The molecular design, synthesis and characterization of a series of ligands and the corresponding novel iridium(III) or platinum(II) complexes are discussed in this thesis. Their photophysical and electrochemical properties, the applications in organic light-emitting diodes (OLEDs), dye-sensitized solar cells (DSSCs), aggregation induced emission (AIE) and time-resolved infrared (TRIR) study are also investigated. Chapter 1 generates a brief overview of the background, principle, and development of OLEDs, DSSCs, AIE materials and the involvement of the TRIR technique. Chapter 2 describes the synthesis, spectroscopic, photophysical and electrochemical characterization of a series of cationic iridium(III) complexes. Strong electron-withdrawing carboxylic acid substituted bipyridyl was involved in the ligand system and the intra-ligand charge transfer character of diphenylamino containing ligand further shift the dominant absorption band to the lower energy region. Some of them were applied for DSSC device fabrication. Chapter 3 presents the synthesis, spectroscopic, photophysical and electrochemical characterization as well as OLED application of a group of cyclometalated iridium(III) complexes by using 2-substituted 9-benzylcarbazolyl, 9-phenylcarbazolyl or 2-methyl-7-phenylcarbazolyl groups as the ligands. They show significant bathochromatic shift from those using 3-substituted ligands. And this can be explained by the fact that more electron density is located at 2-position of carbazole moiety and make them suitable candidates for deep red OLED application. Chapter 4 delivers the synthesis, spectroscopic, photophysical and electrochemical characterization of a series of platinum(II) acetylide complexes for AIE study. All of the complexes contain [4-(1,2,2-triphenylethenyl)phenyl]ethynyl ligand, which is designed from AIE active building block tetraphenylamine (TPE). Some of these metal complexes show AIE behavior. Chapter 5 outlines the synthetic methodology and characterization of another series of cyclometalated iridium(III) and platinum(II) complexes, containing TPE or carbazole units. It is very interesting to find out that there is hardly any emission in all of the TPE-containing cyclometalated complexes, nor any signs of AIE behavior. Meanwhile, for carbazole-containing platinum(II) complexes, remarable AIE results could be generated, which is believed to be important for further organometallic AIE active material development. Chapter 6 describes the synthetic methodology and characterization of a series of symmetric or asymmetric platinum(II) acetylides. Some of them were further applied for TRIR analysis to generate detailed experimental information of the electron transitions during excitation. The results demonstrate that both localized and delocalized metal ligand orbital mixing could be generated according to the variations in electronegativity of the ligand system. Chapter 7 and 8 present the concluding remarks and summarize the experimental details of all of the previous chapters.

Orientador: Lucas Fugikawa Santos / Banca: Marcelo Andres Fossey / Banca: Dante Luis Chinaglia / Resumo: Esta dissertação de mestrado apresenta um estudo sobre as propriedades de foto-geração de portadores de carga e sua condução em dispositivos optoeletrônicos orgânicos construídos em estruturas de diodo tipo sanduíche - ITO/Polímero/Metal - sendo empregados como sua camada ativa dois polímeros orgânicos conjugados distintos, o poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene) ou MDMO-PPV, e o copolímero fenil substituído do poli(p-fenileno vinileno) conhecido como Super Yellow® ou SY-PPV. As características da foto-geração e de transporte de cargas dos dispositivos foram determinada através da análise de medidas de corrente-tensão (I-V) em regime d.c., e de espectroscopia de impedância/capacitância no regime da frequência (1Hz-1MHz). As propriedades elétricas dos dispositivos foram estudadas com os dispositivos iluminados em diferentes faixas de comprimentos de onda na região do visível, a diferentes intensidades, e comparadas com as propriedades dos dispositivos no escuro. Para iluminação através do eletrodo transparente (ITO), tanto um efeito fotovoltaico quanto fotocondutivo foram claramente observados. Em particular, o efeito da foto-geração no espectro de capacitância em função da frequência foi estudado em maiores detalhes. Um modelo semiempírico, levando em conta as distribuições de cargas espaciais devidas à foto-geração de portadores de carga e propriedades de transporte como, por exemplo... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This dissertation presents a study on the properties of photo-generation and conduction of charge carriers in organic optoelectronic devices built in sandwich diode structures - ITO/Polymer/Metal - with the active layer comprised by two different organic conjugated polymers: poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene) MDMO-PPV, and a phenyl-substituted copolymer of poly(p-phenylene vinylene) known as Super Yellow®, SY-PPV. The photo-generation and charge transport properties have been determined from the analysis of current-voltage (I-V) measurements in the d.c. regime and impedance/capacitance spectroscopy in the regime of frequency (1Hz-1MHz). The electrical properties of the devices were studied with the devices under illumination, in different ranges of wavelength in the visible region, at different intensities and compared with the properties of devices in the dark. By illuminating the devices through the transparent electrode (ITO), both photovoltaic and photoconductive effects were clearly observed. Particularly, the photo-generation effect in the frequency-dependent capacitance spectrum was studied in detail. A semiempirical model taking into account the spatial distribution of charges due the photo-generation and material properties... (Complete abstract click electronic access below) / Mestre

Orientador: Luis Vicente de Andrade Scalvi / Coorientador: Julio Ricardo Sambrano / Banca: Margarida Juri Saeki / Banca: Tomaz Catunda / Banca: Valeria Moraes Longo / Resumo: Este trabalho apresenta uma abordagem teórico-experimental na investigação de filmes finos de dióxido de estanho (SnO2) não dopado, de SnO2 dopado com antimônio (Sb), de dióxido de titânio (TiO2) e também de heteroestrutura Tio2/SnO2, produzidos pelo processo sol-gel-dip-coating. O conhecimento dos mecanismos de transporte elétrico de SnO2:Sb é fundamental para o desenvolvimento de dispositivos opto-eletrônicos. Neste sentido, a contribuição deste trabalho está principalmente no estudo das propriedades elétricas de SnO2:Sb, no qual foi analisado a captura de elétrons fotoexcitados por centros de Sb e/ou vacâncias de oxigênios termicamente ativados. Os resultados, surpreendentemente, mostraram que a taxa de variação da condutividade diminui com o aumento temperatura, independente da energia da fonte de excitação (acima ou abaixo da energia do bandgap). Este comportamento está provavelmente relacionado à mobilidade eletrônica, que é dominado pelo espalhamento de portadores de carga na região do contorno de grão. Quanto à heterojunção TiO2/SnO2, o conhecimento do tipo de estrutura cristalina dos semicondutores óxidos é fundamental para sua utilização em determinadas aplicações tecnológicas. A avaliação das propriedades estruturais de filmes finos de TiO2 apresentada nesta tese mostrou que o substrato de quartzo, utilizado para deposição dos filmes, exerce influência na temperatura de transição de fase anatásio-rutilo. De modo geral, apresentamos aqui uma avaliação das propriedades ópticas, estruturais, elétricas e eletrônicas de filmes finos de SnO2 e de SnO2:SB e também das propriedades ópticas, estruturais e eletrônicas de TiO2 e heterojunção TiO2/SnO2. As propriedades eletrônicas foram obtidas a partir de simulações computacionais de SnO2 SnO2:Sb e TiO2 desenvolvidas com o programa CRYSTAL06, baseadas na Teoria do Funcional da Densidade / Abstract: This work presents a theoretical-experimental approach in the investigation of undoped and Sb-doped SnO2 thin flims, TiO2 thin films and also the heterostructure TiO2/SnO2 deposited through the sol-gel-dip-coating technique. The knowledge of the electrical transport mechanisms in SnO2:Sb is fundamental towards the devolping of optoelectronic devices. Then, our contribution concerns the analysis of the electronic structure and, mainly, the investigation of the electrical properties of SnO2:Sb, where the electron capture by thermally activated Sb centers and/or oxygen vacancies was proposed. Results, surpisingly, show that the conductivity variation rate increases with temperature, independent on excitation source energy (above or below the gandgap energy). This behavior is probaly related to the electronic mobility, which is dominated by the charge carrier scattering at boundary layer. Concerning the heterojunction TiO2/SnO2, the determination of the crystalline structure type of oxide semiconductors if fundamental for application in specific technologies. The evalution of structural properties of TiO2 films show that the quartz substrate, used for film deposition, influences the transition temperature of the anatase-rutile phases. In summary, we present an evalution of optical, structural, electrical and electronic properties of SnO2 and SnO2:Sb as well as optical, structured, and electronic properties of TiO2/SnO2. Electronic properties were obtained from computacional simulations of SnO2, SnO2:Sb, TiO2 and TiO2/SnO2, developed with the program CRYSTAL06, through the Density Functional Theory / Doutor

With the progression towards lighter but larger-display self-sustainable mobile devices, device efficiency becomes increasingly important, owing to the higher power display consumption but at the same time more limitation on the size and volume of energy storage. In this thesis, selected aspects regarding to efficiency of three types of optoelectronic devices, indoor photovoltaics (IPVs), perovskite thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs) have been investigated. IPVs can make off-grid devices self-sustainable by harvesting ambient light energy. Its weak irradiance necessitates high-efficiency IPVs to generate sufficient power. Our work addresses the need of knowing the limit of the device parameters for correct evaluation and understanding the efficiency loss for developing clinical tactics. We delivered a general scheme for evaluating the limiting efficiency and the corresponding device parameters of IPVs under various lights, illuminance and material bandgap. In contrast to the AM1.5G conditions, a maximum power conversion efficiency (PCE) of 51-57 % can be achieved under the optimal bandgap of 1.82-1.96 eV. We also propose using the second thickness peak of interference instead of the first as a better optimal absorber thickness after identifying the finite absorption as the major source of efficiency loss. The work provides insights for device evaluation and material design for efficient IPV devices. The novel hybrid organic-inorganic perovskites have gained enormous research interest for its various excellent optoelectronic properties such as high mobility. TFT as an alternative application to the majorly focused photovoltaics is realized in this work. There are few reports on perovskite TFTs due to wetting issues. By employing polymethacrylates with ester groups and aromatic substituents which provide polar and cation-π interactions with the Pb2+ ions, quality films could be fabricated with large crystals and high electron mobility in TFTs. We further improved the performance by resolving interfacial mixing between the perovskite and the polymer using the crosslinkable SU-8, achieving the highest mobility of 1.05 cm2 V−1 s−1. Subsequently, we cured the grain boundaries using methylamine solvent vapor annealing, suppressing the TFT subthreshold swing. The work provides a map for the improvement of perovskite TFTs. It has been revealed that molecular orientations of the emitters in OLEDs with the transition dipole moment lying in plane enhances light outcoupling efficiency. Multiple experimental techniques are needed to provide complementary orientation information and their physical origin. Here, we propose using TFT to probe the orientation of the phosphorescent emitters. Homoleptic fac-Ir(ppy)3 and heteroleptic trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) were deposited on polystyrene (PS) and SiO2 substrates. Compared to the PS surface inducing isotropic orientation as the control, trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) possessed decreased carrier mobilities on SiO2. With the study of initial film growth, we infer that preferred orientation induced by the polar SiO2 surface led to an increase in energetic disorder in the well-stacked trans-Ir(ppy)2(acac) and hopping distance in the amorphous trans-Ir(ppy)2(tmd). The highly symmetric fac-Ir(ppy)3 remained its isotropic orientation despite the dipolar interaction. Surprisingly, the TFT technique gives much higher sensitivity to surface-induced orientation, and thus may potentially serve as a unique electrical probe for molecular orientation.

With the progression towards lighter but larger-display self-sustainable mobile devices, device efficiency becomes increasingly important, owing to the higher power display consumption but at the same time more limitation on the size and volume of energy storage. In this thesis, selected aspects regarding to efficiency of three types of optoelectronic devices, indoor photovoltaics (IPVs), perovskite thin-film transistors (TFTs) and organic light-emitting diodes (OLEDs) have been investigated. IPVs can make off-grid devices self-sustainable by harvesting ambient light energy. Its weak irradiance necessitates high-efficiency IPVs to generate sufficient power. Our work addresses the need of knowing the limit of the device parameters for correct evaluation and understanding the efficiency loss for developing clinical tactics. We delivered a general scheme for evaluating the limiting efficiency and the corresponding device parameters of IPVs under various lights, illuminance and material bandgap. In contrast to the AM1.5G conditions, a maximum power conversion efficiency (PCE) of 51-57 % can be achieved under the optimal bandgap of 1.82-1.96 eV. We also propose using the second thickness peak of interference instead of the first as a better optimal absorber thickness after identifying the finite absorption as the major source of efficiency loss. The work provides insights for device evaluation and material design for efficient IPV devices. The novel hybrid organic-inorganic perovskites have gained enormous research interest for its various excellent optoelectronic properties such as high mobility. TFT as an alternative application to the majorly focused photovoltaics is realized in this work. There are few reports on perovskite TFTs due to wetting issues. By employing polymethacrylates with ester groups and aromatic substituents which provide polar and cation-π interactions with the Pb2+ ions, quality films could be fabricated with large crystals and high electron mobility in TFTs. We further improved the performance by resolving interfacial mixing between the perovskite and the polymer using the crosslinkable SU-8, achieving the highest mobility of 1.05 cm2 V−1 s−1. Subsequently, we cured the grain boundaries using methylamine solvent vapor annealing, suppressing the TFT subthreshold swing. The work provides a map for the improvement of perovskite TFTs. It has been revealed that molecular orientations of the emitters in OLEDs with the transition dipole moment lying in plane enhances light outcoupling efficiency. Multiple experimental techniques are needed to provide complementary orientation information and their physical origin. Here, we propose using TFT to probe the orientation of the phosphorescent emitters. Homoleptic fac-Ir(ppy)3 and heteroleptic trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) were deposited on polystyrene (PS) and SiO2 substrates. Compared to the PS surface inducing isotropic orientation as the control, trans-Ir(ppy)2(acac) and trans-Ir(ppy)2(tmd) possessed decreased carrier mobilities on SiO2. With the study of initial film growth, we infer that preferred orientation induced by the polar SiO2 surface led to an increase in energetic disorder in the well-stacked trans-Ir(ppy)2(acac) and hopping distance in the amorphous trans-Ir(ppy)2(tmd). The highly symmetric fac-Ir(ppy)3 remained its isotropic orientation despite the dipolar interaction. Surprisingly, the TFT technique gives much higher sensitivity to surface-induced orientation, and thus may potentially serve as a unique electrical probe for molecular orientation.

The main subject of this thesis is the synthesis and investigation of the properties and potential applications of a new class of hybrid compounds consisting of a rigid, electroactive 4,4’-bipyridinium core capped by nucleobase terminal groups with hydrogen bonding abilities. A new series of small molecules consisting in a 4,4’-bipyridinium unit carrying thymine or/and adenine as capping groups was synthetized. The synthesis strategy implied the regioselective alkylation of thymine and adenine bases respectively, followed by coupling of the alkylated precursors to 4,4’-bipyridine unit via Menschutkin reaction. Electrochemical, spectroelectrochemical and optical investigations revealed an intramolecular charge transfer (CT) relationship between nucleobases as donors and 4,4’-bipyridinium unit as acceptor which is accompanied by a change in color and a shift of the reduction potentials (approx. 60 mV). The viologen-nucleobase derivatives, particularly viologens capped by thymine, were used as building blocks to create self-assembled functional nanostructures in the presence of complementary templates such as oligonucleotides or ssPNA analogues via thymine-adenine interactions. The viologen-thymine derivatives were found to partially precipitate oligonucleotides or plasmid DNA by mean of coulombic interactions and form stable polyplexes that could be used as potential gene delivery vectors. It was found that the number of positive charges, as well as the number of thymine units per viologen-thymine derivative determines whether the interaction with DNA is dominated by electrostatic or by hydrogen bonding interactions. New electroactive ionic liquid crystals were prepared by ion pairing of viologen-nucleobase dicationic species with amphiphilic 3,4,5-tris(dodecyloxy)benzene sulfonate anion. The nucleobases with ability to self-associate by hydrogen bonding were found to influence not just the thermotropic behavior, by decreasing transition temperature from crystalline to mesophase state, but also the supramolecular arrangement in solution. A versatile approach to functionalize mesoporous TiO2 film with viologen-nucleobase derivatives was developed consisting of hydrogen bonding layer-by-layer deposition of viologen-nucleobase derivatives on TiO2 surface using the thymine-adenine molecular recognition as driving force for immobilization. This method is promising and represents an easy way to construct optoelectronic device components as was demonstrated with the construction of a switchable electrochromic device.

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In neuroscience, optical techniques have become the leading method over electrophysiological techniques because of their ability to target defined populations upon tagging both for in vivo recordings using genetically encoded calcium or voltage indicators and stimulation using optogenetic opsins at the single neuronal level. Additionally, optical imaging has a smaller tissue displacement factor, the ratio of displaced neuronal tissue to field of view (FoV), thus accelerating the ability to simultaneously record from a larger volumes of neurons whereas electrophysiology arrays are limited in the total number of recordable neurons by the amount of sustained tissue damage. Conventional optical approaches, however, typically rely on microscopy techniques which require the subject to be head-fixed thus limiting the applicability especially at the chronic setting, raising the need for fully implantable optical interfaces. As a result, multiple lens-based miniature microscopes have been developed in academia and industry. Nevertheless, a truly implantable optical neurotechnology has remained intractable because traditional miniaturized fluorescence microscopes require an opening in the dura and skull that matches or exceeds the FoV and chronically extends outside the skull, resulting in a poor overall displacement factor. To overcome these limitations, I developed and characterized various implantable optoelectronic platforms designed to optically record from large neuronal FoVs in a minimally invasive implantable form factor. These works culminated in the SCOPe (Subdural CMOS Optical Probe) platform which was validated in multiple in vivo demonstrations involving mouse and nonhuman primate.

Computing as a service is rapidly becoming the new normal for many sectors of the economy. The widespread availability of broadband internet has allowed an extensive range of services to be delivered on-demand from centralized computing systems known as ‘data centers’. These systems have evolved to be enormously complex. Optical-based communication is desired to increase data center capability and efficiency, however traditional optical technologies are not feasible due to cost and size. Silicon photonics aims to deliver optical communications on an integrated and affordable platform for use in data centers by leveraging the existing capabilities of complementary metal-oxide semiconductor manufacturing. This thesis contains a description of the development of monolithic silicon photodiodes for use in photonic integrated circuits in, and beyond, the current telecommunications wavelength windows. The focus is on methods which are compatible with standard silicon processing techniques. This is in contrast to the current approaches which rely on hybrid material systems that increase fabrication complexity. Chapter 1 and 2 provide background information to place this work into context. Chapter 3 presents an experimental study of resonant devices with lattice defects which determines the refractive index change in silicon-on-insulator waveguides. High-speed operation of resonant photodiodes is demonstrated and is found to be limited by resonance instability. Chapter 4 demonstrates high responsivity avalanche photodetectors using lattice defects. The detectors are shown to operate error-free at 10 Gbit/s, thus confirming their capability for optical interconnects. Chapter 5 presents photodiodes operating with absorption through surface-state defects. These detectors show fast operation (10 Gbit/s) and have an extremely simple fabrication process. Chapter 6 demonstrates photodiodes operating beyond the traditional telecommunications window. Operation at 20 Gbit/s, at a wavelength of 1.96 µm is demonstrated, offering potential for their use in the next generation of optical communication systems which will exploit the thulium doped fiber amplifier. / Thesis / Doctor of Philosophy (PhD) / This thesis describes photodiodes constructed on silicon optical waveguides. The photodiodes are notable for their high-speed performance and simple fabrication methods. Such devices may find use within chip-integrated optical transceivers, which are desired for optical interconnects within large-scale computing systems such as data centers.