Thesis (M.S.)--University of North Texas, August, 2008. / Title from title page display. Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xiv, 139 p.; also includes graphics (some col.) Includes bibliographical references (p. 132-139). Available online via OhioLINK's ETD Center

Thesis (Ph. D.)--University of Nebraska, 1933. / Bibliography: p. 31.

Thesis (Ph. D.)--University of Virginia, 1927. / Autographed from typewritten copy. "References": leaf 31.

White organic light-emitting diodes (WOLEDs) resemble light more naturally, with emission spectrum that is comfortable to the human eye. A lot of effort has been devoted to improve the performance of WOLEDs. This research work was aimed at studying the emission behavior of WOLEDs, improving the device performance, and thereby developing several novel device concepts for application in high performing transparent WOLEDs and organic proximity sensors. Emission behavior, in terms of color stability and injection characteristics of phosphorescent organic light-emitting diodes (OLEDs), was investigated systematically and optimized via the experimental optimization and optical simulation. The transparent WOLEDs can be almost invisible at daytime and can emit a pleasant diffused light at night, allowing the surface light source to shine in both directions. It is an exciting new lighting technology that could bring new device concepts. However, undesirable angular-dependent emission and asymmetrical emission characteristics are often observed in transparent WOLEDs. In this work, a pair of optically and electrically comparable transparent anode and cathode was introduced to form weak microcavity transparent WOLEDs, e.g., employing a pair of Ag (10 nm)/MoO3 (2.5 nm)-modified indium tin oxide anode and Al (1.5 nm)/Ag (15 nm)/NPB (50 nm) cathode. It is found that the avoidance of the spectral overlap between the peak wavelengths of the emitters and the resonant wavelength of the organic microcavity moderates the angular-dependent electroluminescence emission behavior, thereby improving the color stability of the transparent white WOLEDs over a broad range of the viewing angles. As a result, the transparent WOLEDs developed possess a visible-light transparency of >50%, a symmetrical bi-directional illumination with an almost identical power efficiency of 11 lm/W (measured at 100 cd/m2) and the similar CIE coordinates of (0.36, 0.43) and (0.38, 0.46) measured from both sides of the devices. Efficient charge injection is a prerequisite for achieving low turn-on voltage and improved hole-electron current balance in OLEDs. Metal oxide (e.g. MoO3) is a commonly used hole-injection layer (HIL) for reducing the energy barrier at the anode/organic interface for efficient charge injection. However, fluctuation in the quality of the metal oxide-based HIL, e.g., changes due to the MoO3 formulation, film fabrication and post-treatment conditions, often places a practical challenge limiting reproducibility of the device performance. In this work, an effective solution-processed HIL that consists of a mixture of PEDOT:PSS and MoO3 was developed for application in OLEDs. It is found that the presence of the solution-processed HIL at the interface between the anode and the organic improves the hole injection and the performance reproducibility of the phosphorescent OLEDs. The effect of the presence of the MoO3 in the solution-processed HIL on charge injection in phosphorescent OLEDs, with a configuration of glass/ITO/CBP/ CBP:Ir(ppy)2acac/TmPyPB/LiF(1.0 nm)/Al(70 nm), was examined. It is shown that solution-processed HIL has a superior hole injection characteristic at the HIL/hole transporting layer (HTL) interface compared to that in the devices fabricated with a pristine PEDOT:PSS or a pure MoO3 HIL, yielded phosphorescent OLEDs with an external quantum efficiency of ~25% and a power efficiency of ~75 lm/W @ 1000 cd/m2. The morphological and surface electronic properties of the hybrid HIL were also investigated by AFM, XPS and UPS measurements, revealing the formation of a good contact at the HIL/HTL interface in the phosphorescent OLEDs. Apart from improving the device performance, a new organic proximity sensor based on the monolithic integration of organic photo-detectors (OPDs) and OLEDs was also developed. A MoO3-modified thin silver interlayer, serving simultaneously as a transparent cathode for the OPDs and an anode for the OLEDs, is used to link the functional organic electronic components. In the integrated OLED/OPD-based proximity sensors, the OLED components function as an illumination source while the coupled OPD units enable a high absorption when light is reflected from objects to create an optical signal. The photosensitivity is enhanced using organic photosensitive bulk heterojunction in the OPDs, thereby realizing a high photosensitivity and the high external quantum yield at a low reverse bias. The signal to noise ratio, optical and frequency responses of the integrated organic proximity sensors were optimized and examined. The design and fabrication flexibility of the integrated OLED/OPD-based organic proximity sensors also have cost benefits, making it possible for application in wearable units and compact information systems.

Ici, la conception, la synthèse et la caractérisation et les propriétés optoélectroniques de complexes Ir(III) pour une application dans des dispositifs optiques non linéaires et électroluminescents sont décrits. Le type de complexes varie de ceux de la forme [Ir(C^N)2(N^N)]+ avec des ligands conjugués et non conjugués (où C^N = ligand cyclométallisant et N^N = ligand neutre) à ceux des forment [Ir (C^N^C)(N^N)Cl] (où C^N^C = ligand tripode tridenté). Le chapitre 1 donne une introduction à la photophysique se produisant dans les complexes de métaux de transition et aux applications possibles dans les affichages visuels. Le contexte des propriétés optiques non linéaires (NLO) et l'utilisation de complexes de métaux de transition en tant que chromophores NLO sont décrits. Dans le chapitre 2, l'impact de l'utilisation de ligands de cyclométallation encombrés stériquement sur les propriétés de photoluminescence des complexes cationiques d'iridium(III) et leur performance dans les cellules électrochimiques émettant de la lumière est étudiée. Le chapitre 3 explore l'utilisation de donneurs d'électrons sur le ligand de cyclométallation pour moduler les propriétés NLO des complexes. La combinaison de substituants fortement donneurs d'électrons sur le ligand C^N et de substituants accepteurs d'électrons sur le ligand N^N conduit à une forte activité NLO. Le chapitre 4 résume une nouvelle série de complexes cationiques d'iridium(III) portant benzylpyridinato comme ligands de cyclométallation. L'espaceur méthylène dans les ligands C^N confère de la flexibilité, ce qui donne deux conformères. Des études par RMN combinées à des études de la théorie fonctionnelle de la densité (DFT) montrent comment le comportement fluxionnel est influencé par le choix du ligand auxiliaire. Dans le chapitre 5, des complexes Ir(III) portant un ligand tripode tridentate bis (six-membres) non conjugué inhabituel de la forme [Ir (C^N^C)(N^N)Cl] sont introduits. En fonction des substitutions du ligand C^N^C, une phosphorescence allant du jaune au rouge a été obtenue. La substitution du N^N donne un colorant NIR panchromatique, adapté aux applications DSSC. Au chapitre 6, le concept d'un ligand non conjugué a été étendu au ligand N^N. Une émission bleu-vert et bleu-ciel a été obtenue, démontrant une stratégie pour régler avec succès l'émission au bleu. / Here, the design, synthesis and characterisation and the optoelectronic properties of Ir(III) complexes for application in nonlinear optical and electroluminescent devices are described. The type of complexes varies from those of the form [Ir(C^N)2(N^N)]+ with conjugated and nonconjugated ligands (where C^N = cyclometalating ligand and N^N = neutral ligand) to those of the form [Ir(C^N^C)(N^N)Cl] (where C^N^C = tridentate tripod ligand). Chapter 1 gives an introduction into photophysics occurring in transition metal complexes and possible applications in visual displays. The background of nonlinear optical (NLO) properties and the use of transition metal complexes as NLO chromophores is described. In Chapter 2, the impact of the use of sterically congested cyclometalating ligands on the photoluminescence properties of cationic Iridium(III) complexes and their performance in light-emitting electrochemical cells is investigated. Chapter 3 explores the use of electron donors on the cyclometalating ligand towards modulating the NLO properties of the complexes. Combining strongly electron-donating substituents on the C^N ligand and electron-accepting substituents on the N^N ligand results in strong NLO activity. Chapter 4 summarises a new series of cationic iridium(III) complexes bearing benzylpyridinato as cyclometalating ligands. The methylene spacer in the C^N ligands provides flexibility, resulting in two conformers. NMR studies combined with density functional theory (DFT) studies show how the fluxional behaviour is influenced by the choice of the ancillary ligand. In Chapter 5, Ir(III) complexes bearing an unusual nonconjugated bis(six-membered) tridentate tripod ligand of the form [Ir(C^N^C)(N^N)Cl] are introduced. Depending on the substitutions of the C^N^C ligand phosphorescence ranging from yellow to red was obtained. Substitution of the N^N results in a panchromatic NIR dye, suitable for DSSC applications. In Chapter 6, the concept of a nonconjugated ligand was expanded to the N^N ligand. Blue-green and sky-blue emission was obtained, demonstrating a strategy to successfully tune the emission to the blue.

Phosphorescent organic light-emitting diodes (PhOLED) have attracted a lot of attention in these years.Blue PhOLED is especially important because of short lifetime and low optoelectronic performance as comparing to red and green PhOLEDs.Researches have shown that performance of OLED devices is highly rely on the deposition rate of organic materials ,which attest the morphology of organic layers. To study how the deposition rate of host material on the performance of blue PhOLED,mCP is chosen a host material for a blue dopant - FIrpic and deposition rate of mCP on the performance of blue PhOLED performance is studied. It was found that UV-Vis spectrum of mCP varied with different deposition rate.Additionally,an PL emission peak (400nm~500nm) appeared on the thermal evaporated mCP,which was possibly originated from the aggregation of mCP.Surface roughness of the evaporated mCP film became smaller as the deposition rate increased.A high performance (8.52 lm/W@1.2mA/cm2) is fabricated at a deposition rate at 3 A/s.

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Thesis (Ph. D.)--University of Wisconsin--Madison, 1965. / Typescript. Vita. Includes bibliographical references.

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