Dye-sensitized solar cells (DSSCs) present an interesting method for the conversion of sunlight into electricity. Unlike in other photovoltaic technologies, the difficult tasks of light absorption and charge transport are handled by two different materials in DSSCs. At the heart of the DSSC, molecular light absorbers (dyes) are responsible for converting light into current. In this thesis the design, synthesis and properties of new metal-free D-π-A dyes for dye-sensitized solar cells will be explored. The thesis is divided into six parts: Part one offers a general introduction to DSSCs, dye design and device characterization. Part two is an investigation of a series of donor substituted dyes where structural benefits are compared against electronic benefits. In part three a dye assembly consisting of a chromophore tethered to two electronically decoupled donors is described. The assembly, capable of intramolecular regeneration, is found to impede recombination. Part four explores a method for rapidly synthesizing new D-π-A dyes by dividing them into donor, linker and acceptor fragments that can be assembled in two simple steps. The method is applied to synthesize a series of linker varied dyes for cobalt based redox mediators that builds upon the experience from part two. Part five describes the synthesis of a bromoacrylic acid based dye and explores the photoisomerization of a few bromo- and cyanoacrylic acid based dyes. Finally, in part six the experiences from previous chapters are combined in the design and synthesis of a D-π-A dye bearing a new pyridinedicarboxylic acid acceptor and anchoring group. / <p>QC 20140509</p>

With an increasing demand for renewable energy sources, research efforts on different solar cell technologies are increasing rapidly. The dye-sensitized solar cell (DSC) is one such technology, taking advantage of light absorption in dye molecules. The liquid based DSC contains several interesting and important interfaces, crucial for the understanding and development of the solar cell performance. Examples of such interfaces include dye-semiconductor, electrode-electrolyte and solute-solvent interfaces. Ultimately, complete interfaces with all these components included are of particular interest. One major challenge is to understand the key functions of these systems at an atomic level and one way to achieve this is to use an element specific and surface sensitive tool, such as photoelectron spectroscopy (PES). This thesis describes the use and development of PES for studying interfaces in the DSC. The materials part of the thesis focuses on interfaces in DSCs studied with PES and the methodology development parts focus on methods to use PES for investigations of solvated heterogeneous interfaces of interest for photoelectrochemical systems such as the DSC. More specifically, beginning with standard vacuum techniques, dye molecules bound to a semiconductor surface have been studied in terms of energy level alignment, surface coverage and binding configuration. To increase the understanding of solvation phenomena present in the liquid DSC, liquid jet experiments have been performed in close combination with theoretical quantum calculations. As a step towards an in-situ method to measure a complete, functioning (in operando) solar cell, methodology development and measurements performed with higher sample pressures are described using new high pressure X-ray photoelectron spectroscopy techniques (HPXPS).

The scalable syntheses of functional, porous nanostructures with tunable three-dimensional morphologies is a significant challenge with potential applications in chemical, electrical, electrochemical, optical, photochemical, and biochemical devices. As a result, several bio-enabled and synthetic approaches are explored in this work (with an emphasis on peptide-enabled deposition) for the generation of aligned nanotubes of nanostructured titania for application as electrodes in dye-sensitized solar cells and biofuel cells. As part of this work, peptide-enabled deposition was used to deposit conformal titania coatings onto porous anodic alumina templates under ambient conditions and near-neutral pH to generate aligned, porous-wall titania nanotube arrays that can be integrated into dye-sensitized solar cells where the arrays displayed improved functional dye loading compared to sol-gel-derived nanotubes. A detailed comparison between synthetic and bioorganic polyamines with respect to titania film properties deposition rate provided valuable information for future titania coating experimental design given specific applications. The development of template-based approaches to single-wall titania nanotube arrays led to the development of a new synthetic method to create aligned, multi-walled titania nanotube arrays. Lastly, peptide-enabled deposition methods were extended beyond inorganic mineral and used for enzyme immobilization by cross-linking the peptide with the multicopper oxidase laccase. Peptide-laccase hybrid enzyme coatings improved both the amount of enzyme adsorbed onto carbon nanotube “buckypaper” and allowed the enzyme to retain more activity upon immobilization onto the surface.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 159-168).

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Electrical and Computer Engineering." Includes bibliographical references (p. 118-122).

Organic field-effect transistors (OFET) have attracted considerable interests as a promising technology for the next-generation flexible electronics. Thioacenes have recently emerged as potential semiconducting materials for OFETs. On the other hand, Photovoltaic (PV) technology is regarded as a prospective alternative for green and renewable energy source. Recently, dye sensitized solar cells (DSSCs) have drawn intensive attention and showed great potential for practical application. Herein, the research in this thesis would include the synthesis and characterization of novel thioacene-based semiconductors for OFET and DSSC applications. To begin with, a general review on the current status of organic semiconductors for OFET and DSSC applications was presented in Chapter 1. In chapter 2, a series of novel benzodithieno[3,2-b]thiophene derivatives (BDTT-n) with different lateral alkyloxy groups were designed and synthesized. In addition, alkyloxy-substituted benzo[2,1-b:3,4-b’]bis-[1]benzothiophenes derivatives (BBBT-n) were also synthesized. The performances of OFETs based on BDTT-n and BBBT-n have been fully investigated. Among them, BDTT-4 based OFET exhibited the highest hole mobility of 1.74 cm 2 /(Vs) with a current on/off ratio above 10 7 without annealing. In chapter 3, a novel series of naphthodithiophene-based oligomers with D-A- D-A- D structure motif were designed and synthesized. All these oligomers have 2 been fully characterized by NMR and mass spectrometry. The hole mobility properties of these oligomers were determined in OFETs as fabricated by drop- coating technique. These oligomers exhibited typical p-type semiconducting behavior. A mobility of 1.6x10 -2 cm 2 /(Vs) was demonstrated by ENBT based OFET with a current on/off ratio in the range of 10 5-7 after annealing at 160ºC. Besides, in chapter 4, a novel [pi]-bridge, namely naphthodithienothiophene was developed and employed to explore photosensitizers for DSSC application. In this work, four novel photosensitizers with D-A-[pi]-A or D-[pi]-A structure motif were designed and synthesized in which the carbazole or triphenylamine derivative was used as a donating group and benzothiadiazole was applied as auxiliary accepting group. The performances of DSSCs based on these photosensitizers have been fully investigated. Among them, CB-NDTT- CA based device exhibited the highest power conversion efficiency (PCE) of 7.29%. Meanwhile, the interfacial properties of these photosensitizers anchored on TiO 2 have also been studied by ab-initio simulation and Gaussian calculations. In chapter 5, another novel series of photosensitizers with benzodithienothiophene as the [pi]-bridge would be presented, in which different donors, auxiliary acceptors, and structures were incorporated into the frameworks of D-[pi]-A motif to investigate the relationship between the structure and properties. The performances of DSSCs based on these photosensitizers have been fully investigated, and BD-5 based device exhibited the best power conversion efficiency (PCE) of 4.66%. Furthermore, it was demonstrated that molecular engineering was an efficient way to modulate the performance of the DSSCs in 3 which benzothiadiazole was used as an effective auxiliary accepting group in constructing photosensitizers with D-A-[pi]-A structure motif. The di-anchoring approach was also found to be a promising method to design photosensitizers with improved performance.

Emerging solar energy technology, including photovoltaics, solar fuels generation and solar thermal systems, is considered as one of the most potential renewable energy resources because of the tremendous and free radiant energy supply by our sun. Unlike burning of fossil fuels, carbon dioxide emission-free energy conversion process is definitely another key feature and attracting scientists to explore these research areas. Besides, this implies a giant business market to compete with traditional fossil fuel companies. Nevertheless, it is too early to realize commercial application since the technologies are in the early development stage and there is still much room to explore and improve. Simply speaking, energy conversion efficiency, robustness, environmental impacts and cost are the major factors the community should deeply concentrate on at this moment. This provides many research opportunities on the creation of novel molecular functional materials and investigates the relationship between the molecular design and functional properties, and they obviously take up significant roles in the technology evolution. The basic concepts and conspectuses regarding organic photovoltaics and light-driven hydrogen generation are collected in Chapter 1. In Chapter 2, a series of new thiophene-based small molecules is presented and the discussion is focused on its application in the bulk-heterojunction organic solar cells. Importantly, the structure-property relationship is elucidated by varying the terminal electron withdrawing group and elongating the central electron donating unit. The highest power conversion efficiency (η) of 2.6% is attained by the device with compound M3 as the active material with traditional device configuration (without any annealing process and additives addition) under AM 1.5G irradiation. In Chapter 3, a series of DπA organic dyes is introduced and the discussion concentrates on its application in the dye-sensitized solar cells. Briefly, a case study on alkyl chain effects is investigated while a new starburst triarylamine donor and uncommon selenophene-containing π-linker are studied separately. The highest power conversion efficiency (η) of 6.7% is achieved by D11 under AM 1.5G irradiation with a high open-circuit voltage of 0.825 V. In Chapter 4, three new platinum(II) diimine complexes are synthesized and they are utilized as photosensitizers with platinized titanium dioxide as catalyst site in the context of light-driven hydrogen generation. Comparison between platinum(II) diimine dithiolate complex and platinum(II) diimine bis(acetylide) complex is accomplished, and the importance of photosensitization using an organic chromophore with a desirable energy transfer consideration is accounted. Finally, Chapter 5 puts forward the concluding remarks and possible future works while Chapter 6 includes all the experimental details of the studied compounds presented in Chapter 24.

abstract: Natural photosynthesis dedicates specific proteins to achieve the modular division of the essential roles of solar energy harvesting, charge separation and carrier transport within natural photosynthesis. The modern understanding of the fundamental photochemistry by which natural photosynthesis operates is well advanced and solution state mimics of the key photochemical processes have been reported previously. All of the early events in natural photosynthesis responsible for the conversion of solar energy to electric potential energy occur within proteins and phospholipid membranes that act as scaffolds for arranging the active chromophores. Accordingly, for creating artificial photovoltaic (PV) systems, scaffolds are required to imbue structure to the systems. An approach to incorporating modular design into solid-state organic mimics of the natural system is presented together with how conductive scaffolds can be utilized in organic PV systems. To support the chromophore arrays present within this design and to extract separated charges from within the structure, linear pyrazine-containing molecular ribbons were chosen as candidates for forming conductive linear scaffolds that could be functionalized orthogonally to the linear axis. A series of donor-wire-acceptor (D-W-A) compounds employing porphyrins as the donors and a C60 fullerene adduct as the acceptors have been synthesized for studying the ability of the pyrazine-containing hetero-aromatic wires to mediate photoinduced electron transfer between the porphyrin donor and fullerene acceptor. Appropriate substitutions were made and the necessary model compounds useful for dissecting the complex photochemistry that the series is expected to display were also synthesized. A dye was synthesized using a pyrazine-containing heteroaromatic spacer that features two porphyrin chromophores. The dye dramatically outperforms the control dye featuring the same porphyrin and a simple benzoic acid linker. A novel, highly soluble 6+kDa extended phthalocyanine was also synthesized and exhibits absorption out to 900nm. The extensive functionalization of the extended phthalocyanine core with dodecyl groups enabled purification and characterization of an otherwise insoluble entity. Finally, in the interest of incorporating modular design into plastic solar cells, a series of porphyrin-containing monomers have been synthesized that are intended to form dyadic and triadic molecular-heterojunction polymers with dedicated hole and electron transport pathways during electrochemical polymerization. / Dissertation/Thesis / Ph.D. Chemistry 2013

Orientador: Ana Flávia Nogueira / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-17T19:59:01Z (GMT). No. of bitstreams: 1 Benedetti_JoaoEduardo_D.pdf: 8810025 bytes, checksum: 02324ef0185baef0d7794ea229fb5cda (MD5) Previous issue date: 2010 / Resumo: Este trabalho consistiu na preparação, caracterização e posterior aplicação de eletrólitos poliméricos gel em celulas solares de TiO2/corante. No Capítulo I, e apresentado uma introdução geral sobre células solares e eletrólitos poliméricos. O Capítulo II contém os objetivos deste trabalho. No Capítulo III, são preparados os eletrólitos polimérico gel utilizando a matriz polimérica de poli(oxido de etileno-co-2-(2-metoxietoxi) etil glicidil eter) (P(EO/EM)) contendo I2 e várias concentrações de g-butirolactona (GBL) e LiI. Esses eletrólitos foram caracterizados por medidas de calorimetria exploratória diferencial (DSC), ressonância magnética de Li (RMN), termogravimetria (TGA), difração de raios-X (DRX), condutividade e voltametria cíclica (VC). O eletrólito polimérico gel P(EO/EM)/GBL/LiI/I2 apresentou excelentes propriedades químicas e eletroquímicas. Esses eletrólitos foram aplicados nas células solares de TiO2/corante, conforme e apresentado no Capítulo IV. As células solares foram caracterizadas por meio das curvas de corrente-potencial (J-V), estimativa do tempo de vida do eletron e espectroscopia de absorção transiente (TAS). De modo geral, os dispositivos montados com o eletrólito polimérico (P(EO/EM)/GBL/LiI/I2 apresentaram um aumento da fotocorrente com a incorporação de GBL no eletrólito. Esse resultado e influência da maior difusão das especies redox no meio. Em contrapartida, o aumento da concentração de GBL no eletrólito também provocou uma acentuada perda no potencial de circuito aberto, o que foi relacionado ao aumento dos processos de recombinação na interfaces, contribuindo para a perda da eficiência das células solares. Para minimizar esses efeitos, no Capítulo V, e apresentada a caracterização por meio das curvas de corrente-potencial da célula solar de TiO2/corante montadas com o eletrólito P(EO/EM)/GBL/LiI/I2 preparado com terc-butilpiridina e éter coroa. A incorporação desses aditivos proporcionou um aumento de Voc das células solares e, consequentemente, da eficiência dos dispositivos. O Capítulo VI apresenta os testes de estabilidade das células solares de TiO2/corante preparadas com o eletrólito polimérico gel, no qual apresentou estabilidade apropriada durante 30 dias de teste. O Capítulo VII contém as principais conclusões deste trabalho e perspectiva de continuação para esta linha de pesquisa / Abstract: This thesis consisted in the preparation, characterization and application of gel polymer electrolytes in dye-sensitized TiO2 solar cells. A general introduction to solar cells and to polymer electrolytes will be presented in Chapter I. Chapter II describes the aims of this work. Chapter III deals with the preparation of gel polymer electrolytes based on the poly(ethylene oxide-co-2-(2-methoxyethoxy) ethyl glycidyl ether) (P(EO/EM)) polymer matrix containing I2 and different concentrations of g-butyrolactone (GBL) and LiI. These electrolyte samples were characterized by differential scanning calorimetry (DSC), Li nuclear magnetic resonance (Li RMN), thermogravimetry (TGA), X-ray diffraction (RDX), conductivity measurements and cyclic voltammetry (VC). The gel polymer electrolyte P(EO/EM)/GBL/LiI/I2 provided excellent chemical and electrochemical properties. The electrolytes were applied in dye-sensitized TiO2 solar cells, as discussed in Chapter IV. Solar cells were characterized by current-voltage (IV) curves, electron lifetime measurements and transient absorption spectroscopy (TAS). Most of the solar cells based on the polymer electrolyte P(EO/EM)/GBL/LiI/I2 presented an increase in photocurrent with the addition of GBL to the electrolyte composition. This result may be explained by the enhanced diffusion of redox species in the medium. However, a significant decrease in open-circuit voltage was observed after increasing the GBL concentration in the electrolyte composition. The decrease in open-circuit voltage was assigned to an increase in recombination losses taking place at the interfaces, which resulted in solar cells with lower performance. In order to minimize these drawbacks, dye-sensitized TiO2 solar cells were assembled with the electrolyte P(EO/EM)/GBL/LiI/I2 containing 4-tert-butylpyridine and crown ether molecules. The addition of these additives provided an increase in Voc and, consequently, improved device performance. The characterization of these solar cells based on gel polymer electrolyte containing additives was carried out by means of current-voltage (I-V) curves, as discussed in Chapter V. Dye-sensitized TiO2 solar cells based on gel polymer electrolyte were subjected to durability tests. Good durability results were achieved during a 30-day test, which are discussed in Chapter VI. Chapter VII deals with the main conclusions of this work and outlines some perspectives for the next steps of this research / Doutorado / Quimica Inorganica / Doutor em Ciências

Orientadores: Francisco das Chagas Marques, Ana Flávia Nogueira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-26T08:45:20Z (GMT). No. of bitstreams: 1 Coutinho_NataliadeFaria_M.pdf: 12394800 bytes, checksum: 1d28bb92259a5c9eb6848a0fe678b6b3 (MD5) Previous issue date: 2014 / Resumo: A demanda mundial de energia elétrica tem crescido muito nas últimas décadas, o que tem levado a uma busca mais expressiva por fontes de energia renováveis e sustentáveis. Deste modo, as células solares, que através do efeito fotovoltaico convertem a energia proveniente do sol em energia elétrica, tem ganhado atenção. Dentre os vários tipos de células solares, se encontram as células solares sensibilizadas por corante, DSSC, que têm ganhado interesse de estudiosos da área por apresentarem uma possibilidade de geração de energia elétrica a baixo custo. Para que essas células ganhem competitividade no mercado, é necessário que suas eficiências aumentem, e é nesse ramo de pesquisa que o presente trabalho se coloca. Este trabalho foi baseado no estudo e otimização da eficiência de células solares sensibilizadas por corante, onde verificamos a influência de vários fatores na eficiência das células. Dentre eles, se encontram o processo de manufatura das células, o pós-tratamento de TiCl4 sobre o filme nanoestruturado de TiO2, a composição da pasta de TiO2 e do eletrólito líquido, o método de deposição da Pt no contra-eletrodo, e a utilização de uma camada espalhadora de luz com nanopartículas de TiO2 da ordem de 200nm. Além disso, um estudo a respeito do efeito de uma blocking layer de TiO2 entre o FTO e o filme nanoestruturado de TiO2, depositada pela técnica conhecida como atomic layer deposition, ALD, também foi realizado, o que levou a um aumento na eficiência das células. Através desses estudos, conseguimos aumentar a eficiência das células em até 90% se comparado às primeiras células que produzimos (de 3,9% a 7,4%), atingindo valores de tensão de circuito aberto Voc, densidade de corrente de curto-circuito Jsc, fator de preenchimento FF e eficiência ? de até 0,71V, 14,38mA/cm2, 0,67 e 7,4%, respectivamente. Deste modo, uma melhora significativa na performance das células foi observada, chegando a resultados comparáveis aos obtidos por diversos grupos de pesquisa em todo o mundo / Abstract: World demand for electricity has grown in the last decades, which has led to a more expressive search for renewable and sustainable energy sources. Consequently, solar cells have been getting attention because of their capacity to convert energy from the sun into electrical energy through the photovoltaic effect. Among the various types of solar cells, there are the dye-sensitized solar cells, DSSC, which have gained interest of the solar cell community for having a possibility of power generation at low cost. In order to these cells get market competitiveness, it is necessary to increase their efficiency, and this is the research field that the present work is placed into. This thesis was based on the study and optimization of dye-sensitized solar cells efficiency, where we could see the influence of various factors in cells efficiency. Among these, there are the cells manufacturing process, the post-treatment on nanostructured TiO2 films using a TiCl4 solution, the composition of the TiO2 paste and the liquid electrolyte, the method of Pt deposition at the counter electrode, and the use of a reflecting layer with 200nm TiO2 nanoparticles. In addition, a study of the effect of a TiO2 blocking layer between the FTO and the nanostructured TiO2 film deposited by the technique known as atomic layer deposition, ALD, was also performed, which led to an increase in cells efficiency. Through these studies, we could increase cells efficiency by up to 90% compared to the first cells we produced (from 3,9% to 7,4%), reaching values of open circuit voltage Voc, short circuit current density Jsc, fill factor FF and efficiency _ of up to 0,71V, 14,38mA/cm2, 0,67 and 7,4%. Thus, a significant improvement in cells performance was observed, reaching results comparable to that obtained by many research groups around the world / Mestrado / Física / Mestra em Física