Molecular self-assembly has recently attracted significant attention for possible application in organic electronic and optoelectronic devices, such as self-assembled monolayer field-effect transistors (SAMFETs) and functional self-assembled integrated circuits. Self-assembly combines the advantages of low temperature solution processability, regio-selective monolayer adsorption and nano-scale control of film thickness. Much progress has been made in improving device performance using self-assembled monolayers (SAMs). However, most SAMFET devices reported to date showed current modulation only with submicrometre channels, with low device yields and poor reproducibility as a result of limited lateral interconnection of the semiconducting layer.In an attempt to address these issues, this thesis presents an investigation of the synthesis and properties of conjugated SAM molecules for use as the charge transporting layer in SAMFETs. Chapter 1 gives a comprehensive introduction to SAM-based surface systems, organic semiconductors and their use in OFETs and SAMFETs. Chapter 2 discusses attempts to design and synthesise p-type conjugated molecules capable of self-assembly on oxide surfaces based on a phenylene-bithiophene semiconducting core. The optical and electrochemical properties, as well as the thermal behaviour of these molecules are studied in detail. This theme is carried over to Chapter 3, which describes the synthesis, chemical and physical characterisation of two families of n-type SAM molecules. These molecules consist of NTCDI cores with hexyl or cyclohexyl chains as end-capping groups. Incorporation of a selection of materials as the active layer in OFETs or SAMFETs to evaluate the charge transport is demonstrated in Chapter 4. Monolayer films based on p-type monochlorosilane-terminated SAM molecules are made using the solution assembly technique and characterised by contact angle and AFM. OFETs made from DH-PTTP by both thermal evaporation and spin coating show high mobilities comparable to the best values reported in the literature. Top-contact SAMFETs show a hole mobility of 1.1 × 10-3 cm2V-1s-1 in air, consistent with those of solution processed DH-PTTP based OFETs. Finally, an overview of the project and some suggestions for future work are presented in Chapter 5.

The investigation carried out in this project allowed for the development of eleven regioregular π-conjugated alternating copolymers and their implementation in organic solar cells. The eleven synthesized polymers, poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(4,7-dithien-2-yl-2,1,3-benzothiadiazole)] (CB), poly[(2,7-(9,9-dioctyl-9H-fluorene-2,7-diyl))-alt-(1,6-pyrene)] (LP), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(5,5’’’-(3,3’’’-dihexyl-2,2':5',2'':5'',2'''-quarterthiophene))] (CT), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(2,7-9H-fluoren-9-one)] (CF), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(1,6-pyrene)] (CP), poly[(2,7-(9,9-dioctyl-9H-fluorene-2,7-diyl))-alt-(4,7-dithien-2-yl-2,1,3-benzothiadiazole)] (LB), poly[(2,7-(9,9-dioctyl-9H-fluorene-2,7-diyl))-alt-(2,7-9H-fluoren-9-one)] (LF), poly[(5,5’’’-(3,3’’’-dihexyl-2,2':5',2'':5'',2'''-quarterthiophene))-alt-(2,7-9H- fluoren-9-one)] (TF), poly[(2,7-(9,9-dioctyl-9H-fluorene-2,7-diyl))-alt-(4,4'-dioctyl-2,2'-bithiophene)] (oTLT), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(4,4'-dioctyl-2,2'-bithiophene)] (oTCT), poly[(2,7-(9-(heptadecan-9-yl)-9H-carbazole))-alt-(4,4'-dihexyl-2,2'-bithiophene)] (TCT), were investigated using theoretical methods that included semi-empirical geometry optimizations, density functional theory (DFT) energy calculations, and time-dependent density functional theory (TD-DFT) optical absorption predictions. The absorption predictions gave credence to our experimental results in which the absorption of the longer polymer chains underwent a redshift from the monomer absorption. With several of the prepared polymers, bulk-heterojunction photovoltaic cells were fabricated and their photovoltaic activity was investigated. Several of the fabricated cells exhibited photovoltaic efficiencies including polymer/PCBM composites with an aluminum back electrode (CF, CT, P3HT, and MEH-PPV), and also inverted cells with a silver back electrode (CT, P3HT, and MEH-PPV). Several polymers (CF, CT, TCT, LP, oTCT, oTLT, P3HT, and MEH-PPV) were used to solubilize single-walled carbon nanotubes (SWNTs). The solubility of the nanotubes occurred by the polymers’ ability to wrap the tubes, disrupt the bundles (ropes of tubes), and allow for the creation of a homogeneous mixture. Polymer:PCBM:SWNT mixtures were prepared and utilized as the active layer in BHJ solar cells. Some of the inverted cells (with a silver back electrode) that incorporated the nanotube composites (CT, oTCT, oTLT, P3HT, and MEH-PPV) displayed photovoltaic activity. These preliminary results illuminate the photovoltaic behavior of the polymer and provide evidence for their future use in polymer solar cells. / Thesis (Master, Chemistry) -- Queen's University, 2011-02-13 22:09:00.464

No description available.

In the last three decades Organic Electronics emerged and established itself as an interdisciplinary field of science and as part of our daily life. Presently, the greatest scientific challenges in this field of research are two: the former relies on the improvement of devices efficiency which can be accomplished by using new materials, whereas the latter consist in the integration of multiple functionalities in a single device. To accomplish these goals one needs to develop a deep understanding on the fundamental physical-chemistry ruling the properties which are on the basis of organic electronics such as charge injection, charge transfer and transport. This PhD project reports the developing of efficient multicomponent electroactive self-assembled systems whose electro- and optical properties can be modulated, in devices, as a response to multiple external and independent stimuli. This goal has been achieved by engineering of the proper building blocks and the study of the the physico-chemical properties to be able to model all the mechanisms involved.

Organic Light-Emitting Devices (OLEDs) have reached industrial maturity in display technology, since OLEDs provide salient advantages such as high brightness, fast response, wide viewing angle, mechanical flexibility, and low cost manufacturing. Due to the ability of electroluminescence (EL) from triplet excited states as well as singlet excited states, phosphorescent OLEDs (PHOLEDs) have a potential to achieve 100% internal quantum efficiency. Therefore, PHOLEDs can offer a competitive external quantum efficiency. However, the operational stability of PHOLEDs is relatively poor. Several mechanisms have been proposed to address the chemical and physical phenomena associated with intrinsic degradation of PHOLEDs, nevertheless, the reasons behind voltage rise and luminance loss accompanying PHOLEDs long term operation are not yet well understood. The state of the art p-i-n PHOLEDs offer relatively high efficiency and low efficiency roll-off. However, this technology is characterized by structure complexity. Therefore, much of the current research on PHOLEDs focuses on the development of the simplest possible and most easily processed architecture that can deliver the optimal combination of device properties. Simplified PHOLEDs, utilizing one material for both hole transport and emitter host, can be a good candidate for replacement of p-i-n technology. Simplified PHOLEDs offer higher efficiency than the p-i-n PHOLEDs , yet, their EL stability is found to be poor. In this thesis, the role of the ITO/organic interface on simplified PHOLEDs efficiency will be investigated. Furthermore, possible degradation mechanisms at the ITO/organic interface will be explored. Moreover, we will correlate degradation at the ITO/organic interface to PHOLEDs operational stability. Eventually, organic layers modifications including but not limited to emissive layer (EML) will be examined. By studying the indium tin oxide (ITO)/organic interface in simplified PHOLEDs, it was found that this interface is critical to PHOLEDs performance. The study shows that, this interface is critical to the PHOLED overall stability and is considered as one of the limiting factors of the long term operational stability of simplified PHOLEDs. The effect of optical excitation on the ITO/organic interface stability in hole-only devices was investigated. It was found that the ITO/organic interface is susceptible to exciton-induced degradation. This degradation affects the device stability severely compared to current-induced degradation. The exciton-induced degradation can be prevented by doping the hole transport layer (HTL), at the interface with an exciton quencher layer or by blocking the electrons from leaking to the ITO/organic interface that may further recombine with holes to form excitons. Further studies showed that upon combining both electrical stress and optical excitation, the device degradation is even more pronounced which is most likely due to interactions between charges and excitons. By using exciton life-time measurements, a new role of molybdenum trioxide (MoO3) in the electrical stability of PHOLEDs, as an exciton quencher layer, is introduced. Delayed EL (DEL) measurements showed that the simplified PHOLEDs are susceptible to triplet-triplet annihilation (TTA) and triplet-polaron quenching (TPQ) which might affect the operational stability of simplified PHOLEDs. Finally, EML modifications showed that the recombination zone of simplified PHOLEDs is located near the HTL/EML interface.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

elementares da eletrônica orgânica, vêm sendo desenvolvidos e integrados para realização de dispositivos eletrônicos de baixo custo, alto volume e flexíveis. Nesta tese foi proposta uma tecnologia para a construção de OFETs sobre substrato flexível e a caracterização destes dispositivos foi feita. Transistores com diferentes comprimentos de canal (L= 5, 10, 20 e 40 μm) foram construídos e avaliados. As características e configuração do poli (álcool vinílico) (PVA) como dielétrico de porta foram definidas através da otimização da reticulação, grau de hidrólise e peso molecular. O PVA utilizado como dielétrico de porta foi de alto peso molecular, hidrolização incompleta e reticulado com dicromato de amônia. O desafio de compatibilização entre os filmes de PVA e poli (3-hexiltiofeno) (P3HT) com diferentes polaridades foi superado e abriu caminho para construção de OFETs e capacitores, estes últimos usados para extrair a capacitância por unidade de área do conjunto PVA-P3HT. Os processos desenvolvidos de fotolitografia e de oxidação por plasma de oxigênio possibilitaram a construção de transistores flexíveis inéditos de Ni-P3HT-PVA-Al com uma arquitetura top-gate, bottom-contacts. Os transistores apresentaram boas características de saída, baixa tensão de operação (< |-6 V|), boa mobilidade (0,015 cm2/V*s) e razões ION/IOFF aceitáveis (~300). A resistência de contato e mobilidade efetiva foram obtidas através do método de linhas de transmissão. Uma boa estabilidade temporal foi atingida, porém ocorreram instabilidades na operação quando os transistores foram testados. A corrente do transistor não se manteve estável, primeiramente aumentou e depois diminuiu com a realização de sucessivas medidas. As razões deste comportamento foram discutidas. Inversores foram demonstrados e caracterizados. O aperfeiçoamento da tecnologia desenvolvida possibilitará a construção de circuitos orgânicos analógicos e digitais para aplicações cotidianas que demandem baixo custo e alto volume. / Organic field effect transistors (OFETs), the elementary components of organic electronics, are constantly developed and integrated to realize low cost, high volume, flexible electronic devices. In this thesis a technology for creating OFETs on flexible substrates is proposed and their characterization is performed. Flexible transistors with different channel lengths (L= 5, 10, 20 and 40 μm) were built and evaluated. The characteristics and configurations of the poly (vinyl alcohol) (PVA) as gate dielectric were defined through the optimization of crosslinking, the degree of hydrolysis and the molecular weight. The chosen PVA is cross-linked with ammonium dichromate, has a high molecular weight and incomplete hydrolization. The challenge of integrating polymers of different polarities: PVA and poly (3-hexyl thiophene) (P3HT), the chosen organic semiconductor, was overcome and opened a path to the construction of OFETs and capacitors. From the later capacitance per unit area was extracted. The developed processes of photolithography and oxygen plasma etching allowed the construction of unprecedented Ni-P3HT-PVA-Al flexible top-gate, bottomcontacts transistors. The transistors showed good output characteristics, low operation voltages (< |-6 V|), acceptable carrier mobilities (0,015 cm2/V*s) and ION/IOFF fractions (~300). Contact resistance and effective mobility were extracted through transmission line method. The transistors showed great temporal stability, but when operated instabilities occurred. The transistor output current first increased and later degraded with successive testing. Organic PMIS inverters were demonstrated and characterized. The optimization of this technology may lead to construction of flexible logic organic devices for everyday applications.

elementares da eletrônica orgânica, vêm sendo desenvolvidos e integrados para realização de dispositivos eletrônicos de baixo custo, alto volume e flexíveis. Nesta tese foi proposta uma tecnologia para a construção de OFETs sobre substrato flexível e a caracterização destes dispositivos foi feita. Transistores com diferentes comprimentos de canal (L= 5, 10, 20 e 40 μm) foram construídos e avaliados. As características e configuração do poli (álcool vinílico) (PVA) como dielétrico de porta foram definidas através da otimização da reticulação, grau de hidrólise e peso molecular. O PVA utilizado como dielétrico de porta foi de alto peso molecular, hidrolização incompleta e reticulado com dicromato de amônia. O desafio de compatibilização entre os filmes de PVA e poli (3-hexiltiofeno) (P3HT) com diferentes polaridades foi superado e abriu caminho para construção de OFETs e capacitores, estes últimos usados para extrair a capacitância por unidade de área do conjunto PVA-P3HT. Os processos desenvolvidos de fotolitografia e de oxidação por plasma de oxigênio possibilitaram a construção de transistores flexíveis inéditos de Ni-P3HT-PVA-Al com uma arquitetura top-gate, bottom-contacts. Os transistores apresentaram boas características de saída, baixa tensão de operação (< |-6 V|), boa mobilidade (0,015 cm2/V*s) e razões ION/IOFF aceitáveis (~300). A resistência de contato e mobilidade efetiva foram obtidas através do método de linhas de transmissão. Uma boa estabilidade temporal foi atingida, porém ocorreram instabilidades na operação quando os transistores foram testados. A corrente do transistor não se manteve estável, primeiramente aumentou e depois diminuiu com a realização de sucessivas medidas. As razões deste comportamento foram discutidas. Inversores foram demonstrados e caracterizados. O aperfeiçoamento da tecnologia desenvolvida possibilitará a construção de circuitos orgânicos analógicos e digitais para aplicações cotidianas que demandem baixo custo e alto volume. / Organic field effect transistors (OFETs), the elementary components of organic electronics, are constantly developed and integrated to realize low cost, high volume, flexible electronic devices. In this thesis a technology for creating OFETs on flexible substrates is proposed and their characterization is performed. Flexible transistors with different channel lengths (L= 5, 10, 20 and 40 μm) were built and evaluated. The characteristics and configurations of the poly (vinyl alcohol) (PVA) as gate dielectric were defined through the optimization of crosslinking, the degree of hydrolysis and the molecular weight. The chosen PVA is cross-linked with ammonium dichromate, has a high molecular weight and incomplete hydrolization. The challenge of integrating polymers of different polarities: PVA and poly (3-hexyl thiophene) (P3HT), the chosen organic semiconductor, was overcome and opened a path to the construction of OFETs and capacitors. From the later capacitance per unit area was extracted. The developed processes of photolithography and oxygen plasma etching allowed the construction of unprecedented Ni-P3HT-PVA-Al flexible top-gate, bottomcontacts transistors. The transistors showed good output characteristics, low operation voltages (< |-6 V|), acceptable carrier mobilities (0,015 cm2/V*s) and ION/IOFF fractions (~300). Contact resistance and effective mobility were extracted through transmission line method. The transistors showed great temporal stability, but when operated instabilities occurred. The transistor output current first increased and later degraded with successive testing. Organic PMIS inverters were demonstrated and characterized. The optimization of this technology may lead to construction of flexible logic organic devices for everyday applications.

Existem algumas técnicas destinadas ao estudo das características fotofísicas de materiais orgânicos ou dispositivos eletrônicos e optoeletrônicos a base de semicondutores orgânicos. A exemplo disso, a técnica de espectroscopia de absorção fotoinduzida de onda contínua (Continuous Wave Photoinduced Absorption/cw-PIA) apresenta grande sensibilidade como método destinado ao estudo dos processos eletrônicos envolvendo espécies excitadas de vida longa. Esta técnica emprega dois feixes ópticos distintos, um para excitação da amostra e outro (feixe de prova) para investigar os estados excitados remanescentes em amostra após bombeio óptico. O presente trabalho tem como objetivo a construção, desenvolvimento e caracterização de um aparato experimental para espectroscopia cw-PIA. A montagem bem sucedida da técnica foi testada em filme do polímero semicondutor P3HT, em filme de blenda (1:1) de P3HT/PCBM (comumente utilizada como camada ativa em células solares orgânicas) e em filmes automontados camada-a-camada (LbL) do tipo doador-aceitador de carga (P3KHT/P6N), sendo que a molécula P6N foi sintetizada pelo Grupo de Polímeros Bernhard Gross do IFSC-USP. Os filmes LbL de P3KHT/P6N, em comparação aos filmes blenda de P3HT/PCBM, demonstraram uma eficiência maior quanto a geração de portadores de carga com tempo de vida longo. / There are some techniques for the study of photophysical characteristics of organic materials or electronic and optoelectronic devices based on organic semiconductors. For example, the technique of continuous wave photoinduced absorption spectroscopy (cw-PIA) is a highly sensitive method for the study of the electronic processes involving long-lived excited species. This technique uses two distinct optical beams, one for sample excitation and another for probing the excited states remaining in the sample after optical pumping. The present work aims at the construction, development and characterization of an experimental apparatus for cw-PIA spectroscopy. The successful implementation of the technique was tested in a film of the semiconducting polymer P3HT and of the blend (1:1) P3HT/ PCBM (usually employed as active layer in organic solar cells), and also in a Layer-by-Layer (LbL) film of donor-acceptor molecules P3KHT/P6N, where the P6N molecule has been synthesized by Polymer Group Bernhard Gross at IFSC- USP. The comparison between P3KHT / P6N LbL film and the blend P3HT/PCBM has demonstrated higher charge carrier generation efficiency (with long lifetime) for the LbL film.

Dans ce travail, différentes solutions aqueuses de PEDOT: polyelectrolyte ont été synthétisées à partir de polymères anioniques de types polysaccharides et polystyrènes substitués par des groupements bis(sulfonylimide). Leurs morphologies, dopages,comportements rhéologiques ainsi que leurs propriétés opto-électroniques ont notammen tété caractérisés. Une étude systématique a révélé que les polyélectrolytes de masse molaire élevée portant un groupement fortement acide et ayant un squelette rigide permettent d'obtenir un dopage élevé, une dispersion efficace du PEDOT et donc des complexes PEDOT : polyelectrolyte plus conducteurs. L'utilisation du polyelectrolyte PSTFSI en tant qu'agent de complexation pour le PEDOT donne une dispersion stable montrant les caractéristiques d'un gel, ce qui facilite la fabrication de films minces par 'spin coating' ou doctor blade. Les films de PEDOT : PSTFSI ainsi obtenus montrent une transparence élevée et une conductivité de 330S.cm-1. Ces propriétés ont permis de les intégrer avec succès comme matériaux d'électrodes dans des dispositifs OLED, OPV et OECT. / In this work different aqueous dispersions of conducting poly(3,4-ethylenedioxythiophene) :polyelectrolyte (PEDOT:polyelectrolyte) complexes,made from anionic polysaccharides and from synthetic bis(sulfonylimide) substituted polystyrenes, have been synthesized and characterized regarding their doping, morphology, rheological behavior and opto-electronic properties. A systematic study revealed, that high molar mass polyelectrolytes with strongly acidic groups and a rigid backbone structure were favorable for a high doping and an efficient dispersion of PEDOT and allowed the development of highly conducting PEDOT:polyelectrolyte complexes. The use of the polyelectrolyte poly(4-styrenetrifluoromethane(bissulfonylimide)) (PSTFSI) as complexing agent for PEDOT resultedin stable dispersions with gel character, which allowed easy processing by spin coating and doctor blading. The obtained PEDOT:PSTFSI films were highly transparent,displayed a conductivity of up to 330S.cm-1 and were successfully integrated as electrodes in OLED, OPV and OECT devices.