Dissertations / Theses on the topic 'OLEDs'

In the last decades, investigations of organic light-emitting diodes (OLEDs) have tackled several key challenges of this lighting technology and have brought the electron to photon conversion efficiency close to unity. However, currently only 20% to 30% of the photons can typically be extracted from OLED structures, as total internal reflection traps the major amount of the generated light inside the devices. This work focuses on the optimization of the optical properties of top-emitting OLEDs, in which the emission is directed away from the substrate. In this case, opaque materials, e.g. a metal foil or a display backplane can be used as substrate as well. Even though top-emitting OLEDs are often preferred for applications such as displays, two main challenges remain: the application of light extraction structures and the deposition of highly transparent materials as top electrode, without harming the organic layers below. Both issues are addressed in this work. First, top-emitting OLEDs are deposited on top of periodically corrugated light outcoupling structures, in order to extract internally trapped light modes by Bragg scattering and to investigate the basic scattering mechanisms in these devices. It is shown for the first time that the electrical performance is maintained in corrugated top-emitting OLEDs deposited on top of light extraction structures. Furthermore, as no adverse effects to the internal quantum efficiency have been observed, the additional emission from previously trapped light modes directly increases the device efficiency. It has been proven that the spectral emission of corrugated OLEDs is determined by the interference of all light modes inside the air light-cone, including the observation of destructive interference and anti-crossing phenomena. The formation of a coherently coupled mode pair of the initial radiative cavity mode and a Bragg scattered mode has been first observed, when grating structures with an aspect ratio > 0.2 are applied. There, the radiative cavity mode partially vanishes. The observation and analysis of such new emission phenomena in corrugated top-emitting OLEDs has been essential in obtaining a detailed insight on fundamental scattering processes as well as for the optimization and control of the spectral emission by light extraction structures. Second, the adverse impact of using only moderately transparent silver electrodes in white top-emitting OLEDs has been compensated improving the metal film morphology, as the organic materials often prevent a replacement by state-of-the-art electrodes, like Indium-tin-oxide (ITO). A high surface energy Au wetting layer, also in combination with MoO3, deposited underneath the Ag leads to smooth, homogeneous, and closed films. This allows to decrease the silver thickness from the state-of-the-art 15 nm to 3 nm, which has the advantage of increasing the transmittance significantly while maintaining a high conductivity. Thereby, a transmittance comparable to the ITO benchmark has been reached in the wavelength regime of the emitters. White top-emitting OLEDs using the wetting layer electrodes outperform state-of-the art top-emitting devices with neat Ag top electrodes, by improving the angular colorstability, the color rendering, and the device efficiency, further reaching sightly improved characteristics compared to references with ITO bottom electrode. The enormous potential of wetting layer metal electrodes in improving the performance of OLEDs has been further validated in inverted top-emitting devices, which are preferred for display applications, as well as transparent OLEDs, in which the brittle ITO electrode is replaced by a wetting layer electrode. Combining both concepts, wetting layer electrodes and light extraction structures, allows for the optimization of the grating-OLED system. The impact of destructive mode interference has been reduced and thus the efficiency increased by a decrease of the top electrode thickness, which would have not been achieved without a wetting layer. The optimization of corrugated white top-emitting OLEDs with a top electrode of only 2 nm gold and 7 nm silver on top of a grating with depth of 150 nm and period of 0.8 µm have yielded a reliable device performance and increased efficiency by a factor of 1.85 compared to a planar reference (5.0% to 9.1% EQE at 1000 cd/m2). This enhancement is comparable to common light extraction structures, such as half-sphere lenses or microlens foils, which are typically restricted to bottom-emitting devices. Overall, the deposition of top-emitting OLEDs on top of light extraction structures finally allow for an efficient extraction of internally trapped light modes from these devices, while maintaining a high device yield. Finally, the investigations have resulted in a significant efficiency improvement of top-emitting OLEDs and the compensation of drawbacks (optimization of the white light emission and the extraction of internal light modes) in comparison to the bottom-emitting devices. The investigated concepts are beneficial for OLEDs in general, since the replacement of the brittle ITO electrodes and the fabrication of roll-to-roll processing compatible light extraction structures are also desirable for bottom-emitting, or transparent OLEDs.

The merging fields of photonics and organic electronics into organic optoelectronics has created a surge of enthusiasm over the possibility of developing low-cost and large-area advanced optoelectronic systems. These applications can combine the best functionalities of both fields, such as tailoring the organic semiconductors by chemical means, engineering the structure in which organic materials are embedded in, are to name a few. These advances have stimulated the excitement over the next generation of optoelectronic systems with enhanced capabilities and low-cost manufacturing processes compared to their inorganic counterparts. Such technology direction is mainly reflected by the high investments towards the aim of developing flexible, and roll-to-roll organic light-emitting diodes and organic solar cells. Interestingly, more sophisticated applications require a deeper understanding of the underlying mechanisms at play that merge concepts from the fields of photonics and organic electronics. Particularly, organic light-emitting diodes (OLEDs) under certain constraints (such as cavity light confinement, strong exciton-photon interaction) exhibit modified spectral emission compared to OLED devices that are not bounded by the same conditions. The introduction of the polariton concept as a quasi-particle, which is part-light and part-matter, has emerged to describe such new physical phenomena caused by this photon-exciton intricate interaction. Polariton physics is well established in inorganic semiconductors were a plethora of physical phenomena have been demonstrated, such as the appearance of Bose-Einstein Condensation or low-threshold laser devices. The later is what has as yet to be demonstrated from the field of solid state physics utilising organic semiconductors. This thesis is focused on the study of the physics and the engineering of organic light-emitting diodes that will aid in the realization of efficient organic polariton LEDs. The main body of work examines various organic semiconductor materials in their ability to reach the strong light and matter interaction regime and, subsequently, to be used in OLEDs as the emissive component. Furthermore, a degradation investigation highlights the issues that affect small-molecule based OLEDs, and finally, the possible pathways for achieving efficient polariton OLEDs are discussed.

This work focuses on a better understanding of the behavior of organic light emitting devices (OLEDs) under intense electrical excitation. Attaining high exciton densities in organic semiconductors by electrical excitation is of special interest for the field of organic semiconductor lasers (OSLs). In these devices, the high singlet exciton density needed in the active layer to obtain population inversion is easily created by pulsed optical pumping, but direct electrical pumping has not been achieved yet. First, the steps necessary to achieve stable high current densities in organic semiconductors are discussed. After determining the optimal excitation scheme using single p-doped transport layers, the device complexity is increased up to full p-i-n OLEDs with their power dependent emission spectra. For this purpose, two exemplary emitter systems are chosen: the fluorescent laser dye 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) doped into Aluminum(III)bis (2-methyl-8-quinolinato)-4-phenylphenolate (Alq3) and the efficient phosphorescent emitter system N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-benzidine (alpha-NPD) doped by Iridium(III) bis(2-methyl-dibenzo[f,h]quinoxaline)(acetylacetonate) (Ir(MDQ)2(acac)). For pulsed excitation using 50 ns pulses and a repetition rate of 1 kHz, single 100 nm thin p- and n-doped transport layers sustain current densities of over 6 kA/cm2. While the maximum current density decreases with increasing device thickness, the full OLEDs still sustain current densities beyond 800 A/cm2 and exhibit a continuously increasing emission intensity with increasing input power. Next, the time-resolved emission behavior of the singlet and triplet emitter device at high excitation densities is analyzed on the nanosecond scale. Here, the peak emission intensity of the phosphorescent emitter system is found to be more than eight times lower than for the singlet emitter system at comparable current densities. The triplet emitter system exhibits a slow rise of the EL after turn-on which prevents the usage of shorter pulses to enable higher current densities. The singlet emitter system, in contrast, exhibits a fast turn-on and reaches the maximum emission intensity within less than 20 ns. By several additional experiments including streak camera measurements and pump-probe experiments, the strong EL overshoot observed in the first few ns is successfully attributed to a reduced emission intensity in the steady state due to singlet-triplet annihilation. Hence, the separation of singlet emission and singlet-triplet quenching in time domain is demonstrated. At 550 A/cm2 and 10 ns pulse rise time, a peak luminance of 1.5E6 cd/m2 is recorded. Finally, the experimental results are validated by modeling the singlet and triplet population dynamics in the emission layer of the fluorescent system to explain the time-resolved emission characteristics. Using a set of rate equations for the polaron density and the singlet and triplet exciton densities, the overshoot in singlet exciton density at the device turn-on is attributed to the separation of singlet emission and triplet quenching in time domain. Furthermore, by fitting the experimental data, the triplet-triplet annihilation rate in the host guest system is shown to become exciton density dependent at sufficiently high excitation density
Der Schwerpunkt dieser Arbeit liegt auf dem besseren Verständnis des Verhaltens von organischen Leuchtdioden (OLEDs) bei intensiver elektrischer Anregung. Das Erreichen hoher Exzitonendichten in organischen Halbleitern ist insbesondere für organische Halbleiterlaser (organic semiconductor lasers, OSLs) von Interesse. Hierbei werden die für die Inversion benötigten hohen Singulett Exzitonendichten zwar leicht mittels gepulstem optischen Anregen (Pumpen) erreicht, jedoch konnte eine elektrische Anregung bisher noch nicht realisiert werden. Der erste Abschnitt befasst sich mit dem Erreichen von hohen Stromdichten und den dazu nötigen Schritten. Nach dem Ermitteln des optimalen Anregungsschemas an p-dotierten Einzelschichten wird die Komplexität des Systems Schritt für Schritt bis zur kompletten p-i-n OLED erhöht. Hierfür wurden exemplarisch zwei verschiedene Emittersysteme ausgewählt: Aluminum(III)bis (2-methyl-8-quinolinato)-4-phenylphenolate (Alq3) dotiert mit dem fluoreszenten Laserfarbstoff 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) und der effiziente phosphoreszente Emitter Iridium(III)bis(2-methyl-dibenzo[f,h]quinoxaline)(acetylacetonate) (Ir(MDQ)2(acac)) in einer N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-benzidine (alpha-NPD) Matrix.Bei gepulster Anregung mit einer Pulsweite von 50 ns und einer Wiederholungsrate von 1 kHz sind in 100 nm dünnen p- und n-dotierten Transportschichten Stromdichten von mehr als 6 kA/cm2 möglich. Der Maximalstrom sinkt mit zunehmender Gesamtschichtdicke ab. Die kompletten p-i-n OLEDs ermöglichen eine Stromdichte von über 800 kA/cm2 und weisen eine kontinuierlich mit der Stromdichte steigende Emissionsintensität auf. Anschließend wird die zeitlich aufgelöste Elektrolumineszenz der Singulett- und Triplett-Emitter OLEDs mit Nanosekunden-Auflösung untersucht. Die phosphoreszente OLED weist hierbei, im Vergleich zur fluoreszenten OLED bei vergleichbarer Stromdichte, eine mehr als achtmal geringere Emissionsintensität auf. Des Weiteren steigt die Emissionsintensität nur langsam an, die maximale Intensität wird erst nach 120 ns erreicht. Dies steht im Widerspruch zum Erreichen höherer Stromdichten mittels kürzerer Pulse. Die fluoreszente OLED hingegen zeigt ein schnelles Ansteigen der Emissionsintensität, die maximale Intensität wird nach weniger als 20 ns erreicht. Anhand von zusätzlichen Untersuchungen kann das beobachtete starke Überschießen der Elektrolumineszenz innerhalb der ersten Nanosekunden einer durch Singulett-Triplett Annihilation reduzierten Emission im Gleichgewichtszustand zugeordnet werden. Diese Experimente dokumentieren somit die zeitliche Trennung von Fluoreszenz und Singulett-Triplett Annihilation. Bei einer Stromdichte von 550 A/cm2 und 10 ns Flankenanstiegszeit wird eine maximale Lumineszenz von 1.5E6 cd/m2 gemessen. Der letzte Abschnitt befasst sich mit der Bestätigung der experimentellen Ergebnisse durch die Simulation der Dynamik von Singulett- und Triplett-Exzitonendichte in der Emissionsschicht. Mit Hilfe eines Satzes von gekoppelten Differenzialgleichungen für die Dichte der Polaronen, Singulett Exzitonen und Triplett Exzitonen lässt sich das Überschießen der Elektrolumineszenz der fluoreszenten OLED eindeutig der zeitlichen Trennung von Singulett Emission und Singulett-Triplett Annihilation zuordnen. Außerdem kann durch das Fitten der experimentellen Daten dargestellt werden, dass die Triplett-Triplett Annihilationsrate in dem untersuchten fluoreszenten Emittersystem bei ausreichend hohen Anregungsdichten eine starke Abhängigkeit von der Dichte der Triplett Exzitonen aufweist

This work focusses on the development of top-emitting white organic light-emitting diodes (OLEDs), which can be fabricated on metal substrates. Bottom-emitting OLEDs have been studied intensively over the years and show promising perspectives for future commercial applications in general lighting. The development of top-emitting devices has fallen behind despite the opportunities to produce these devices also on low-cost opaque substrates. This is due to the challenges of top-light-emission concerning the achievement of a broad and well-balanced white emission spectrum in presence of a strong microcavity. The following work is a further step towards the detailed understanding and optimization of white top-emitting OLEDs. First, the available metal substrates and the deposited silver electrodes are examined microscopically to determine their surface characteristics and morphology in order to assess their applicability for thin-film organic stacks of OLEDs. The examination shows the suitability for untreated Alanod metal substrates, which display low surface roughness and almost no surface defects. For the deposited silver anodes, investigations via AFM show a strong influence of the deposition rate on the surface roughness. In the main part of the work top-emissive devices with both hybrid and all-phosphorescent architecture are investigated, in which three or four emitter materials are utilized to achieve maximum performance. The feasibility for top-emitting white OLEDs in first and second order devices is investigated via optical simulations, using the example of a three-color hybrid OLED. Here, the concept of a dielectric capping layer on top of the cathode is an essential criterion for broadband and nearly angle independent light emission. The main focus concerning the investigation of fabricated devices is the optimization of the organic stacks to achieve high efficiencies as well as excellent color quality of warm white emission. The optimization of the hybrid layer structure based on three emitter materials using a combined aluminum-silver anode mirror resulted in luminous efficacies up to 13.3 lm/W and 5.3 % external quantum efficiency. Optical analysis by means of simulation revealed a superior position concerning internal quantum efficiency compared to bottom-emitting devices with similar layer structure. The devices show an enhanced emission in forward direction compared to an ideal Lambertian emitter, which is highly preferred for lighting applications. The color quality - especially for devices based on a pure Al anode - is showing excellent color coordinates near the Planckian locus and color rending indices up to 77. The introduction of an additional yellow emitter material improves the luminous efficacy up to values of 16.1 lm/W and external quantum efficiencies of 5.9 %. With the choice of a all-phosphorescent approach, using orange-red, light blue and green emitter materials, luminous efficacies of 21.7 lm/W are realized with external quantum efficiencies of 8.5 %. Thereby, color coordinates of (x, y) = (0.41, 0.45) are achieved. Moreover, the application of different crystalline capping layers and alternative cathode materials aim at a scattering of light that further reduces the angular dependence of emission. Experiments with the crystallizing material BPhen and thin carbon nanotube films (CNT) are performed. Heated BPhen capping layer with a thickness of 250 nm show a lower color shift compared to the NPB reference capping layer. Using CNT films as cathode leads to a broadband white emission at a cavity thickness of 160 nm. However, due to very high driving voltages needed, the device shows low luminous efficacy. Finally, white top-emitting organic LEDs are successfully processed on metal substrates. A comparison of three and four color based hybrid devices reveal similar performance for the devices on glass and metal substrate. Only the devices on metal substrate show slightly higher leakaged currents. During repeated mechanical bending experiments with white devices deposited on 0.3 mm thin flexible Alanod substrates, bending radii up to 1.0 cm can be realized without device failure
Diese Arbeit richtet ihren Schwerpunkt auf die Entwicklung von top-emittierenden weißen organischen Leuchtdioden (OLEDs), welche auch auf Metallsubstraten gefertigt werden können. Im Laufe der letzten Jahre wurden bottom-emittierende OLEDs sehr intensiv studiert, da sie vielversprechende Perspektiven für zukünftige kommerzielle Anwendungen in der Allgemeinbeleuchtung bieten. Trotz der Möglichkeit, OLEDs auch auf kostengünstigen lichtundurchlässigen Substraten fertigen zu können, blieb die Entwicklung von top-emittierenden Bauteilen dabei allerdings zurück. Dies läßt sich auf die enormen Herausforderungen von top-emittierenden OLEDs zurückführen, ein breites und ausgeglichenes weißes Abstrahlungsspektrum in Gegenwart einer Mikrokavität zu generieren. Die folgende Arbeit liefert einen Beitrag zum detaillierten Verständnis und der Optimierung von weißen top-emittierenden OLEDs. Zunächst werden die verfügbaren Metallsubstrate und abgeschiedenen Silberelektroden auf ihre Oberflächeneigenschaften und Morphologie mikroskopisch untersucht, um damit ihre Verwendbarkeit für organische Dünnfilmstrukturen in OLEDs einzuschätzen. Die Untersuchung zeigt eine Eignung von unbehandelten Alanod Metallsubstraten auf, welche eine niedrige Oberflächenrauigkeit und fast keine Oberflächendefekte besitzen. Bei den abgeschiedenen Silberelektroden zeigen Untersuchungen mit dem Rasterkraftmikroskop eine starke Beeinflussung der Oberflächenrauigkeit durch die Aufdampfrate. Im Hauptteil der Arbeit werden top-emittierende Dioden mit hybrid und voll-phosphoreszenter Architektur untersucht, in welcher drei oder vier Emittermaterialien verwendet werden, um eine optimale Leistungscharakteristik zu erreichen. Die Realisierbarkeit von top-emittierenden weißen OLEDs in Dioden erster und zweiter Ordnung wird durch optische Simulation am Beispiel einer dreifarb-OLED mit Hybridstruktur ermittelt. Dabei ist das Konzept der dielektrischen Deckschicht - aufgebracht auf die Kathode - ein essenzielles Kriterium für breitbandige und annähernd winkelunabhängige Lichtemission. Der Schwerpunkt im Hinblick auf die Untersuchung von hergestellten Dioden liegt in der Optimierung der organischen Schichtstrukturen, um hohe Effizienzen sowie exzellente warmweiße Farbqualität zu erreichen. Im Rahmen der Optimierung von hybriden Schichtstrukturen basierend auf drei Emittermaterialien resultiert die Verwendung eines kombinierten Aluminium-Silber Anodenspiegels in einer Lichtausbeute von 13.3 lm/W und einer externen Quanteneffizienz von 5.3 %.Eine optische Analyse mit Hilfe von Simulationen zeigt eine überlegene Stellung hinsichtlich der internen Quanteneffizient verglichen mit bottom-emittierenden Dioden ähnlicher Schichtstruktur. Die Dioden zeigen eine verstärkte vorwärts gerichtete Emission im Vergleich zu einem idealen Lambertschen Emitter, welche in hohem Maße für Beleuchtungsanwendungen erwünscht ist. Es kann eine ausgezeichnete Farbqualität erreicht werden - insbesondere für Dioden basierend auf einer reinen Aluminiumanode - mit Farbkoordinaten nahe der Planckschen Strahlungskurve und Farbwiedergabeindizes bis zu 77. Die weitere Einführung eines zusätzlichen gelben Emittermaterials verbessert die Lichtausbeute auf Werte von 16.1 lm/W und die externe Quanteneffizient auf 5.9 %. Mit der Wahl eines voll-phosphoreszenten Ansatzes unter der Verwendung eines orange-roten, hellblauen und grünen Emittermaterials werden Lichtausbeuten von 21.7 lm/W und externe Quanteneffizienten von 8.5 % erzielt. Damit werden Farbkoordinaten von (x, y) = (0.41, 0.45) erreicht. Darüberhinaus zielt die Verwendung von verschiedenen kristallinen Deckschichten und alternativen Kathodenmaterialien auf eine Streuung des ausgekoppelten Lichts ab, was die Winkelabhängigkeit der Emission vermindern soll. Experimente mit dem kristallisierenden Material BPhen und dünnen Filmen aus Kohlenstoffnanoröhren werden dabei durchgeführt. Geheizte BPhen Deckschichten mit einer Schichtdicke von 250 nm zeigen eine geringere Farbverschiebung verglichen mit einer NPB Referenzdeckschicht. Die Verwendung von Kohlenstoffnanoröhren als Kathode führt zu einer breitbandigen weißen Emission bei einer Kavitätsschichtdicke von 160 nm. Schließlich werden weiße top-emittierende organische Leuchtdioden erfolgreich auf Metallsubstraten prozessiert. Ein Vergleich von drei- und vierfarb-basierten hybriden Bauteilen zeigt ähnliche Leistungsmerkmale für Dioden auf Glas- und Metallsubstraten. Während wiederholten mechanischen Biegeexperimenten mit weißen Dioden auf 0.3 mm dicken flexiblen Alanodsubstraten können Biegeradien bis zu 1.0 cm ohne Bauteilausfall realisiert werden

The development of new charge transport materials for use in phosphorescent organic light-emitting diodes (OLEDs) remains an important area of research. In this thesis, several examples of carbazole-containing norbornene-based side-chain polymers were synthesized and studied. In addition, several examples of ambipolar transport moieties were produced by combining hole- (carbazole) and electron- (oxadiazole or triazole) transport groups and examined as both small molecules and as norbornene-based side-chain polymers. UV-visible absorption, fluorescence spectroscopy, cyclic voltammetry, and other methods were used to evaluate the properties of the charge transport materials for use as hole- and/or host layers. It was found that side-functionalization produced polymers with photophysical and electrochemical properties corresponding to the charge transport side groups attached. In addition, several crosslinkable hole-transporting materials (copolymer or small molecule-based) incorporating either benzocyclobutenes, trifluorovinyl ethers, oxetanes, or bis(styrene)s were developed. Thin-films of the crosslinkable materials were shown to be readily insolubilized by thermal treatment permitting the deposition of a subsequent layer from solution onto the crosslinked layer. OLEDs fabricated using several of these materials produced efficient devices. Overall, it was shown that side-chain functionalization can be used to afford solution-processable charge transport polymers where the properties are determined mainly by the side group attached. As such, this approach could be extended to additional examples of charge transport moieties.

Mestrado em Engenharia Física
Este trabalho foca essencialmente o fabrico e completa caracterização de OLEDs para fins de iluminação decorativa. Os dispositivos foram fabricados por evaporação térmica usando small molecules. Foram obtidos resultados que mostram a viabilidade das soluções de estrutura que foram usadas, nomeadamente o brilho, a pureza de cor e as relativamente boas curvas de corrente-tensão que mostram igualmente a possível viabilidade em termos comerciais. Como conclusão final, este trabalho mostra que efetivamente é possível com soluções de estruturas simples fabricar e desenvolver OLEDs para os fins acima descritos.
This work focuses essentially on the conception and complete characterization of OLEDs for luminous decoration purposes. The devices were produced by thermal evaporation of small molecules. The results obtained demonstrate that the viability of the used structures, mainly the brightness levels, the colour purity and the reasonably acceptable current-voltage behaviour show that these devices are equally viable to extend to commercial production. As a final conclusion, this work shows that effectively it is possible with simple structure solutions to produce and develop OLEDs for the purposes described above.

Mestrado em Ciência e Engenharia de Materiais
Os díodos orgânicos emissores de luz (organic light-emitting diodes ou OLEDs) têm como elemento funcional um filme fino de um semicondutor orgânico para a criação de excitões (pares electrão-lacuna), que emitem luz quando relaxam. O objetivo desta dissertação de mestrado é investigar o efeito da orientação dipolar de filmes baseados em perilenos de tetraphenyldibenzoperiflanthene (DBP) e diindenoperylene ( DIP), e das mesmas moléculas dispersas numa ma matriz de 5,6,11,12- tetraphenylnaphthacene (rubreno). O estudo tenta identificar uma possível relação entre o comportamento destes filmes e a eficiência do respetivo OLED. Observa-se que os filmes de DBP são amorfos, apresentam uma superfície lisa e absorvem mais luz do que os filmes de DIP, que se caracterizam por uma estrutura cristalina e uma superfície irregular. Os resultados combinados de simulações e de medições de fotoluminescência com dependência angular revelam que as moléculas de DBP apresentam orientação horizontal, estando as moléculas de DIP orientadas verticalmente. Este facto pode explicar o acoplamento mais forte das moléculas de DIP aos plasmões de superfície, em comparação com o DBP. As características gerais dos filmes de DBP ou DIP mantêm-se mesmo quando estes são depositados nos substratos de N, N '-di(1-naftil-N,N-difenil-(1,1'- bifenil)-4,4' –diamina utilizados ma preparação dos OLEDs, o que permite a comparação direta entre as duas configurações. Os resultados obtidos com os OLEDs baseados em filmes puros de DBP ou DIP apresentam valores de eficiência quântica externa (EQE) da ordem de 0,2 e 0,04 %, respetivamente. Estes valores baixos podem explicar-se pela orientação vertical dos dipolos do DIP, conduzindo a um fator de emissão de 27% (light outcoupling), claramente superior ao obtido com o OLED baseado no DBP (16%). Estas diferenças acentuam-se quando na comparação destes filmes com o comportamento dos filmes rubreno equivalentes dopados com 1% de DBP e DIP. Se por um lado não se observa nenhuma orientação dipolar preferencial no caso do DIP, as moléculas de DBP na matriz de rubreno estão quase na sua totalidade orientadas horizontalmente, o que aumenta o factor de emissão. A forte orientação preferencial no caso do DBP pode igualmente justificar o aumento de EQE de 0,2 % e 0,04% nos OLEDs com os filmes puros de DBP e DIP, para 3% e 0,5% no caso dos OLEDs com os filmes dopados. O aumento da eficiência pode também dever-se ao aumento da transferência energética da matriz de rubreno para os centros emissores. O forte efeito da orientação horizontal do emissor na eficiência dos OLEDs manifesta-se igualmente no notável aumento do factor de emissão de luz observado entre os filmes de DBP (fortemente orientados) e DIP (pouco orientados), que é de cerca de 70% no caso das camadas de emissão baseadas nos filmes puros, e de 44 % no caso dos filmes dopados.
Organic light-emitting diodes (OLEDs) contain thin films of organic semiconductors to create excitons (electron-hole-pairs), which will emit light if they de-excite. The aim of this master thesis is to investigate a possible link between the dipole orientation of perylene based films of tetraphenyldibenzoperiflanthene (DBP) and diindenoperylene (DIP), and of the same molecules dispersed in a 5,6,11,12-tetraphenylnaphthacene matrix. The study also compares the behavior of these films with that of the corresponding OLEDs. It is shown that DBP neat films are essentially amorphous, with a rather smooth surface and they absorb more light than the DIP films, which are crystalline and have a rough surface. Simulation results and angle-dependent p-polarised photoluminescence measurements reveal that the DBP molecules have a horizontal orientation, while the DIP molecules are vertically oriented. This explains the stronger coupling of DIP molecules to the surface plasmons, when compared to the DBP molecules. The general characteristics of the DBP or DIP films do not change when these are deposited onto N,N’-di(1-naphtyl-N,N’-diphenyl-(1,1’-biphenyl)-4,4’diamine hole transport layers used as substrates in OLEDs, thus allowing a direct comparison between both configurations. The OLEDs comprising neat films of DBP or DIP have small external quantum efficiency (EQE) values of 0.2 and 0.04%, respectively. This is probably due to the strong vertical molecular orientation of the DBP, leading to a high lightoutcoupling factor of 27%, when compared to 16% of the DIP OLED. These differences are accentuated when comparing the behavior of the neat films with equivalent rubrene films doped with 1% of DBP or DIP. While the DIP exhibits a rather isotropic orientation, the DBP molecules are fully horizontal within the doped film, thus improving the light-outcoupling. This may partly justify the increase of EQE from 0.2% and 0.04% of the neat film OLEDs to 3% and 0.5% for the doped DBP and DIP OLEDs, respectively. The improvement of the efficiency may also be due to the enhancement of the energy transfer from the rubrene matrix to the emitter dyes. The horizontal orientation of the emitter has a huge effect on the efficiency of perylene-based OLEDs, apparent also on the remarkable increase of the lightoutcoupling of strongly oriented DBP dipoles in comparison to the weakly oriented DIP, which is of the order of 70% in the case of the neat emission layers, and of 44% in the case of the doped counterparts.

Mestrado em Engenharia Físic
O objetivo deste trabalho consistiu em contribuir para o desenvolvimento de um novo dispositivo, com fins decorativos, baseado num Díodo Emissor de Luz Orgânico (em inglês: OLED) construído sobre um ladrilho de (aço) inox. Este estudo enquadra-se num projecto SI I&DT (Sistema de Incentivos a Investigação e Desenvolvimento Tecnológico) Individual com uma empresa portuguesa da area dos ladrilhos metálicos. O inox possui características ópticas particulares que deveriam ser mantidas após a construção do OLED. Um dos principais problemas consiste na transparência ótica, na gama do visível, das várias camadas que constituem o dispositivo. Neste trabalho foram abordados essencialmente dois problemas: o isolamento elétrico da superfície de inox e a eficácia de uma barreira flexível que deverá proteger o OLED da exposição ambiental. Deste modo, a primeira parte deste trabalho focou-se na avaliação da possibilidade de crescimento de uma camada isolante no ladrilho de inox, espessa o suficiente para aplanar a sua rugosidade mas sem comprometer severamente a sua identidade característica. A ultima camada de um OLED e uma barreira protetora que tem como objetivo evitar a exposição ambiental que afecta o tempo de vida do dispositivo. Para esse fim, testou-se uma barreira comercial flexível. Por conseguinte, a segunda parte deste trabalho focou-se no estudo da degradação de um OLED, comparando para isso OLEDs não encapsulados com encapsulados - com vidro (uma barreira de referência) ou com a nova barreira flexível. A comparação baseou-se na evolução temporal do consumo de corrente eléctrica e da electroluminescência do dispositivo. Adicionalmente, utilizaram-se imagens de microscópio para compreender melhor a evolução da degradação. Os resultados sugerem que a degradação dos dispositivos é governada por diferentes processos, quer nos encapsulados ou não encapsulados. No entanto, a barreira encapsulante utilizada permitiu alterar (ou eliminar) os tempos de ativação de alguns desses processos. Estes processos de degradação foram estudados e analisados de forma a permitir uma compreensão mais clara da progressão da degradação que afeta o tempo de vida do OLED tão severamente.
The goal of this work was to contribute to the development of a new device, for decorative purposes, based on an Organic Light-Emitting Diode (OLED) built on top of a stainless steel (StS) tile. The framework of these studies was a SI I&DT (Sistema de Incentivos a Investiga c~ao e Desenvolvimento Tecnol ogico) Individual Project with a Portuguese company in the area of metallic tiles. StS possesses particular optical characteristics that were supposed to be maintained after the OLED was built. One of the major problems is the optical transparency, in the visible range, of the several layers that constitute the device. In this work two particular issues have been addressed: the electric insulation of the StS surface and the e ectiveness of a exible barrier to protect the OLED from environmental exposure. Therefore, the rst part of this work focused on evaluating if an insulating layer could be grown on a StS tile, thick enough to smooth its roughness but without compromising its characteristic identity too severely. The last layer in an OLED is a protective barrier which aims to avoid ambient exposure that a ects the life time of the device. In order to accomplish that, a very thin exible commercial barrier was tested. Hence the second part of this work focused on studying the OLED degradation by comparing notencapsulated OLEDs with encapsulated ones - either by glass (a reference barrier) or the new exible barrier. The comparison was based on the time evolution of the electric current consumption and the electro-luminescence of the device. Plus, microscopy images were used to better understand the evolution of the degradation. Results suggest that di erent processes rule the degradation of the devices, either encapsulated or not. However, the encapsulation barrier used was able to change (or eliminate) the activation timings of some processes. These degradation processes were studied and analysed in order to accomplish a clear understanding of the degradation's progression that severely a ects OLED life time.

2014 - 2015
The fast technological evolution of our world requests the necessity to make this development sustainable. In order to achieve this goal more relevance has been given to the energy consumption and environmental impact of the modern society consumerism. These considerations point out the need to increase the effort in research of unconventional materials, new concept and system architecture for devices that could help to overcome these challenges. Nanotechnologies offer the best chance for this innovation and particularly organic electronics has been encouraged thanks to new attractive properties and promising applications. Organic materials could be processed in thin film accommodating the issue of preservation of manufacturing energy usage despite from bulky and costly processes of inorganic industries. Fabrication techniques, including spin or spray coating, ink-jet or roll-to-roll printing, can be applied at low-temperature and over large area substrates. This is promising to maximize production throughput and to reduce costs. Also many other advances have been reached in the electronic applications of organic materials such as the spread of light-weight, transparent, flexible and disposable devices. Particularly, in recent years, OLEDs (Organic Light Emitting Diode) have been successful commercialized both for display applications and light source. OLED-based displays are nowadays commercialized both for high performances cell displays and TVs, becoming the major competitors of other well established technologies, like LCD or LED. In imaging application, very often Active Matrix approach is used to supply the display. In recent years the use of another Organic Electronics device, Organic TFT (OTFT), has been exploited as Active Matrix driver with encouraging results. In the last years also OLED-based light source have been introduced on the market. OLED panel technology allows overcoming some of the more critical issues of the preceding technologies such as very low energy conversion, as for incandescence source light, lack of good colors and the use toxic elements as for fluorescent tube and costly manufacturing processes and point light source as for the more recent LED technology. Despite all these amazing results, important drawbacks still remain in the field of organic electronic devices. Low charge carrier mobilities or still expensive manufacturing cost, but the more critical is extreme sensitivity to ambient conditions, temperature, light, and particularly oxygen and moisture, which could degrade their optical and electrical characteristics. This work of thesis sets in this scenario and the aim of this research is the study of degradation phenomena through methodology that leads to the identification of the different mechanisms of degradation involved, responsible of device short life time. The present work has been developed focusing the attention on the various degradation mechanisms in OLED and the possibility to use their nature to develop innovative analysis methods. For this purpose has been exploited both extrinsic and intrinsic degradation. Critical issues in this field are the complexity of the involved phenomena and the relatively recent interest of the scientific community in the intrinsic degradation topic. In the organization of the thesis work, after a brief presentation of the main features of organic electronics, an overview of the basic principles of permeation and typical encapsulation solutions are presented. In particular, specific attention has been paid on barrier requirements and solutions presented to protect the devices. These solutions, besides being the way to control extrinsic degradation, are also used to isolate other degradation components becoming a tool for studying the intrinsic degradation in organic devices. It has been also pointed out the importance to evaluate the barrier characteristic in terms of WVTR and here has been presented some solution to evaluate ultra-high barrier permeation. The study has been then centered on the design and development of a Calcium corrosion test for the evaluation of ultra-high barrier. It has been investigated all the aspect of layout and setup to achieve a higher sensitivity level. This measurement method has been employed for the design and optimization of both a glass to glass and Thin Film Encapsulation barrier permeation system. In the first case (glass to glass) the developed encapsulated system has been used in an effective way to estimate lifetime of a simple OLED structure and validate the system performances. Afterwards, the investigations have been focused on intrinsic degradation process. For this purpose the glass to glass encapsulation system has been also used to neglect external agents within the development of an innovative method based on accelerated environmental aging conditions for the study of intrinsic degradation phenomena components. Thus an innovative methodology to study this issue has been proposed and tested on a case study. In order to reach this goal resulted very important to separate extrinsic degradation component from the intrinsic one so in this thesis we worked on the following topics reaching very satisfying results: • reliable evaluation of permeation barriers using the electrical calcium corrosion test • glass to glass and thin film encapsulation permeation barrier system • devices (OLED) lifetime under accelerated aging conditions • intrinsic degradation study: methodology and application Regarding the first topic a measurement system based on Calcium corrosion test has been first studied, designed and developed taking into account every detail leading to a result alteration. Then first a glass to glass and later a thin film encapsulation system has been designed and developed in the same way. The Calcium corrosion test measurement system was then used to measure the barrier performances of the developed encapsulation systems revealing values of WVTR in line with literature results obtained through the selected techniques. Particularly had been detected a WVTR value of 4 10-6 g m-2 day-1 and approximately 10-2 g m-2 day-1 respectively for glass to glass and Thin Film Encapsulation system. Regarding OLED lifetime, using simple devices, experiments were conducted for one OLED-structure processed on glass. The structure used an ITO bottom contact as well as an aluminum top contact. The realized devices after 3000 hours have lost only a 20% in luminance from the initial value validating the performances of the developed encapsulation solution for devices realized on glass substrate in the same time of observation. This result if from one side is very encouraging for lifetime issue on the other side is the key element that allows neglecting external effect during further degradation study. The results achieved on these topics results precious to focus on the last aspect faced during this work. In fact using our encapsulation system and applying different experimental techniques, typically not employed, has been possible to put in light single intrinsic degradation mechanism involved. Particularly has been decided to focus on possible phenomena that can occur during OFF-time periods (without electrically stressing the samples). Experiments have been conducted at different storage conditions on two types of blue OLEDs representing the worst stability case. This study revealed , in condition that allow to neglect other degradation source, that physical aging occurs for both types of devices, leading to irreversible time-dependent luminance loss. The proposed method in this case study (accelerated environmental aging conditions) coupled with other more common used analysis conditions allows to study the degradation topic in a more complete way. [edited by author]
Il rapido sviluppo tecnologico dell’era contemporanea richiede la necessità di rendere questo processo evolutivo sostenibile. Per raggiungere questo obiettivo una grande rilevanza è stato assegnata al consumo energetico e all'impatto ambientale del moderno consumismo della nostra società. Queste considerazioni sottolineano la necessità di aumentare gli sforzi nella ricerca di materiali non convenzionali, di nuova concezione e architetture di sistema per i dispositivi che possano aiutare a superare queste sfide. Il campo delle nanotecnologie offre le migliori possibilità per rendere attuabile questo tipo di innovazione ed in particolare l’elettronica organica si è messa in luce grazie alle sue interessanti proprietà e promettenti applicazioni. I materiali organici possono essere processati sotto in film sottili mitigando così il problema del consumo di energia di produzione, a differenza dei processi complessi e costosi usati dalle industrie di produzione di materiali inorganici. I dispositivi organici inoltre possono essere realizzati impiegando tecniche di fabbricazione innovative che comprendono il rivestimento a spruzzo, la stampa a getto d'inchiostro o la stampa roll-to-roll; tali tecniche richiedono basse temperature e offrono la possibilità di realizzare dispositivi su larga scala. Anche questo aspetto risulta promettente nell’ottica della massimizzazione del throughput di produzione e della riduzione dei costi. Molti altri vantaggi sono stati raggiunti con l’applicazione all’elettronica di materiali organici come ad esempio la diffusione di dispositivi leggeri, trasparenti, flessibili e smaltibili più facilmente rispetto a quelli classici. In particolare, negli ultimi anni, gli OLED (Organic Light Emitting Diode) hanno avuto un enorme successo commerciale sia per applicazioni nei display sia come sorgente luminosa. I display OLED sono oggi utilizzati sia in schermi ad alte prestazioni per cellulari che per televisori, diventando i principali concorrenti di altre tecnologie consolidate, come LCD o LED. In applicazione di questo tipo, molto spesso l'approccio a matrice attiva è utilizzato per alimentare il display stesso. Negli ultimi anni l'uso di un altro dispositivo elettronico basato su materiali organici, il TFT organico (OTFT), è stato sfruttato per polarizzare circuiti a matrice attiva con risultati incoraggianti. Negli ultimi anni anche sorgenti di luce OLED sono state introdotte sul mercato. Questo tipo di tecnologia infatti permette di superare alcuni dei problemi più critici delle tecnologie precedenti, come la bassa conversione di energia tipica delle lampadine ad incandescenza, la mancanza di buoni colori e l'uso di elementi tossici tipiche dei tubi a fluorescenza e processi produttivi costosi e sorgenti di luce puntiformi tipici della più recente tecnologia LED. Nonostante tutti questi risultati sorprendenti, esistono ancora alcune problematiche aperte nel campo dei dispositivi elettronici organici. La scarsa mobilità dei portatori o i costi di produzione ancora oggi piuttosto elevati ne limitano per ora la diffusione massiccia, ma l’aspetto più critico riguarda l’estrema sensibilità alle condizioni ambientali, temperatura, luce, e in particolare l'ossigeno e l'umidità, che possono modificare sensibilmente le caratteristiche ottiche ed elettriche di questi materiali. Questo lavoro di tesi si sviluppa in questo contesto con lo scopo di studiare i fenomeni di degrado mediante metodologie che portino all'identificazione dei diversi meccanismi di degrado coinvolti, responsabili del breve tempo di vita dei dispositivi. Il presente lavoro è stato sviluppato focalizzando l'attenzione sui vari meccanismi di degrado nei dispositivi OLED e sulla possibilità di utilizzare la loro natura per sviluppare metodi di analisi innovativi. A questo scopo è stato studiato sia il degrado estrinseco che quello intrinseco. Le criticità di questo studio sono la complessità dei fenomeni coinvolti e l’interesse relativamente recente che la comunità scientifica ha rivolto allo studio del degrado intrinseco. Nel lavoro di tesi, dopo una breve presentazione delle caratteristiche principali dell’ elettronica organica, è stata presentata dapprima una panoramica dei principi di base dei processi di permeazione e successivamente tipiche soluzioni di incapsulamento. In particolare, l’attenzione è stata focalizzata sui requisiti di barriera e sulle soluzioni per proteggere i dispositivi. Queste soluzioni, oltre ad essere il modo per controllare la degrado estrinseca, vengono anche utilizzati per isolare altre componenti di degrado diventando uno strumento per studiare il degrado intrinseco in dispositivi organici. È stata poi sottolineata l'importanza di poter valutare le prestazioni di materiali barriera in termini di WVTR e sono state presentate alcune soluzioni per la caratterizzazione di alte barriere alla permeazione di gas. Lo studio è stato poi centrato sulla progettazione e lo sviluppo di un Calcium Test per la valutazione di barriere alla permeazione di vapor d’acqua tenendo in conto tutti gli elementi che potessero garantire un livello maggiore di sensibilità. Questo metodo di misura è stato poi impiegato per la progettazione e ottimizzazione sia di un sistema di incapsulamento rigido su vetro e sia di un sistema di incapsulamento flessibile con la tecnica Thin Film Encapsulation. Nel primo caso (vetro su vetro) il sistema incapsulato sviluppato è stato utilizzato in in modo efficace per stimare il tempo di vita di una semplice struttura OLED e convalidare le prestazioni del sistema stesso. In seguito, le indagini si sono concentrate sul processo di degradazione intrinseca. A questo scopo il sistema di incapsulamento rigido è stato utilizzato anche per trascurare agenti esterni nell'ambito dello sviluppo di un metodo innovativo per lo studio dei vari fenomeni che concorrono al degrado intrinseco basato su condizioni ambientali di invecchiamento accelerato. Infine è stata proposta e testata su un caso studio una metodologia innovativa per studiare questo problema. Per raggiungere questo obiettivo è risultato molto importante separare la componente di degrado estrinseca da quella intrinseca così in questa tesi abbiamo lavorato sui seguenti argomenti raggiungendo risultati molto soddisfacenti: • valutazione attendibile delle barriere di permeazione tramite Calcium test elettrico • sistemi di incapsulamento rigido e flessibile • tempo di vita di dispositivi OLED in condizioni di invecchiamento accelerato • studio del degrado intrinseco: metodologia e applicazioni Per quanto riguarda il primo argomento un sistema di misura basato sul Calcium test elettrico è stato dapprima studiato, progettato e sviluppato tenendo conto ogni dettaglio che potesse portare ad un'alterazione risultato. Successivamente sono stati progettati e sviluppati sia un sistema di incapsulamento rigido su vetro sia un sistema di incapsulamento flessibile. Il sistema di misura tramite Calcium test è stato poi utilizzato per valutare le proprietà barriera dei sistemi di incapsulamento sviluppati rivelando valori di WVTR in linea con i risultati di letteratura ottenuti con le tecniche selezionate. In particolare è stato rilevato un valore di WVTR pari a 4 10-6 g m-2 day-1 e circa 10-2 g m-2 day-1 rispettivamente per il sistema vetro-vetro e quello flessibile. Riguardo al tempo di vita di dispositivi OLED, sono stati realizzati, incapsulati e caraterizzati nel tempo dispositivi su vetro utilizzando semplici strutture. I dispositivi realizzati dopo 3000 ore hanno perso solo 20% di luminanza rispetto al valore iniziale validando le prestazioni della soluzione di incapsulamento rigido sviluppata. Questo risultato se da un lato è molto incoraggiante per il tempo di vita dei dispositivi dall'altra parte rappresenta l'elemento chiave che permette di trascurare gli effetti esterni durante gli ulteriori studi sul degrado. I risultati ottenuti su questi argomenti sono risultati indispensabili per concentrarsi sul degrado intrinseco. Infatti utilizzando il nostro sistema di incapsulamento e l'applicazione di diverse tecniche sperimentali, non convenzionali, è stato possibile mettere in luce un singolo meccanismo di degrado intrinseco. In particolare, è stato deciso di concentrarsi su eventuali fenomeni che possono verificarsi durante i periodi di OFF-time (senza sollecitare elettricamente i campioni). Gli esperimenti sono stati condotti in diverse condizioni di conservazione su due tipi di OLED blu che rappresentano il caso peggiore in termini di stabilità. Questo studio ha rivelato, in condizioni che permettono di trascurare le altre fonti di degrado, che entrambi i tipi di dispositivi soffrono di un degrado di tipo fisico. Il metodo proposto in questo caso studio (condizioni ambientali di invecchiamento accelerato) combinato con altre condizioni di analisi (anche utilizzate comunemente) consente di studiare l'argomento degrado in modo più completo. [a cura dell'autore]
XIV n.s.

Ce travail porte sur l'étude de la dégradation accélérées des diodes électroluminescentes organiques (OLEDs) pour l'éclairage. Nous avons choisi d'étudier des OLEDs commerciales (Philips lumiblade GL55 et OSRAM Orbeos RMW-046) afin d'éliminer l'effet de l'humidité et de l'oxygène et ainsi que les processus de fabrication sur les mécanismes de dégradation. Une étude bibliographique préalable nous a permis de comprendre les mécanismes de fonctionnement des OLEDs et d'analyser les différentes causes de dégradations. Elle nous a également permis de définir des conditions de vieillissement accéléré (stress thermique et électrique) que nous avons appliquées à nos échantillons. Afin d'appliquer ces conditions de stress particulières, nous avons conçu et réalisé un dispositif expérimental spécifique qui nous permet à la fois d'appliquer ces différentes conditions de vieillissement et de réaliser des mesures électriques et optiques in situ. Ces mesures ont été réalisées avant dégradation, puis jusqu'à une perte de 50% du flux lumineux. L'évolution des caractéristiques électriques et photométriques des OLEDs ainsi que certaines analyses structurales complémentaires nous ont permis d'établir et de comprendre les mécanismes mis en jeu
This work reports on the study of accelerated ageing of white organic light-emitting diodes (OLEDs) for lighting. We chose to apply our study on commercial products (Philips lumiblade GL55 and OSRAM Orbeos RMW-046) to eliminate the moisture, oxygen and manufacturing process effects on the degradation mechanisms. A preliminary bibliographic study enabled us to understand the operation mechanism of the OLEDs and to analyze the different degradation causes. This one also allowed us to determine the accelerated ageing test conditions (thermal and electrical stresses). In order, to apply these particular stress conditions, we designed and realized a specific and custom-made experimental ageing bench which allows us at the same time to apply these various ageing conditions and carry out electrical and optical measurement in situ. These measurements were realized before degradations and then until a loss of 50% of the luminous flow. The evolution of the electrical and optical characteristics of the OLEDs as well as the results obtained from some additional structural analysis enabled us to establish and understand the involved mechanisms

In this work, three different classes of colour converting layers (CCLs) for the down-conversion of blue and green Organic Light Emitting Devices (OLEDs) have been developed. In Chapter 3, the dispersion of organic dyes into polymer matrices via solution processing and solid state methods is presented. Application of hybrid organic-inorganic fluorescent particles, composed of organic fluorescent molecules absorbed into porous supporting materials, is discussed in Chapter 4. This solution allows for the dispersion of the organic molecule into an otherwise non-miscible polysiloxane matrix and resulted in the discovery of unusual optical properties of one of the organic dye (fluorescein disodium salt). This peculiar emission has been studied in more detail during Chapter 5. In addition, the possible use of fluorescent nanodiamonds, produced by gamma radiation, as luminescent materials, has been investigated in Chapter 6.

This thesis presents the photophysical characterization and device performance of a series of small molecules and copolymers showing thermally activated delayed fluorescence (TADF). This triplet harvesting mechanism allows triplet states to contribute to the light generation process, thus increasing the efficiency of organic light emitting diodes (OLEDs). TADF based OLEDs with internal quantum efficiency (IQE) close to 100% have already been demonstrated. However, many aspects of the mechanism still remain unclear and need to be tackled in order to design novel and more efficient TADF molecules, with emission in different regions of the spectrum. In order to maximize the TADF mechanism in different organic systems, the interplay between the charge transfer state and local triplet excited states are studied in detail and it was found that the mixing of CT and local triplet states is essential to achieve efficient reverse intersystem crossing (RISC). The consequence of introducing bulky side groups on the D unit was also studied and the luminescence from these molecules varies from efficient TADF to strong phosphorescence at room temperature. Remarkably, in clear contrast with the donor substituted molecules, their acceptor substituted analogues are strong TADF emitters. Furthermore, the fine-tuning of TADF efficiency in copolymers was explored by using spacer groups in a range of polymeric structures, overcoming the theoretical IQE limit for pure fluorescent compounds in solution-processed OLEDs. Moreover, the contribution of TADF emission in Cu-complexes showing aggregated induced emission was studied to probe the effects of vibrations on the luminescence quenching in these complexes.

Organic light emitting diodes are polymer-based devices which promise higher efficiency and lower cost than other lighting devices, and will enable new applications which were not previously possible. An important component of OLEDs is the transparent conducting electrode (TCE), which is commonly indium tin oxide (ITO). It has a low sheet resistance (15 OD) and a high transmission (87 % on average in the visible wavelength range). However, it is also brittle, expensive and has issues from indium and oxygen migration into the polymer layers of the OLED. There are many alternatives that have been proposed to ITO, one of which is a nanometre thin metal grid. It has been shown to be flexible and if a cheap metal is used, then it can be a low cost solution. The sheet resistance can reach very low levels (e.g. 1 OD), and the transmission can be above 90 %. In this thesis, a thorough study is undertaken to investigate how the grid TCE affects the OLED. The grid TCE was optimised using a computer simulation. Then OLEDs were fabricated on them and characterised to investigate how their performance varies as the grid thickness increases. Surprisingly, it was concluded that the best TeE does not make the best OLED. Several possible reasons for this were considered. Grids with different line spacings were also tested and it was found that if the line spacing was too large, the light emission would not be uniform. To overcome this problem, small spacing grids or hybrid grid TCEs consisting of the metal grid and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) PHIOOO, or regioregular poly(3-hexythiophene) (P3HT) wrapped single-wall carbon nanotubes, were used. The OLEDs fabricated on the hybrid grid OLEDs had a luminance as high as the ITO OLED. These results demonstrated the feasibility of thin metal grids as an alternative for ITO, and will lead to better grid TCE design and optimisation for use in OLEDs.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas, Programa de Pós-Graduação em Física, Florianópolis, 2015.
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Complexos de metais de transição (MT) têm se mostrado promissores para aplicações eletro-ópticas devido a sua intensa emissão de luz resultante da mistura de estados excitados singleto e tripleto através do acoplamento spin-órbita (SOC), que teoricamente permite um rendimento quântico ( ) de 100%. Complexos utilizando Ir, Pt, Cu, Os e Ru são os emissores fosforescentes mais conhecidos com estas características e têm sido extensivamente estudados nos últimos anos, principalmente os complexos de Ru, que são de particular interesse devido à sua versatilidade e facilidade de modificações moleculares. Desta forma, este trabalho apresenta a síntese, caracterização e aplicação em estruturas de diodos orgânicos emissores de luz (OLEDs) de quatro complexos de Ru: dois conhecidos na literatura (Ru(Bpy)3 e Ru(Phen)3) e dois inéditos (Ru(TDZP)3 e Ru(PhenSe)3). Os compostos foram sintetizados a partir de uma rota simples já conhecida e de bom rendimento. A caracterização estrutural foi feita a partir da espectroscopia de infravermelho (IV), espectroscopia Raman, espectroscopia de ressonância magnética nuclear de H (RMN 1H) e espectrometria de massa de alta resolução (HRMS). As propriedades térmicas foram investigadas através da termogravimetria (TGA). As propriedades fotofísicas dos compostos em solução e filme, bem como o band gap (Eg) ótico e o rendimento quântico ( ), foram obtidos a partir da espectroscopia óptica UV-vis. As propriedades eletroquímicas e os níveis de energia (HOMO, LUMO e Eg) foram estimados a partir da voltametria cíclica (CV). A caracterização morfológica dos filmes finos produzidos via spin-coating foi feita com um microscópio de força atômica (AFM). Um comparativo interno permitiu observar que os complexos estudados apresentam características estruturais, térmicas, óticas, eletroquímicas e morfológicas semelhantes. Os filmes produzidos via spin-coating foram posteriormente empregados como camada emissora (EL) em diferentes estruturas de OLED, as quais foram caracterizadas em suas propriedades elétricas, óticas e radiométricas. Em geral, os dispositivos operaram em baixas tensões e exibiram uma banda larga de emissão no vermelho-alaranjado decorrente das transições de caráter MLCT, típica dos complexos de Ru. As estruturas de dispositivo que empregaram PVK como camada transportadora de buracos (HTL) mostraram valores de potência de radiação inferiores. Os complexos inéditos, ao contrário do que se esperava, também apresentaram baixos valores de potência de radiação em relação aos jáconhecidos. No intuito de compreender os resultados obtidos a partir dos mecanismos intrínsecos dos dispositivos, foram realizados estudos de mobilidade através da aplicação de um modelo teórico. Por fim, um breve estudo utilizando as estruturas de diodo produzidas demonstrou que os complexos inéditos apresentaram propriedades de fotocorrente e potencial para aplicações fotovoltaicas.

Abstract : Transition metal complexes (MT) have shown promising results for electro-optical applications due to their intense emission of light resulting from the mixture of singlet and triplet excited states through spin-orbit coupling (SOC), which theoretically allows quantum yield (F) of 100%. Complexes using of Ir, Pt, Cu, Os and Ru are the best known phosphorescent emitters with these characteristics and have been extensively studied in recent years, particularly the Ru complexes, which are of particular interest because of their versatility and facility for molecular changes. On this way, this study presents the synthesis, characterization and application on organic light emitting diodes (OLEDs) structures of four Ru complexes: two known in the literature (Ru (bpy)3 and Ru (phen)3) and two new (Ru (TDZP)3 and Ru (PhenSe)3). The compounds were synthesized from an already known simple route with good yield. Structural characterization was made from the infrared spectroscopy (IR), Raman spectroscopy, nuclear magnetic resonance spectroscopy NMR (NMR 1H) and high resolution mass spectrometry (HRMS). The thermal properties were studied by thermogravimetric analysis (TGA). The photophysical properties of the compounds in solution and film, as well as, the optical band gap (Eg) and the quantum yield (F), were obtained from optical UV-vis spectroscopy. The electrochemical properties and energy levels (HOMO, LUMO and Eg) were estimated by cyclic voltammetry (CV). The morphological characterization of thin films produced via spin-coating was made with an atomic force microscope (AFM). An internal comparison allowed us to notice that the studied complexes have similar structural, thermal, optical, electrochemical and morphological. The films produced via spin-coating were subsequently used as emitting layer (EL) in different OLED structures that were characterized in their electric, optical and radiometric properties. In general, the devices worked at low voltages and exhibited a wide emission band in the red-orange arising from the characteristic MLCT transitions, typical of Ru complexes. Device structures that employed PVK as hole transporting layer (HTL) showed lower radiation power values. The new complexes, contrary to what was expected, also had low radiation power values in relation to those already known. In order to understand the results obtained from the intrinsic mechanisms of the devices, studies of mobility were done by applying a theoretical model. Finally, a brief study using the diode structures produced showed that the newcomplexes exhibited photocurrent properties and potential for photovoltaic applications.

Este trabalho de tese apresenta novas evidências experimentais que ajudam no conhecimento atual das propriedades de transporte em semicondutores orgânicos, aprofundando o conhecimento dos processos de condução dependentes de spin em dispositivos eletrônicos baseados nestes materiais. O trabalho apresentado pode ser dividido em dois temas principais, o primeiro relacionado ao aumento das qualidades espectroscópicas da técnica de ressonância magnética detectada eletricamente (RMDE) por meio de um estudo da dependência do sinal vetorial de RMDE em função da freqüência do campo magnético de modulação. O segundo tema, encontrase relacionado aos efeitos de campos magnéticos externos na condutividade de semicondutores orgânicos. Através de uma análise de fase cuidadosa do sinal vetorial de RMDE foi demonstrado que o espectro de RMDE de diodos orgânicos emissores de luz (OLEDs) baseados em alumínio (III) 8-hidroxiquinolina (\'Alq IND. 3\') pôde ser separado em dois sinais componentes com fatores-g de: \'g IND. h\'= 2,007 e \'g IND. e\'= 2,0035. O espectro de RMDE de OLEDs baseados em \'Alq IND. 3\' foi atribuído ao processo de formação de éxcitons, e os sinais componentes foram atribuídos ao par precursor do éxciton, um à ressonância em ânions de \'Alq IND. 3\', enquanto que o outro a estados catiônicos no \'Alq IND. 3\'. Foi demonstrado que a utilização de diferentes freqüências de modulação de campo magnético aumenta a resolução temporal do sistema de detecção de RMDE, não influenciando os valores dos parâmetros espectroscópicos dos sinais. Desta forma, foi observado que os sistemas ou processos dependentes de spin diferentes que dão origem ao sinal de RMDE de OLEDs baseados em \'Alq IND. 3\', têm uma diferença entre os tempos de resposta menor que 6.0 x \'10 POT. -7\'s. Neste trabalho se propõe um modelo de circuito para simular a origem do sinal de RMDE de OLEDs baseados em \'Alq IND. 3\'. Os resultados deste modelo têm uma grande concordância com os resultados experimentais, observando-se que os dois sistemas ou processos de spin diferentes que dão origem ao sinal, podem ser representados por uma combinação paralela de capacitâncias e \"resistores\" que tomam a forma de funções gaussianas em condições de ressonância magnética. A generalidade deste modelo indica que ele poderia ser utilizado em outros problemas de transporte dependentes de spin de outros dispositivos eletrônicos orgânicos, inorgânicos ou híbridos (inorgânico-orgânico). Resultados de estudos de RMDE de OLEDs baseados em \'Alq IND. 3\', dopados e não dopados, em baixas temperaturas (até 100 K), mostraram que no OLED dopado com rubreno pode existir um mecanismo de formação de éxcitons similar ao já observado para o OLED dopado com DCM-TPA, indicando que o mecanismo de formação de éxcitons no OLED dopado com rubreno seria uma reação direta entre um elétron no \'Alq IND. 3\' com um buraco aprisionado no dopante. Foram observados efeitos do campomagnético na condutividade de dispositivos baseados em semicondutores orgânicos demonstrando a ocorrência do fenômeno de magneto-resistência (MR) em dispositivos orgânicos e híbridos (orgânico-inorgânico). Estes estudos mostraram que a melhor forma de detecção destes efeitos é através do monitoramento da resistência em função do tempo sob a aplicação de campos magnéticos externos. Para os dispositivos baseados em \'Alq IND. 3\', OLEDs dopados e não dopados e um dispositivo e-only, foi observada somente MR negativa, enquanto que para um dispositivo h-only foi observado um novo efeito quase constante e positivo. Para campos magnéticos aplicados de até 1 T, os dispositivos unipolares mostraram baixos efeitos de campo magnético na condutividade alcançando MR de até 0,08%, enquanto que os OLEDs mostraram efeitos maiores alcançando MR de até 3,2%. Apesar do mecanismo exato que origina os efeitos de campo magnético na condutividade de semicondutores orgânicos ainda permanecer desconhecido, os resultados apresentados neste trabalho indicam que este fenômeno não está relacionado com a formação de éxcitons.
This thesis presents new experimental evidences that can improve the current knowledge of the transport properties in organic semiconductors, particularly the spin dependent conduction processes in electronic devices based in those materials. This work can be divided in two main subjects, the first one related to the increasing in the spectroscopic qualities of the electrically detected magnetic resonance (EDMR) technique and the second one related to the external magnetic field effects in the conductivity of the organic semiconductors. Using a careful phase analysis of the vectorial EDMR signal it was demonstrated that the aluminium (III) 9-hydroxyquinoline (\'Alq IND. 3\')-based organic light emitting diodes (OLEDs) spectrum cam be separated in two component signais with different g-factors: \"G IND. h\'= 2,007 and \'g IND. e\'= 2,0035. The EDMR spectrum of \'Alq IND. 3\'-based OLEDs was attributed to the exciton formation process and the component signals were attributed to the resonance in \'Alq IND. 3\' anions (electrons) and in cationic states (holes) into \'Alq IND. 3\'. It was demonstrated that the use of different magnetic field modulations frequencies (MFMF) improves the temporal resolution of the EDMR system detection. It observed that the difference in the lifetime of the two EDMR signal components is smaller than 6.0x\'10 POT -7\'s. We proposed a novel circuit model to explain the observed EDMR signals. Results from this model are in agreement with the experimentalresults showing that the EDMR signal of \'Alq IND. 3\'-based OLEDS comes fromtwo different spin systems that can be represented by a parallel combination of capacitance and resistances which acquires a Gaussian form is magnetic resonance conditions. The simplest circuit model indicates that it can be used in other spin-dependent transport problems of different electronic devices (organic, inorganic or hybrid) studied by EDMR experiments. Results from a EDMR investigation of the effects of dye doping on spin dependent exciton formation in \'Alq IND. 3\'-based OLEDs at low temperatures (up to 100 K) showed that the Rubrene dye doped \'Alq IND. 3\'-based OLEDs presents a similar mechanism for exciton formation that the DCM--TPA doped OLED indicating that the recombination occurs by a direct reaction between an electron in the \'Alq IND. 3\' and a hole into the dopant. Magnetic field effects in the conductivity of organic semiconductors based devices were observed, showing the existence of the magnetoresistance (MR) phenomena in both organic and hybrids (organic-inorganic) devices. The studies showed that the best way to detect this effects is by monitoring the resistance as a function of time under the application of different magnetic field pulses. Only negative magnetoresistance was observed for the \'Alq IND. 3\'-based devices: undoped and dye doped OLEDs and an electron only device. A very small, positive and almost constant MR was observedin the hole-only device. For the unipolar devices were observed small magnetic field effects in the conductivity reaching a MR= 0.08%. The OLEDs showed bigger effects reaching a MR= 3.2%. Despite the exact mechanism that origins the magnetic field effects in the conductivity of organic semiconductors remains unknown the results presented in this thesis indicates that this phenomena is not related to the exciton formation.

A presente tese de doutorado apresenta um estudo comparativo das características elétricas de dispositivos emissores de luz poliméricos (PLEDs) confeccionados com óxido de índio dopado com zinco (IZO) como eletrodo transparente alternativamente ao ITO comumente usado em dispositivos poliméricos. As propriedades elétricas de filmes de IZO depositados a frio foram obtidas através da técnica de impedanciometria. Descrevemos detalhadamente todo o processo de fabricação dos dispositivos, com os respectivos eletrodos, em estrutura simples ou contendo uma camada adicional de PEDOT. Dois polímeros luminescentes foram utilizados como camada ativa em nossos dispositivos: MEH-PPV e uma blenda de derivados de Polifluoreno. Nossos resultados mostram que o IZO apresenta todas as características para substituir o ITO enquanto anodo transparente em dispositivos optoeletrônicos poliméricos. Realizamos estudos detalhados das propriedades elétricas de dispositivos fabricados com MEH-PPV e com blendas de derivados de polifluorenos, com ITO ou com IZO e com ou sem camada intermediária de PEDOT, e para isso usamos as técnicas de medida estacionária (J-V) e alternada (impedanciometria). Os resultados foram analisados à luz dos modelos de injeção de Arkhipov, para resposta estacionária, e de circuitos equivalentes e de Dyre para espectroscopia em freqüência. Ao modelo de Arkhipov, adicionamos um termo de corrente de tunelamento que melhorou o ajuste para região de campos altos. Dos ajustes teórico-experimentais obtivemos importantes parâmetros dos dispositivos.
In this thesis we presented a detailed study of polymer light-emitting diodes (PLEDs) made with IZO as transparent electrode alternative to ITO. The electrical properties of thin film of IZO were studied by impedance measurements. Measurements with devices containing an additional transport layer of PEDOT were also performed. We used two different thin polymeric films for such studies: the MEH-PPV and a blend made by two polyfluorene derivatives. We also carried out a detailed investigation of several devices, making use of two techniques: by stationary J-V and by impedance measurements. The results were analyzed by the Arkhipov model (for stationary results), and by equivalent circuits and Dyre´s model for the spectroscopic results. We introduced an additional term of tunneling effect to the Arkhipov model, which improved the theoretical fitting over the experimental results at high fields. From the fittings we obtained important parameters of the produced devices.

Organic semiconductors (OSCs) present an electron mobility lower by several orders of magnitude than the hole mobility, giving rise to an electron-hole charge imbalance in organic devices such as organic light-emitting diodes (OLEDs) and organic light-emitting transistors (OLETs). In this thesis project, I tried to achieve an efficient electron transport and injection properties in opto-electronic devices, using inorganic n-type metal oxides (MOs) instead of organic n-type materials and a polyethyleneimine ethoxylated (PEIE) thin layer as electron transport (ETLs) and injection layers (EILs), respectively. In the first part of this thesis, inverted OLEDs were fabricated in order to study the effect of the PEIE layer in-between ZnO and two different emissive layers (EMLs): poly(9,9-dioctylfluorene-alt-benzothiadiazole) polymer (F8BT) and tris(8-hydroxyquinolinato) aluminum small molecule (Alq3), based on a solution and thermal evaporation processes, respectively. Different concentrations (0.80 %, 0.40 %) of PEIE layers were used to further study electron injection capability in OLEDs. After a series of optimizations in the fabrication process, the opto-electrical characterization showed high-performance of devices. The inverted OLEDs reported a maximum luminance over 104 cd m-2 and a maximum external quantum efficiency (EQE) around 1.11 %. The results were attributed to the additional PEIE layer which provided a good electron injection from MOs into EMLs. In the last part of the thesis, OLETs were fabricated and discussed by directly transferring the energy modification layer from OLEDs to OLETs. As metal oxide layer, ZnO:N was employed for OLETs since ZnO:N-based thin film transistors (TFTs) showed better performance than ZnO-based TFTs. Finally, due to their short life-time, OLETs were characterized electrically but not optically.

Organic Light Emitting Diodes (OLEDs) have become attractive for flat panel display industry, with applications ranging from mobile phone screens to TVs. They have several advantages over inorganic LEDs such as high contrast ratio, wide viewing angle, faster response time, scalable large area processing and most importantly mechanical flexibility. OLEDs on flexible substrates can endure certain level of mechanical deformation such as bending, rolling or folding without disruption of the performance. The current demonstrated flexibility for OLEDs is up to a few centimeters or millimeters bending radius, depending on the materials, substrates and device structures. More flexible OLEDs with bending radius of curvature on the order of microns will be needed for applications in wearable, roll-up, or foldable displays and bezel-free screens and flexible signage systems. This thesis presents the design, fabrication and characterization of highly flexible and foldable top-emitting OLEDs made on 50 micron thick polyimide (PI) plastic substrates, which can achieve approximately 200 microns bending radius of curvature (folding) without visible damage or impact on emission brightness and uniformity. To the best of our knowledge these are the most flexible phosphorescent OLEDs and first foldable OLEDs ever reported. We believe such flexibility is the benefit of the mechanical stability and low film thickness of the PI substrate. The surface roughness of PI had been the major limitation of its application as OLED substrates, and in this thesis a special side-angle evaporation method is proposed to improve the step coverage of deposited thin films of materials on PI without the requirement of buffer layers. The same method is also proved to be applicable for fabricating OLEDs on much rougher substrates such as Scotch tapes, and fiberglass and transparency sheets. The OLEDs fabricated on above substrates are also presented and characterized.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

Large area OLEDs show pronounced Joule self-heating at high brightness. This heating induces brightness inhomogeneities, drastically increasing beyond a certain current level. We discuss this behavior considering 'S'-shaped negative differential resistance upon self-heating, even allowing for 'switched-back' regions where the luminance finally decreases (Fischer et al., Adv. Funct. Mater. 2014, 24, 3367). By using a multi-physics simulation the device characteristics can be modeled, resulting in a comprehensive understanding of the problem. Here, we present results for an OLED lighting panel considered for commercial application. It turns out that the strong electrothermal feedback in OLEDs prevents high luminance combined with a high degree of homogeneity unless new optimization strategies are considered.

Mestrado em Engenharia Física
Neste trabalho foram fabricados e caracterizados díodos orgânicos emissores de luz (OLEDs) à base de Európio em estruturas multicamada. A caracterização eléctrica e óptica foi efectuada em função da espessura da camada emissiva de Európio e envolveu as curvas corrente – potencial aplicado, potência óptica, rendimento e electroluminescência. Os resultados mostraram a possibilidade de se construir um dispositivo eficiente com baixas correntes eléctricas e elevados rendimentos ABSTRACT: In this work Organic Light Emitting Diodes (OLEDs) based on Europium have been build and characterized. The electrical and optical characterization has been carried out using current – applied voltage curves and optical power, efficiency and electroluminescence. The final result shows that it is possible to use europium complex to build efficient devices with low electrical current and high efficiencies.

Mestrado em Engenharia Física
Díodos orgânicos emissores de luz (OLEDs) são dispositivos eletroluminescentes baseados em materiais orgânicos que inerentemente se degradam quando em funcionamento quando expostos às condições ambientais normais. Este trabalho consistiu no desenvolvimento e construção de um protótipo de um sistema de encapsulamento automatizado para os OLEDs fabricados no Departamento de Física da Universidade de Aveiro (DFUA) com o objetivo de prolongar o seu tempo de vida para fins de investigação. O principal constrangimento deste projeto foi a limitação de gastos imposta ao projeto. O sistema teria que ser construído utilizando ao máximo componentes existentes da reciclagem de equipamentos eletrónicos e informáticos fora de uso, da utilização de materiais reaproveitados e técnicas de construção de baixo custo. Outra das condições impostas foi a possibilidade de utilizar o sistema desenvolvido dentro de uma caixa de luvas com atmosfera de azoto, pelo que se pretendia que a operação do equipamento exigisse o mínimo envolvimento do operador. Tendo em conta os fatores de degradação extrínsecos, o design dos OLEDs de uma forma geral e em particular dos construídos no DFUA, e os métodos de encapsulamento existentes no mercado e possíveis de implementar com os constrangimentos referidos, desenvolveu-se e construiu-se um protótipo em conformidade. Este sistema realiza o encapsulamento por colagem e vedação lateral, utilizando uma resina epoxy apropriada, de um vidro de proteção aplicado sobre o substrato, isolando as várias camadas de construção do OLED do meio ambiente. Todo o controlo do sistema de encapsulamento é feito remotamente num software desenvolvido para o efeito. Com o sistema construído foram realizados vários ensaios para determinar os melhores parâmetros de funcionamento e otimizar as condições do encapsulamento. O protótipo desenvolvido permite encapsular diversos formatos e dimensões de OLEDs com uma intervenção mínima do operador, possuindo a precisão de posicionamento necessária para a realização do encapsulamento nas condições pretendidas.
Organic light emitting diodes (OLEDs) are electroluminescent devices based on organic materials which inherently degrade when in operation when exposed to normal environmental conditions. This work consisted on the development and construction of a prototype of an automated system for encapsulating OLEDs manufactured in the Department of Physics, University of Aveiro (DFUA) in order to prolong their operating lifetime for research purposes. The main constraint of this project was the limitation imposed on the project budget. The system would have to be built maximizing the use of recycled electronic and computer out of use components and also using low cost construction techniques. Another condition was imposed on the possibility of using the system developed inside a glove box with nitrogen atmosphere, and it is intended that the operation of the equipment require minimal operator involvement. Considering the extrinsic degradation factors; the design of OLEDs in general and the ones manufactured in DFUA, in particular; and the methods of encapsulation on the market that are possible to implement with the specified constraints, a prototype was developed and built accordingly. This system performs encapsulation by lateral sealing and bonding, using a suitable epoxy resin, of a protective glass applied on the substrate, insulating layers of the OLED construction from the environment. The control of the entire encapsulation system is done remotely with specific software developed in this project for this purpose. With the system build, several tests were performed to determine the best operating parameters to optimize the conditions of encapsulation. The prototype allows to encapsulate many different shapes and dimensions of OLEDs with minimal operator intervention, having the positioning accuracy required to achieve the desired conditions of encapsulation.

Phosphorescent organic light emitting diodes (PHOLEDs) based on efficient electrophosphorescent dopant, platinum(II)-pyridyltriazolate complex, bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II) (Pt(ptp)2) have been studied and improved with respect to power efficiency, external efficiency, chromacity and efficiency roll-off. By studying the electrical and optical behavior of the doped devices and functionality of the various constituent layers, devices with a maximum EQE of 20.8±0.2 % and power efficiency of 45.1±0.9 lm/W (77lm/W with luminaries) have been engineered. This improvement compares to devices whose emission initially could only be detected by a photomultiplier tube in a darkened environment. These devices consisted of a 65 % bis[3,5-bis(2-pyridyl)-1,2,4-triazolato]platinum(II) (Pt(ptp)2) doped into 4,4'-bis(carbazol-9-yl)triphenylamine (CBP) an EML layer, a hole transporting layer/electron blocker of 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), an electron transport layer of 1,3,5-tris(phenyl-2-benzimidazolyl)-benzene (TPBI), and a LiF/Al cathode. These devices show the acceptable range for warm white light quadrants and qualify to be called "warm white" even w/o adding another emissive layer. Dual EML devices composed of neat Pt(ptp)2 films emitting orange and CBP: Pt(ptp)2 film emitting blue-green produced a color rendering index (CRI) of 59 and color coordinates (CIE) of (0.47,0.49) at 1000Cd/m² with power efficiency of 12.6±0.2 lm/W and EQE of 10.8±0.2 %. Devices with two blue fluorescent emission layers as singlet filters and one broad yellow emission layer from CBP: Pt(ptp)2 displayed a CRI of 78 and CIE of (0.28,0.31) at 100Cd/m² with maximum power efficiency of 6.7±0.3 lm/W and EQE of 5.7±0.2 %.

Ein vielversprechendes Design für organische lichtemittierende Dioden (OLEDs) verwendet eine Wirt-Gast-Strategie durch Dispergieren einer kleinen Menge eines hocheffizienten Emitters (der Gast) in eine passende Transportmatrix (der Wirt). Die Aufgabe des Wirts ist den Exzitonentranport zum Emitter sicherzustellen und den Zerfall von Triplet-Exzitonen zu verhindern, und damit eine hohe Bauteilperformance zu erreichen. Die vorliegende Arbeit konzentriert sich auf die Beziehung zwischen Molekülstruktur und optoelektrischer Eigenschaften von Carbazol/Dibenzothiophen-Derivaten. Die Untersuchung umfasst sieben dieser Derivate für den Wirt, bei denen die Carbazoleinheit als Donator und die Dibenzothiopheneinheit als Akzeptor fungiert, wobei beide durch einen oder mehrere Phenylabstandshalter verbunden sind. Diese Wahl der Wirtsmaterialien erlaubt es den Einfluss der erweiterten Phenylabstandshalter und der unterschiedlichen molaren Verhältnisse von Akzeptor zu Donator zu untersuchen. Es ergab sich, dass eine kürzere Phenylabstandshalterlänge die Bauteilperformance durch eine größere Löcher- und Elektronendichte in der Emitterschicht verbessert; und ein 1:1 Carbazol-zu-Dibenzothiophen-Verhältnis der Bauteilperformance zuträglich ist, da es zu einem Ladungsträgergleichgewicht in der Emitterschicht führt. Diese Arbeit zeigt, unter Verwendung dieser Wirtsmaterialien, blaue FIrpic-basierte phosphoreszierende OLEDs (PhOLEDs) und grüne 4CzIPN-basierte thermisch aktivierte verzögerte Phosphoreszenz (TADF) OLEDs. Die blauen PhOLEDs und grünen TADF OLEDs mit mDCP zeigten Effizienzen von 43 cd/A (18.6%) beziehungsweise 66 cd/A (21%).
A particularly interesting organic light-emitting diodes (OLEDs) design adopts a host-guest strategy by dispersing a small amount of highly efficient emitter (the guest) into an appropriate transport matrix (the host). The host is utilized to transfer excitons to the emitter and to prevent triplet exciton quenching, thus high device performance can be achieved. The present thesis focuses on the relationship between the molecular structure and opto-electrical properties of carbazole/dibenzothiophene derivatives. The investigation encompasses seven of these derivatives for the host, in which the carbazole unit acts as a donor and the dibenzothiophene as an acceptor while they are linked through phenyl spacer(s). This choice of host materials enables to assess the impact of extended phenyl spacers and different acceptor to donor molar ratios. It was found that decreasing the phenyl spacer length enhances the device performance due to the larger both hole and electron densities in the emitting layer; and a 1:1 carbazole to dibenzothiophene ratio is favorable for device performance, since it balances the charge carriers in the emitting layer. Using these host materials, the work presented in this thesis demonstrates high-performance blue FIrpic-based phosphorescent OLEDs (PhOLEDs) and green 4CzIPN-based thermally activated delayed fluorescence (TADF) OLEDs. The blue PhOLEDs and green TADF OLEDs with mDCP showed efficiencies of 43 cd/A (18.6%) and 66 cd/A (21%), respectively.

Este trabalho tem como principais objetivos: desenvolver procedimentos sintéticos e novos materiais poliméricos que apresentem boa condutividade elétrica, estudar o comportamento eletro-óptico dos polímeros obtidos, desenvolver procedimentos para a construção de dispositivos eletroluminescentes, caracterizá-los e correlacionar as características eletro-ópticas observadas com a constituição da camada ativa polimérica. Foram realizadas diversas sínteses objetivando a preparação de polifluorenos com diferentes estruturas químicas a partir de monômeros difuncionais aromáticos boronados e bromados, utilizando uma mesma rota de acoplamento de Suzuki. Assim, foram preparados três polímeros, poli[2,7-(9,9-dioctilfluoreno)] (PF, polifluoreno), poli[1,4-fenileno-alt-2,7- (9,9-dioctilfluoreno)] [PFP, poli(fluoreno-fenileno)] e poli[(1,4-fenileno-2-flúor)-alt-2,7-(9,9- dioctilfluoreno)] [PFPF, poli(fluoreno-fenileno)fluorado]. Para obtenção destes polifluorenos com bom rendimento e com pureza adequada para a preparação de dispositivos poliméricos eletroluminescentes, foi necessário testar diversas condições de reação, até a otimização de um procedimento sintético robusto. Os polifluorenos preparados foram exaustivamente purificados por extração e solubilização-precipitação. Todos os polifluorenos tiveram a sua estrutura e composição químicas caracterizadas e confirmadas pelas técnicas de espectroscopia no infravermelho (FTIR), espectroscopia de ressonância magnética nuclear de hidrogênio (¹HNMR) e espectroscopia de energia dispersiva de raios-X (EDX). As massas molares médias e a polidispersão foram determinadas por cromatografia de permeação em gel (GPC). Soluções em clorofórmio dos polifluorenos foram analisadas por espectroscopias de absorção e emissão no UV-Vis. Estes resultados nos forneceram informações importantes quanto às propriedades de fotoluminescência dos polifluorenos obtidos. Até o momento, sabe-se que todos os três polímeros emitem cor azul e dentre as três estruturas estudadas, o PFPF apresentou maior intensidade de fluorescência. Para a fabricação dos P-OLEDs (Diodos Orgânico-Polimérico Emissor de Luz) foram feitas soluções de clorofórmio em concentrações de 1% dos três tipos de polímeros. Também foi estudada a influência dos compostos ETL (electron transport layer) (Alq3 ou butyl-PBD) com concentrações de 0,5%. Quando aplicada uma tensão no dispositivo, o PFPF apresentou menor tensão de operação entre os polímeros estudados. A partir das curvas de tensão vs. corrente, verificou-se que a adição do butyl-PBD nos três tipos de polímeros diminui a tensão de limiar em comparação com os dispositivos sem composto ETL. Os comprimentos de onda de eletroluminescência dos dispositivos polarizados permaneceram constante mesmo com a adição dos dois compostos ETL (Alq3 ou butyl-PBD).
This work has as main objectives: develop synthetic procedures and new electroluminescent polymeric materials that have good electrical conductivity, study the behavior of polymer systems thus obtained, and develop procedures for the construction of electroluminescent devices, characterize them and correlate the photo- electrical behavior with the features of the constitutive active polymeric layer Several syntheses were performed aiming at preparing polyfluorenes with different structures from boronated and brominated difunctional aromatic monomers using a Suzuki coupling route. So far, three polymers were prepared, poly[2,7-(9,9-dioctylfluorene)] (PF, polyfluorene), poly[1,4-phenylene-alt-2,7-(9,9-dioctylfluorene)] [PFP, poly(fluorenephenylene)] and poly[1,4-phenylene-2-fluoro)-alt-2,7-(9,9-dioctylfluorene)] [PFPF, fluorinated poly(fluorene-phenylene)]. To obtain these polyfluorenos with good yield and purity suitable for preparing polymeric electroluminescent devices, it was necessary to test various reaction conditions and to optimize a robust synthetic procedure. The polyfluorenes prepared were thoroughly purified by extraction and solubilization-precipitation. All polyfluorenes have had their structures and chemical composition characterized and confirmed by infrared spectroscopy (FTIR), and hydrogen and carbon-13 nuclear magnetic resonance spectroscopy (¹HNMR and 13CNMR). The average molar masses and polydispersity were determined by gel permeation chromatography (GPC). Polyfluorenes in chloroform solutions were analyzed by the UV-Vis absorption and emission spectroscopy. These results provided us with important information regarding the photoluminescence properties of polyfluorenes thus obtained. Until now, it is known that all three polymers emit in the blue region and among the three structures, the PFPF has the highest fluorescence intensity. The construction of PLEDs was carried out from the chloroform solutions at concentrations of 1% for each of the all three types of polymers. The influence of an ETL (electron transport layer) compound (Alq3, PBD) was also studied, and its concentration was kept constant at 5% in the polymer solution. Tests of the devices under applied voltage have shown a higher stability for PFPF among all. From the voltage vs. current curves, it was possible to observe that the addition of PBD decreased the threshold voltage for the devices prepared from the three types of polymers. The wavelength of electroluminescence remained constant despite the addition of the ETL compound (Alq3 or butyl-PBD).

Voici maintenant plus de 20 ans naquirent les premières diodes électroluminescentes à base de semi conducteurs organiques, usant soit de petites molécules (OLED), soit de polymères conjugués (PLED). A ces travaux pionniers, succédèrent de nombreuses recherches qui permirent d’améliorer notablement les performances de telles structures, tant en termes de rendements, de stabilité, que de couleur. Leur commercialisation fut alors possible. Le présent travail contribue à conforter, voire à amplifier la part des Oleds sur le marché des afficheurs. Il consiste à réaliser des Oleds à émission blanche ou presque blanche visant à être intégrée à un afficheur de taille réduite. Aussi, avons-nous préalablement recensées les diverses architectures émissives créant une émission blanche. Leurs inconvénients et avantages respectifs nous ont convaincus d’adopter une structure comportant trois zones émissives, configuration satisfaisant au mieux notre cahier des charges initial. Afin d’isoler et de pallier aux diverses difficultés de réalisation, nous avons scindé notre raisonnement en trois étapes. La première vise à identifier les paramètres structuraux influençant l’émission blanche, et à quantifier leur impact. Afin de s’affranchir des effets optiques et des difficultés de dépôt induits des substrats, nous n’avons ici considéré que les diodes à émission dirigée vers le substrat, devant par nécessité être transparent. La seconde étape consiste à évaluer les modulations du spectre émissif dues aux effets optiques du multicouche qui compose la diode. Nous restreignons cette fois nos investigations aux structures à émission dirigée vers l’électrode supérieure, mais pourvue d’une anode très réflective. L’ultime travail traite de l’intégration de l’Oled à émission extraite par l’électrode supérieure au substrat de l’afficheur. Ce-dernier, de part ses caractéristiques optiques et topographiques, nécessite des optimisations spécifiques. Un effort tout particulier fut porté sur sa planarisation
More than twenty years ago were born the first electroluminescent devices based on organic semiconductors, using small molecules (OLED) or conjugated polymers (PLED). Since these pioneering works, many studies have been realized to improve the device performances, in terms of efficiencies, stability and colour. Their marketing has so been possible. The present work aims at strengthening and spreading out the Oled part on lighting market. It consists in realizing a highly efficient white or nearly white organic light emitting diode for a micro display application. So, we firstly made an inventory of the different emitting configurations inducing a white emission. Their own drawbacks and advantages convince us to focus on three-emitting-layer structure, this one that better satisfies our initial requirements. In order to identify and solve the difficulties of realization, we have divided our logic into three parts. The first one helped to identify the structural parameters acting in white emission, and evaluate their effects. In order to annihilate the optical effects and problems due to substrates, we here only considered bottom emitting devices, whose substrate is obviously transparent. The second work consisted in recording variations of the emissive spectrum due to cavity effects. We here focused on to top emitting device, whose anode is highly reflective. The last works aimed at integrating a top emitting device to a substrate induced from the final micro display. Its optical and topographic properties involved specific optimizations. A particular attention is paid to the planarisation of the substrate

Mestrado em Engenharia Física
Neste trabalho foi desenvolvido um emissor W-OLED (white organic light emitting diode) para aplicações em iluminação genérica, recorrendo a dois materiais orgânicos emissores em cores complementares, NPB (N,N′-Bis (naphthalen-1-yl)-N, N′-bis(phenyl)benzidine) e DCM1 (4-(Dicyanomethylene)- 2-methyl-6-(4-dimethylaminostyryl)-4H-pyran), o primeiro emissor na região do azul-verde e o segundo na região vermelha do espectro eletromagnético. Foi feito um estudo do desempenho para diferentes espessuras da camada ativa em dois tipos de substratos: rígido (vidro) e flexível (PET). Os dispositivos foram caracterizados no seu comportamento corrente – tensão, espectro de eletroluminescência, coordenadas de cor, luminância e eficiência luminosa. Foi feito um estudo complementar do TCO usado como contacto, tanto no vidro como no PET. O melhor resultado foi obtido para 400Å espessura da camada ativa, tanto em substrato de vidro como PET. Em substrato de vidro obteve-se uma luminância máxima de 351,5 Cd/m2 e coordenadas de cor x=0.335 y=0.408.
We have developed a W - OLED (organic light emitting diode white) for general lighting applications, using two organic materials emitting in complementary colors, NPB (N,N' - Bis(naphthalen-1-yl)-N, N'-bis(phenyl)benzidine) and DCM1 (4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran), the first emitter in the blue-green region and the second in the red region of the electromagnetic spectrum. A study of the performance for different thicknesses of the active layer was made on two types of substrates: rigid (glass) and flexible (PET). The devices were characterized in their current-voltage behavior, electroluminescence spectrum, color coordinates, luminance and luminous efficiency. An additional study was made on TCO used as contact, on glass and on PET. The best result was obtained for 400Å thickness of the active layer in both glass and PET substrates. In the glass substrate was obtained 351.5 Cd/m2 maximum luminance and color coordinates x=0.335 y=0.408.

The majority of research on Organic Light-Emitting Diodes (OLEDs) has focused on a top-cathode, conventional bottom-emitting architecture. Yet bottom-cathode, inverted top-emitting OLEDs offer some advantages from an applications point of view. In this thesis, the development of high performance green electroluminescent inverted top-emitting diodes is first presented. The challenges in producing an inverted structure are discussed and the advantages of high efficiency inverted top-emitting OLEDs are provided. Next, the transition to a stacked architecture with separate orange and blue emitting layers is demonstrated, allowing for white emission. The pros and cons of the existing device structure is described, with an eye to future developments and proposed follow-up research.

Depuis quelques années, un essor important est observé pour les diodes électroluminescentes organiques (OLEDs) se traduisant par une intégration progressive dans de nombreux appareils électroniques destinés au grand public : smartphones, tablettes tactiles, téléviseurs, … Cependant, malgré de nombreux avantages, la haute sensibilité des empilements organiques à l'atmosphère ambiante, et l'observation de dégradations à la surface des dispositifs, sont les causes principales limitant l'utilisation massive de cette technologie. L'encapsulation des dispositifs à l'aide d'empilements barrières est susceptible de résoudre tout ou en partie ces problèmes, L'objectif de cette thèse est de développer et de caractériser de nouveaux empilements multicouches inorganique-organique barrières à l'humidité et à l'oxygène, afin de maintenir les performances des OLEDs le plus longtemps possibles. Des solutions d'encapsulations couches minces, réalisées directement à la surface des dispositifs, ont été développées et évaluées sur OLEDs. Les empilements sont composés d'une alternance entre un film d'oxyde d'aluminium déposé par ALD (Atomic Layer Deposition) et une couche de résine organique. Les empilements OLEDs utilisés étant fragiles, les dépôts ont été effectués dans des conditions douces, notamment à basse température (T < 100 °C). Parallèlement, une méthode de caractérisation des propriétés barrières a été mise en place, afin d'évaluer les performances intrinsèques des différentes couches ou empilements d'encapsulation utilisés, et apporter une compréhension sur le mécanisme de protection
Over the last few years, a significant growth is observed for OLEDs (Organic Light-Emitting Diodes) resulting in the gradual integration into many electronic devices for mass-market applications: smartphones, touchscreen tablet, TV … However, despite many advantages, the high sensitivity of the organic stacks in ambient atmosphere, and the surface degradation of the devices, are the main causes limiting the massive use of this technology. The encapsulation of the devices thanks to barrier multilayers can solve some or all these problems. The aim of this thesis is to develop and to characterize new inorganic-organic multilayers as a barrier against moisture and oxygen, in order to preserve OLEDs performances. Solutions for the thin layer encapsulation, made directly in the surface of the devices, have been developed and evaluated on OLEDs. The encapsulation stacks are based on alternating between a film of aluminum oxide deposited by ALD (Atomic Layer Deposition) and a layer of organic resin. Stacks of OLEDs are fragile, and the deposits have been carried out under mild conditions, especially when temperatures are low (T < 100 °C). A the same time, a method for the characterization of the barrier properties has been carried out, in order to evaluate the intrinsic performances of thin films or encapsulation stacks used, and to provide an understanding of the protection mechanism

Over the last three decades, the performance of OLEDs has been improved rapidly, however, as an important assessment for OLED, the EQE data are still quite low. As outlined in the theoretical background, the EQE is the product of out-coupling efficiency and internal quantum efficiency (IQE). Therefore, this thesis focuses on designing two types of polymers with different optical functionalities, to increase the EQE addressing the two aforementioned determining factors. Thus, the first part of the thesis addresses the light out-coupling efficiency in OLED devices. Here high refractive index (HRI) polymers are aimed for as potential material for the out-coupling layer, which are so far scarily reported for application in OLED devices, due to existing limitations, such as limited transparency, extra fluorescence, tedious synthesis, poor thermal stability and low solubility. However, if suitable polymers are becoming easily available, they will offer the unique advantage, compared to low molar mass HRI compounds, of being able to using cost-effective solution based technology for large area film preparation. In addition, polymeric materials will allow to introducing fully new concepts for increasing the light-out-coupling efficiency, like patterning allowing micro-lens preparation, or the incorporation of light scattering particles into the out-coupling layer. The approach described in this thesis is based on a previous work where HRI polymers were prepared via metal-free thiol-yne “A2+B3” polyaddition reaction, which led in an easy one-pot synthesis to hyperbranched polyvinylsulfides of high solubility and already reasonable high RI. For further increasing RI, in this work B3 as well as finally A2 monomers with high naphthalene content were chosen which should, in addition to the positive effect of the sulfur-containing units, render polymers with even higher RI, and hopefully also of high solubility due to the branching. A challenging aspect of this work was to find reaction conditions which allow the preparation of high molar mass as well as highly soluble, highly aromatic polymers by that A2+B3 approach, even so very sterically demanding monomers are used. In addition, the material properties should be fine-tuned by careful selection of the monomer ratio. It was expected that these new, easily available HRI polymers will be of high potential in OLED application. Thus, the work in this part of the thesis comprises on the one hand monomer and polymer synthesis as well as detailed characterization of the structure and the solution and thermal properties of the new materials. But on the other hand, the elucidation of the thin film preparation and the quality and optical properties of the resulting polymer films are major objectives. Finally, evaluation of the performance of the polymer films in an OLED device compared to conventionally low molar mass our-coupling layers was aimed for, which could be realized with the help of partners from the Institute of Applied Photophysics at TU Dresden. For increasing the IQE in OLEDs, this thesis focuses on the development of a new type of polymeric thermally activated delayed fluorescence (TADF) material. TADF materials have the potential of theoretical 100% IQE and are considered as key materials for the next generation of OLEDs. So far, a significant amount of low molar mass TADF molecules has been developed, however, only a limited number of design rules are reported so far for polymers, even though polymers would offer, as already outlined above, significant advantages with regard to processing cost-effectively more efficient OLEDs for large area application. The new concept described in this thesis for TADF polymers is based on a new monomer which exhibits individual promising structural units for achieving TAFD properties but does not emit TADF itself due to its large ΔEST (the energy gap between singlet S1 and triple T1 state). However, it has to be expected that once the monomer is polymerized, the resulting polymeric product will have reduced ΔEST due to the increased conjugation length and thus can be expected to emit TADF. This new concept has the potential to significantly increase the scope of polymeric materials with TADF properties. Thus the second part on the thesis focuses on the design of a new monomer based on carbazole units with a pendant benzophenone moiety and its polymerization and full structural elucidation with the help of model compounds involving intensive NMR and MALDI-TOF analysis. In addition to the expect TADF properties, the benzophenone unit will also provide the possibility for film stabilization and even photopatterning due to photo-crosslinking. Thus the study of film formation and photo-crosslinking of the new TADF polymers was a further objective of this thesis. Finally, first theoretical as well as experimental studies of the photo physical properties of the monomer, a low molar mass model compound and the polymer, again together with the partners from the Institute of Applied Photophysics, should provide evidence on the suitability of the new polymer design principle.

Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US); 12 Dec 2003.
Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2100" Gang Li. 12/12/2003. Report is also available in paper and microfiche from NTIS.

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, plusieurs molécules de type Donneur-Accepteur incorporant des cœurs azotés électrodéficients variés ont été préparées avec succès, leur design étant conçu dans le but d’obtenir des émetteurs TADF. Leurs propriétés photo-physiques ont été étudiées en solution et à l’état solide. Dans ces structures, le transfert de charge intramoléculaire est produit via des interactions intermoléculaires entre les groupements D et A, et leur étude a révélé que certains d’entre eux présentent un caractère TADF. Les propriétés d’électroluminescence des composés les plus prometteurs ont été également étudiées en configuration OLED, même si à ce jour les rendements observes restent faibles. Ensuite, une série de molécules à gain basées sur des structures pi-conjuguées, toujours constituées de coeurs azotés, 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, certains 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 série
In this work, new organic emitting materials have been developed for applications in the field of light emitting diodes or organic lasers. First of all, several molecules of the Donor-Acceptor type incorporating various electro-deficient nitrogenous hearts have been successfully prepared, their design being designed with the aim of obtaining TADF emitters. Their photophysical properties have been studied in solution and in the solid state. In these structures, intramolecular charge transfer is produced via intermolecular interactions between the D and A groups, and their study revealed that some of them exhibit a TADF character. The electroluminescence properties of the most promising compounds have also been studied in OLED configuration, even if to date the observed yields remain low. Then, a series of gain molecules based on pi-conjugated structures, still consisting of nitrogenous cores, have been successfully synthesized for laser applications. Their chemical structures have been characterized by nuclear magnetic resonance (NMR) and high-resolution mass spectroscopy (HRMS). Good luminescence properties such as high quantum photoluminescence yields (PLQY) and short fluorescence lifetimes have been demonstrated in solution and in the solid state for most derivatives. Finally, some emissive materials exhibit good amplified spontaneous emission (ASE) properties with low threshold values, and optically pumped laser devices could also be made from some of the derivatives of the series

REDE DE NANOTECNOLOGIA MOLECULAR E DE INTERFACES
Neste trabalho são apresentados os resultados da produção e caracterização de novos dispositivos orgânicos eletroluminescentes (OLEDs), que podem ser divididos idealmente em três grupos. O primeiro composto pelos OLEDs que utilizam os distirilbenzenos (DSBs) como camada eletroluminescente. Os DSBs são sistemas utilizados em química supramolecular como pontes para transferência de carga. No segundo colocamos os OLEDs baseados em 2; 6 - bis(dietanolamina) - 4; 8 - dipiperidinopirimida (5; 4-d) pirimidina (DIP), que é uma droga amplamente conhecida e utilizada no tratamento de doenças cardiovasculares, que por possuir uma intensa fluorescência despertou a curiosidade para investigarmos a possibilidade da sua utilização com camada eletroluminescente. A utilização do DIP como camada eletroluminescente resultou em um OLED com a maior luminância dos grupos estudados, 1500 cd/m2. O terceiro grupo é formado por OLEDs que utilizam moléculas de calixarenos ([Al . 1]3+ e [Zn . 1]2+ onde 1 = 8- oxiquinolinacalix[4]areno) como camada transportadora de elétrons e eletroluminescente. Foram estudados dois sistemas calixarenos, o primeiro sistema é coordenado com alumínio (calix[Al]3+) e o segundo coordenado com zinco (calix[Zn]2+). O sistema calix[Al]3+ apresentou uma interessante propriedade de cooperação entre o anel central calix e um grupamento quinolina coordenado com Al. Utilizando este mecanismo de sinergia produzimos um OLED sintonizável, o qual varia o pico de sua banda de eletroluminescência de 510 nm pra 470 nm em função da tensão aplicada. Desta forma a cor da luz emitida pelo dispositivo pode ser variada com continuidade do azul (X=0,26 : Y=0,33 coordenadas CIE) até o verde claro (X=0,18 : Y=0,25).Todos os sistemas orgânicos foram analisados de um ponto de vista térmico através da analise de calorimetria diferencial de varredura (DSC), com a qual determinamos sua temperatura de transição vítrea (Tg). Com o auxilio de medidas eletroquímicas, estabelecemos um procedimento experimental simples e rápido para determinar os níveis energéticos HOMO (highest occupied molecular orbital) dos materiais orgânicos estudados na forma de filmes. Enfim, através da caracterização elétrica foi possível determinar o tipo de injeção de portadores que governa os dispositivos bem como o modelo que controla o transporte de cargas no interior dos OLEDs.
In this work the results of the production and characterization of new organic electroluminescent devices (OLEDs) are presented and discussed. The work can be ideally divided in three parts. The first is composed by the OLEDs that use the distyrilbenzene (DSBs) compounds as electroluminescent layer. The DSBs are systems used in supramolecular Chemistry as bridges for load transfer. This is the first time that they are used in small molecule OLEDs. The second part deals with OLEDs based on dipyridamole (2; 6-bis(diethanolamino) - 4; 8 - dipiperidinopyrimido (5; 4-d)pyrimidine) (DIP) molecule, which is a very well known anti-platelet drug thoroughly used in the treatment of hearth diseases that for possessing an intense fluorescence woke up our curiosity in order to investigate the possibility of its use as electroluminescent layer. The use of DIP as electroluminescent layer resulted in a particular OLED with the highest luminance of the investigated devices, about 1500 cd/m2. Finally, the third part involves OLEDs that use calixarenes molecules [Al . 1]3+ and [Zn . 1] 2+ (1 = 8- oxyquinolinecalix[4]arene) as electroluminescent and electron transporting layer. In this work were studied two calixarenes systems: the first system is coordinated with aluminum (calix[Al]3+) and the second one is coordinated with zinc (calix[Zn]2+). The first one presented an interesting cooperation property among the central calix ring and the quinolina group coordinated with the Al metal. Using this synergic mechanism we were able to produce a tunable OLED, which electroluminescent emission varies continuously from 510 nm to 446 nm as a function of the applied bias voltage. All the organic compounds used in this work were analyzed from a thermal point of view through a Differential Scanning Calorimetry (DSC), in order to determine their transition glass temperature (Tg). By using electrochemistry measurements it was possible to establish a systematic and simple experimental procedure to determine the HOMO (highest occupied molecular orbital) energy levels of the organic materials studied in the form of films. Finally, through the electrical characterization it was possible to determine the type of carrier injection that governs the fabricated devices as well as the model that controls the carrier transport inside the OLEDs.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
Neste trabalho é apresentado o estudo de três complexos tetrakis betadicetonatos de európio: Li[Eu(dbm)(4)].(4)H(2)O, TMPip[Eu(dbm)(4)] e Morf[Eu(dbm)(4)]. Todos os compostos foram caracterizados à temperatura ambiente por diversas técnicas, tais como absorção óptica, fotoluminescência estacionária (PL) e voltametria cíclica. Já os dispositivos eletroluminescentes orgânicos (OLEDs) baseados nestes materiais e fabricados por evaporação térmica resistiva foram caracterizados eletro-opticamente. Os espectros de PL dos compostos apresentaram as linhas características de emissão das transições (5)D(0)→(7)F(0-3) do íon európio, e não exibiram bandas relativas à emissão dos ligantes. Porém, comparações entre os espectros de PL dos materiais na forma de pó e de filme fino indicaram prováveis mudanças na estrutura dos compostos TMPip[Eu(dbm)(4)] e Morf[Eu(dbm)(4)]. Uma das possibilidades é a de que a deposição térmica estaria degradando estes materiais, dando origem às espécies tris beta-dicetonato. Os OLEDs com complexos de európio atuando simultaneamente como camada emissora e transportadora de elétrons apresentaram também, em seus espectros, os picos relativos às transições do íon Eu(3+). Para aumentar a eficiência luminosa dos dispositivos foi testada uma nova configuração, acrescentando-se uma camada bloqueadora de buracos e uma transportadora de elétrons. Esta nova arquitetura aprimorou o funcionamento dos OLEDs, cuja eletroluminescência (EL) passou a ser visível a olho nu. Por outro lado, ela causou o aparecimento de uma banda larga centrada em 480nm no espectro de EL. O estudo realizado para investigar a origem desta banda mostrou que ela é proveniente da emissão da camada bloqueadora de buracos.
Rare-earth complexes present extremely sharp line emission making possible to use them in organic light-emitting devices (OLEDs) technology. This dissertation reports the study of three europium tetrakis beta-diketonate complexes: Li[Eu(dbm)(4)].(4)H(2)O, TMPip[Eu(dbm)(4)] and Morf[Eu(dbm)(4)]. UV-Vis absorption, photoluminescence (PL) and cyclic voltammetry measurements were used to characterize the complexes, at room temperature. The PL spectra displayed the characteristic europium narrow bands from (5)D(0)→(7)F(0-3) transitions and exhibited red color emission, without a contribution from ligand emission. However, a comparison between thin films spectra and powder spectra suggested probable changes in the TMPip[Eu(dbm)(4)] e Morf[Eu(dbm)(4)] complexes composition. One possibility is that the thermal deposition is causing degradation, breaking the tetrakis structure into tris beta-diketonate complexes. This hypothesis was investigated using TGA technique associated with FTIR analysis of chemical species. Europium complexes based OLEDs produced by thermal evaporation and using different device configuration were characterized by electroluminescence (EL) measurements. Bilayer OLEDs fabricated with a europium complex acting simultaneously as the emissive layer and as the electron transporting layer showed the bands from Eu(3+) transitions in the EL spectra. Another configuration was used to increase the device efficiency, adding a hole-blocking layer and an electron transporting layer. This new architecture improved the OLEDs performance, enabling the electroluminescence to be visible with the naked eye. On the other hand, it caused the appearance of a wide emission band centered at 480nm. A study performed about the source of this emission band showed that it was originated by the hole-blocking layer.

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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Nesse trabalho são apresentados os resultados da produção e caracterização de diodos orgânicos emissores de luz sensível ao infravermelho próximo, OLEDs de conversão ascendente de energia que são conhecidos como OLEDs tipo up-converter. O desempenho da camada sensível ao infravermelho é um fator fundamental para o funcionamento do dispositivo. Neste sentido, moléculas de ftalocianinas apresentam respostas eletrônicas quando são expostas a radiação infravermelha. Na primeira parte do trabalho foram investigadas as propriedades ópticas e elétricas de filmes de ftalocianinas fabricados por evaporação térmica a vácuo. As ftalocianinas estudadas foram: ftalocianina de cobalto, ftalocianina de cobre, ftalocianina de magnésio, ftalocianina de platina e naftalocianina de estanho. Essas moléculas foram caracterizadas usando diferentes técnicas, tais como, espectroscopia de absorção UV-VIS e voltametria cíclica, espectrometria de massa, difratometria de raios-X e medidas elétricas, a fim de se obter suporte para o uso dessas moléculas como camada ativa nos dispositivos up-converters. Entre as ftalocianinas estudadas, a naftalocianina de estanho se mostrou a melhor candidata para atuar como camada sensível para a fabricação dos dispositivos. Porém, OLEDs up-converters usando naftalocianina de estanho como camada sensível ao infravermelho apresentaram baixa resposta a radiação infravermelha e baixa eficiência de conversão. Assim, para tentar solucionar esse problema, foi necessário fabricar alguns OLEDs up-converters usando uma camada de ftalocianina codepositada com fulereno como a camada sensível ao infravermelho. A codeposição consiste em uma técnica em que as moléculas de ftalocianinas e de fulereno são sublimadas simultaneamente. A partir da técnica de codeposição, é possível obter uma blenda com diferentes propriedades ópticas e elétricas. A camada codepositada apresentou uma redução significativa na mobilidade de buracos, o que levou a um aumento da eficiência de conversão do dispositivo, evidenciando o uso destes materiais para a fabricação de OLEDs sensíveis ao infravermelho para aplicações em sistemas de visão noturna.
In this work the results of the production and characterization of Organic Light Emitting Diodes with near-infrared sensitive layer up-converter are presented. The infrared sensitive layer performance is a key factor for the operation of the device. Phthalocyanine molecules have an electronic response when they are exposed to the infrared radiation. In the first part of the work the optical and electrical properties of phthalocyanine films manufactured by vacuum thermal evaporation were investigated. The phthalocyanines studied were: cobalt phthalocyanine, copper phthalocyanine, magnesium phthalocyanine platinum phthalocyanine and tin naphthalocyanine. These molecules were characterized using different techniques, such as UV-VIS absorption spectroscopy and cyclic voltammetry, mass spectrometry, X-ray diffractometry and electrical measurements, in order to obtain support for the use of these molecules as active layer of up-converter devices. Among the studied phthalocyanines, tin naphthalocyanine was the best candidate to act as a sensitive layer for the manufacture of the devices. However, OLEDs up-converters using tin naphthalocyanine as an infrared sensitive layer showed low response to infrared radiation and low conversion efficiency. Thus, to solve this problem, it was necessary to manufacture OLEDs up-converters using a phthalocyanine layer co-deposited with fullerene as infrared sensitive layer. Co deposition consists of a technique in which the phthalocyanine and fullerene molecules are simultaneously sublimated. From the co-deposition technique, it is possible to obtain a blend with different optical and electrical properties. The co-deposited layer showed a significant reduction in hole mobility, which led to an increase in the conversion efficiency of the device, evidencing the use of these materials for the manufacture of infrared sensitive OLEDs for applications in night vision systems.

Cette thèse a pour objet l'étude du champ électrique dans les diodes électroluminescentes et les cellules photovoltaïques organiques par l'application de la spectroscopie d'électro-absorption. Cette technique, basée sur un phénomène d'optique non-linéaire (effet Stark), permet la caractérisation des composants en fonctionnement. L'effet des couches d'injection déposées sur l'ITO, et des métaux de cathode, sur l'injection des porteurs de charge a été étudié. Les propriétés électriques et optiques d'OLEDs à base d'Alq3 et de PFV ont été mises en relation avec la variation de la tension de bandes plates. L'effet du PEDOT:PSS sur la tension en circuit ouvert de cellules photovoltaïques à base de molécules discotiques a été étudié, et les différentes composantes du champ électrique interne (champs d'interface et de volume) ont été mises en évidence
The object of this thesis is the study of electric field in organic light-emitting diodes and photovoltaic cells by use of electroabsorption spectroscopy. This technique, based on a nonlinear optical (Stark) effect, allows the characterization of operating components. The effect of injecting layers deposited on ITO, and of cathode metals, on charge carrier injection, has been studied. Electrical and optical properties of Alq3 and PFV based OLEDs have been related to flat band voltage variation. The effect of PEDOT:PSS on the open-circuit voltage of photovoltaic cells based on discotic molecules has been investigated. The presence of different components of internal electric field (interface and bulk electric field) has been evidenced