complex and more white emission. Blending of the deep-blue emitting carbazole compound with a yellow-emitting phosphorescent iridium dye produced a single-active-layer white-emitting OLED with CIE (x, y) coordinates (0.30, 0.31), very close to the pure white point of (0.33, 0.33). The efficiency of the device was shown to improve with addition of an OXD7 layer, resulting in simple, white-emitting OLEDs, with an external quantum efficiency of 2.5%. White OLEDs were also tested based on the blending of yellow dye with a carbazole analogue consisting of chemically attached OXD groups, but the efficiency was lower at 0.42%. Incorporation of the ambipolar donor-acceptor compounds into organic field-effect transistors (OFETs) generally resulted in electrical behaviour that was atypical of a classical transistor, and apparent ambipolar conduction was identified as an artefact due to current from the gate contact leaking to the drain. Further experiments utilised pentacene as a hole transporter to favour ambipolar conduction, but measurements confirmed that the properties of the resulting devices resembled pentacene-only OFETs. Further study concentrated on devices based on the ambipolar polymer F8BT. The development of in-plane OLEDs was used to characterise the electroluminescent properties of the material. Several contradictions with literature reports were identified during the study of F8BT, including the correct solvent for spin-coating and the effect of annealing temperature. Notably, high temperature annealing was linked to a reduction in F8BT film crystallinity, as identified by Atomic Force Microscopy (AFM) and a resulting instability in electrical characteristics. Blending of F8BT with an ionic liquid (IL) in a transistor structure produced a device that emitted light, although further study suggested the device in fact behaved as an OLED. However, IL blended with F8BT was successfully used in place of calcium and PEDOT:PSS to produce functioning F8BT OLEDs.
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Ho, Cheuk Lam. "Conjugated metal-organic phosphorescent materials and polymers containing fluorene and carbazole units." HKBU Institutional Repository, 2007. http://repository.hkbu.edu.hk/etd_ra/808.
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McClary, LaKeisha Michelle. "Synthesis and characterization of norbornene-functionalized side-chain monomers for potential use as transport materials in organic light-emitting diodes." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/26696.
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Thesis (M.S.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2008.Committee Chair: Marder, Seth; Committee Member: Bredas, Jean-Luc; Committee Member: Tolber, Laren. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Anikeeva, Polina Olegovna. "Physical properties and design of light-emitting devices based on organic materials and nanoparticles." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/46680.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.Includes bibliographical references (p. 201-213).
This thesis presents the detailed experimental and theoretical characterization of light-emitting devices (LEDs) based on organic semiconductors and colloidal quantum dots (QDs). This hybrid material system has several advantages over crystalline semiconductor technology; first, it is compatible with inexpensive fabrication methods such as solution processing and roll-to-roll deposition; second, hybrid devices can be fabricated on flexible plastic substrates and glass, avoiding expensive crystalline wafers; third, this technology is compatible with patterning methods, allowing multicolor light sources to be fabricated on the same substrate by simply changing the emissive colloidal QD layer. While the fabrication methods for QD-LEDs have been extensively investigated, the basic physical processes governing the performance of QD-LEDs remained unclear. In this thesis we use electronic and optical measurements combined with morphological analysis to understand the origins of QD-LED operation. We investigate charge transport and exciton energy transfer between organic materials and colloidal QDs and use our findings as guidelines for the device design and material choices. We fabricate hybrid QD-LEDs with efficiencies exceeding those of previously reported devices by 50-300%. Novel deposition methods allow us to fabricate QD-LEDs of controlled and tunable color by simply changing the emissive QD layer without altering the structure of organic charge transport layers. For example, we fabricate white light sources with tunable color temperature and color rendering index close to that of sunlight, inaccessible by crystalline semiconductor based lighting or fluorescent sources. Our physical modeling of hybrid QD-LEDs provides insights on carrier transport and exciton generation in hybrid organic-QD devices that are in agreement with our experimental data. The general nature of our experimental and theoretical findings makes them applicable to a variety of hybrid organic-QD optoelectronic devices such as LEDs, solar cells, photodetectors and chemical sensors.
by Polina Olegovna Anikeeva.
Ph.D.
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Lau, Tsz-wai Raymond, and 劉子偉. "Organic light emitting diodes: effects of anode treatments to device efficiency and stability." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B31227545.
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Anderson, Jeffrey David. "Characterization and synthesis of organic semiconductor materials for light-emitting diodes: Structure-property relationships." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/284304.
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Light generation in organic light emitting diodes (OLEDs) requires the recombination of electron-hole pairs at a p-n junction. Radiative recombination has been investigated with solution electrochemical studies of the principal lumophores, dopants, and hole-transport agents of small molecule OLEDs. We have found that solution electrogenerated chemiluminescent (ECL) reactions between radical anion and cation states of OLED components model the spectral output and efficiency of solid-state electroluminescence. These studies have shown that the molecular structures of commonly used materials in OLEDs are not optimized. ECL has been used to develop and optimize new materials that dramatically improve device performance. The results of the ECL experiments can be explained using commonly accepted electron transfer theories. Nonaqueous electrochemistry and spectroelectrochemistry have been used to study the energetics and stability of radical cation states of new and existing biphenyl-bis-triarylamines (TPDs), triphenylamines, and carbazoles, common hole-transport materials in OLEDs. We have established that these triarylamines, upon anodic oxidation, cation radicals with widely variable stability that react via coupling-deprotonation to form a neutral dimer. We have quantified the decay of these reactions by following the visible absorption decay of the cation radicals. The stability of these states to dimerization reactions is critically dependent on molecular structure. We speculate that these dimerization reactions could occur in the solid state, and that this reaction could lead to OLED degradation, since it involves the loss of a proton. Derivatives of 9,10-diphenylanthracene were synthesized for use as Forster energy transfer dopants and stable charge traps in OLEDs. Cyclic voltarnmetry shows that these compounds form stable radical cation and anion states in nonaqueous electrolytes. Introduction of substituents to the anthracene ring can modify the HOMO - LUMO gap of these structures. When these molecules are doped into poly(N-vinylcarbazole), they act as Foster energy acceptors. Photoluminescent and electroluminescent spectra of these doped polymer composite films show that the luminescence originates from the singlet excited state of the diphenylanthracenes. Preliminary results of single layer OLEDs made from these materials are promising; device external quantum efficiencies attained up to ca. 1.2 % and brightness up to 800 cd/m² at 12 volts.
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Gaj, Michael Peter. "High-performance organic light-emitting diodes for flexible and wearable electronics." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/55011.
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Optoelectronic devices based on organic semiconductors have been the focus of increasing research over the past two decades. While many of the potential organic electronic concepts (solar cells, transistors, detectors etc.) are still in their infancy stage, organic light-emitting diodes have gained commercial acceptance for their potential in high resolution displays and solid-state lighting. However, in order for these devices to reach their full potential significant advances need to make to address their fundamental limitations, specifically: device life-time, thin-film encapsulation and scalability to a high volume manufacturing setting.
The work presented in this thesis demonstrates new strategies to design and manufacture high-performance OLEDs for next generation electronics. In the first part, high-performance OLEDS using a simple three-layer organic semiconductor device structure are demonstrated. These devices utilize two novel materials (Poly-TriCZ and mCPSOB) to achieve efficient charge balance and exciton confinement in the emissive region of the device. Moreover, the electrical properties of these materials allow them to serve as a suitable ‘universal’ material combination to yield high-performance OLEDs with high-energy phosphors (i.e. blue- or deep-blue-emitting dopants). To demonstrate this feature, green- and blue-emitting OLED results are provided that define the state-of-the-art for phosphorescent OLEDs. These results are then extended to show high-performance with a new set of high-efficiency blue- and green-emitting dopants based on thermally activated delayed fluorescence (TADF), which also proceed to define the state-of-the-art in electroluminescence from TADF. The second part of this thesis continues this work and extends the results to a new class of polymeric substrates, called shape memory polymers (SMPs). SMPs provide a new alternative to flexible, polymeric substrates due to their unique mechanical properties. When an external stimuli is applied to these materials (heat), they have the ability to form a temporary phase that has a Young’s modulus orders of magnitude lower than its original state. The material can then be re- shaped, deformed or conform to any object until the stimuli is removed, at which point the Young’s modulus returns to its original state and the temporary geometric configuration is retained. Re-applying the stimulus will trigger a response in its molecular network, which induces a recovery of its original shape. By using mCPSOB in an inverted top-emitting OLED architecture, high performance green-emitting OLEDs are demonstrated on SMP substrates that define the state-of-the-art in performance for deformable light-emitting devices. The combination of the unique properties of SMP substrates with the light-emitting properties of OLEDs pave to the way for new class of applications, including conformable smart skin devices, minimally invasive biomedical devices, and flexible lighting/display technologies.
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Ho, Kai Wai. "Evaluation and characterization of efficient organic optoelectronic materials and devices." HKBU Institutional Repository, 2020. https://repository.hkbu.edu.hk/etd_oa/816.
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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.
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Ho, Ka Wai. "Evaluation and characterization of efficient organic optoelectronic materials and devices." HKBU Institutional Repository, 2020. https://repository.hkbu.edu.hk/etd_oa/873.
Full textAbstract:
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.
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Blochwitz, Jan. "Organic light-emitting diodes with doped charge transport layers." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2001. http://nbn-resolving.de/urn:nbn:de:swb:14-997196106312-42499.
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Organische Farbstoffe mit einem konjugierten pi-Elektronen System zeigen überwiegend ein halbleitendes Verhalten. Daher sind sie potentielle Materialien für elektronische und optoelektronische Anwendungen. Erste Anwendungen in Flachbildschirmen sind bereits in (noch) geringen Mengen auf dem Markt. Die kontrollierte Dotierung anorganischer Halbleiter bereitete die Basis für den Durchbruch der bekannten Halbleitertechnologie. Die Kontrolle des Leitungstypes und der Lage des Fermi-Niveaus erlaubte es, stabile pn-Übergänge herzustellen. LEDs können daher mit Betriebsspannungen nahe dem thermodynamischen Limit betrieben werden (ca. 2.5V für eine Emission im grünen Spektralbereich). Im Gegensatz dazu bestehen organische Leuchtdioden (OLEDs) typischerweise aus einer Folge intrinsischer Schichten. Diese weisen eine ineffiziente Injektion aus Kontakten und eine relative geringe Leitfähigkeit auf, welche mit hohen ohmschen Verlusten verbunden ist. Andererseits besitzen organische Materialien einige technologische Vorteile, wie geringe Herstellungskosten, große Vielfalt der chemischen Verbindungen und die Möglichkeit sie auf flexible große Substrate aufzubringen. Sie unterscheiden sich ebenso in einigen fundamentalen physikalischen Parametern wie Brechungsindex, Dielektrizitätskonstante, Absorptionskoeffizient und Stokes-Verschiebung der Emissionswellenlänge gegenüber der Absorption. Das Konzept der Dotierung wurde für organische Halbleiter bisher kaum untersucht und angewandt. Unser Ziel ist die Erniedrigung der Betriebsspannung herkömmlicher OLEDs durch den Einsatz der gezielten Dotierung der Transportschichten mit organischen Molekülen. Um die verbesserte Injektion aus der Anode in die dotierte Löchertransportschicht zu verstehen, wurden UPS/XPS Messungen durchgeführt (ultraviolette und Röntgen-Photoelektronenspektroskopie). Messungen wurden an mit F4-TCNQ dotiertem Zink-Phthalocyanin auf ITO und Gold-Kontakten durchgeführt. Die Schlussfolgerungen aus den Experimenten ist, das (i) die Fermi-Energie sich durch Dotierung dem Transportniveau (also dem HOMO im Falle der vorliegenden p-Dotierung) annähert, (ii) die Diffusionspannung an der Grenzfläche durch Dotierung entsprechend verändert wird, und (iii) die Verarmungszone am Kontakt zum ITO sehr dünn wird. Der Kontakt aus organischem Material und leitfähigem Substrat verhält sich also ganz analog zum Fall der Dotierung anorganischer Halbleiter. Es entsteht ein stark dotierter Schottky-Kontakt dessen schmale Verarmungszone leicht durchtunnelt werden kann (quasi-ohmscher Kontakt). Die Leistungseffizienz von OLEDs mit dotierten Transportschichten konnte sukzessive erhöht werden, vom einfachen 2-Schicht Design mit dotiertem Phthalocyanine als Löchertransportschicht, über einen 3-Schicht-Aufbau mit einer Elektronen-Blockschicht bis zu OLEDs mit dotierten 'wide-gap' Löchertransport-Materialien, mit und ohne zusätzlicher Schicht zur Verbesserung der Elektroneninjektion. Sehr effiziente OLEDs mit immer noch niedriger Betriebsspannung wurden durch die Dotierung der Emissionsschicht mit Molekülen erhöhter Photolumineszenzquantenausbeute (Laser-Farbstoffe) erreicht. Eine optimierte LED-Struktur weist eine Betriebsspannung von 3.2-3.2V für eine Lichtemission von 100cd/m2 auf. Diese Resultate entsprechen den zur Zeit niedrigsten Betriebsspannungen für OLEDs mit ausschließlich im Vakuum aufgedampften Schichten. Die Stromeffizienz liegt bei ca. 10cd/A, was einer Leistungseffizienz bei 100cd/m2 von 10lm/W entspricht. Diese hohe Leistungseffizienz war nur möglich durch die Verwendung einer Blockschicht zwischen der dotierten Transportschicht und der Lichtemissions-Schicht. Im Rahmen der Arbeit konnte gezeigt werden, dass die Dotierung die Betriebsspannungen von OLEDs senken kann und damit die Leistungseffizienz erhöht wird. Zusammen mit einer sehr dünnen Blockschicht konnte einen niedrige Betriebsspannung bei gleichzeitig hoher Effizienz erreicht werden (Blockschicht-Konzept)Organic dyes with a conjugated pi-electron system usually exhibit semiconducting behavior. Hence, they are potential materials for electronic and optoelectronic devices. Nowadays, some applications are already commercial on small scales. Controlled doping of inorganic semiconductors was the key step for today's inorganic semiconductor technology. The control of the conduction type and Fermi-level is crucial for the realization of stable pn-junctions. This allows for optimized light emitting diode (LED) structures with operating voltages close to the optical limit (around 2.5V for a green emitting LED). Despite that, organic light emitting diodes (OLEDs) generally consist of a series of intrinsic layers based on organic molecules. These intrinsic organic charge transport layers suffer from non-ideal injection and noticeable ohmic losses. However, organic materials feature some technological advantages for device applications like low cost, an almost unlimited variety of materials, and possible preparation on large and flexible substrates. They also differ in some basic physical parameters, like the index of refraction in the visible wavelength region, the absorption coefficient and the Stokes-shift of the emission wavelength. Doping of organic semiconductors has only been scarcely addressed. Our aim is the lowering of the operating voltages of OLEDs by the use of doped organic charge transport layers. The present work is focused mainly on the p-type doping of weakly donor-type molecules with strong acceptor molecules by co-evaporation of the two types of molecules in a vacuum system. In order to understand the improved hole injection from a contact material into a p-type doped organic layer, ultraviolet photoelectron spectroscopy combined with X-ray photoelectron spectroscopy (UPS/XPS) was carried out. The experimental results of the UPS/XPS measurements on F4-TCNQ doped zinc-phthalocyanine (ZnPc) and their interpretation is given. Measurements were done on the typical transparent anode material for OLEDs, indium-tin-oxide (ITO) and on gold. The conclusion from these experiments is that (i) the Fermi-energy comes closer to the transport energy (the HOMO for p-type doping), (ii) the built-in potential is changed accordingly, and (iii) the depletion layer becomes very thin because of the high space charge density in the doped layer. The junction between a doped organic layer and the conductive substrate behaves rather similar to a heavily doped Schottky junction, known from inorganic semicondcutor physics. This behavior favors charge injection from the contact into the organic semiconductor due to tunneling through a very small Schottky barrier (quasi-ohmic contact). The performance of OLEDs with doped charge transport layers improves successively from a simple two-layer design with doped phthalocyanine as hole transport layer over a three-layer design with an electron blocking layer until OLEDs with doped amorphous wide gap materials, with and without additional electron injection enhancement and electron blocking layers. Based on the experience with the first OLEDs featuring doped hole transport layers, an ideal device concept which is based on realistic material parameters is proposed (blocking layer concept). Very high efficient OLEDs with still low operating voltage have been prepared by using an additional emitter dopant molecule with very high photoluminescence quantum yield in the recombination zone of a conventional OLED. An OLED with an operating voltage of 3.2-3.2V for a brightness of 100cd/m2 could be demonstrated. These results represent the lowest ever reported operating voltage for LEDs consisting of exclusively vacuum sublimed molecular layers. The current efficiency for this device is above 10cd/A, hence, the power efficiency at 100cd/m2 is about 10lm/W. This high power efficiency could be achieved by the use of a blocking layer between the transport and the emission layer
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Schrögel, Pamela [Verfasser], and Peter [Akademischer Betreuer] Strohriegl. "Novel Host Materials for Blue Phosphorescent Organic Light-Emitting Diodes / Pamela Schrögel. Betreuer: Peter Strohriegl." Bayreuth : Universitätsbibliothek Bayreuth, 2011. http://d-nb.info/1015875351/34.
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Montes, Victor A. "Synthesis and Electro-optical Properties of Novel Materials for Application in Organic Light-Emitting Diodes." Bowling Green State University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1173835623.
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Furitsu, Suzuki. "Structural Studies on Charge-Transport and Emission Properties of Materials for Organic Light-Emitting Diodes." Kyoto University, 2017. http://hdl.handle.net/2433/226785.
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Sewagudde, Deborah Nabbosa Miriam. "Why did video screens get slimmer? : a study of the role of Intellectual Property in the commercial development of organic light-emitting diodes." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/25944.
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This research project consists of a critical analysis of the role of intellectual property amongst other factors in the successful commercial development at the Cavendish Laboratory of optoelectronic light emitting diode display devices based on novel organic semiconductor materials. It begins by giving the background to the quantum mechanical properties upon which the technology is based, followed by a discussion of the path of innovation, describing the interaction between the different socioeconomic factors that influence this path. It then draws an analogy with the development of an analogous technology - inorganic semiconductors - to signpost the factors that may affect the developmental history of the technology. This is followed by an analysis of a chronology derived initially from patents downloaded from the World Patents Database of the European Patent Office to showcase the technology's development steps, and to study the patenting strategy of Cambridge Display Technology (CDT) - the company that was set up to commercialise the novel technology - through a patent trends analysis. From that, the major socioeconomic factors critical to the technology's development are analysed, followed by a test and extension of an existing Black Box mathematical model for studying the dynamics of innovation that is based on the interaction of those factors. Finally, through a patent citation analysis, CDT's commercial strategy for the technology is shown as being based on its patents portfolio to build an extensive licensing programme that pooled major academic, industry and commercial partners for the furtherance of the technology. This later evolved into a new ecosystem for the innovation, of which CDT occupied a central and indispensable position.
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"High-Performance Organic Light Emitting Diodes." Doctoral diss., 2019. http://hdl.handle.net/2286/R.I.53867.
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abstract: Organic electronics have remained a research topic of great interest over the past few decades, with organic light emitting diodes (OLEDs) emerging as a disruptive technology for lighting and display applications. While OLED performance has improved significantly over the past decade, key issues remain unsolved such as the development of stable and efficient blue devices. In order to further the development of OLEDs and increase their commercial potential, innovative device architectures, novel emissive materials and high-energy hosts are designed and reported.
OLEDs employing step-wide graded-doped emissive layers were designed to improve charge balance and center the exciton formation zone leading to improved device performance. A red OLED with a peak efficiency of 16.9% and an estimated LT97 over 2,000 hours at 1,000 cd/m2 was achieved. Employing a similar structure, a sky-blue OLED was demonstrated with a peak efficiency of 17.4% and estimated LT70 over 1,300 hours at 1,000 cd/m2. Furthermore, the sky-blue OLEDs color was improved to CIE coordinates of (0.15, 0.25) while maintaining an efficiency of 16.9% and estimated LT70 over 600 hours by incorporating a fluorescent sensitizer. These devices represent literature records at the time of publication for efficient and stable platinum phosphorescent OLEDs.
A newly developed class of emitters, metal-assisted delayed-fluorescence (MADF), are demonstrated to achieve higher-energy emission from a relatively low triplet energy. A green MADF device reaches a peak efficiency of 22% with an estimated LT95 over 350 hours at 1,000 cd/m2. Additionally, a blue charge confined OLED of PtON1a-tBu demonstrated a peak efficiency above 20%, CIE coordinated of (0.16, 0.27), and emission onset at 425 nm.
High triplet energy hosts are required for the realization of stable and efficient deep blue emission. A rigid “M”-type carbazole/fluorene hybrid called mDCzPF and a carbazole/9-silafluorene hybrid called mDCzPSiF are demonstrated to have high triplet energies ET=2.88 eV and 3.03 eV respectively. Both hosts are demonstrated to have reasonable stability and can serve as a template for future material design. The techniques presented here demonstrate alternative approaches for improving the performance of OLED devices and help to bring this technology closer to widespread commercialization.Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2019
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Lin, Yu-Ting, and 林于庭. "Short-Wavelength Organic Light-Emitting Materials and Devices." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/39451445580511000633.
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博士國立臺灣大學
光電工程學研究所
94
Organic light-emitting devices (OLEDs) have been the subjects of intense investigation in recent years due to their applications in displays and lighting. In all these applications, the short-wavelength emitting materials and devices with high efficiency, good color purity and thermal stability have been essential. In this thesis, we investigate of various device architectures to study the optical and electrical properties of the short-wavelength emitting materials. In the first part of the work, we employed an efficient and morphologically stable pyrimidine-containing spirobifluorene-cored oligoaryl, as a blue emitter or emitting host for blue OLEDs. These devices exhibit unique endurance for high currents, leading to a very high brightness under dc driving. In the second part of the work, we investigate various device architectures of OLEDs incorporating highly efficient blue-emitting and ambipolar carrier-transport ter(9,9-diarylfluorene)s, and their influences on device characteristics. Using the double heterostructure that provides effective double confinement on both carriers and excitons, results in a high EL external quantum efficiency, low-voltage, and very saturated blue emission without doping the emitting layer. Finally, we studied a series of UV emitter based on ambipolar carrier-transport bi(9,9-diaryfluorene)s that exhibited promising physical properties including high morphological and thermal stability, and high neat-film quantum yields for UV emission. The UV OLEDs using the double heterostructure can exhibit high EL external quantum efficiency, low device voltage, and UV emission without emissive dopants.
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Huang, Ming Hong, and 黃名宏. "Light Emitting Devices Based on Organic and Organic-Inorganic Hybrid Materials." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/jxp9x2.
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Lee, Yung-Chih, and 李勇志. "Fabrication of Organic Light-Emitting Diodes Using Semiconductor Nanocrystal as Emitting Materials." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/68772436620111505183.
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碩士國立臺灣師範大學
化學研究所
89
We have synthesized CdSe and CdSe(CdS) core/shell nanorcrystals in tri-n-octylphosphine oxide (TOPO) micellar solution using dimethylcadmium (Cd(CH3)2), selenium (Se) powder and bis-trimethylsilane sulfide ((TMS)2S) as the reactants. The sizes of the nanocrystals were controlled by varying the experimental conditions such as the concentration of Cd(CH3)2, reaction temperature, and reaction time. The nanocrystals were characterized using UV-Vis absorption and fluorescence spectra. The absorption and fluorescence spectra suggested that the band edges of the resulting nanocrystals shift to higher energy than that of the bulk CdSe crystals. The transmission electron microscopy images indicated that the CdSe nanocrystals are about 3 nm. We have demonstrated the electrical and optical characteristics of the organic light emitting diode (OLED) devices using nanocrystals as the emitting layer, Poly (9-vinylcarbazole) (PVK) as the hole-transport layer, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) as the electron-transport layer, and poly(3,4-ethylenedioxythiophene) -poly(4-styrenesulphonate) (PEDT-PSS) as the hole-injection layer. We have investigated the characteristics of CdSe for ITO/PEDT-PSS/PVK/CdSe/BCP/Mg:Ag structure and CdSe(CdS) for ITO/PEDT-PSS/PVK/CdS(CdS)/BCP/Mg:Ag structure. Then, we change the thickness of CdSe for ITO/PEDT-PSS/PVK/CdSe/BCP/Mg:Ag structure. We found that emission wavelength of these heterostructure devices was affected by the thickness of the light emitting layer of LED. The intensity of the electroluminescence (EL) at the position of 600 nm from nanocrystals and at 400 nm from PVK change with different voltages applied to the devices. We also found that ITO/PEDT-PSS/PVK/CdSe/BCP/Mg:Ag structure using CdSe nanocrystals in their emitting layer can provide emission tunable in the visible spectrum, because of the size-dependent luminescence of the quantum dots.
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Kuo, Ming-Yu, and 郭明裕. "Investigations of Photocatalyst TiO2 and Organic Light-emitting Materials." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/03534176068177368220.
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博士國立中山大學
材料科學研究所
92
TiO2. Structural and electronic properties of TiO2 polymorphs denser than rutile, i.e. α-PbO2-, baddeleyite, fluorite, and cotunnite-type were calculated by a first-principle pseudo-potential method based on density functional theory with local density approximation. Using experimental and theoretical lattice parameters of ambient TiO2, i.e. anatase and rutile as standard, the fluorite-type TiO2 has the narrowest band gap among the post-rutile phases. This character is important for the potential applications as visible-light-responsive photocatalyst. In additional to the bulk properties of dense TiO2 polymorphs the surface energies of ��-PbO2-type TiO2 were also calculated. The calculated surface energies were in the following decreasing order (100) > (001) > > (010). The calculation showed that the surface energy was affected by the undercoordination/distortion of the polyhedron upon relaxation beside the factor of atom packing density of the surface. The (010) surface has the lowest surface energy due to the exposure of highly symmetrical TiO4 polyhedra. Another potential application for TiO2 polymorphs is hard coating for surface modification technology. Dense TiO2 polymorphs with theoretical hardness exceeding 30 GPa, 20 % higher than their ambient pressure polymorphs, i.e. rutile and anatase, are worthwhile to fabricate as coatings on suitable substrate for such application. This proposal is encouraged by the agreement of theoretical and experimental hardness of cotunnite-type TiO2 with strong linkage of 9-oxygen coordinated Ti polyhedra. PPV. Molecular dynamics (MD) simulation was employed to investigate structure features and segment orientation of four poly(phenylene vinylene) (PPV) derivatives with long flexible side chains at room temperature. In the simulations, the main chains of the polymers were found to be semi-rigid and exhibit a tendency to coil into ellipsoidal helices or form zigzag conformations of only limited regularity. The simulations show that continuous quasi-coplanar segments along the backbone are in a range of 2~4 repeat units. The ordered orientation and coupling distance of interchain aromatic rings can be correlated to optical properties of materials. This work implies that long-range electron transfer along same backbones of these polymers may not happen but be mediated by interchain interactions. Oxadiazole. The aim of this work is the investigation of the correlation between the chemical structure of a substance and its corresponding vapor deposition (VD) film structure. The influence of film preparation conditions on the film structure is also investigated in this work. For a given molecule, the film structure could be controlled through the variation of the physical deposition parameters such as the film growth rate, the substrate temperature (Ts) and the vacuum. The study of the influence of these deposition parameters on film formation provides the possibility of controlling molecular arrangement and the subsequent physical properties of the films.
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Chen, Kuei-Bai, and 陳奎百. "Nano-Structure Enhanced Organic Light Emitting Materials and Devices." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/69313460674782550942.
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Wu, Sheng-Yu, and 武昇佑. "Synthesis and Numerical Simulation for Organic Light-Emitting Materials." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/27246846269658274972.
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碩士國立臺北科技大學
有機高分子研究所
92
In the first part of this dissertation, two soluble PPV derived polymers, BDMO-PPV [poly 2,5-bis(3,7-dimethyloctyl)-1,4-phenylene vinylene] and MEH-PPV [poly 2-methoxy-5-(2’ethyl-hexyloxyl)-1,4-phenylene vinylene] have been synthesized. The effect of the base and monomer injection conditions on the formation of polymer has been investigated. The result shows that BDMO-PPV with longer alkyl side-chains than MEH-PPV gave less gel formation during polymerization. The experiment shows a better polymerization occurred with the addition sequence of monomer slowly dropped into base. In the second part, molecular simulation program was applied to calculate the physical properties of light-emitting materials. Fluorescent polymer MEH-PPV and small molecules, such as 2-(2-Hydroxyphenyl)benzothiazole (HBT), 2-(3-hydroxy-naphthalene)benzothiazole (HNBT), 2-(2-hydroxypyridine)benzothiazole (HPBT) have been chosen as models. The simulation methods are applying Castep module for simulating UV/Vis absorption spectra, VAMP module for simulating electrostatic potential map, DMol3 module for simulating band gap. In the case of polymer MEH-PPV, the simulation method is choosing 5 monomer units and 2 polymer chains as a simulation unit and applying Discover module for simulating the minimum energy model. The result of simulations shows a fair match with the experimental data.
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Sharma, Nidhi. "Maleimide Based Materials for Organic Light-Emitting Diodes (OLEDs)." Thesis, 2015. http://etd.iisc.ac.in/handle/2005/3678.
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Maleimide based highly luminescent material Cbz-MI with donor acceptor donor (D-A-D) backbone has been synthesized and characterized. An organic light emitting diode fabricated using this material
as emitting layer exhibited EQE of 2.5% in the yellow region of visible spectrum. Due to the small energy gap of materials emitting in this region of spectrum, EQE of OLED is usually limited by various non-radiative decays and high EQE of OLED using this material proves that most of the nonradiative
decay pathways have been avoided by the careful design of molecule and device structure.
Although Cbz-MI did not show TADF properties, but if tailored with right electron donor along with maleimide as an acceptor, such derivatives may exhibit TADF properties
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Sharma, Nidhi. "Maleimide Based Materials for Organic Light-Emitting Diodes (OLEDs)." Thesis, 2015. http://etd.iisc.ernet.in/2005/3678.
Full textAbstract:
Maleimide based highly luminescent material Cbz-MI with donor acceptor donor (D-A-D) backbone has been synthesized and characterized. An organic light emitting diode fabricated using this material
as emitting layer exhibited EQE of 2.5% in the yellow region of visible spectrum. Due to the small energy gap of materials emitting in this region of spectrum, EQE of OLED is usually limited by various non-radiative decays and high EQE of OLED using this material proves that most of the nonradiative
decay pathways have been avoided by the careful design of molecule and device structure.
Although Cbz-MI did not show TADF properties, but if tailored with right electron donor along with maleimide as an acceptor, such derivatives may exhibit TADF properties
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葉子豪. "Effects of Deuterated Light Emitting Materials on the Performance of Green Phosphorescence Organic Light Emitting Devices." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/85450800776059472795.
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"Phosphorescent Organic Light Emitting Diodes Implementing Platinum Complexes." Doctoral diss., 2014. http://hdl.handle.net/2286/R.I.25889.
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abstract: Organic light emitting diodes (OLEDs) are a promising approach for display and solid state lighting applications. However, further work is needed in establishing the availability of efficient and stable materials for OLEDs with high external quantum efficiency's (EQE) and high operational lifetimes. Recently, significant improvements in the internal quantum efficiency or ratio of generated photons to injected electrons have been achieved with the advent of phosphorescent complexes with the ability to harvest both singlet and triplet excitons. Since then, a variety of phosphorescent complexes containing heavy metal centers including Os, Ni, Ir, Pd, and Pt have been developed. Thus far, the majority of the work in the field has focused on iridium based complexes. Platinum based complexes, however, have received considerably less attention despite demonstrating efficiency's equal to or better than their iridium analogs. In this study, a series of OLEDs implementing newly developed platinum based complexes were demonstrated with efficiency's or operational lifetimes equal to or better than their iridium analogs for select cases.
In addition to demonstrating excellent device performance in OLEDs, platinum based complexes exhibit unique photophysical properties including the ability to form excimer emission capable of generating broad white light emission from a single emitter and the ability to form narrow band emission from a rigid, tetradentate molecular structure for select cases. These unique photophysical properties were exploited and their optical and electrical properties in a device setting were elucidated.
Utilizing the unique properties of a tridentate Pt complex, Pt-16, a highly efficient white device employing a single emissive layer exhibited a peak EQE of over 20% and high color quality with a CRI of 80 and color coordinates CIE(x=0.33, y=0.33). Furthermore, by employing a rigid, tetradentate platinum complex, PtN1N, with a narrow band emission into a microcavity organic light emitting diode (MOLED), significant enhancement in the external quantum efficiency was achieved. The optimized MOLED structure achieved a light out-coupling enhancement of 1.35 compared to the non-cavity structure with a peak EQE of 34.2%. In addition to demonstrating a high light out-coupling enhancement, the microcavity effect of a narrow band emitter in a MOLED was elucidated.Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2014
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Tsai, Wei-Lung, and 蔡維隆. "Investigation of high-efficiency organic light-emitting materials and devices." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/38910972303402611812.
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博士國立臺灣大學
電子工程學研究所
105
Organic light-emitting diodes (OLEDs) have attracted much attention due to their potential for future display and lighting applications. To enhance OLED performances and reduce cost for displays and lighting, we focused on the investigation of high-efficiency organic light-emitting materials in this thesis. In the first part of this thesis, a new class of neutral bis-tridentate Ir(III) metal complexes that show nearly unitary red, green, and blue emissions are employed for the fabrication of both monochrome and white emitting organic light-emitting diodes, among which greens can device gives the external quantum efficiency exceeding 31%. In the second part, Ir(III) complexes incorporating diazine-containing cyclometalating ligands are highly promising blue phosphorescent emitters having nearly unitary PLQYs and preferential horizontal emitting dipole orientations. Using these Ir complexes, we obtained efficient blue phosphorescent OLEDs with external quantum efficiency (EQE) exceeding 31%, small efficiency roll-off, and long operation lifetimes. Finally, a thermally activated delayed fluorescent (TADF) emitter (DMAC-TRZ) was used either as the emitting dopant in a host or as the non-doped (neat) emitting layer to achieve high EL EQEs of up to 26.5% and 20% in OLEDs, respectively.
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Hsin-Hung, Tsai. "Study of Host Materials for Phosphorescent Organic Light-emitting Devices." 2005. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-1901200612230700.
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王雅琪. "Electron Transporting Materials for High-efficiency Organic Light Emitting Diodes." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/5925pv.
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Tsai, Hsin-Hung, and 蔡信弘. "Study of Host Materials for Phosphorescent Organic Light-emitting Devices." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/70463449150842084304.
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碩士國立臺灣大學
光電工程學研究所
94
In this thesis, we demonstrated phosphorescent organic light-emitting devices (PHOLEDs) by using a novel host material and two transporting materials as the host of PHOLED. We used an n-type transporting material as the host of green PHOLED. Due to the better energy alignment with adjacent transporting materials, our device exhibits a lower turn-on voltage by about 2.5 volts with the current density of 100 mA/cm2 as compared to the conventional carbazole OLED. The power efficiency is increased from 8 to 10 lm/W at the luminance of 1000 cd/m2.However, the current efficiency at 10000 cd/m2 is slightly decreased from 24 to 21 cd/A. Besides, we used two conventional transporting materials as the host of the red PHOLED and evaluate the necessity of the hole blocking layer (HBL) by using two Ir (iridium) based red emitter. Device with electron transporting material as the host with HBL structure exhibited the highest current efficiency of 16.1 cd/A at the luminance of 50 cd/m2. Besides, devices showed limited triplet-triplet annihilation.