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.

Neste trabalho foram crescidos filmes finos de oxinitreto de silício (SiOxNy) por processamento térmico rápido (RTP) utilizando um forno térmico convencional adaptado, objetivando fabricar células solares MOS com baixo custo agregado e bom rendimento de conversão de baixas intensidades luminosas em energia elétrica de forma reprodutível. A receita de oxinitretação otimizada foi desenvolvida em ambiente misto de 5N2:1O2 na temperatura de 850°C para tempos de processo, na faixa de 10 a 80s seguido por uma passivação em 2L/min de N2 por 80s. Os dielétricos crescidos foram caracterizados fisicamente quanto à espessura (entre 1,50 e 2,95nm), à microrugosidade (<0,95nmRMS) e à concentração de nitrogênio (1,0-2,1%atm). As características de tunelamento foram investigadas em capacitores MOS e apontaram para a existência de armadilhas interfaciais do tipo K capazes de armazenar cargas positivas. Nas células solares MOS, a corrente de fundo foi característica para todos os processos de oxinitretação empregados (~0,5-2µA/cm2) e apresentaram níveis de resposta à luz incidente na faixa de 1 a 8mA/cm2 compatível com aplicações de conversão de energia em ambientes internos e externos (energy harvesting). A característica densidade de corrente x tensão de porta (JxVG) das células solares apresentou um comportamento aproximadamente linear desde a densidade de corrente de curto-circuito (JSC) até a tensão de curto-circuito (VOC) implicando em potência gerada máximas (PGmáx) de até centenas de µA/cm2 para VG ? VOC/2 para uma ampla faixa de intensidade radiante incidente (11,8 - 105,7mW/cm2) alcançando rendimentos de conversão de até 5,5%. / In this work, silicon oxynitrides (SiOxNy) were grown by means of a homemade Rapid Thermal Processing (RTP). The goal was to manufacture MOS solar cells with a reduced price and reasonable light conversion efficiency for low light intensity. The optimized oxidation recipe consisted of using an environment with gas mixture of 5N2:1O2 at a temperature of 850°C and different processing times in the range of 10 to 80s followed by a passivation step in ultrapure N2 (2L/min) at the same temperature of 850oC for 80s. The oxynitrides were grown with thickness in the range of 1.50 to 2.95nm with surface microroughness lower than 0.95nmRMS and nitrogen concentration in the range of 1.0 to 2.1%atm. The tunneling characteristics were studied with the aid of MOS capacitor and K-type interfacial traps related to Si(p)/Si?N structure were detected positively charged for VG > 0. The background current in the MOS solar cells (~0.5-2µA/cm2) were similar for all samples and the current response to the incident light was in the range of 1 to 8mA/cm2, which is compatible with energy conversion for indoor and outdoor environments (energy harvesting). The current density x gate voltage (JxVG) characteristics of the MOS solar cells presented a nearly linear behavior since the short-circuit current density (JSC) till to the open circuit voltage (VOC) so that the maximum generated power was of hundreds of µA/cm2 for VG ? VOC/2 for a large range of radiant intensities (11.8 - 105.7 mW/cm2) and achieving efficiency conversion up to 5.5%.

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.

O presente trabalho visou estudar e caracterizar eletrólitos sólidos poliméricos (ESP) à base de gelatina plastificada com glicerol, entrecruzada com formaldeído e contendo LiI/I2 para a aplicação em células solares. O objetivo foi obter os eletrólitos à base de gelatina comercial (Dr. Oetker) de origem animal, uma vez que a mistura de aminoácidos presentes na mesma apresenta propriedades mecânicas interessantes e torna-se um gel transparente na região do visível. Glicerol foi usado para promover a plastificação e o formaldeído para promover as ligações cruzadas na mistura das proteínas aumentando a estabilidade e resistência dos filmes. As fontes iônicas foram o LiI.2H2O e I2 na proporção de 10:1 m/m. O estudo revelou que as amostras apresentaram os valores de condutividade iônica de 7,68 x 10-5 S.cm-1, 6,38 x 10-5 S.cm-1, 8,81 x 10-5 S.cm-1, 9,97 x 10-5 S.cm-1 e 7,87 x 10-5 S.cm-1 dependendo da concentração da mistura LiI.2H2O / I2 . As medidas de condutividade em função da temperatura mostraram que o mecanismo que governa a condutividade é do tipo VTF. As análises de estrutura das membranas por difração de Raios-X mostraram o caráter predominantemente amorfo e as análises térmicas (DSC) os valores da temperatura de transição vítrea (Tg) da ordem de -77ºC. A transparência das amostras de 80 a 90% foi confirmada por espectroscopia UV-Vis e as análises microscópicas (MEV) mostraram a presença de pequenos pontos brancos nas superfícies das amostras. Os eletrólitos aplicados em um pequeno protótipo de célula solar renderam um máximo de 0,15% de eficiência. / This present work aimed study and characterization of solid polymer electrolytes (SPE) based on gelatin plasticized with glycerol, crosslinked with formaldehyde and containing LiI/I2 for application in solar cells. The plan was to get the electrolytes based on commercial gelatin (Dr. Oetker) of animal, since the mixture of amino acids present interesting mechanical properties and becomes a transparent gel in the visible region. Glycerol was used to promote plasticization and formaldehyde to promote cross-linking of the mixture of proteins leading to increase the stability and strength of the films. The ion sources were LiI.2H2O and I2 at a ratio of 10:1 m/m. The study revealed that the samples showed the values of ionic conductivity of 7.68 x 10-5 S.cm-1, 6.38 x 10-5 S.cm-1, 8.81 x 10-5 S.cm-1, 9.97 x 10-5 S.cm-1 and 7.87 x 10-5 S.cm-1, depending on the concentration of the mixture LiI.2H2O / I2. Ionic conductivity measurements as a function of temperature revealed VTF conducting model. X-ray diffractogramms showed the predominantly amorphous nature and thermal analysis (DSC) values of the glass transition temperature (Tg) of about -77 ° C. The transparency of the samples of 80 and 90% was confirmed by UV-Vis and the microscopic analysis (SEM) showed the presence of small white points in the surface of the samples. The electrolytes used in small solar cell prototypes yielded a maximum of 0.15% efficiency.

abstract: Photovoltaic (PV) energy has shown tremendous improvements in the past few decades showing great promises for future sustainable energy sources. Among all PV energy sources, III-V-based solar cells have demonstrated the highest efficiencies. This dissertation investigates the two different III-V solar cells with low (III-antimonide) and high (III-nitride) bandgaps. III-antimonide semiconductors, particularly aluminum (indium) gallium antimonide alloys, with relatively low bandgaps, are promising candidates for the absorption of long wavelength photons and thermophotovoltaic applications. GaSb and its alloys can be grown metamorphically on non-native substrates such as GaAs allowing for the understanding of different multijunction solar cell designs. The work in this dissertation presents the molecular beam epitaxy growth, crystal quality, and device performance of AlxGa1−xSb solar cells grown on GaAs substrates. The motivation is on the optimization of the growth of AlxGa1−xSb on GaAs (001) substrates to decrease the threading dislocation density resulting from the significant lattice mismatch between GaSb and GaAs. GaSb, Al0.15Ga0.85Sb, and Al0.5Ga0.5Sb cells grown on GaAs substrates demonstrate open-circuit voltages of 0.16, 0.17, and 0.35 V, respectively. In addition, a detailed study is presented to demonstrate the temperature dependence of (Al)GaSb PV cells. III-nitride semiconductors are promising candidates for high-efficiency solar cells due to their inherent properties and pre-existing infrastructures that can be used as a leverage to improve future nitride-based solar cells. However, to unleash the full potential of III-nitride alloys for PV and PV-thermal (PVT) applications, significant progress in growth, design, and device fabrication are required. In this dissertation, first, the performance of ii InGaN solar cells designed for high temperature application (such as PVT) are presented showing robust cell performance up to 600 ⁰C with no significant degradation. In the final section, extremely low-resistance GaN-based tunnel junctions with different structures are demonstrated showing highly efficient tunneling characteristics with negative differential resistance (NDR). To improve the efficiency of optoelectronic devices such as UV emitters the first AlGaN tunnel diode with Zener characteristic is presented. Finally, enabled by GaN tunnel junction, the first tunnel contacted InGaN solar cell with a high VOC value of 2.22 V is demonstrated. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2019

Ce travail porte sur l'élaboration de cellules solaires CuInSe2 (CIS) en couches minces. Différentes techniques de croissance ont été mises en œuvre pour concevoir les matériaux composant la structure photovoltaïque. Ainsi, l'absorbeur CuInSe2 a été déposé par coévaporation sous vide (PVD) sur un substrat de verre recouvert de molybdène. Un système de détection de la lumière diffusée (SLS) par l'échantillon a été développé pour permettre le suivi in situ des transitions de phases pauvres/riches en cuivre. Cela a permis la croissance de couches de CuInSe2 à larges grains ainsi que le contrôle de leurs propriétés électro-optiques. La couche tampon de CdS a été obtenue par bain chimique (CBD) et son épaiseur optimisée par un procédé original où le substrat est directement chauffé par conduction. Enfin, la couche fenêtre de ZnO a été élaborée par divers procédés de croissance tels que l'électrodéposition (ED) et le dépôt par couches atomiques (ALD). Les propriétés structurales, optiques et électriques des différentes couches minces sont étudiées et mises en relation avec les performances photovoltaïques des cellules élaborées. / The aim of this work is the design of thin film CuInSe2 solar cells. Different growth techniques have been used to elaborate the layers involved in this photovoltaic stack. Thus, the absorber CuInSe2 has been deposited by coevaporation under vacuum (PVD) onto a molybdenum coated glass substrate. A scattered light monitoring system (SLS) has been designed in order to follow in situ the copper poor/rich phases transitions. It has led to the growth of CuInSe2 layers made of large crystalline grains with both high optical and electrical properties. The CdS buffer layer has been elaborated by chemical bath deposition (CBD) and its thickness has been tuned by an original process involving a conduction heated holder. Finally, the ZnO window layer has been grown by various techniques such as electrodeposition (ED) and atomic layer deposition (ALD). Structural, optical and electrical properties of all these thin films have been studied and correlated with the photovoltaic parameters of the solar cells elaborated.

Ce travail est consacré à l‟étude de la stabilité photochimique de nanocomposites polymère / argile en vue de leur insertion dans un système multicouche organique / inorganique pour l‟encapsulation des cellules solaires organiques. L‟objectif est d‟obtenir des films de nanocomposites polymère / argile flexibles, transparents, pouvant être mis en oeuvre par voie liquide, et photochimiquement stables. Dans une première partie, la caractérisation de nanocomposites à base d‟alcool polyvinylique (PVA) a montré leur aptitude à être insérés dans un système multicouche, notamment en ce qui concerne les propriétés barrière aux gaz. L‟étude du comportement photochimique du PVA basée sur l‟identification des produits de dégradation a permis de proposer un mécanisme de photooxydation du PVA et de déterminer les effets du photovieillissement sur les propriétés du film (rugosité, perméabilité, transparence). L‟insertion de nanocharges lamellaires (Montmorillonite, Laponite ou Hydroxydes Doubles Lamellaires) dans le PVA induit des effets différents (prodégradant ou stabilisant) en fonction de la nature de l‟argile (naturelle ou synthétique). Cependant, lors d‟irradiations en absence d‟oxygène, le PVA et les nanocomposites PVA / argile sont très stables. Enfin, l‟encapsulation alternant couche inorganique SiOx et couche organique PVA ou nanocomposite PVA / argile, permet d‟atteindre les niveaux de perméation requis pour les cellules solaires organiques pour des applications nomades. / This work was devoted to the study of the photochemical behavior of polymer / clay nanocomposites with the aim to use these nanocomposites in a multilayer organic / inorganic coating for organic solar cells encapsulation. The goal of this work was to obtain polymer / clay nanocomposite films that are flexible, transparent, which can be processed by solution, and that are photochemically stable. In the first part, the characterization of nanocomposites based on polyvinyl alcohol (PVA) has shown their ability to be inserted into a multilayer system, particularly for gas barrier properties. The study of the photochemical behavior of PVA with the identification of photodegradation products allows us to propose a photooxidation mechanism of PVA and to determine the effects of photoageing on the film properties (roughness, permeability, transparency). The insertion of lamellar nanofillers (Montmorillonite, Laponite or Layered Double Hydroxide) in PVA induces different effects (prodegradant or stabilising) depending on the nature of the clay (natural or synthetic). However, in absence of oxygen, the PVA and PVA / clay nanocomposites are very photostable. Finally, encapsulation alternating inorganic SiOx layer and PVA or PVA / clay nanocomposite layer permits to obtain the permeability levels required for organic solar cells in niche markets (consumer electronics).

The main aim of this thesis work is to investigate the electrical, optical and thermal impact characteristics of cobalt oxide doped antimony tin oxide (CoO-ATO) in the form of thin films and nanofiber membranes. CoO-ATO is a novel composite material that has the potential to be used as reinforced aircraft coatings, military garment coatings, or more specifically as an anti-reflective (AR) top coating for photovoltaic (PV) cells. This work will be critical in determining the effectiveness of using a CoO-ATO layer in these applications. Electrospun nanofibers and spin coated thin films consisting of a polymeric solution of CoO-ATO will be used. Thin films are created using spin coating techniques, and nanofiber membranes are created using an electrospinning technique. Polystyrene (PS) will be used as a solute, and chloroform as a solvent, to create the solution. It is hypothesized that coatings of this material will have improved optical characteristics as compared to traditional ATO coatings and minimum impact from thermal cycling making it a favorable candidate for PV cells. This work will do an electrical, optical and thermal cycling impact characterization of CoO-ATO thin films and nanofiber membranes for a doping range of x% CoO where x ranged from 0.2

<p>Over the last few decades, bulk-heterojunction organic photovoltaic devices comprising an intimately mixed donor-acceptor blend have gained serious attention due to their potential for being cheap, light weight, flexible and environmentally friendly. In this thesis, APFO-3/PCBM bulk-heterojunction based organic photovoltaic devices with an inverted layer sequence were investigated systematically. Doctor blade coating is a technique that is roll-to-roll compatible and cost efficient and has been used to fabricate the solar cells.</p><p>Initial studies focused on optimization of the electrodes. A thin film of the conductive polymer PEDOT:PSS was chosen to be the transparent anode. Different PEDOT:PSS films with respect to the film thickness and deposition temperature were characterized in terms of conductivity and transmission. Decent conductance and transmittance were obtained in the films deposited with wet film thickness setting of 35 μm, The cathode was fabricated from a metal bilayer comprising Al and Ti with an area about 1 cm², and the best-working cathodes contained a 70 nm thick Al layer covered by a thin Ti layer of about 10 -15 nm.</p><p>Optimized coating temperature and wet film thickness settings for the active layer and PEDOT:PSS layer were experimentally determined. The highest efficiency of the APFO-3/PCBM based inverted solar cells fabricated by doctor blading was 0.69%, which exceeded the efficiency of spin-coated inverted cells.</p><p>A higher efficiency (0.8 %) was achieved by adding a small amount of high molecular weight polystyrene to the active layer. Morphological changes after adding of the polystyrene were observed by optical microscopy and AFM. A coating temperature dependent phase separation of the APFO-3/PCBM/polystyrene blend was found.</p><p> </p>