Este trabalho apresenta os resultados da preparação e caracterização de eletrólitos poliméricos a partir de DNA-CTMA e DNA-DODA com adição de 7, 9, 10 e 11% (m/m) de LiClO4 e/ou LiI/I2. O objetivo é usar estes eletrólitos poliméricos em pequenas células solares sensibilizadas com corante (DSSC). O DNA com a massa molecular de 5,41x108 ± 1179,6 g/mol foi usado para a síntese de complexos de DNA-CTMA e DNA-DODA através da reação de substituição de DNA com os agentes surfactantes: CTMA e DODA. As amostras na forma de filmes foram caracterizadas por espectroscopia de impedância, difração de raios-X, UV-Vis, FT-IR e análises térmicas (DSC e TGA). Os espectros de FT-IR confirmaram a obtenção dos complexos de DNA-CTMA e DNA-DODA. A espectroscopia no UV/Vis revelou a presença de absorção em 260 nm atribuída às transições eletrônicas π- π* das bases nitrogenadas do DNA. As análises térmicas dos complexos de DNA-CTMA e DNA-DODA mostraram a estabilidade térmica de 226°C e 232°C e a transição vítrea de -67°C e -40,0°C, respectivamente. A difração de raios-X das amostras permitiu a determinação da porcentagem de cristalinidade sendo entre 43,74 e 63,20% para DNA-CTMA e entre 49,4 e 76,25% para DNA-DODA. Os filmes foram submetidos às medidas de condutividade iônica revelando os melhores resultados de 8,21x10-4 S/cm a 25°C para as amostras de DNA-CTMA com 10% (m/m) de LiClO4 e 2,87x10-4 S/cm para o DNA-DODA com 10% (m/m) de LiClO4. Os eletrólitos de DNA-CTMA com 9 e 10 % (m/m) de LiI/I2 e DNA-DODA com 9 e 10% (m/m) de LiI/I2 foram aplicados em pequenas células solares mostrando a eficiência de 0,14, 0,31, 0,177 e 0,66% respectivamente, valores considerados promissores para futuros estudos. / The present work describes the preparation and characterization of polymeric electrolytes of DNA-CTMA and DNA-DODA with addition of 7, 9, 10 and 11% (m/m) LiClO4 and/or LiI/I2. The objective is use of these polymer electrolytes in dye sensitized solar cells (DSSC). The DNA with molecular weight of 5,41x108 ± 1179,6 g/mol was used to synthesize DNA-CTMA and DNA-DODA complexes by substitution reaction. The obtained samples in the film form were then characterized by impedance spectroscopy, X-ray diffraction, UV-Vis, FT-IR and thermal analyses (DSC and TGA). The FT-IR spectra confirmed both, DNA-CTMA and DNA-DODA complexes obtaining. The UV-Vis spectroscopy of the samples evidenced an absorption band at 260 nm attributed to electronic transitions π-π * of DNA nitrogenous bases. The TGA and DSC analyses shoved a thermal stability of the DNA-CTMA and DNA-DODA samples of 226°C and 232°C and, glass transition of -67°C and -40°C, respectively. The X-ray diffraction allowed determining the crystallinity of 43.74 to 63.20% for the samples of DNA-CTMA and 49.4 to 76.25% for the DNA-DODA. The films were subjected to ionic conductivity measurements showing the best results of 8.21x10-4 S/cm at 25°C for the DNA-CTMA with 10% (w/w) of LiClO4 and of 2.87x10-4 S/cm for DNA-DODA with 10% (w/w) of LiClO4. Finally the electrolytes of DNA-CTMA with 9 and 10% (m/m) of LiI/I2 and of DNA-DODA 9 and 10% (m/m) of LiI/I2 were applied in small solar cells exhibiting the efficiency of 0,14, 0,31, 0,177 and 0,66%, respectively. The obtained results are promising for future investigations.

Thesis advisor: Dunwei Wang / Solar energy, the most abundant and free renewable energy, holds great promise for humanity's sustainable development. How to efficiently and inexpensively capture, covert solar energy and store it for off peak usages constitutes a grand challenge for the scientific community. Photovoltaic devices are promising candidates but are too costly to be implemented in large scales. On a fundamental level, this is due to the dilemma that the length scales of the optical pathways and electrical pathways often do not match within the photovoltaic device materials. Consider traditional Si solar cell as an example, effective light absorption requires up to hundreds of microns material while the photogenerated charge carries can only diffuse less than a few microns or even shorter before recombination. Such a problem may be solved by using Si nanowires (SiNWs) because vertically aligned nanowires can orthogonalize the light absorption and charge carrier collection pathways, thereby enabling the use of low-cost materials for practically appealing solar energy conversion devices. The objective of this thesis work is to explore low-cost synthesis of vertically aligned SiNW arrays and study their performance in both solar energy conversion and storage devices. We developed a method to synthesize vertically aligned SiNW arrays in a hot-wall chemical vapor deposition system with tunable length, doping level, and diameter for systematical studies. Empowered by the synthetic control, various types of vertical SiNW arrays were characterized by both steady-state (photoelectrochemical measurement) and transient (electrochemical impedance spectroscopy) techniques in a photoelectrochemical cell platform. Additionally, SiNWs were demonstrated to be a promising candidate for photoelectrochemical aromatic ketone reduction and CO₂ fixation. The reactions studied in this thesis are in close resemblance to natural photosynthesis and the resulted product molecules are precursors to nonsteroidal anti-inflammatory drugs, ibuprofen and naproxen. Lastly, vertical transparent conductive oxide nanotubes were prepared from vertical SiNW array templates. Ultrathin hematite (Fe₂O₃) film was coated on the nanotube scaffold by atomic layer deposition to form a heteronanostructure photoelectrode for efficient solar water oxidation. Our results highlight the potential of vertically aligned SiNW arrays in solar cell, solar water splitting and artificial photosynthesis applications. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Orientador: Luiz Carlos da Silva Filho / Resumo: Derivados de cumarina representam uma grande e importante classe de produtos naturais com diversas atividades biológicas. Entretanto, com a eletrônica orgânica e a utilização de novos materiais como absorvedores de luz, derivados de cumarina têm despertado grande interesse da comunidade científica. As cumarinas possuem grande absorção na região visível e alto rendimento quântico de fluorescência, o que sugere ser um material promissor para aplicação como corantes em células solares. Entre os métodos de síntese de cumarina descritos na literatura, podemos citar a reação de Knoevenagel, Pechmann e Perkin. A reação multicomponente (RMC) é outro método de síntese dos derivados de cumarina e foi desenvolvido pelo nosso grupo de pesquisa. As RMCs ocorrem entre três ou mais reagentes em uma única etapa reacional, no mesmo frasco. Os compostos de interesse foram obtidos através dos reagentes de partida: 4-aminocumarina, derivados de aldeído e benzoilacetato de etila, catalisados por ácidos de Lewis. A reação ocorreu na presença de NbCl5, em N2, sob refluxo, em DCM, DCE, MeCN, MeOH ou THF durante 5, 24 ou 48 h. Essas foram as condições reacionais estudadas para se estabelecer protocolos de síntese para a formação dos produtos de interesse. Os resultados mais promissores foram obtidos em 24 h, com DCE e NbCl5, com rendimentos que variam entre 38 e 58%. As caracterizações ópticas mostraram um comprimento de onda de absorção em torno de 355 nm, emissão de fluorescência em torno de 420 nm... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Coumarin derivatives represent a large and important class of natural products with diverse biological activities. However, with organic electronics and the use of new materials as light absorbers, coumarin derivatives have aroused great interest from the scientific community. Coumarins have high absorption in the visible region and high fluorescence quantum yield, which suggests to be a promising material for application as dyes sensitized solar cells. Among the methods of coumarin synthesis described in the literature, we can mention the reaction of Knoevenagel, Pechmann and Perkin. The multicomponent reaction (MCR) is another method of synthesis of coumarin derivatives and was developed by our research group. MCRs occur between three or more reactants in a single reaction step, in the same flask. Compounds of interest were obtained from the starting reagents: 4-aminocoumarin, aldehyde derivatives and ethyl benzoylacetate, catalysed by Lewis acids. The reaction occurred in the presence of NbCl5, in N2, under reflux in DCM, DCE, MeCN, MeOH or THF for 5, 24 or 48 h. These were the reactional conditions studied to establish synthesis protocols for the formation of the products of interest. The most promising results were obtained in 24 h with DCE and NbCl5 with yields ranging from 38 to 58%. The optical characterizations showed an absorption wavelength around 355 nm, fluorescence emission around 420 nm and fluorescence quantum yield reaching 0.129%. Also, the reactants: furan-... (Complete abstract click electronic access below) / Doutor

A method was developed to access the interior of light-guiding structures in order to exploit the enhanced sensing potential of the highly confined electromagnetic field distributions, located within the core of a waveguide. The work presented in this thesis explores therefore the possibilities of optical waveguide spectroscopy utilising transparent mesoporous thin-film waveguides deposited on top of athin gold layer. These multi-layer assemblies are employed in a prism-coupling attenuated total internal reflection (ATR) configuration. The angular read-out of the reflected light intensity allows label-free detection schemes with high sensitivity to changes of the dielectric environment in the case of the presence of analyte molecules within the probing region. This optical waveguide spectroscopy technique has been used to study the real-timediffusion of Ruthenium 535-bisTBA (N-719) dye into mesoporous nanocrystalline titaniumdioxide films. The porous films were prepared on top of gold substrates and prism coupling was used to create a guided wave in the nanocrystalline film. Dying was carried out by bring the film into contact with a 3 x 10-4 moldm-3 dye solution and using optical waveguide spectroscopy to monitor the change in both the refractive index and theextinction coefficient of the nanoporous layer as dye diffused into the porous network. Dyeuptake in a 1.27 μm film was slow with the refractive index of the film still increasing after 22 hours.

Semicondutores orgânicos têm atraído cada vez mais atenção da comunidade científica e de indústrias. O grande interesse se divide entre a riqueza de fenômenos físicos e químicos a serem estudados e o seu grande potencial de aplicação tecnológica nas mais diversas áreas: diodos emissores de luz (OLEDs), células solares e fotodiodos, transistores, biosensores, sensores de radiação ionizante, entre outros. O objetivo deste trabalho foi de contribuir para o avanço de duas áreas de aplicação, ambas relacionadas com a interação de radiação eletromagnética com a matéria: células solares e dosimetria de radiação gama. Na área de células solares, foram explorados dois dos principais limitadores do aumento de eficiência de conversão de potência: a falta de materiais com absorção na região em que o Sol emite mais fótons (infravermelho próximo (NIR)) e a dificuldade de controle da morfologia interna das células. Foi demonstrado um novo conceito de fabricação de células solares através da nanoestruturação de filmes finos poliméricos. A metodologia de estruturação se baseia no processo de separação de fases em blendas poliméricas durante o processo de deposição por spin-coating e a subseqüente remoção de uma das componentes. Assim é possível obter uma camada ativa cobrindo todo o substrato e apresentando ondulações na superfície que podem ser variadas desde alguns nanômetros de altura e largura até micrômetros. O processo de nanoestruturação é discutido e dispositivos fotovoltaicos foram produzidos cobrindo filmes nanoestruturados de MEH-PPV com fulereno C60. A eficiência de conversão de potência destas células é três vezes maior do que o melhor resultado já reportado para este par de materiais até o momento e atinge quase 3% sob irradiação monocromática. Utilizando corantes cianinos, dispositivos fotovoltaicos e fotodiodos com resposta desde no visível até o infravermelhor próximo (~1000 nm) foram demonstrados e foi observado um papel importante dos íons móveis presentes nos corantes. Finalmente, foi demonstrada a aplicabilidade de um corante polimerizado como dosímetro de radiação gama. A faixa de operação do dosímetro pode ser alterada variando-se a concentração da solução do corante, que poderia ser utilizado na região de doses de irradiação de alimentos. / Organic semiconductors have atracted much attention from the scientific community and from the industry. The large interest is divided between the rich number of basic physical and chemical phenomena to be investigated and the great technological potential for application in different areas, such as light emitting diodes (OLEDs), solar cells, photodiodes, transistors, biosensors, ionizing radiation sensors, among others. The subject of this work was to contribute to a deeper understanding of two areas of application, both related to the interaction of electromagnetic radiation with matter: solar cells and gamma ray dosimetry. In the area of solar cells, the lack of materials absorbing in the near infrared (NIR) and the poor control of the morphology of the active films are limiting factor to increasing device efficiency. Therefore both this aspects were explored. A new concept of organic solar cell fabrication was presented based on the anostructuration of polymeric thin films. The methodology is based on phase separation of polymer blends during spin-coating followed by the selective removal of one component. This allows the controlled formation of thin films with characteristic features varying from a few nanometers to micrometers. The effects of molecular weigth, solvent and relative composition were investigated and discussed based on the analysis of AFM images and phase separation models. Devices using structured MEH-PPV layers, covered by C60 were fabricated and showed white light power conversion efficiencies (?) up to 400 % higher than a flat double layer device. Monochromatic ? achieved 2.95 % (480 nm), three times higher than the best reported value for this material combination so far. Using cyanine dyes, photovoltaic devices and photodiodes active in the NIR (~1000 nm) were demosntrated and an important effect of movable ions present in the dyes was observed. Finally, the application of a polymerized dye as gamma ray dosimeter was demonstrated. The operation range can be altered by varying the concentration of polymer in solution, and are useful in the range of low dose food irradiation.

Submitted by Willian Henrique dos Santos null (willian_santos@fc.unesp.br) on 2017-03-02T13:42:56Z No. of bitstreams: 1 DEFESA-24-02-2017.pdf: 11727986 bytes, checksum: 5e700d656e3faf3c665363a77b6371b2 (MD5) / Approved for entry into archive by LUIZA DE MENEZES ROMANETTO (luizamenezes@reitoria.unesp.br) on 2017-03-08T12:53:39Z (GMT) No. of bitstreams: 1 santos_wh_dr_bauru.pdf: 11727986 bytes, checksum: 5e700d656e3faf3c665363a77b6371b2 (MD5) / Made available in DSpace on 2017-03-08T12:53:39Z (GMT). No. of bitstreams: 1 santos_wh_dr_bauru.pdf: 11727986 bytes, checksum: 5e700d656e3faf3c665363a77b6371b2 (MD5) Previous issue date: 2017-02-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A demanda por fontes de energias renováveis já é uma necessidade mundial, pois, o crescimento populacional e industrial trouxe concomitantemente um aumento no consumo de energia. Infelizmente, a matriz energética dos países que estão em pleno desenvolvimento se baseia na queima de combustíveis fósseis, o que traz sérios problemas ambientais e para a saúde da população. Tendo em vista esta necessidade, este trabalho retrata o estudo sobre o uso do pentacloreto de nióbio (NbCl5) como ácido de Lewis em reações multicomponentes para a síntese de compostos derivados de cumarinas e xantenos, compostos com potencial aplicação como corantes sensibilizadores em dispositivos fotovoltaicos. Os compostos de interesse foram obtidos através dos reagentes de partida: 4-hidróxicumarina, derivados fenólicos 3,5-dimetóxifenol e 3,4,5-trimetóxifenol, aldeídos aromáticos e 1,3-ciclo-hexanodiona. Foram estudadas as condições reacionais (% NbCl5, solvente utilizado e tempo reacional) para se estabelecer protocólos de síntese para a formação dos produtos de interesse na presença do pentacloreto de nióbio. O pentacloreto de nióbio demonstrou ser capaz de promover as reações estudadas neste trabalho. Esta nova possibilidade de obtenção destes compostos é de fundamental importância, pois, estes compostos possuem um leque muito amplo de aplicações, das quais algumas foram citadas neste trabalho. / The demand for renewable energy sources is already a worldwide need, because, the population and industrial growth concurrently brought an increase in energy consumption. Unfortunately, the energy matrix of the countries that are in full development is based on burning fossil fuels, which causes serious environmental problems and the health of the population. In view of this need, this work shows that the study about the use of niobium pentachloride (NbCl5) as Lewis acid in multicomponent reactions for the synthesis of coumarin and xanthene derivatives of compounds with potential application as sensitizing dyes in photovoltaic devices. These compounds were obtained from the starting materials: 4-hydroxycoumarin, phenolic derivatives (3,5-dimethoxyphenol and 3,4,5-trimethoxyfenol, aromatic aldehydes and 1,3-cyclohexanedione. The reaction conditions (% NbCl5, solvent and reaction time) to establish protocols synthesis for the formation of the products in the presence of niobium pentachloride were studied.Niobium pentachloride has been shown to be capable of promoting the reactions studied in this work. This new method of obtaining these compounds is of fundamental importance, considering that these compounds have a wide range of applications, some of which have been cited in this work.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / Desde o desenvolvimento da primeira cÃlula solar sensibilizada por corante em 1991, este campo de pesquisa vem crescendo consideravelmente. As nanopartÃculas de TiO2 tÃm sido o principal semicondutor aplicado neste tipo de cÃlula. PorÃm com o advento da nanociÃncia e nanotecnologia, novas estruturas semicondutoras com caracterÃsticas morfolÃgicas variadas tÃm sido bastante investigadas para este tipo de aplicaÃÃo. Nesse trabalho foi obtido nanotubos de titanato de sÃdio (NTT-Na+) com composiÃÃo Na2Ti3O7, a partir do TiO2 comercial, pelo mÃtodo hidrotÃmico em meio altamente alcalino e nanotubos de titanato protonados (NTT-H+) com composiÃÃo H2Ti3O7 a partir da lavagem dos Na2Ti3O7 em soluÃÃo de HCl 0,1 mol/L para realizaÃÃo da troca iÃnica Na+ por H+. Utilizou-se, tanto os produtos Na2Ti3O7 e H2Ti3O7 quanto o material de partida TiO2 em fotoeletrodos de cÃlulas solares sensibilizadas por mesoporfirina. Para isso, algumas lÃminas de vidro para microscopia receberam a aplicaÃÃo de filmes finos de SnO2-F por meio da tÃcnica de spray pirÃlise, adquirindo propriedades condutoras. ApÃs isso, as camadas de TiO2, Na2Ti3O7 e H2Ti3O7 foram depositadas com auxÃlio de um bastÃo de vidro sobre os substratos condutores para servirem como suportes durante a aplicaÃÃo do corante. ApÃs a adsorÃÃo do corante pelas camadas as cÃlulas foram fechadas por meio de um eletrÃlito com par redox (I3-/3I-) utilizando como contra eletrodos, vidros condutores com camadas contendo carbono em suas superfÃcies. As diferentes amostras de vidros condutores apresentaram resistÃncias elÃtricas de 4,66 â 8,66 Ω/□. As camadas de TiO2, Na2Ti3O7 e H2Ti3O7 sobre as lÃminas condutores foram analisadas por diversas tÃcnicas de microscopias e apresentaram, entre outras, caracterÃsticas porosas com superfÃcies bastantes irregulares. Por fim, ao expor as trÃs cÃlulas fotovoltaicas à radiaÃÃo solar de 1258 W/m2 foram verificados corrente elÃtrica de 13 ÂA e tensÃo de 370 mV para a cÃlula com eletrodo de Na2Ti3O7, corrente de 7,6 ÂA e tensÃo de 256 mV para a cÃlula com eletrodo de H2Ti3O7, corrente de 1,1 ÂA e tensÃo de 1,6 mV para a cÃlula com eletrodo de TiO2. / Since the development of the first dye sensitized solar cell in 1991, this field of research has grown considerably. TiO2 nanoparticles have been the main semiconductor on this kind of cell. With the advance in nanoscience and nanotechnology, new semiconductor structures with various morphological characteristics have been deeply studied for this sort of application. In this work, it was chosen to synthesize sodium titanate nanotubes (NTT-Na+) composed of Na2Ti3O7, by using anatase TiO2 associated with the hidrothermic method in high alkaline mean and titanate protonned nanotubes (NTT-H+) composed of H2Ti3O7 obtained by the washing of Na2Ti3O7 in 0,1mol/L HCl solution to perform the ionic trade, Na+ by H+. Both Na2Ti3O7 and H2Ti3O7 were used, as well as TiO2, on solar cell electrodes sensitized by mesoporfirin. In order to do that, some microscopy glass blades received the application of SnO2-F thin films by the use of the spray pyrolyse technique, acquiring conductive properties. After that, layers of TiO2, Na2Ti3O7 and H2Ti3O7 were deposited by using a glass stick over the conductive substrates, to work as support during the dye application. After the dye is adsorbed, the cells were closed using an electrolyte as redox pair (I3-/3I-) and conductive glass with layers of carbon in its surface, as counter electrode. The different samples of conductive glass showed electric resistance of 4,66 â 8,66 Ω/□. The layers of TiO2, Na2Ti3O7 and H2Ti3O7 over the conductive blades were analyzed through several microscopic techniques and presented, amongst others, porous characteristics with very irregular surfaces. While exposing the three photovoltaic devices to solar radiation of 1258 W/mÂ, the following values of current and tension were verified: 13 μA and 370 mV for the cell with Na2Ti3O7 electrode; 7,6 μA and 256 mV for the cell with H2Ti3O7 electrode; 1,1 μA and 1,6 mV for the cell with TiO2 electrode.

Dye design is one of the most important and challenging areas in dye-sensitised solar cell research. The purpose of the work in this thesis is to synthesise and characterise novel ruthenium(II) and copper(I) dyes that will provide insight into the number of binding groups required and the potential use of chromophoric ligands. A series of four simple Ru(II) dyes have been synthesised with the general formula Ru(4,4’- (R)-bipyridine)2(NCS)2 where R represents CH3 or CO2H. The study investigates the number of acid groups required to successfully bind to TiO2 whilst maintaining efficient charge injection. The series consists of one acid group, two acids, two acids on adjacent bipyridines, and three acids groups. Dye uptake was studied via optical waveguide spectroscopy, providing information on dye diffusion, adsorption and desorption kinetics, and surface coverage. Interestingly, the two acid groups on adjacent ligands suggested poor/slow binding to TiO2 surface and a high degree of dye aggregation in comparison to two acid groups on the same ligand. The dye with three binding groups showed strong adsorption to TiO2 and better dye coverage, resulting in a high efficiency. The complexes were all fully characterised by electrochemistry, photoluminescence, absorption spectroscopy, DFT calculations and solar cell performance testing. To date, there has been limited exploration of copper(I) complexes as potential alternatives to ruthenium(II) sensitisers, with even fewer publications reported for Cu(I) heteroleptic species. The neutral complexes that were synthesised are of the general formula: Cu(4,4’- (R)-6,6’-(CH3)-bipyridine)(β-diketonate) and Cu(4,4’-(R)-6,6’-(CH3)-bipyridine)(dipyrrin) where R represents CH3 or CO2Et. Additional blocking groups on the ligands are introduced to minimise structural change during oxidation or MLCT excitation. Improved stability and reproducibility have been shown for complexes containing the dipyrrin ligand, likely due to better steric constraints and better π-overlap with the bipyridine. There has also been a remarkable improvement in light absorption, from 450 nm to 600 nm. In-situ solar studies have been carried out on the Cu(4,4’-(R)-6,6’-(CH3)-bipyridine)(dipyrrin) series and a 0.41% efficiency has been achieved. Computational studies supports the experimental data in which the main transition appears to be ligand centred (dipyrrin) with a small MLCT contribution.

Neste trabalho foram estudados diferentes vidros de telureto dopados com íons de terras raras (TR) e nanopartículas (NPs) metálicas visando aplicação sobre a superfície de dispositivos fotovoltaicos. O objetivo foi utilizar os processos luminescentes de tais íons para otimizar a eficiência de conversão de energia de células solares. Os vidros de telureto foram escolhidos por apresentarem boas características ópticas, físicas e luminescência na presença de íons de terra rara e de NPs. Diferentes composições de telureto foram estudadas (TeO2-ZnO, TeO2-ZnO-Na2CO3) para observar a influência de diferentes janelas de transmissão sobre o desempenho de células solares, conciliando a máxima luminescência com a máxima transmitância do vidro. As amostras vítreas foram produzidas mediante o processo tradicional conhecido por \"melting quenching\" seguido por tratamento térmico. Os dopantes utilizados foram os íons de Tb3+, Yb3+, Eu3+ e nanopartículas de prata (NPs de Ag). Através dos mecanismos de conversão descendente apresentados por tais íons é possível converter comprimentos de onda que o dispositivo fotovoltaico não absorveria, para comprimentos compreendidos no seu \"band gap\" de forma a aumentar a eficiência da célula solar. Foram feitas caracterizações espectroscópicas de luminescência, absorbância e transmitância para caracterizar as propriedades ópticas dos vidros e microscopias para observar a forma e tamanho das NPs. Também foram feitas caracterizações elétricas de dispositivos fotovoltaicos com as amostras vítreas colocadas sobre suas superfícies, a fim de verificar influencias em suas eficiências. Observou-se que o tipo de célula solar e o tipo de sistema vítreo influenciam os resultados de eficiência para cada combinação de íons de terras raras. Ressaltam-se que foram obtidos aumentos na eficiência relativa de dispositivos fotovoltaicos comerciais fabricados em Si e GaP em 14% e 34,5%, respectivamente, com a utilização de vidros TeO2-ZnO dopados com Eu3+ e NPs de Ag. Foi utilizado óleo para acoplamento entre o vidro e a célula solar para aumentar o contato óptico, que possibilitou fazer a comparação da eficiência da célula coberta em relação à célula descoberta. Usando a célula solar de Si monocristalino foi observado aumento de 12,8% de eficiência relativa, quando coberta com vidros TeO2-ZnO dopados com Eu3+ e NPs de Ag. Os resultados apresentados neste trabalho demonstram que a utilização de processos de conversão descendente de íons de TR em vidros de telureto são promissores para incrementar a eficiência de células solares, assim como, o uso de NPs metálicas. / In this work, different tellurite glasses doped with rare earth ions and metallic nanoparticles (NPs) were studied for applications on solar cells surface. The goal was to use the luminescent processes of the rare earth ions to optimize the solar cells energy conversion efficiency. Tellurite glasses were chosen because of the good optical and physical characteristics and luminescence in the presence of rare earth ions and metallic NPs. Different tellurite compositions were studied (TeO2-ZnO, TeO2-ZnO-Na2CO3) to observe the influence of different transmission windows on the solar cell performance, conciliating maximum luminescence with the maximum transmittance of the glasses. The vitreous samples were produced using the traditional \"melting quenching\" procedure followed by heat treatment. The dopants used were Tb3+, Yb3+, Eu3+ ions and silver NPs. The purpose was to use the downconversion processes of rare earth ions to convert the wavelengths that the photovoltaic device cannot absorb into wavelengths situated in its the band gap and enhance the energy conversion efficiency. Luminescence, absorption and transmittance spectroscopic characterizations were made to determine the optical properties of the glasses and microscopic measurements were used to observe the NPs size and shape. Electrical characterizations of the photovoltaic devices were also done with the glasses placed on their surfaces to verify the influence on their energy conversion efficiencies. It was observed that the type of solar cell and the glass host influenced the results, for each rare-earth ions combination. The results obtained with TeO2-ZnO glasses doped with Eu3+ and silver NPs can be highlighted, which show efficiency increase in 14% and 34,5%, when covering Si and GaP commercial solar cells, respectively. The oil matching was used between the solar cell and the glasses in order to enhance the optical contact and to allow the comparison between the results of the covered solar cell with the uncovered solar cell. It was observed for the energy conversion efficiency enhancement of 12% when the Si solar cell was covered with the TeO2-ZnO glasses doped with Eu3+ and with silver NPs. The results presented in this work demonstrate that the use of the rare earth ions downconversion processes are promising for improving the solar cells energy conversion efficiency as well as the use of metallic NPs.

Le but de ce travail est d'étudier et de développer des voies pour améliorer l'efficacité des cellules solaires à base de Kesterite. La première partie de ce manuscrit traite du développement d’un procédé de base : le mécanisme de formation de l’absorbeur est étudié en fonction des conditions de croissance du composé Cu2ZnSnS4 (CZTS à base de soufre pur) et Cu2ZnSnSe4 (CZTSe à base de sélénium pur). Un procédé séquentiel en deux étapes a été utilisé pour synthétiser l’absorbeur en Kesterite. La première étape est un dépôt par pulvérisation cathodique des précurseurs métalliques (Cu, Zn et Sn élémentaires) et la deuxième étape consiste en un recuit des précurseurs sous atmosphère de sélénium (pour le CZTSe dans un réacteur semi-ouvert) ou de soufre (pour le CZTS dans un réacteur ouvert). Différentes optimisations du procédé sont réalisées pour améliorer la microstructure et les performances des dispositifs. Dans le cas du dispositif à base de CZTSe, le meilleur rendement de conversion photovoltaïque obtenu est de 7,6% en utilisant un profil de température en deux étapes et un suscepteur fermé. Pour les cellules solaires à base de CZTS, la meilleure performance obtenue est de 5,9% grâce à l’optimisation de la température et de la pression partielle ensoufre : Les performances des dispositifs augmentent avec la pression partielle en soufre.L’incorporation de Na (Sodium) et de Sb (Antimoine) dans les absorbeurs Kesterite en pur soufre a été testée comme la première stratégie pour améliorer les performances des dispositifs à base de CZTS. L'incorporation de Sb n‘entraîne pas d'amélioration en termes de propriétés des matériaux ou des dispositifs, tandis que le co-dopage avec Na et Sb a montré une morphologie améliorée des absorbeurs. Cependant, cette amélioration n’est suivie d’aucun effet sur les propriétés photovoltaïques du dispositif. L’incorporation de Sb n’est donc pas bénéfique pour la cellule solaire à base de CZTS. D'autre part, la contamination intentionnelle avec du Na s'est avérée bénéfique pour les cellules solaires, particulièrement pour la tension en circuit ouvert. Par conséquent, l’efficacité des dispositifs avec une teneur en Na optimisée est doublée (> 4,5 %) par rapport à celle des échantillons de référence sans Na.La seconde étude pour améliorer les performances des cellules solaires à base de Kesterite concerne l’introduction de gradients de chalcogènes (S/Se) dans l’épaisseur de l’absorbeur. Le but est d’obtenir des gradients de bande interdite afin d’augmenter la longueur de collection des porteurs et de diminuer les phénomènes de recombinaison. Dans ce but, deux procédés sont développés pour réaliser des gradients simples (en face avant ou en face arrière de l’absorbeur). Ces procédés consistent en des recuits successifs (sulfurisation/sélénisation) d’empilements de précurseurs. Pour obtenir un gradient en face avant, un recuit de sulfurisation à différentes températures et durées est appliqué après un recuit de sélénisation standard. Une température plus importante entraîne un gradient plus marqué. Une couche de défaut à base de soufre pur est également formée au cours de ce processus, qui peut être éliminée à l'aide d'une gravure au HCl. Le rendement de conversion photovoltaïque le plus élevé obtenu à l’aide de ce procédé est de 3,5%. Pour obtenir un gradient en face arrière, un recuit de sulfurisation à différentes températures avant un recuit de sélénisation standard a été utilisé. A faible température de sulfurisation, des absorbeurs avec une bonne morphologie ont été obtenus mais sans gradient de composition en chalcogène tandis que l’utilisation de températures de sulfurisation plus importantes ont entraîné l’apparition de gradients de composition mais ont détérioré la morphologie des absorbeurs. Ainsi, les voies et limites pour réaliser des absorbeurs de Kesterite à gradient de bande interdite sont proposées. / The goal of this work is to study and to develop routes toward efficiency improvement of Kesterite based solar cells. The first part of the manuscript deals with the development of a baseline process: formation mechanism of the absorber is studied according to the growth condition for both Cu2ZnSnS4 (pure sulfur absorber CZTS) and Cu2ZnSnSe4 (pure selenium absorber CZTSe) compounds. Two-step sequential process is used for synthesizing Kesterite material. The first step consists in the sputtering deposition of pure metallic precursors (elemental Cu, Zn, and Sn) and the second step consists in the annealing of precursors under selenium (for CZTSe in a semi-open reactor) or sulfur (for CZTS in an open reactor). In the case of CZTSe based solar cell, a maximum power conversion efficiency of 7.6% has been obtained using a two-step temperature profile and a closed susceptor. The best performance for a CZTS based device is 5.9%, this result has been obtained by optimizing the process temperature and sulfur vapor pressure: the higher sulfur vapor pressure the better device performance.Incorporation of Na (Sodium) and Sb (Antimony) in the pure sulfur Kesterite absorber has been tested as a first strategy to enhance performances of CZTS devices. Incorporation of Sb does not show any improvement in terms of material or device properties, whereas improved morphology is obtained by co-doping with Na and Sb. However, this improvement is not related to any effect on device properties. Thus, using Sb proved to be not beneficial for the CZTS-based solar cell. On the other hand, intentional contamination with Na is found to be beneficial particularly in terms of open circuit voltage. As a result, the device power conversion efficiency with optimized Na content is doubled (> 4.5%) compared to the reference sample without Na.The second study to increase efficiencies in Kesterite solar cells deals with the introduction of chalcogen (S/Se) gradients as the function of depth in the absorber. The aim is to obtain bandgap gradients in order to increase carrier collection length as well as decrease carrier recombination. For this purpose, two processes are developed to realize only simple grading (front or back surface gradients) which consist of sequential annealing stages (sulfurization/selenization) of precursor stacks. To obtain a front surface gradient, a sulfurization step at various temperatures and for different duration has been tested after a standard selenization process. A higher sulfurization temperature shows a higher degree of grading. A pure sulfur-based defect layer is also formed during this process, which can be removed using an HCl etching. A maximum efficiency of 3.5% is achieved with a CZTS-based device using this synthesis process. To realize back grading, variable temperature sulfurization annealing prior to a standard selenization process has been used. At a low temperature of sulfurization, good absorber morphologies are obtained but without the evidence of chalcogen gradient while using higher sulfurization temperature leads to graded absorbers but with poor morphology. Thus, the routes and limitations to realize kesterite absorber with gradient are proposed.