Organic photovoltaics has emerged as a promising technology for electricity generation. The essential component in an organic solar cell is the bulk heterojunction absorber layer, typically a blend of an electron donor and an electron acceptor. Efforts have been made to design new materials such as donor polymers and novel acceptors to improve the power conversion efficiencies. New fullerene free acceptors providing low cost synthesis routes and tenability of their optoelectronic and electrochemical properties have been designed. Despite the efforts, still not much is known about the photopysical processes in these blends that limit the performance. In this respect, time-resolved spectroscopy such as transient absorption and time-resolved photoluminescence, can provide in-depth insight into the various (photo) physical processes in bulk heterojunction solar cell. In this thesis, PCE10 was used as donor and paired with different non fullerene acceptors. In the first part of this thesis the impact of the core structure (cyclopenta-[2, 1-b:3, 4-b’]dithiophene (CDT) versus indacenodithiophene (IDTT)) of malononitrile (BM)-terminated acceptors, abbreviated as CDTBM and IDTTBM, on the photophysical characteristics of BHJ solar cells is reported. The IDTT-based acceptor achieves power conversion efficiencies of 8.4%, higher than the CDT-based acceptor (5.6%), due to concurrent increase in short-circuit current and open-circuit voltage. Using (ultra)fast transient spectroscopy we demonstrate that reduced geminate recombination in PCE10: IDTTBM blends is the reason for the difference in short-circuit currents. External quantum efficiency measurements indicate that the higher energy of interfacial charge-transfer states observed for the IDTT-based acceptor blends is the origin of the higher open-circuit voltage. In the second part of this thesis, I report the impact of acceptor side chains on the photo-physical processes of BHJ solar cells using three different IDT-based acceptors, namely O-IDTBR, EH-IDTBR and O-IDTBCN blended with PCE10. Power conversion efficiencies as high as 10 % were achieved. The transient absorption spectroscopy experiments provide insight into sub-picosecond exciton dissociation and charge generation which is followed by nanosecond triplet state formation in PCE10:O-DTBR and PCE10:EH-IDTBR blends, while in O-IDTBCN triplets are not observed. Time delayed collection field experiments (TDCF) were performed to address the charge carrier generation and examine its dependence on the electric field.

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>Magister Scientiae - MSc / TiO2 nanoparticle films are important electron transport layers (ETLs) in photovoltaics such as dye-sensitised, perovskite and polymer hetero-junction solar cells. These films, however, have significant electron trap-sites as a result of the large density of oxygen vacancies present in nanosized TiO2. These trap-sites cause electron-hole recombination and ultimately lower photon-tocurrent conversion efficiency of the underlying cell during operation. Doping the TiO2 lattice with low atomic number elements such as nitrogen is a proven method to overcoming the charge transport inefficiency of TiO2 ETLs; another is the use of one-dimensional (1D) nanowires (NWs), instead of nanoparticles. Modification of TiO2 with non-metals leads to optical bandgap narrowing, improvement in electron conductivity and increased electron lifetime in the ETL layer. However, a lot of scope exists in understanding and fully quantifying the relationship between optical property, for example light transmission and bandgap modification, versus the doping concentration and type. Most doping approaches are in-situ and involve the addition of a dopant precursor (usually a salt) during the synthesis of TiO2 nanostructures – this invariably leads to uncontrolled doping levels, anion contamination and poor-quality materials – a need thus exists to develop simple, controllable doping approaches. One such approach, which forms the basis of this study, is ex-situ doping by means of plasma generated species in a controlled environment. This field of study is fairly novel and not widely studied, requiring more research to understand the doping mechanisms and influence on the optical and electronic properties of the underlying nanomaterials. In particular, controlled doping of TiO2 with nitrogen using radio-frequency generated (RF) plasma requires vigorous experimentation and characterisation. Inaccuracy of the deposition parameters during exposure remains a common drawback for this approach in addition to a lack of understanding of the surface interaction between the N2 species and specimen during irradiation.

The study of the new materials potentially usable for organic photovoltaic and electronics are getting very important from the point of ecological and financial view. Organic electronic devices are getting more and more popular and it is only up to us to search for the new ones that are able to improve their physical properties. The aim of this thesis is to search for materials like have been mentioned above which have very good semiconducting properties. Solutions of pure materials and its mixtures with different concentrations of fullerene have been investigated by ultra-violet spectroscopy, classical fluorescence and time resolved spectrometry. Mainly, were studied the influence of the central atom and side substituents for the optical and electronical properties of our materials of interest. With adding fullerene was observed quenching phenomena of the fluorescence, because all these new materials show usually high photoluminescence. Based on the given results, the most suitable materials had been chosen to provide trial of making organic solar cell, and therefore investigated by the mean of electric measurements (direct current).

This thesis deals with processing the current issue of trends in on-grid photovoltaic system with accumulation. It examines the posibility of accumulation of photovoltaic systems, analyzing their strengths and weaknesses in the practical deployment. It compares the different storage technologies based on indicators of cycles, durability and price ranges. The practical part deals with the technical design of hybrid power system and then comparing with the standard on-grid system in technical and economical point of view.

The main goal of the master’s thesis SIMULATION OF INTERCONNECTION OF SOLAR CELLS IN MATLAB is introduction of conversion principle of solar radiation into electrical energy in photovoltaic cells. The thesis deals with mathematical models and equations that describe the solar cell and their interconnection. The main task was to develop a user interface program using MATLAB. The produced program is intended to simulate a single cells or series connection, parallel or in series – parallel cells, and so simulate a photovoltaic panel.

Dans ce travail, nous avons appliqué des techniques de photoluminescence en régime stationnaire (PL) et photoluminescence en régime modulé (MPL) à l'étude d'hétérojonctions formées entre du silicium cristallin (c-Si) et du silicium amorphe hydrogéné (a-Si:H). Plus précisément, nous avons comparé des échantillons constitués de dépôts de (n)a-Si:H, (i)a-Si:H, (n)a-Si:H/(i)a-Si:H, et (p)a-Si:H/(i)a-Si:H sur des wafers de (n) c-Si de haute qualité électronique. Les mesures en fonction de la température montrent que la durée de vie des porteurs en excès diminue lorsque la température diminue, ce qui peut être qualitativement reproduit par la simulation dans un mécanisme de recombinaison de type Shokley-Read-Hall (SRH) en tenant compte du niveau d’énergie du dopant (phosphore) dans le substrat et de niveaux peu profonds électroniquement actifs à l'interface.Nous avons également étudié des échantillons dopés par implantation d'ions puis passivés par AlOx, a-Si:H et SiC. Des signatures de dislocations sont révélées à basse température par des pics supplémentaires de PL.Nous avons également comparé les résultats de cartographies de PL et de durée de vie obtenues par l'analyse de l'amplitude de MPL, et par l'analyse de son déphasage. Il est constaté que les propriétés optiques des échantillons ont un grand impact sur la cartographie PL, ce qui pourrait conduire à une conclusion erronée sur leur homogénéité. En revanche, les cartographies de durée de vie sont moins sujettes à des variations de paramètres optiques et au bruit provenant du processus de mesure, phénomènes qui ne sont pas intrinsèques à l'échantillon étudié.La nature différentielle de la mesure MPL est étudiée. Nous démontrons la notion de durée de vie à l'état stationnaire et de durée de vie différentielle. Nous analysons différents types de recombinaisons avec la durée de vie MPL et avons mis en œuvre des simulations des hétérojonctions a-Si:H/c-Si. Nous constatons que dans le domaine d'excitation intéressant pour le photovoltaïque, la durée de vie différentielle est souvent inférieure à la durée de vie à l'état stationnaire. Nous faisons aussi des comparaisons entre les durées de vie obtenues par mesures dites QSSPC et MPL et montrons qu'elles sont en fait égales.La combinaison des techniques de PL et de MPL nous a permis d'étudier le coefficient de recombinaison radiative en fonction de la température. Les résultats publiés jusqu'ici dans la littérature couvrent la plage de température de 300 K à 90 K. Dans cette plage, nos résultats sont en très bon accord avec ces résultats publiés précédemment. Mais, grâce à notre système de mesure et à la combinaison PL/MPL, nous avons obtenu des valeurs de ce coefficient jusqu’à 20 K et nous avons pu proposer une fonction polynômiale du cinquième degré qui permet de bien reproduire les variations en fonction de la température sur toute la plage de 20 K à 300 K.Dans une dernière partie de la thèse, les propriétés de transport de porteurs et l'effet de couplages sont étudiés dans des empilements de quantum dots. Nous avons examiné les quantum dots de InAs qui croissent de manière ordonnée en formant des chaînes à partir d'une couche tampon en InGaAs (couche dite de "cross hatch pattern"). Nous avons caractérisé par PL des monocouches ainsi que des multicouches empilées de chaînes de quantum dots. L'effet de couplage entre dots dans le plan est observé sur des échantillons de monocouches, et nous remarquons une inhibition du couplage vertical entre couches qui est expliqué par l'effet du champ de déformation de la couche de cross hatch pattern. / Silicon solar cells remain the driving technology and dominate the photovoltaics market. Hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction cells achieve the best efficiency in silicon cells to date (25.6%). A great part of this achievement is assigned to the improvement of the passivation of the emitter/absorber interface. In that regard, luminescence techniques whether Photoluminescence (PL) or Modulated photoluminescence (MPL), are particularly appropriate to investigate surface defects and effective carrier lifetime.In this work, we developed a PL/MPL setup coupled to a helium cooled cryostat to the study of a-Si:H/c-Si heterojunctions. Considering the modulated nature of the MPL, we introduced the concept of steady state lifetime and differential lifetime. Through simulations, we analyzed different types of recombination mechanisms and found that the differential lifetime is lower than the steady state lifetime. We also benchmarked the lifetime determined by photoconductance decay measurements and the MPL lifetime and demonstrated that they are actually equal.We have analyzed various samples of a-Si:H/c-Si heterojunctions from multiple sources, particularly within the framework of the European project HERCULES (High Efficiency Rear Contact solar cells and Ultra powerful moduLES). The samples are composed of various doping and passivation layers such as AlOx, a-Si:H and a-SiC:H fabricated on high quality (n)c-Si wafers. The temperature dependent measurements show that the excess carrier lifetime decreases when temperature decreases, which is explained by the Shockley-Read-Hall recombination model at the heterojunction interface. The combination of PL and MPL measurements have enabled us to determine the radiative recombination coefficient in crystal silicon as a function of temperature. Our measurements have extended the original data to 20 K. We propose a fifth order polynomial of the radiative recombination coefficient as a function of temperature in the range of 20 to 300 K and it agrees very well to others’ work.We also investigated the possibility to extend the system to carry out PL and MPL mapping in order to extract the cell homogeneity and the lifetime distribution across the sample. We found that the optical property of sample has a significant impact on the PL mapping and could lead to incorrect conclusion with respect to the homogeneity. However the lifetime mapping from MPL produces imaging that is less prone to variation of optical properties.At last, we utilized the temperature dependent micro PL to investigate the coupling of InAs quantum dot chains (QDC) stacks grown on InGaAs cross hatch patterns separated with a 10 nm GaAs layer. The PL spectra are dominated by the top-most stack, indicating that the QDC layers are nominally uncoupled. However, under the high excitation power densities achievable with the micro PL system, when the high-energy peaks of the top stack are saturated, low-energy PL peaks from the bottom stacks emerge as a result of the carrier transfer across the GaAs spacers. These unique PL signatures contrast with the state-filling effects in conventional, coupled QD stacks and serve as a means to quickly assess the presence of electronic coupling in stacks of dissimilar-sized nanostructures.

Crystalline open-framework intermetallics have long attracted the attention of chemists, physicists, and materials scientists. The intriguing structures such materials exhibit are often intimately related to the unique physical properties they possess. The present work is focused on the preparation and characterization of open-framework intermetallic materials based on group 14 elements, in particular those crystallizing in clathrate and related structures such as the clathrate-II phases. Materials possessing the clathrate-II crystal structure have received increased attention in recent years, as a result of both the unique properties they exhibit as well as potential for use in technologically important applications such as thermoelectrics, photovoltaics, and optoelectronics. However, in comparison with other clathrate structure types, characterization of clathrate-II materials has in general been far less extensive. Moreover, many conceivable compositions have yet to be realized. The purpose of this work is to expand the current knowledge of the structural, chemical, and physical properties of these materials, while simultaneously exploring new compositions and synthetic routes to clathrate-II phases. One of the unique and promising aspects of clathrate-II materials is the ability to vary the guest concentration, which is shown to have significant implications for the structural and physical properties of NaxSi136 (0< x< 24) materials. It is demonstrated that new compositions can be explored by novel approaches to chemical design. Framework substitution in clathrate-II compounds is explored in an effort to assess possibilities for influencing the physical properties of these materials. A novel zeolite-like framework phase, Na1-xGe3+z, has been discovered, and is shown to be a new low-thermal conductivity crystalline solid, suggesting a new approach to the design of crystalline intermetallic materials with low thermal conductivity. New directions in synthesis of intermetallics are identified, with emphasis on unconventional preparative methods and the opportunities they offer. Processing of reactive precursors by spark plasma sintering is demonstrated as a new preparative tool for crystal growth, identifying the first method for preparation of clathrate-II Na24Si136single-crystals since the discovery of these compounds more than four decades ago.

>Magister Scientiae - MSc / TiO2 nanoparticle films are important electron transport layers (ETLs) in photovoltaics such as dye-sensitised, perovskite and polymer hetero-junction solar cells. These films, however, have significant electron trap-sites as a result of the large density of oxygen vacancies present in nano-sized TiO2. These trap-sites cause electron-hole recombination and ultimately lower photon-to-current conversion efficiency of the underlying cell during operation. Doping the TiO2 lattice with low atomic number elements such as nitrogen is a proven method to overcoming the charge transport inefficiency of TiO2 ETLs; another is the use of one-dimensional (1D) nanowires (NWs), instead of nanoparticles.

This paper describes the process of developing a product for the solar industry. It is the story of starting a business in the solar market by designing a product, manufacturing the product and growing sales to over $1 million USD in 2011 and 2012. The author is describing the actual details of a manufacturing company that produces solar racking systems in the USA. The author founded the company in 2009 and left the company at the end of 2012. The document describes the changing landscape of the racking sector of the US PV market, and makes the case for industry standards in solar module dimensions. The range of current sizes of solar modules is described. The inconsistency in sizes creates additional overhead for manufacturers to accommodate different sized parts to hold the different solar panels. A uniform standard size would result in cost reductions for the end customers.