The installed base of photovoltaic power plants in the United States has roughly doubled every 1 to 2 years between 2008 and 2015. The primary economic drivers of this are government mandates for renewable power, falling prices for all PV system components, 3rd party ownership models, and a generous tariff scheme known as net-metering. Other drivers include a desire for decreasing the environmental impact of electricity generation and a desire for some degree of independence from the local electric utility. The result is that in coming years, PV power will move from being a minor niche to a mainstream source of energy. As additional PV power comes online this will create challenges for the electric grid operators. We examine some problems related to large scale adoption of PV power in the United States. We do this by first discussing questions of reliability and efficiency at the PV system level. We measure the output of a fleet of small PV systems installed at Tucson Electric Power, and we characterize the degradation of those PV systems over several years. We develop methods to predict energy output from PV systems and quantify the impact of negatives such as partial shading, inverter inefficiency and malfunction of bypass diodes. Later we characterize the variability from large PV systems, including fleets of geographically diverse utility scale power plants. We also consider the power and energy requirements needed to smooth those systems, both from the perspective of an individual system and as a fleet. Finally we report on experiments from a utility scale PV plus battery hybrid system deployed near Tucson, Arizona where we characterize the ability of this system to produce smoothly ramping power as well as production of ancillary energy services such as frequency response.

Le travail de thèse effectué a pour objectif le développement d’un concept innovant de module photovoltaïque à faible concentration ultra-intégré, nommé HIRL pour Highly Integrated ReceiverLess module.Un premier Chapitre est consacré à la présentation du photovoltaïque à concentration (CPV) afin de positionner ce développement d’un concept original innovant. Le module développé est basé sur des concentrateurs réflectifs cylindro-paraboliques et il intègre des cellules multi-jonctions haut rendement. L’ambition est de travailler sur la simplification de la mise en module des cellules, en proposant d’une part, une architecture ultra-intégrée. L’optique de concentration en aluminium est multifonction puisqu’elle combine les fonctions de concentrateur, de support des cellules et de dissipateur thermique. D’autre part nous souhaitons appliquer pour ce concept des procédés de fabrication simples et éprouvés issus de l’industrie du photovoltaïque, tels que l’encapsulation par lamination. Enfin le module doit offrir une acceptance angulaire suffisante (> ±1°) pour utiliser un tracker un axe bas coût.Dans un second Chapitre, après avoir défini l’architecture de module envisagée, la modélisation thermique du système est présentée. Une étude a permis de définir les dimensions optimisées du concentrateur vis-à-vis de son rôle de dissipateur thermique. Ensuite, nous avons pu explorer les procédés de mise en forme des optiques mais également les méthodes d’interconnexion des cellules. Nous avons également mis en œuvre le procédé de lamination pour l’encapsulation des cellules multi-jonctions et démontrer la faisabilité de ce procédé pour le concept HIRL. Les procédés de fabrication identifiés ont été mis en œuvre pour la fabrication d’un prototype atteignant une efficacité électrique de 28%. La mesure de l’acceptance angulaire, de ±0.55°, a cependant montré les limites de ce premier design.Le troisième Chapitre est donc consacré à l’optimisation de l’architecture et des procédés au regard des résultats du Chapitre 2. Nous avons pu montrer comment modifier le design pour augmenter l’acceptance angulaire du module en conservant une bonne dissipation thermique. Enfin, de nouveaux procédés ont été mis en œuvre pour la réalisation d’un nouveau prototype fabriqué selon ce nouveau design et intégrant des cellules multi-jonctions optimisées pour la faible concentration. Ce nouveau prototype V3 présente un rendement de 30,5% et un angle d’acceptance de +/-1.4°.Dans le quatrième Chapitre, nous nous sommes attachés à caractériser les performances optiques des concentrateurs réalisés. Un banc de caractérisation optique a spécialement été développé pour ce type de module. Il a permis la comparaison des rendements optiques des différents concentrateurs, associés à leur procédé de mise en forme, ainsi que la comparaison de leur acceptance angulaire. Enfin, nous avons pu constater les effets de l’échauffement du concentrateur - du fait de son rôle de dissipateur thermique – sur les performances optiques.Enfin, dans un dernier Chapitre, une analyse de la chaine de pertes de la cellule au module est présentée. La caractérisation optiques du revêtement réflectif mais également des matériaux d’encapsulation des cellules ont été réalisés. En combinant ces résultats avec la mesure de réponse spectrale des cellules, nous avons pu calculer les performances optiques théoriques maximales atteignables par le module avec ces matériaux. Les moyens de caractérisations en simulateur solaire ont été adaptés afin de permettre la mesure de rendement de la cellule au module. Ces caractérisations ont permis de dresser un bilan de la distribution des pertes de puissance de la cellule au module. Ainsi, nous avons pu identifier les voies d’optimisation de ce module HIRL qui pourrait atteindre une efficacité électrique de 33%. / The aim of the work presented in this thesis is to develop an innovative low-concentration photovoltaic (PV) module with a high level of integration, a “Highly Integrated ReceiverLess” module named “HIRL”.The concentrated photovoltaic (CPV) technology is presented in the first Chapter with the aim to position the development of this novel concept. The developed module is based on a parabolic-trough concentrator and on the integration of high-efficiency multi-junction solar cells. The idea is to simplify the cell integration in the module via an optimized architecture. The innovation is the multi-functionality of the concentrator mirror acting as primary optical element (POE), which, in addition to having an optical function, becomes both the mechanical support of the cell arrays and the heat sink responsible of the cell cooling. Moreover, this concept relies on well-known, high-throughput, reliable and cost-effective flat-plate PV manufacturing techniques, such as lamination, for the cell array assembly into the rear of the POE. Finally the module is developed to reach an angular acceptance compatible with low cost one axis trackers (> ±1°).The thermal modeling of the module is presented in the second Chapter. This model is used to define the mirror dimensions that guarantee an optimized thermal cooling within the mirror element. Then, we have studied and tested different fabrication processes for the optics forming and cells interconnection. Moreover the feasibility of the lamination process for multi-junction cells encapsulation has been demonstrated for the HIRL concept. The application of the identified processes for prototype fabrication has allowed to fabricate a module reaching an electrical efficiency of 28%. However, the measured acceptance angle is of ±0.55°. It has shown that this design cannot reach the expected acceptance angle value.Based on Chapter 2 results, the architecture and fabrication processes are optimized in the third Chapter. The design has been modified with the aim to increase the angular acceptance while maintaining a sufficient thermal cooling. Moreover, new fabrication processes have been applied on a new prototype which integrates multi-junction cells optimized for low concentration. This new prototype reached 30.5% electrical efficiency and a ±1.4° acceptance angle compatible with low cost one axis tracker.In the Chapter 4, an optical characterization bench has been developed to compare the optical performances of the different optical concentrators fabricated. It allowed to compare the optical efficiency and the angular acceptance of these optical elements, related to different mirror forming techniques. Moreover, the capability of controlling the mirror temperature is also implemented to study thermal effects on the optical performances. It is shown that the mirror heating decreases significantly the acceptance angle of the module.Finally, in the fifth Chapter, an advanced characterization of the power loss mechanisms is presented, from the cell to the module. We calculated the maximum theoretical reachable cell to module ratio for the considered cell and materials based on experimental spectral response and mirror reflectivity measurements. Furthermore a solar simulator has been adapted for cell and module IV measurements to quantify total cell-to-module losses. These characterizations allowed to define the different power loss sources from the cell to the module. The optimization of mirror reflectivity and concentrator forming could increase the electrical efficiency to 33%.

A theoretical model describing photophysics of π-conjugated aggregates, such as molecular crystals and polymer thin films, is developed. A Holstein-like Hamiltonian expressed with a multi-particle basis set is used to evaluate absorption and photoluminescence (PL) spectra of neutral excitons as well as charge modulation spectra (CMS) and transient absorption spectra (TAS) of positively charges hole-type polarons. The results are used to develop a better theoretical understanding of the organic electronics being studied and their photophysics, and also to probe the morphology of poly(3-hexylthiophene) (P3HT) thin films, which are used in photovoltaic devices. / Chemistry

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.

During the past few years there has been a significant interest in spectrum splitting systems to increase the overall efficiency of photovoltaic solar energy systems. However, methods for comparing the performance of spectrum splitting systems and the effects of optical spectral filter design on system performance are not well developed. This dissertation first establishes a method to analyze and compare spectrum splitting systems with different filters, PV cells types and geometries. The method examines the system conversion efficiency in detail and the role of optical spectral filters. A new metric termed the Improvement over Best Bandgap is defined which expresses the efficiency gain of the spectrum splitting system with respect to a similar system that contains the highest constituent single bandgap photovoltaic cell. Also, this work expands the analysis on dispersive spectrum splitting systems. The dispersive effects of transmission type filters are evaluated using a cross-correlation analysis. Lastly, this work presents a grating-over-lens design for dispersive spectrum splitting. In this geometry, a transmission grating is placed at the entrance of a lens. Part of the incident solar spectrum is diffracted off-axis from normal incidence to the lens. The diffracted spectral range comes to a focus at an off-axis point and the undiffracted spectrum comes to a focus at the paraxial focus of the lens. Since the diffracted wave is planar and off-axis, the off-axis focal points suffer from aberrations that increase system loss. In this work, a novel aberration compensation technique is presented using non-planar transmission gratings recorded using a conjugate object beam to modify the off-axis wavefront. Diverging sources are used as conjugate object and reference beams. The spherical waves are incident at the lens and the grating is recorded at the entrance aperture of the solar concentrator. The on-axis source is adjusted to produce an on-axis planar wavefront at the hologram plane. The off-axis source is approximated to a diffraction limited spot producing a non-planar off-axis wavefront on the hologram plane. Illumination with a planar AM1.5 spectrum reproduces an off-axis diffraction-limited spot on the focal plane. Models and experimental data are presented to quantify the reduction in losses achieved with aberration correction.

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.