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Celulas fotovoltaicas hibridas de polimeros condutores e nanoparticulas inorganicas / Hybrid solar cells based on conducting polymers and inorganic nanoparticlesFreitas, Jilian Nei de 14 August 2018 (has links)
Orientadores: Ana Flavia Nogueira, Jonas Gruber / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-14T17:00:59Z (GMT). No. of bitstreams: 1
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Previous issue date: 2009 / Resumo: Este trabalho consistiu no desenvolvimento e caracterização de materiais para aplicação em células fotovoltaicas híbridas. No Capítulo I, uma introdução geral sobre o funcionamento e estado da arte de células solares, e sobre as propriedades de polímeros condutores e nanopartículas inorgâncias é apresentada. O Capítulo II contém os objetivos deste trabalho. No Capítulo III, foram investigados novos polímeros condutores, baseados na combinação de unidades fluoreno com unidades tiofeno e/ou benzeno. As propriedades fotofísicas, eletroquímicas e de transporte de cargas foram caracterizadas, e esses polímeros foram então combinados com um derivado solúvel de fulereno (PCBM) e os compósitos formados (heterojunção) foram aplicados em células solares com configuração ITO | PEDOT:PSS | Heterojunção | LiF | Al. A seguir, foram sintetizadas nanopartículas de CdSe com diferentes tamanhos, usando um método descrito na literatura. Essas partículas foram caracterizadas por medidas de absorção e emissão, voltametria cíclica (VC), difração de Raios-X (DRX) e microscopia eletrônica de transmissão (TEM), conforme apresentado no Capítulo IV. Os polímeros investigados inicialmente foram combinados com as nanopartículas de CdSe, e esses materiais foram utilizados na montagem de células solares híbridas. De modo geral, os dispositivos apresentaram valores baixos de fotocorrente, o que foi atribuído ao fato de as nanopartículas inorgânicas não transportarem elétrons de forma efetiva nesses dispositivos. A seguir, propôs-se um novo sistema, em que a heterojunção constitui na mistura ternária polímero/CdSe/PCBM. Esses dispositivos foram caracterizados por curvas de corrente-potencial e pela resposta espectral do sistema, mostrando resultados extremamente promissores. Os sistemas ternários foram então investigados por diversas técnicas, como absorção, emissão, DRX, VC, TEM e microscopia de força atômica, a fim de determinar a atuação de cada componente da mistura ternária quando aplicados nas células solares. Esses resultados são apresentados no Capítulo V. No Capítulo VI, novos polímeros condutores derivados do polifluoreno, contendo unidades funcionais como grupos piridina, ou compostos aromáticos do tipo "push-pull", foram sintetizados pelo método de Gilch. A estrutura desses polímeros foi desenhada visando sua aplicação nas células híbridas, combinandoos com as nanopartículas de CdSe previamente sintetizadas. Esses materiais foram caracterizados por ressonância magnética nuclear de hidrogênio, espectroscopia no Infravermelho com transformada de Fourier. cromatografia por permeação em gel, análises térmicas e medidas eletroquímicas e de fotofísica. No Capítulo VII, propôs-se a introdução de um corante orgânico comercial (Disperse Red 1), como terceiro componente em uma mistura de poli(fluorenilenovinileno) e PCBM, visando aumentar a absorção de luz pela camada ativa do dispositivo. Foi realizado um extenso estudo usando técnicas fotofísicas e eletroquímicas para investigar o efeito da adição do corante, bem como determinar quais os tipos de processos (transferência de elétrons ou energia) ocorrem no sistema ternário. Finalmente o Capítulo VIII contém as principais conclusões deste trabalho e perspectivas de continuação para esta linha de pesquisa. / Abstract: This PhD Thesis investigated the development and characterization of new materials aiming at the application in hybrid solar cells. In Chapter I, a general introduction on the working principles and state-of-the-art of the organic solar cells, properties of the conducting polymers and the inorganic nanoparticles are presented. Chpater II highlights the aims of this work. In Chapter III, new conducting polymers based on the combination of fluorene, thiophene and/or benzene units are investigated. The photophysical and electrochemical characteristics, and charge mobility, are discussed. The polymers were also combined with a soluble fullerene derivative (PCBM) and these composites were used as active layer in bulk-heterojunction solar cells with the following configuration: ITO | PEDOT:PSS | Heterojunction | LiF | Al. Then, CdSe nanoparticles with different sizes were synthesized using a well-established method, and characterized using absorption and emission measurements, cyclic voltammetry (CV), X-ray diffraction (XRD) and transmission electron microscopy (TEM), as presented in Chapter IV. The previously characterized polymers were combined with the CdSe nanoparticles, and the nanocomposites were used to assemble hybrid solar cells. The devices showed very low photocurrent values, which were attributed to a poor electronic transport in the nanoparticles phase. Thus, a new system was suggested, based on a mixture of polymer/CdSe/PCBM. The photocurrent-potential curves and spectral response of the devices assembled with the ternary systems were evaluated, leading to very promising results. The absorption, emission, XRD, CV, TEM and atomic force microscopy measurements of the films were also performed to investigate/elucidate the role of each component in the ternary systems, as discussed in Chapter V. In Chapter VI, new conducting polymers based on poly(fluorenylenevinylene) containing functional units, such as pyridine or push-pull type aromatic units, were synthesized via the Gilch route. The structures of these materials were designed aiming at their application in hybrid solar cells, in combination with the previously synthesized CdSe nanoparticles. The polymers were characterized by magnetic nuclear resonance, Fourier transform infrared spectroscopy, gel permeation chromatography, and thermal, electrochemical and photophysical measurements. These polymers were combined with CdSe and/or PCBM and used as active layer in solar cells. In Chapter VII the addition of the commercial organic dye Disperse Red 1 in the mixture of poly(fluorenylenevinylene)/PCBM to enhance the light absorption in the active layer was investigated. A systematic study using photophysical and electrochemical measurements was performed in order to elucidate the effect of the dye addition, as well as the energy or electron transfer processes in this new ternary system. Finally, Chapter VIII summarizes the main conclusions of this work and highlights some perspectives for this exciting research filed. / Doutorado / Quimica Inorganica / Doutor em Ciências
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Incorporation des principes de la chimie verte dans la synthèse de semi-conducteurs organiques / Incorporation of the green chemistry principles in the synthesis of organic semiconductorsFaurie, Alexandre 06 November 2015 (has links)
Les travaux réalisés aux cours de cette thèse ont pour but de proposer une alternative verte à la synthèse de nouveaux systèmes conjugués linéaires pour des applications en électronique plastique. La première partie sera consacrée à l’élaboration de systèmes conjugués de type D-A par une combinaison de réactions vertes : substitution nucléophile aromatique et condensation de Knoevenagel réalisées,respectivement, dans l’eau et l’éthanol. De plus, une nouvelle méthodologie sera explorée pour rendre le couplage de Stille plus éco-compatible : l’utilisation de réactifs stannylés supportés sur liquide ionique ou billes de polymère. Par cette nouvelle approche, de nouvelles structures moléculaires ont été synthétisées et ont aussi montré leur efficacité comme matériau donneur pour cellules solaires organiques.La deuxième partie s’intéressera aux relations entre structure, organisation à l’état solide et luminescence des distyrylfuranes, lorsque les substituants aromatiques latéraux varient. Le coeur furane est produit à partir de la biomasse, et les substituants sont insérés par condensation de Knoevenagel. Une étude similaire sera mise en place pour deux dérivés de benzodifurane,qui seront en plus testés en tant que matériau donneur. / This work stands for an alternative and green synthesis of new linear conjugated systems that will serve for applications in organic electronics.The first part is devoted to the design and synthesis of D-A-type conjugated systems by a combination of green reactions: nucleophilic aromatic substitution and Knoevenagel condensation, which are performed in water and ethanol, respectively. Also, a green methodology will be applied to the Stille cross-coupling by using ionic liquid, or polymer,-supported reagents. By this new approach, efficient donor materials for solar cells have been produced.The second part will focus on the relationships between the structure, the solid state organization and the luminescence of distyrylfurans with the variation of thearomatic substituants. The center of the molecule, a furan, is produced from biomass, and the aromatic substituants are incorporated by Knoevenagel condensation. A similar study will be performed on two benzodifuran derivatives, which will be also tested for solar cell applications.
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Optimalizace organických solárních článků / Optimization of organic solar cellsKratochvíl, Matouš January 2017 (has links)
This diploma thesis focuses on the preparation of large-scale organic solar cells using techniques compatible with large volume production. The theoretical part consists of research summarizing the basic theoretical background of the function of organic solar cells and the current state of investigation of the shift from laboratory to large-scale production. The experimental part deals with the optimization of methods of preparation of layers of structure of solar cells, which can be converted into industrial scale.
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Investigation of Low Optical-Gap Donor and Acceptor Materials for Organic Solar CellsShivhare, Rishi Ramdas 29 January 2020 (has links)
Development of efficient and clean energy sources to meet the ever-increasing de- mand of humankind is one of the greatest challenges of the 21st century. There is a dire need to decarbonise the power sector, and the focus needs to shift to re- newable resources such as wind and solar energy. In this regard, organic solar cells are a promising and novel technology owing to its low carbon footprint, innovative applications, and possible integration into the current infrastructure. Due to its unique advantages, a considerable research effort has been put into its development in the last decades. As a result, the power conversion efficiency (PCE) of the organic photovoltaics has steadily risen from as low as 0.5% to around 17 % at the current stage. This improvement primarily originates from the better understanding of the underlying physical processes and as a result of extensive material development.
In the most general case, organic solar cells consist of a binary blend of an electron donating and an electron accepting organic semiconductor forming the so-called ‘bulk-heterojunction’ (BHJ) morphology. Thermodynamics places an upper limit on the power conversion efficiency (PCE) of binary blend BHJ devices and for further enhancement in efficiency novel device concepts like the use of ternary blends and tandem device architectures is being investigated. In relation to these approaches, the development of low optical-gap (Eopt ≤ 1.5 eV) organic semiconductors has gained importance as these materials provide for the complementary absorption with respect to the other components and better harvesting of the solar spectrum.
This work mainly deals with the investigation of low optical gap donor and acceptor materials for organic solar cells. We investigate the effect of the molecular structure on the device performance and the photophysical processes in the binary and ternary blend configuration. In the first part of the thesis, we study a family of low optical- gap diketopyrrolopyrrole (DPP) based polymers while varying the conjugated core and the branching position and length of the solubilizing alkyl side chains. The branching position of the side chains is found to have a significant influence on the polymers ability to crystallize, which in turn influences the mobility of free charge carriers. The branching position also affects the solubility of the polymer, which in turn influences the morphology of the bulk-heterojunction (BHJ) and ultimately the yield of photogenerated charge carriers.
To investigate the electron transfer and charge separation dynamics in the blends consisting of DPP polymers and fullerene, we employed ultrafast pump-probe spec- troscopic techniques. In the spectroscopy data, we observe signatures suggesting an ultrafast electron transfer process and an efficient charge separation process due to the high mobility of the free charge carriers shortly after separation (∼10-100 ps).
Lastly, we investigated indacenodithiophene (IDT) based non-fullerene acceptor (NFA) molecules. In particular, we studied the effect of fluorination on the device performance when these acceptors are blended with PTB7-Th and P3HT donor polymers. The kinetics of the photophysical processes in the binary and ternary blends are characterized using ultrafast spectroscopy and related to the morphology of the blend and the molecular structure of the acceptors.
Overall, we investigated the structural variations in the DPP polymers and flu- orinated non-fullerene acceptor (NFA) molecules and suggest design rules for the synthesis of optimal DPP polymers and non-fullerene acceptors to achieve supe- rior device performance. Additionally, we also shed light on the phenomenological processes happening on an ultrafast time scale (0.2-1000 ps) in the binary and the ternary blends with the aim of developing a better understanding of the photophys- ical processes in these promising material systems.
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Combined MD/DFT protocol for the simulation of molecular materials for organic solar cellsTurelli, Michele 05 March 2021 (has links)
In much of the literature about organic photovoltaics, the topic is framed within the current landscape of energy production and the research on these materials is cited as a possible solution to the energy crisis looming ahead. Despite being the most frequent, this is by no means the only perspective that can be offered. Indeed, the same research may also be set within the larger perspective offered by the field of functional materials. These materials are usually exploited for their particular responses to electrical, magnetic and chemical stimuli and are at the basis of many technologies fundamental to our society.
The prominent position of functional materials in modern science is due to the emergence of novel technological needs that such materials have been able to satisfy thanks to their peculiar properties. These properties have been rationalised and mastered by expanding the theoretical description of the underlying physical mechanisms. This theoretical body, combined with the growth and diffusion of computational capabilities has fostered a change in the scientific paradigm underpinning the research effort. More and more, the predictive power of numerical approaches is exploited to lead the way in the exploration of the immense chemical space. The ultimate promise is to achieve the purpose-driven design of compounds thanks to which the molecular structure can be engineered before the actual synthesis to meet the demands dictated by a specific application. To fulfil this role, computational approaches need to be able to simulate the solid state properties at the most relevant time and length scales. If this can be accomplished then a reliable prediction of the performance can be achieved. The current work deals with the development and application of one such protocol, for the particular case of organic photovoltaic semiconductors. Given the specific application, the properties targeted are light absorption and charge transport. Particular effort is put in the simulation of local morphologies at scales above the molecular one to describe supramolecular organisation with sufficient resolution. In this thesis, the protocol is applied to two molecular systems employed in solar devices. Both systems have been selected on the basis of data suggesting that a detailed microscopic description of their behaviour could be highly informative about the aspects responsible for their photovoltaic performance. In particular, chapter 3 details the investigation of a small-molecule donor that has been shown in the literature to have a remarkable behaviour in absorption. While chapter 4 reports the study of a donor-acceptor dyad used as active layer in single-component solar devices with relatively high conversion efficiency. In both cases, the computational protocol has proven capable of providing a detailed microscopic description of the systems. The picture drawn has allowed to clarify the plausible mechanisms behind the observations and to rationalise these behaviours in a broader and more general theoretical framework.
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Charakterisierung von organischen Solarzellen an einem neu aufgebauten Laser-basierten DSR-MessplatzFey, Thomas 23 October 2015 (has links) (PDF)
Die Physikalisch-Technische Bundesanstalt (PTB) unterstützt vielfältig die Gesellschaft, Wirtschaft und Wissenschaft. Eine ihrer Kernkompetenzen als das nationale Metrologie-Institut der Bundesrepublik Deutschland ist die Messtechnik. In diesem Sinne kalibriert die Arbeitsgruppe „Solarzellen“ der PTB
i. d. R. den Kurzschlussstrom unter Standardtestbedingungen (I_STC) von Referenzsolarzellen. Der I_STC von Referenzsolarzellen ist in Photovoltaik-Kalibrierketten bei der Bestimmung der Bestrahlungsstärke von zentraler Bedeutung und fließt signifikant in die Berechnung der Wirkungsgrad von Solarzellen und Solarmodulen ein.
Um den I_STC einer Solarzelle mit geringster Messunsicherheit zu bestimmen, wurde die Differential Spectral Responsivity (DSR)-Methode verwendet. Sie basiert auf der Messung der differentiellen spektralen Empfindlichkeit bei unterschiedlichen Bestrahlungsstärken. Anhand dieser kann die absolute spektrale Empfindlichkeit s(λ) unter Standardtestbedingungen sowie der I_STC berechnet werden. Da jedoch die Umgebungsbedingungen meistens von den STC abweichen, reichen letztere nicht zum umfassenden Vergleich der Wirkungsgrade in der Praxis aus. Um Einflussfaktoren (Temperatur, Bestrahlungsstärke, Winkelabhängigkeit,...) genauer untersuchen zu können, wurde im Rahmen dieser Arbeit an der PTB ein neuer Laser-basierter DSR-Messplatz aufgebaut und charakterisiert.
Mit dem neuen Messplatz wurden c-Si Referenzsolarzellen, organische Solarzellen auf Basis kleiner Moleküle sowie Farbstoffsolarzellen umfassend untersucht. Unter anderem wurden die elektrischen Leistungsparameter einer organischen Solarzelle (aktive Schicht: DCV5T-Me:C60) mit denen einer c-Si Solarzelle verglichen. Es zeigt sich, dass der Wirkungsgrad der organischen Solarzelle mit zunehmender Bestrahlungsstärke sinkt und mit zunehmender Temperatur steigt, während die c-Si Solarzelle ein gegensätzliches Verhalten aufweist.
Darüber hinaus wurde u.a. die Winkelabhängigkeit der zweiten organischen Solarzelle (aktive Schicht: C60:DCV5T-Me(3,3)) untersucht und mit den Resultaten einer c-Si Solarzelle verglichen. Diese Untersuchungen haben ergeben, dass die Winkelabhängigkeit des Kurzschlussstroms der organischen Solarzelle im Vergleich zu einer c-Si Solarzelle insbesondere zwischen 20° < ϑ < 60° eine „Super-Kosinus-Anpassung“ aufweist.
Ergänzend wurde an der PTB im Rahmen dieser Arbeit ein mobiler Messplatz für Outdoormessungen aufgebaut. Mit diesem konnten die mittels Indoor-Untersuchungen erhaltenen spektralen Empfindlichkeiten mit Outdoor-Messungen verglichen werden. Des Weiteren wurden spektrale Charakterisierungen der Himmelshalbkugel durchgeführt und Methoden für Korrekturen von Sekundärkalibrierungen untersucht.
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Transparent Silver Nanowire Bottom Electrodes in Organic Solar Cells / Transparente Grundelektroden aus Silbernanodrähten in organischen SolarzellenBormann, Jan Ludwig 25 January 2017 (has links) (PDF)
Organic solar cells (OSCs) is an emerging photovoltaic technology that opens up new application areas where common inorganic techniques are not able to score. Some of those key features are flexibility, light weight, semitransparency, and low cost processing. The current industry-standard for the transparent electrode, indium tin oxide (ITO), cannot provide these properties because it is brittle and expensive. This thesis aims to investigate an alternative type of promising transparent electrode: silver nanowire (AgNW) networks. They exhibit similar or even better optical and electrical performance than ITO down to a sheet resistance of 12 Ohm/sq at 84% transmission (including the glass substrate). Furthermore, AgNWs are more flexible, solution-processable, and more cost-effective than ITO. However, two challenges occur during implementation as bottom electrode in OSCs. First, their inherently high roughness causes devices to shunt. Second, the AgNW network structure exhibits – in contrast to the continuous ITO – µm²-sized voids that have to be bridged electrically by the organic layers.
In the first part of this thesis, solution-processed small molecule charge transport layers are investigated. In the case of hole transport layers (HTL), the host BF-DPB and the dopant NDP9 are investigated using tetrahydrofuran as a solvent. It is shown that BF-DPB is already doped by NDP9 in solution via the formation of a hybrid molecule complex. Solution-processed layers exhibit similar conductivities as compared to the reference deposition, which is thermal evaporation in high vacuum. The layers sufficiently smoothen the AgNW electrode such that DCV5T-Me:C60 organic solar cells with an efficiency up to 4.4% are obtained. Moreover, the influence of the square micrometer large network voids is investigated using HTLs of varying conductivity. As a result, a minimum conductivity of 1e−4 S/cm is needed to avoid macroscopic performance losses. Equivalent circuit simulations are performed to confirm these results.
As a second planarization method, the AgNWs are buried in an insulating polymer that serves concurrently as flexible and ultrathin substrate. Out of three different polymers tested, the optical adhesive ’NOA63’ gives the best results. The roughness is strongly reduced from 30 nm down to (2 ± 1) nm. Two different OSC types are employed as testing devices with fully-flexible alumina encapsulation against moisture ingress. Maximum power conversion efficiencies of 5.0% and 5.6% are achieved with a fullerene-free cascade layer architecture and a DCV5T-Me:C60 OSC, respectively. To evaluate the applicability of these fully-flexible and encapsulated devices, degradation studies are performed under continuous illumination and a humid climate. Although employing the intrinsically stable DCV5T-Me:C60 stack design, within one day a fast degradation of the fully-flexible solar cells is observed. The degradation is attributed to AgNW electrode failure that results from photo-oxidation and -sulfurization, photo-migration, and electromigration.
It is further shown that the cascade organic solar cell lacks intrinsic stability. In summary, efficient, fully-flexible, and encapsulated devices are shown. However, in terms of competitive OSCs, the low stability of AgNW electrodes is a challenge to be taken care of. In current research, this issue needs to be addressed more frequently. / Organische Solarzellen (OSZ) sind ein junges Forschungsgebiet der Photovoltaik, welches neue Anwendungsgebiete erschließt, für die herkömmliche anorganische Solarzellen nicht einsetzbar sind. Einige der Haupteigenschaften sind Flexibilität, niedriges Gewicht, Teiltransparenz und geringe Herstellungskosten. Indiumzinnoxid (ITO), der aktuelle Industriestandard transparenter Elektrodentechnologie, ist nicht in der Lage, diese Eigenschaften zu gewährleisten. Dies liegt vor allem an der Brüchigkeit von ITO und der begrenzten Verfügbarkeit von Indium, welche mit einem hohen Preis einhergeht.
Das Ziel dieser Dissertation ist die Integration einer alternativen und vielversprechenden Elektrodentechnologie: Netzwerke aus Silbernanodrähten (AgNWs). Mit einem Schichtwiderstand von 12 Ohm/sq bei einer Transmission von 84% (inklusive Glassubstrat) besitzen sie ähnliche oder sogar bessere optische und elektrische Eigenschaften als ITO. Des Weiteren sind AgNW-Elektroden flexibler und kostengünstiger als ITO und aus flüssiger Phase prozessierbar. Es gibt allerdings zwei Herausforderungen, welche die Integration als Grundelektrode in OSZ erschweren. Zum einen sind AgNW-Netzwerke sehr rauh, sodass organische Bauteile kurzgeschlossen werden. Zum anderen weisen AgNW-Elektroden, im Gegensatz zu einer vollflächigen ITO-Schicht, Lücken zwischen den einzelnen Drähten auf. Diese Lücken müssen von den organischen Schichten der OSZ elektrisch überbrückt werden.
Im ersten Teil der Arbeit werden daher flüssigprozessierte Ladungsträgertransportschichten aus kleinen Molekülen untersucht, welche die AgNW-Elektroden glätten und die verhältnismäßig großen Lücken füllen sollen. Im Falle von Lochleitschichten (HTL) wird BF-DPB als Matrix und NDP9 als Dotand in Tetrahydrofuran gelöst und zur Anwendung gebracht. BF-DPB wird dabei schon in Lösung von NDP9 dotiert, wobei sich ein Hybridmolekülkomplex ausbildet. Die Leitfähigkeit der entstehenden Schichten ist ähnlich zu Referenzschichten, die durch thermisches Verdampfen im Hochvakuum hergestellt wurden. Die erhaltenen HTLs glätten die AgNW-Elektroden, sodass DCV5T-Me:C60-Solarzellen mit einer Effizienz von maximal 4.4% hergestellt werden können. Weiterhin wird der Einfluss der quadratmikrometergroßen Löcher auf die makroskopische Effizienz der Solarzelle in Abhängigkeit der HTL Leitfähigkeit untersucht. Um signifikante Effizienzverluste zu verhindern, muss der HTL eine minimale Leitfähigkeit von etwa 1e−4 S/cm aufweisen. Simulationen eines Ersatzschaltkreises bestätigen hierbei die experimentellen Ergebnisse.
Im zweiten Teil der Arbeit wird eine Planarisierungsmethode untersucht, in welcher die AgNWs in nichtleitfähigen Polymeren eingebettet werden. Diese Polymere fungieren anschließend als flexibles Substrat. Der optische Kleber ”NOA63” erzielt hierbei die besten Ergebnisse. Die Rauheit der AgNW-Elektroden wird von etwa 30 nm auf 1 bis 3 nm stark reduziert. Anschließend werden diese AgNW-Elektroden in zwei unterschiedlichen OSZ Konfigurationen getestet und mit einer vollflexiblen Schicht aus Aluminiumoxid gegen Wasserdampfpermeation verkapselt. Somit können maximale Effizienzen von 5% mithilfe einer organischen Kaskadenstruktur und 5.6% mit DCV5T-Me:C60 OSZ erreicht werden.
Um die Anwendbarkeit dieser vollflexiblen und verkapselten OSZ zu bewerten, werden Alterungsstudien unter konstanter Beleuchtung und feuchtem Klima durchgeführt. Es wird gezeigt, dass die in das Polymer eingebettete AgNW-Elektrode aufgrund von Photooxidation und -schwefelung und Photo- und Elektromigration instabil ist. Dieser Sachverhalt ist für die Anwendung von AgNW-Elektroden in kommerziellen OSZ von großer Bedeutung und wurde in der Forschung bisher nicht ausreichend thematisiert.
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Estudos sobre fotogeração, efeitos de interfaces e de transporte de portadores em células solares orgânicas / Studies about photogeneration, interface effects, and charge carrier transport in organic solar cellsCoutinho, Douglas José 18 June 2015 (has links)
Esta tese teve por objetivo, desde seu início, investigar as propriedades elétricas de um dispositivo ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al, o qual é uma estrutura bem conhecida de célula solar orgânica do tipo de heterojunção de volume (bulk-heterojunction – BHJ), e com isso dar uma contribuição à melhora de seu desempenho. Porém, o primeiro passo foi introduzir no Grupo de Polímeros Bernhard Gross, um método eficaz de produzir células solares do tipo BHJ com boa eficiência e reprodutibilidade. Esse primeiro desafio foi alcançado com sucesso. A eficiência (η) de um dispositivo fotovoltaico de multicamadas depende de muitos fatores. Dentre eles, uma boa superposição entre o espectro solar e a curva de absorção da camada absorvedora, uma excelente conversão da energia luminosa em portadores de carga, um eficiente processo de condução e uma perda mínima por recombinação e armadilhamento de portadores. Além disso, a compatibilidade eletrônica entre as interfaces tem um papel fundamental na definição na tensão de circuito aberto (VOC), no valor da corrente de curto-circuito (JSC), e no fator de preenchimento (FF). Baseado nesses efeitos, realizamos uma série de medidas experimentais, que auxiliado por um modelo teórico proporcionaram um estudo detalhado da evolução em função da temperatura da mobilidade dos portadores (μ) e de seu tempo de vida (τ). Os principais experimentos nessa tese foram realizados em diferentes temperaturas (entre 100 e 340 K). Foram eles: medidas de fotocorrente - Jph(V), a técnica de foto-CELIV, e medidas de transiente de fotovoltagem (TPV). Em paralelo, desenvolvemos o modelo teórico para a descrição analítica de Jph(V) que assumiu contatos não-injetores e que o livre caminho médio (w = μτF) de elétrons e buracos eram iguais (F é o campo elétrico). Nos ajustes teórico/experimental usamos a probabilidade de dissociação dos estados de transferência de carga (P) e o produto μτ como parâmetros de ajuste. A condição na qual o livre caminho médio é maior que a espessura da amostra (w >> L) reproduz a corrente de saturação reversa, Jsat = qGPLG é a taxa de geração dos éxcitons. Para w << L, a fotocorrente varia linearmente com o livre caminho médio, ou seja, J(F) = qGPμτF. A comparação entre os resultados experimentais e os teóricos permitiram, além da obtenção da evolução das grandezas μ e τ com a temperatura, estabelecer uma relação efetiva entre os parâmetros da célula (η, JSC, e FF) e as propriedades elétricas da camada ativa P3HT:PCBM. As medidas termo-mecânicas (DMA) forneceram informações adicionais sobre mudanças estruturais da camada ativa, as quais foram correlacionadas com variações dos parâmetros da célula e com fatores de perda. Finalmente, medidas de tempo-de-voo (TOF) e de CELIV foram realizadas para estudos mais detalhados sobre mecanismos de transporte ao longo da camada ativa, a efeitos de injeção pelos eletrodos, e para o entendimento de efeitos de degradação pela ação do oxigênio. / This thesis aims to investigate electrical characteristics of an ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al device, which is a well-known structure of a bulk-heterojunction (BHJ) organic solar cell, and to contribute to improve its performance. However, the first step was to introduce in the Group of Polymer Bernhard Gross an effective method for producing BHJ solar cells, manufacturing thus devices exhibiting excellent performance and reproducibility. This thesis aims to investigate electrical characteristics of an ITO/PEDOT:PSS/P3HT:PCBM/Ca/Al device, which is a well-known structure of a bulk-heterojunction (BHJ) organic solar cell, and to contribute to improve its performance. However, the first step was to introduce in the Group of Polymer Bernhard Gross an effective method for producing BHJ solar cells, manufacturing thus devices exhibiting excellent performance and reproducibility. This goal was successfully achieved. The good efficiency (η) of a multilayer photovoltaic cell depends on many factors, including good overlap between the solar spectrum and the light absorbing layer, an excellent conversion of the absorbed light energy in pairs of electronic carriers, efficient charge transport and the minimum losses by recombination or by the action of deep traps for the carriers. Furthermore, the compatibility between electronic interfaces plays a crucial role in defining the open-circuit voltage (VOC) and the value of short-circuit current (JSC), and on the fill factor (FF). Anchored on these effects, we carried out a series of experiments, aided by a theoretical modeling, which provided a detailed study of the temperature evolution of fundamental electric quantities such as carrier mobility (μ) and its lifetime (τ). These studies were performed with the help of different experiments: photocurrent in function of the applied voltage Jph(V), Photo-CELIV technique, and Transient Photovoltage (TPV) measurements, which were carried out at several temperatures in the 100 to 340 K range. In parallel, we developed an analytical model for Jph(V) that assumed non-injecting contacts and equal mean-free-paths for electrons and holes. The theoretical/experimental entities used as fitting parameters were the charge-transfer-state dissociation probability (P) and the μτ product. The condition in which the mean-free-path (w = μτF) is higher the sample thickness (L), the model reproduces the experimental reverse saturation current, Jsat = qGPL, which is coincident with the experimental value. F is the internal electric field and G is the generation rate of excitons by the absorbed light. When w << L, J(F) = qGPμτF, which is also coincident with experimental behavior. The confrontation between the experimental results and the theoretical model provided, in addition to the study of the evolution of μ and τ with temperature, to establish a more effective relationship between the parameters (η, JSC, e FF) of the cell and the electrical properties of the P3HT:PCBM active layer. Thermomechanical analysis (DMA) provided additional information of structural changes of active layer, which can be correlated with change in the loss factor and in the cell parameters. Finally, Time-of-Flight (TOF) and CELIV techniques were used in the more accurate study of charge transport along the active layers, effects of injection by the electrodes, and the degradation effect caused by oxygen.
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Studies of Materials and Interfaces for Organic ElectronicsBraun, Slawomir January 2007 (has links)
Organic electronics is a rapidly evolving field with vast number of applications having high potential for commercial success. Although a great progress has been made, many organic electronic applications: organic light-emitting diodes (OLEDs), organic fieldeffect transistors (OFETs), organic solar cells, etc; still require further optimization to fulfill the requirements for successful commercialization. For many applications, available at this time organic materials do not provide satisfactory performance and stability, which hinders the possibility of a large-scale production. Therefore, the key ingredient needed for a successful improvement in performance and stability of organic electronic devices is in-depth knowledge of physical and chemical properties of molecular and polymeric materials. Since many applications encompass several thin film layers made of organics, and often also inorganic materials, the understanding of both organic-organic and hybrid interfaces is yet another important issue necessary for the successful development of organic electronics. The research presented in this thesis is based mainly on photoelectron spectroscopy, which is an experimental technique especially suited to study both surfaces and interfaces of materials. In the thesis, the properties of one of the most successful polymeric materials, poly(3,4-ethylenedioxythiophene), often abbreviated as PEDOT, have been extensively studied. The research was done in close cooperation with an industrial partner – AGFA Gevaert, Belgium. The study was focused on the exploration of the intrinsic properties of the material, such as stability, morphology and conductivity. In addition, however, a possibility of alternation of these properties was also explored. This thesis reports also about investigations of the properties of various organic-organic and hybrid interfaces. The energy level alignment at such interfaces plays important role in charge injection and performance of the thin film organic-based devices. The conditions for different energy level alignment regimes at the various interfaces have been studied. The studies on interfaces were performed in close collaboration with the R&D division of DuPont Corporation, USA. This work led to the significant advances in understanding of the interface energetics and properties of industryrelevant organic materials, as represented not only by published scientific papers, but also patent applications.
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Determination via computational modeling of the structure-properties relationships in intercalated polymer:fullerene blends found in bulk-heterojunction solar cellsCho, Eunkyung 13 November 2012 (has links)
In bulk-heterojunction solar cells, device performance is influenced by both the intrinsic properties of the individual components - typically conjugated polymers and fullerene derivatives - and how they assemble and interact at their interface. The ability of fullerene to intercalate within the side-chains of a conjugated polymer can significantly affect the microstructure and overall device performance. Here, a series of computational chemistry approaches are applied to investigate the relationships between structure and property in intercalated polymer:fullerene blend. Using a combination of molecular mechanics (MM) calculation and simulations of 2D grazing incidence X-ray diffraction (GIXD) patterns, we have determined the molecular packing configuration of poly (2,5-bis (3-tetradecyl thiophene-2-yl) thieno[3,2-b]thiophene) (PBTTT-C₁₄) and a blend of PBTTT-C₁₄ and [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM). Based on the confirmed packing structures, the electronic properties and morphological disorder were examined using density functional theory (DFT) and molecular dynamics (MD) calculations, respectively; we also investigated the intermolecular interaction energies behind the structure formation. Finally, we examined the vibrational, redox, and optical properties of the pristine polymer and a series of fullerene derivatives to understand the characteristic modes related to the various charged states of the systems.
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