Ces travaux de thèse portent sur l'évaluation des propriétés de nanofils InGaN/GaN en vue de la réalisation de diodes électroluminescentes (LEDs). Deux types d'architecture, obtenus par des techniques de croissance différentes, ont été étudiés. La technique MBE a conduit à la réalisation de LEDs en structure axiale émettant du domaine spectral bleu au rouge. Les émetteurs uniques présentent dans ce cas des diamètres typiquement inférieurs à 100 nm. La technique MOCVD a conduit quant à elle la fabrication de LEDs émettant des longueurs d'onde plus courtes à partir d'hétérostructures InGaN/GaN en Coeur/Coquille présentant des dimensions micrométriques. Dans les deux cas, la croissance est réalisée de manière spontanée sur un substrat Silicium (111) de conductivité élevée permettant l'injection verticale du courant dans les dispositifs intégrés à l'échelle macroscopique. L'ensemble des briques technologiques nécessaires à la fabrication de LEDs a été évalué par un panel important de techniques expérimentales adaptées aux structures à fort rapport de forme. Ainsi, l'effet de l'incorporation d'espèces dopantes de type n (Silicium) et de type p (Magnésium) a été caractérisé par des expériences de spectroscopie optique couplées à des mesures électriques sur fils uniques. De plus, la cathodoluminescence basse température a été largement utilisée afin d'étudier les propriétés optiques de la zone active à base d'InGaN dans les deux architectures considérées. Après intégration technologique, des caractérisations électro-optiques résolues à l'échelle du fil unique ont montré que les performances des LEDs à nanofils restent principalement limitées par la fluctuation des propriétés électriques et optiques entre émetteurs uniques. / This thesis aims at studying the intrinsic properties of InGaN/GaN nanowires (NWs) in order to fabricate efficient light emitting diodes (LEDs). Two active region designs, obtained through different growth techniques, have been extensively investigated. Axial NW-based LEDs emitting from the blue to the red spectral range have been grown by MBE. In this case, single emitters present diameters typically smaller than 100 nm. MOCVD allowed the fabrication of LEDs emitting shorter wavelengths from Core/Shell heterostructures with typical dimensions in the micrometre range. In both cases, the spontaneous growth has been conducted on Silicon (111) highly conductive substrates in order to inject the current vertically into macroscopically contacted devices. Technological building blocks needed to fabricate LEDs have been investigated using a wide range of characterization techniques adapted for high aspect ratio structures. Thus, n-type (Silicon) and p-type (Magnesium) dopings have been assessed thanks to optical spectroscopy techniques, and these results have been confirmed by electrical measurements carried out on single wires. Furthermore, low temperature cathodoluminescence has been widely used to study the optical properties of InGaN-based active regions. After technological integration, electro-optical characterizations with spatial resolution down to the single wire level have revealed that device performances are mainly limited by the fluctuation of electrical and optical properties between single emitters.

Gallium nitride (GaN)-based light-emitting diodes (LEDs) with cylindrical nanostructures have been the subject of significant research interest in the past decade, due to the potential of such structures to increase light extraction efficiency and deliver highly directional light emission. Nanorod LEDs, where the light emission is within the nanocylinder, have the additional potential to increase internal quantum efficiency and emit in colours previously thought impractical with GaN-based LEDs. Optical modelling of nanostructured LEDs is usually carried out using finite-difference time-domain methods, which are computationally intensive and do not always provide sufficient insight into the physics underlying the simulation results. This thesis proposes an intuitive, quasi-analytic method based on modal expansion. It is found that it is possible to calculate the far field diffraction patterns of all guided modes supported by a single nanorod, with full consideration of Fabry-Perot effects, in minutes using a standard office desktop computer. Focus is placed on the case of a nanorod of radius 140 nm, for which angular photoluminescence measurements were available to provide a means of validating the model. Consideration of the guided modes alone provides a compelling explanation for gross features in the measured data where none previously existed. It is shown that, using a standard equation from a textbook, it is possible to calculate how much each of the guided and radiation modes of a single nanorod is excited by a Hertzian dipole of known position and orientation with respect to the nanorod geometry. When interference between these modes is considered, it is possible to calculate the total far field angular emission pattern due to that dipole. Comparing these patterns with photoluminescence measurements allows one to infer the locations and orientations of dipole current sources; the results are found to be consistent with those of cathodoluminescence studies.

Gallium nitride (GaN) and its related semiconductor alloys are attracting tremendous interest for their wide range of applications in blue and green LEDs, diode lasers, high-temperature and high-power electronics. Nanomaterials such as InGaN/GaN core-shell three-dimensional nanostructures are seen as a breakthrough technology for future solid-state lighting and nano-electronics devices. In a core-shell LED, the active semiconductor layers grown around a GaN core enable control over a wide range of wavelengths and applications. In this thesis the capability for the heteroepitaxial growth of a proof-of-principle core-shell LED is advanced. A design that can be applied at the wafer scale using metalorganic vapor phase epitaxy (MOVPE) crystal growth on highly uniform GaN nanorod (NR) structures is proposed. This project demonstrates understanding over the growth constraints of active layers and dopant layers. The impact of reactor pressure and temperature on the morphology and on the incorporated InN mole fraction was studied for thick InGaN shells on the different GaN crystal facets. Mg doping and effectiveness of the p-n junction for a core-shell structure was studied by extensive growth experiments and characterization. Sapphire and Si substrates were used, and at all the stages of growth and fabrication. The structures were optimized to achieve geometry homogeneity, high-aspect-ratio, incorporation homogeneity for InN and Mg dopant. The three-dimensional nature of NRs and their light emission provided ample challenges which required adaptation of characterization and fabrication techniques for a core-shell device. Finally, an electrically contacted core-shell LED is demonstrated and characterized. Achieving a proof-of-principle core-shell device could be the starting point in the development of nanostructure-based devices and new physics, or in solving technical problems in planar LEDs, such as the polarization of emitted light, the quantum-confined Stark effect, efficiency droop, or the green gap.

Denna rapport beskriver ett examensarbete där optiska fibrer av plast integrerades i varpled i en väv. Syftet med examensarbetet var att undersöka om det är möjligt att industriellt producera ljusemitterande vävar med optiska fibrer. Arbetet delades upp i olika delar, både teoretiska och praktiska. Den teoretiska delen innebar informationssökning inom olika medier, såsom vetenskapliga artiklar och intervjuer med insatta människor inom de berörda områdena. Den praktiska delen i examensarbetet bestod av flera olika moment. Först utfördes en provvävning i en handvävstol, för att finna en lämplig bindning och lära känna materialen. Därefter konstruerades en metod för att testa olika slipmaterial att slipa den optiska fibern med, och utifrån resultaten valdes två slipmaterial ut. Sedan sattes en väv med optiska fibrer upp i en vävmaskin och ett flertal provvävar vävdes. I ett optiklaboratorium skedde sedan mätningar på provvävarnas ljusemittering.Resultatet av mätningarna visade att de optiska fibrerna inte klarade av krökningarna i väven. För mycket ljus läckte ut i krökningarna så väven lyste inte mer än 50 cm. Slutsatsen är att det är fullt möjligt att väva med optisk fiber i varpled, men en bindning där de optiska fibrerna ligger rakt i väven måste konstrueras. In this bachelor thesis has plastic optical fibres been integrated in the warp of a weave. The purpose of the thesis was to make a research if it is possible to produce light emitting weaves with optical fibres in an industrial production. The thesis was divided into several parts, both theoretical and practical. The theoretical part involved taking part of different types of information, such as scientific articles and interviews with knowledgeable people within the related areas.The practical part in this thesis was composed of several different phases. A test weave in a handloom was first performed to find out which weave to use and to understand the materials behaviour. Then a method for testing different materials to grind the optical fibre with was constructed, and out of the results two materials were chosen. After that, a warp with optical fibres was placed into a loom and several prototypes were woven. In an optic laboratory were measurements made on the prototypes’ light emitting ability. The results of the measurements showed that the optical fibres did not cope with the bends in the weave. Too much light emitted out of the bends so the weave only emitted light for 50 cm. The conclusion is that it is possible to weave with optical fibres in the warp, but a new weave where the optical fibres lie straight in the fabric must be constructed. / Program: Textilingenjörsutbildningen

Submitted by Erika Demachki (erikademachki@gmail.com) on 2014-09-25T20:32:22Z No. of bitstreams: 3 Dissertacao_JLFB_VFinal.pdf: 18601269 bytes, checksum: ec6c9955a2f1d95120cab2f797232e97 (MD5) Capa Dissertacao_JLFB_VFinal.pdf: 4769532 bytes, checksum: 3d15c52d57be870999449e2a7b78fbb3 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2014-09-26T11:57:17Z (GMT) No. of bitstreams: 3 Dissertacao_JLFB_VFinal.pdf: 18601269 bytes, checksum: ec6c9955a2f1d95120cab2f797232e97 (MD5) Capa Dissertacao_JLFB_VFinal.pdf: 4769532 bytes, checksum: 3d15c52d57be870999449e2a7b78fbb3 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2014-09-26T11:57:17Z (GMT). No. of bitstreams: 3 Dissertacao_JLFB_VFinal.pdf: 18601269 bytes, checksum: ec6c9955a2f1d95120cab2f797232e97 (MD5) Capa Dissertacao_JLFB_VFinal.pdf: 4769532 bytes, checksum: 3d15c52d57be870999449e2a7b78fbb3 (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2013-06-14 / The purpose of this work is to present a methodology for optimizing the geometry of the Light Emitting Diode (LED) secondary lens, in non-imaging applications, which focuses on the distribution of illuminance on a target plane. The simulation of Ray Tracing is produced by stochastic method and the optimization process based on heuristic search interacts with Ray Tracing to nd the optimized parameters of the LED secondary lens geometry. / O propósito deste trabalho e apresentar uma metodologia para otimiza ção da geometria da lente secund ária de Light Emitting Diode (LED) para aplica ção em iluminação, tendo como enfoque a distribuição da iluminância sobre um plano alvo. A simulação do Ray Tracing e produzida através do m etodo estoc astico e o processo de otimização interage com o Ray Tracing através de um m étodo heur ístico na busca dos parâmetros otimizados da geometria da lente secundária do LED.

As microalgas são candidatas promissoras para a produção em larga escala de biocombustíveis devido a sua alta eficiência fotossintética. No entanto, os custos relativamente altos de produção por baixas produtividades em lipídios têm sido um dos principais obstáculos que impedem sua produção comercial. Portanto, é necessário focar a pesquisa no aumento da biomassa e na produtividade em lipídios, através do desenvolvimento de biorreatores e técnicas de cultivo inovadoras. Numa primeira fase, este estudo mostra a otimização dos regimes de adição de nutrientes no cultivo de Neochloris oleoabundans em fotobiorreatores tubulares, determinando que a melhor metodologia de adição de CO2 é adicionando-o de forma intermitente e automatizada, enquanto que o melhor processo de alimentação de nitrogênio é por meio de um processo em batelada alimentada tomando como uma referência a produtividade diária de biomassa. Na segunda etapa, foi testada a influência de agentes estressores adicionados ao cultivo sob carência de nitrogênio, tais como tiossulfato de sódio como agente redutor e cloreto de sódio e glicerina como agentes de choque osmótico, buscando um acúmulo de lipídios na biomassa. Os resultados mostraram que o tiossulfato de sódio em 1,2 mM e o cloreto de sódio em 2,2 mM aumentaram o total de lipídios em 21% e 25%, respectivamente. Finalmente, foram testados diferentes regimes de luz, com um esquema 12:12, sendo 12 horas de luz fluorescente e 12 horas com um sistema distinto: escuro, diodos emissores de luz (LED) vermelha e LED branca. Os melhores resultados foram obtidos com LED branca, com um acúmulo de lipídios de até 27% da biomassa seca e uma concentração final de células de 2335mg/L, estabelecendo assim um método de iluminação econômica com alta produtividade (145mg / L dia). / Microalgae are promising candidates for large-scale global biofuel production because of their high photosynthetic efficiency. However, relatively high production costs due to low lipid productivity have been one of the major obstacles impeding their commercial production. Therefore, it is necessary to accurate the research into an increase in biomass and oil productivity, by means of novel bioreactors\' design and cultivation techniques. On a first stage, this study shows the optimization of nutrients\' addition regimes in Neochloris oleoabundans cultivation in tubular photobioreactors, finding that the best CO2 addition methodology is an automatized intermittent adding and the best feeding process for nitrogen is a fed-batch process taking as a reference the daily biomass productivity. On the second step, it was tested the influence of stressing agents added to the culture under nitrogen starvation, such as sodium thiosulphate for reducing environment and sodium chloride and glycerol for osmotic shock, aiming lipid accumulation in the biomass. The results showed that sodium thiosulphate at 1,2mM and sodium chloride at 2,2mM raised the total lipids up to 21% and 25% respectively. Finally, there were tested different light regimes, with a scheme 12:12, being 12 hours of fluorescent light and 12 hours of a singular system: dark, red light-emitting-diodes (LED) and white LED. The best results were obtained with white LED, with an accumulation up to 27% of dry biomass and a final cell concentration up to 2335mg/L, establishing an economic illumination method with high productivity.

Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-05-24T17:46:47Z No. of bitstreams: 1 BeneditaCosta.pdf: 3463817 bytes, checksum: f105e5bbf653ecaa37f7e7f59c1026ce (MD5) / Made available in DSpace on 2017-05-24T17:46:47Z (GMT). No. of bitstreams: 1 BeneditaCosta.pdf: 3463817 bytes, checksum: f105e5bbf653ecaa37f7e7f59c1026ce (MD5) Previous issue date: 2017-03-29 / Fundação de Amparo à Pesquisa e ao Desenvolvimento Científico e Tecnológico do Maranhão (FAPEMA) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPQ) / The use of LEDs was evaluated as attractants for insect vectors and there are several advantages over the standard incandescent lamp favoring the use of LED technology as alternative light source for sampling medically important mosquitoes. Therefore, other studies were conducted in order to evaluate the response to the different wavelengths; however data on the use of LEDs and light intensity to attract anopheline mosquitoes are scarce. This study main purpose was to evaluate the efficiency of LEDs and the influence of the light intensity in the captures of malaria vectors upon the lunar phases, in a peridomiciliary area in northeastern Maranhão, Brazil. In the first essay, incandescent lamps routinely used in CDC-type light traps were replaced for 5 mm LEDs (green – 520 nm; blue – 470 nm) to evaluate the response of anopheline mosquitoes to those alternative light sources. However, the incandescent lamp was used as control. To test the influence of moonlight, the collections were undertaken under the four lunar phases during the study period. In the second essay, it was analyzed the influence of light intensity on the captures of mosquitoes, six light traps with LEDs of different light intensities were used: green (10,000 mCD, 15,000 mCD and 20,000 mCD) and blue (4,000 mCD, 12,000 mCD and 15,000 mCD). As a result in the first essay, 1,845 specimens and eight species foi was sampled. The most frequent species were Anopheles evansae, accounting for 35.2%, followed by An. triannulatus s.l.(21,9%), An. goeldii (12,9%) and An. argyritarsis (11,5%). The green LED was the most efficient light source, it had attracted 43.3% of the individuals, followed by the blue LED (31.8%) and the control (24.9%). The LED traps were more attractive than the control, regardless the lunar phase. In all tests, the captures were more efficient when LEDs were used to attract the anopheline mosquitoes than when the control was used. As a result in the second essay, a total of 1,650 specimens and five species of anopheline mosquitoes were sampled. The blue LED attracted more individuals (953) than the green one (697). According to the light intensity, the green LED 20.000mCD had a greater attractiveness showing 39.2% increase related to the others intensities. While the blue LED 15.000mCD has attracted 50.2% of the specimens captured. The efficiency of LEDs improves light trapping results and it is suggested that the use of LEDs as an attractant for anopheline mosquitoes should be taken into consideration when monitoring mosquito populations. Thus, the light intensity was a very important factor in enhancing the light trap performance in attracting the mosquitoes; more intense the light, more insects attracted. However, the light intensity is an important attribute for sampling more efficiently insect vectors. / O uso diodo emissor de luz (LED) foi avaliado como atrativo para insetos vetores e tem apresentado varias vantagens sobre a lâmpada incandescente convencional, favorecendo o uso da tecnologia LED como uma fonte de luz alternativa para a amostragem de mosquitos de importância médica. Além disso, outros estudos foram realizados a fim de examinar a resposta a diferentes comprimentos de onda, entretanto dados sobre o uso de LED e sua intensidade luminosa para atrair mosquitos anofelinos são escassos. Esse estudo teve como propósito avaliar a eficácia de LEDs e a influência da intensidade da luz nas capturas de mosquitos anofelinos, diante das fases lunares, em área peridomiciliar no Nordeste do Maranhão. No primeiro ensaio as lâmpadas incandescentes convencionais utilizadas em armadilhas luminosas do tipo CDC foram substituídas por LEDs de 5 mm (verde: 520 nm; azul: 470 nm) para avaliar a resposta de mosquitos anofelinos às fontes de luz alternativas, a lâmpada incandescente foi utilizada como controle. Para testar a influência da fase lunar, as coletas foram realizadas sob as quatro fases lunares durante o período de estudo. No segundo ensaio foi analisado a influência da intensidade luminosa nas capturas de mosquitos, foram utilizadas seis armadilhas luminosas com diferentes intensidades de luz: verde (10.000mCD, 15.000mCD, 20.000mCD) e azul (4.000mCD, 12.000mCD, 15.000mCD). Como resultado do primeiro ensaio, um total de 1.845 espécimes e oito espécies foram coletados. As espécies mais frequentes foram Anopheles evansae, representando 35,2%, seguido por An. triannulatus s.l. (21,9%), An. goeldii (12,9%) e An. argyritarsis (11,5%). O LED verde foi à fonte de luz mais eficaz, tendo atraído 43,3% dos indivíduos, seguido do LED azul (31,8%) e o controle (24,9%). As armadilhas com LED foram mais atrativas do que o controle, independentemente da fase lunar. Em todos os testes, as capturas foram mais eficientes quando os LEDs foram usados para atrair os mosquitos anofelinos do que quando utilizou-se o controle. Como resultado do segundo ensaio, um total de 1.650 espécimes e cinco espécies de mosquitos anofelinos foram capturados. A armadilha com LED azul atraiu mais indivíduos (953) do que o verde (697). Quanto às intensidades de luz, o LED verde de 20.000mCD obteve maior atratividade com 39,2% em relação às demais intensidades. Enquanto o LED azul de 15.000mCD atraiu 50,2% dos individuos capturados. A eficiência dos LEDs melhora os resultados de captura com luz, sugere-se o uso de LEDs como atrativo para mosquitos anofelinos e deve ser levado em consideração nas atividades de monitoramento de populações de mosquitos. Além disso, a intensidade luminosa é um fator importante para aumentar o desempenho da armadilha luminosa na atração dos mosquitos, quanto mais intensa a luz, mais insetos são atraídos. Portanto, a intensidade luminosa dos LEDs é um importante atributo para amostragem de insetos vetores.

Observando o atual interesse em polímeros organometálicos para diversas aplicações, foi feita a síntese de uma série de polímeros conjugados contendo ferroceno na cadeia principal visando à investigação de suas propriedades, em especial fenômenos magnetorresistivos, magneto-ópticos e de óxido-redução. Os polímeros preparados pelo método de McMurry foram os seguintes: PFV: poli(1,1\'-ferrocenilenovinileno) e PFV-DOPPV-M: poli[1,1\'-ferrocenilenovinileno-alt-(2,5-di-n-octilóxi)-1,4-fenilenovinileno]. Outros dois polímeros foram preparados utilizando o método de polimerização de Wittig, o PFV-DOPPV-W: poli[1,1\'-ferrocenilenovinileno-alt-(2,5-di-n-octilóxi)-1,4-fenilenovinileno] e o PFV-DMPPV: poli[1,1\'-ferrocenileno-vinileno-alt-(2,5-dimetóxi)-1,4-fenilenovinileno]. A síntese de polímeros contendo segmentos π-conjugados equenos e bem definidos separados por segmentos não-conjugados é uma das melhores stratégias para a obtenção de polímeros emissores de luz azul. Com base nesse argumento foi feita a síntese de uma série de polímeros contendo um derivado metoxilado de bisfenol-A (BPA) na cadeia principal, alternando-se com unidades de PPV ou PFV que apresentam segmentos conjugados bem definidos. Os polímeros preparados foram os seguintes: BPA-DOPPV:poli[2,2-bis(4-metoxifenil)-propano-alt-2,5-(di-n-octilóxi)-1,4-divinilbenzeno]; BPA-PPV: poli[2,2-bis(4-metoxifenil)-propano-alt-1,4-ivinilbenzeno]; BPA-DMPPV: poli[2,2-bis(4-metoxifenil)-propano-alt-2,5-dimetóxi-1,4-ivinilbenzeno]; BPA-DBPPV: poli[2,2-bis(4-metoxifenil)-propano-alt-2,5-dibromo-1,4-divinilbenzeno] e BPA-PFV: poli[2,2-bis(4-metoxifenil)-propano-alt-1,1\'-divinil-ferroceno]. Todos os polímeros obtidos foram caracterizados por métodos espectroscópicos (UV-VIS, IR, RMN), análises térmicas, SEC, entre outras. Algumas aplicações foram estudadas para esses polímeros, tais como a construção de um eletrodo de ORP modificado, a produção de diodos orgânicos emissores de luz (OLEDs) e a determinação da resposta \"olfativa\" de sensores de gases. / Owing to the current interest in organometallic polymers and their applications, a group of conducting polymers containing ferrocene in the main chain was synthesized aiming the study of their magnetoresistive, magneto-optic and redox properties. The following polymers were prepared via McMurry method: poly(1,1\'-ferrocenylenevinylene) (PFV) and poly[1,1\'-ferrocenylenevinylene-alt-(2,5-di-n-octiloxy)-1,4-phenylenevinylene] (PFV-DOPPV-M). Two other polymers were synthesized via Wittig method: poly[1,1\'-ferrocenylenevinylene-alt-(2,5-di-n-octiloxy)-1,4-phenylenevinylene] (PFV-DOPPV-W) and poly[1,1\'-ferrocenylene-vinylene-alt-(2,5-dimethoxy)-1,4-phenylenevinylene] (PFV-DMPPV). The synthesis of polymers with well-defined small π-conjugated segments separated by non-conjugated segments is one of the best strategies to obtain blue light emitting polymers. Based on this statement the synthesis of several polymers formed by methoxylated bisphenol-A (BPA) alternated with PPV or PFV units was performed. The prepared polymers were the following: poly[2,2-bis(4-methoxyphenyl)-propane-alt-2,5-(di-n-octiloxy)-1,4-divinylbenzene] (BPA-DOPPV), poly [2,2-bis(4-methoxyphenyl)-propane-alt-1,4-divinylbenzene] (BPA-PPV), poly[2,2-bis(4-methoxyphenyl)-propane-alt-2,5-dimethoxy-1,4-divinylbenzene] (BPA-DMPPV), poly[2,2-bis(4-methoxyphenyl)-propane-alt-2,5-dibromo-1,4-divinylbenzene] (BPA-DBPPV) and poly[2,2-bis(4-methoxyphenyl)-propane-alt-1,1\'-divinylferrocene] (BPA-PFV). All the synthesized polymers were characterized by spectroscopic methods (UV/VIS, IR, NMR), thermal analysis, SEC, among others. Some applications to these polymers were studied: a modified ORP electrode, organic light emitting devices (OLEDs) and gas sensors.

This thesis consists of three main studies: magnetic field effects in thermally activated delayed fluorescent (TADF) organic light emitting diodes (OLEDs), magnetic field effects in bipolar and unipolar polythiophene (P3HT) devices and a study of hybrid organic/inorganic perovskite devices. Spin-dependent transport and recombination processes of spin-pair species have been detected by magnetic field effect (MFE) technique in carbon-based semi- conductor devices. Magneto-electroluminescence (MEL) and magneto-conductivity have been measured as a function of the applied magnetic field, B, in light emitting diodes. TADF materials have been used instead of simple fluorescent materials in OLEDs. We have observed very large magnetic response with TADF materials. The second study is magnetic field effects of regio-regular P3HT based OLED devices. P3HT is a well known semiconducting polymer, and its electrical properties such as magneto-conductance can be affected by an applied magnetic field. P3HT was chosen because it exhibits a sign change in magnetoresistance (MR) as the bias is increased. Unipolar and bipolar devices have been fabricated with different electrode materials to understand which model can be best to explain organic magnetoresistance effect, possibly depending on the operating regime of the device. Transport and luminescence spectroscopies were studied to isolate the different mechanisms and identify their fingerprints. The third study is on hybrid organic-inorganic perovskite devices. With the potential of achieving very high efficiencies and the very low production costs, perovskite solar cells have become commercially attractive. Scanning electron microscopy (SEM) images and absorption spectrum of the films were compared in single-step solution, two-step solution and solution-assisted vapor deposition techniques. Grain size, morphology and thickness parameters of perovskite films were studied within these techniques. Perovskite solar cells were fabricated and their efficiencies were measured.

Organic semiconductors (OSCs) have already been shown to have great potential to play an important role in the future of clean energy generation (organic solar cells) and provide energy efficient lighting (organic light-emitting diodes, OLED). Prior research has found that the light-emission efficiency of OLED is severely limited by the magnetic state (technically the spin-configuration) of the light-emission process. In this thesis, we work on the processes using external magnetic fields that can overcome these magnetic limitations. A major focus of this research is to enhance the performance of OLED, while at the same time to unravel the scientific mechanisms by which magnetic fields act on OSCs devices. Thermally activated delayed fluorescence (TADF) is a next-generation OLED emission technology which enables nearly 100% light-emission efficiency without using heavy precious metals. TADF characteristics depend on the probability of reverse intersystem crossing (RISC) from the triplet excited states (T1) to singlet excited states (S1). The conversion (T1 to S1) process depends strongly on spin dynamics, thus we predict a dramatic magnetic field effects (MFEs) in such TADF OLED devices. In subsequent experiments we observed that changes in TADF devices due to various forms of electrical stress can lead to enormous increases in magnetic field effects (MFEs) on the current (> 1400%) and electroluminescence (> 4000%). Our work provides a flexible and inexpensive pathway towards magnetic functionality and field sensitivity in current organic devices. Such OLED pave the way for novel magnetic sensitive OSCs devices with integrated optical, electronic and magnetic characteristics. Organic magnetoresistance (OMAR) has been observed to alter the current and efficiency of OLED without any ferromagnetic components. Here we utilizes slight alterations to the device properties, the addition of a radical-doped functional layer, in which the spin-relaxing effects of localized nuclear spins and electronic spins interfere, to address the assumption about the importance of the hyperfine interaction and to attempt to differentiate between the different models for OMAR. A feature where the magnitude of OMAR exhibits a plateau over a wide range of doping fraction was observed at all temperatures investigated. This phenomenon is well explained by a theory in which a single dopant spin strongly interacts, by exchange, with one of the bottleneck sites. A similar can be used to explain the efficiency increases observed in organic solar cells for certain doping fractions.