Hocheffiziente Solarzellen beruhen auf der exzellenten Oberflächenpassivierung, die minimale Rekombinationsverluste gewährleistet. Innerhalb des letzten Jahrzehnts wurde Al2O3 in der Photovoltaikindustrie zum bevorzugten Material für p-leitendes Si. Unterschiedliche Abscheidetechnologien erreichten Passivierungen mit effektiven Minoritätsladungsträgerlebensdauern nahe der AUGER–Grenze. Die ausgezeichnete Passivierungswirkung von Al2O3wird zwei Effekten zugeschrieben: Einerseits werden Si−SiO2-grenzflächennahe Rekombinationszentren passiviert, wenn Wasserstoff, beispielsweise aus der Al2O3-Schicht, offene Bindungen absättigt. Bedingt durch die hohe Konzentration intrinsischer negativer Ladungen an der SiO2-Grenzfläche weist Al2O3 andererseits einen charakteristischen Feldeffekt auf. Das resultierende elektrische Feld hält Elektronen von Oberflächenrekombinationszentren fern. Negative Ladungen im Al2O3 werden generell als fest bezeichnet. Allerdings hat Al2O3 zusätzlich eine hohe Dichte an Haftstellen, die von Elektronen besetzt werden können. Die Dichte negativer Ladungen im Al2O3-Passivierungsschichten hängt vom elektrischen Feld und der Bestrahlungsintensität ab. Ziel dieser Arbeit ist die systematische Untersuchung dielektrischer Passivierungsschichtstapel für die Anwendung auf Si-Solarzellen. Der Qualität und Dicke der SiO2-Grenzschicht kommt in diesem Kontext eine besondere Rolle zu, da sie Ladungsträgertunneln ermöglicht. Der Elektronentransport ist eine Funktion der Oxiddicke und das Optimum zwischen Ladungseinfang und -haltung liegt bei etwa 2 nm SiO2. Vier relevante Al2O3-Abscheidetechnologien werden untersucht: Atomlagenabscheidung, Kathodenzerstäubung, Sprühpyrolyse und Rotationsbeschichtung, wobei die erstgenannte dominiert. Es werden Nanolaminate verglichen, die aus Al2O3 und TiO2, HfO2 oder SiO2 mit subnanometerdicken Zwischenschichten bestehen. Während letztgenannte die Oberflächenrekombination nicht vermindern, beeinflussen TiO2- und HfO2-Nanolaminate die Passivierungswirkung. Ein dynamisches Wachstumsmodell, das initiale und stationäre Wachstumsraten der beteiligten Metalloxide berücksichtigt, beschreibt die physikalischen Parameter. Schichtsysteme mit 0,2 % TiO2 oder 7 % HfO2 sind konventionellen Al2O3-Schichten überlegen. In beiden Fällen überwiegt die veränderte Feldeffekt- der chemischen Passivierung, die mit einer Grenzflächenzustandsdichte von maximal 5·1010 eV−1·cm−2 unverändert auf hohem Niveau verbleibt. Die Ladungsdichte beider Schichtsysteme wird entweder über die Änderung ihrer Polarität der festen Ladungen oder der Fähigkeit zum Ladungseinfang bestimmt. Das Tunneln von Elektronen wird durch ein mathematisches Modell erklärt, dass eine bewegliche Ladungsfront innerhalb der Oxidschicht beschreibt. / High-efficiency solar cells rely on excellent passivation of the surface to ensure minimal recombination losses. In the last decade, Al2O3 became the material of choice for p-type Si in the photovoltaic industry. A remarkable surface passivation with effective minority carrier lifetimes close to the AUGER–limit was demonstrated with different deposition techniques. The excellent passivation effect of Al2O3 is attributed to two effects: Firstly, recombination centers at the Si−SiO2 interface get chemically passivated when hydrogen, for instance from the Al2O3 layer, saturates dangling bonds. Secondly, Al2O3 presents an outstanding level of field effect passivation due to its high concentration of intrinsic negative charges close to the SiO2 interface. The generated electrical field effectively repels electrons from surface recombination centers. Negative charges in Al2O3 are generally termed fixed charges. However, Al2O3 incorporates a high density of trap sites, too, that can be occupied by electrons. It was shown that the negative charge density in Al2O3 passivation layers depends on the electrical field and on the illumination intensity. The goal of this work is to systematically investigate dielectric passivation layer stacks for application on Si solar cells. The SiO2 interface quality and thickness plays a major role in this context, enabling or inhibiting carrier tunneling. Since the electron transport is a function of the oxide thickness, the balance between charge trapping and retention is achieved with approximately 2 nm of SiO2. Additionally, four relevant Al2O3 deposition techniques are compared: atomic layer deposition, sputtering, spray pyrolysis and spin–on coating, whereas the former is predominant. Using its flexibility, laminates comprising of Al2O3 and TiO2, HfO2 or SiO2 with subnanometer layers are compared. Although the latter do not show decreased surface recombination, nanolaminates with TiO2 and HfO2 contribute to the passivation. Their physical properties are described with a dynamic growth model that considers initial and steady–state growth rates for the involved metal oxides. Thin films with 0.2 % TiO2 or 7 % HfO2 are superior to conventional Al2O3 layers. In both cases, the modification of the field effect prevails the chemical effect, that is, however, virtually unchanged on a very high level with a density of interface traps of 5·1010 eV−1·cm−2 and below. The density of charges in both systems is changed via modifying either the polarity of intrinsic fixed charges or the ability of trapping charges within the layers. The observations of electron tunneling are explained by means of a mathematical model, describing a charging front, which moves through the dielectric layer.

Cette thèse est divisée en trois parties. La première traite la synthèse de la polyaniline (PANI), un polymère conducteur de trou, utilisé dans plusieurs applications. En variant les quantités du monomère et de l’oxydant tout en fixant leur rapport molaire à 1:1,25, et en ajoutant de l’oxyde de magnésium, des aiguilles et des nouvelles structures semblables aux échinides sont formées. Le mécanisme de formation des structures unidimensionnelles est expliqué à l’aide de la théorie des multicouches. La deuxième partie est consacrée à la fabrication des monocouches photovoltaïques à faible coût en se basant sur le principe de fonctionnement des cellules à pigment photosensible (en anglais DSSC, Dye-Sensitized Solar Cell). En 1991, Grätzel a réintroduit l’effet photo-électrochimique en développant la première DSSC, une des cellules solaire troisième génération, formée d’un film de TiO2 (photo-anode) pigmenté à l’aide d’un colorant et d’un électrolyte qui sert à régénérer le pigment oxydé. Malgré leur faible coût, les DSSCs font face à de nombreux problèmes tels que le coût élevé du pigment, la fuite de l’électrolyte, la sublimation du couple I-/I3- à travers I2, etc. Afin de résoudre ces problèmes, des monocouches photovoltaïques ont été développées. Des composites formés de PANI et TiO2 sont la base de ces dispositifs nouvelle génération. La polymérisation in-situ de l’aniline en présence des nanoparticules de TiO2 conduit à une forte interaction entre la PANI et les particules de TiO2 où une structure « core (TiO2)/shell (PANI) » existe dans le composite. Dans le dispositif photovoltaïque basé sur le composite PANI-TiO2, PANI est considérée comme pigment à la photo-anode et comme poly-électrolyte plus profondément dans le composite. En plus, des textiles fabriqués utilisant ces composites photo-génèrent une tension de 0,6 V et un courant de 1 A/m2 lorsque l’éthanol est injecté dans le dispositif. Une nouvelle architecture a été développée qui sert à améliorer la performance de la cellule et en même temps stocker l’énergie pour des utilisations ultérieures. La dernière partie est consacrée à la fabrication des DSSCs basées sur les pigments naturels. L’anthocyane, un pigment naturel halochromique responsable de la couleur rouge dans les plantes, a été extrait du chou rouge et utilisé pour pigmenter les films de TiO2. Cette propriété se traduit par la fabrication des DSSCs de différentes couleurs et comportement photovoltaïque. Avec un pH égal à 0, une Vco et une Jcc de 520 mV et 185 μA/cm2 sont respectivement obtenues prouvant la possibilité d’utiliser le chou rouge comme source de pigment à très faible coût des DSSCs. / This thesis is divided in three parts. The first one deals with the synthesis of polyaniline (PANI), a hole conducting polymer, used in many applications. By varying the quantities of the monomer and the oxidant while fixing the molar ratio at 1:1.25, and by adding magnesium oxide, novel echinoid-like and PANI needles were formed. The formation mechanism of the 1D structures is explained using the multi-layer theory. The second section is devoted for the fabrication of low cost single-layered photovoltaic devices based on the working principle of dye-sensitized solar cells (DSSCs). In 1991, Grätzel reintroduced the photo-electrochemical effect by developing the first DSSC, one of the third generation solar cells, formed of a TiO2 film (photoanode) sensitized using a dye and an electrolyte regenerating the excited dye. Despite their low cost, DSSCs face many problems such as the high cost of the dye, leaking of the electrolyte, sublimation of the I-/I3- through I2, etc. To solve these problems a single layer photovoltaic device has been developed. Composites formed of PANI, and TiO2 are the basis of the new generation photovoltaics. The in-situ polymerization of aniline inside a titania solution results in a strong interaction between PANI and TiO2 particles where a core (TiO2)/shell (PANI) structure exists inside the composite. In the single-layered photovoltaic device based on PANI-TiO2 composite, PANI is considered as sensitizer at the photoanode and as polyelectrolyte deeper inside the composite layer. In addition, textiles fabricated using such composites generated a voltage of 0.6 V and a current of 1 A/m2 when ethanol is injected in the solar cell. A new architecture has been developed to enhance the performance of the device and at the same time to store the converted energy for later use. The final part is devoted to the fabrication of DSSCs based on natural dyes. Anthocyanin; a halochromic natural dye responsible for the red color in plants, extracted from red cabbage was used to sensitize TiO2 films. This property results in the fabrication of DSSCs with different colors and photovoltaic behavior. At a pH equal to 0, a Voc and Jsc of 520 mV and 185 μA/cm2 were respectively recorded proving the possibility of using red cabbages as a very low cost dye source for DSSCs.

Les cellules solaires en couches minces permettent de produire de l'énergie à bas-coût et sans émission de gaz à effet de serre. Dans le but de réaliser des dispositifs toujours plus performants, nous étudions l'impact de l'intégration de nanostructures métalliques (NSs) au sein de cellules solaires organiques (CSO). Ces NSs peuvent alors générer des effets diffusifs et des résonances issues de plasmons de surface. A l'aide d'un modèle numérique FDTD, nous démontrons que l'ingénierie plasmonique peut servir à augmenter l'absorption dans le matériau photoactif tout en limitant l'énergie perdue sous forme de chaleur dans les NSs. L'influence de paramètres opto-géométriques de structures associant matériaux organiques et effets plasmoniques est étudiée (diamètre, position des particules dans la couche et période du réseau de particules sphériques). Expérimentalement, des NSs d'argent ont été réalisées par évaporation sous vide puis intégrées dans des couches organiques. Nous avons mesuré une exaltation de l'absorption optique dans la gamme spectrale utile à la photo-conversion. Trois architectures différentes de CSO plasmonique ont été fabriquées et caractérisées par MEB, TEM et ToF-SIMS, puis modélisées, permettant d'identifier des verrous technologiques et de proposer des pistes d'amélioration. Nous avons aussi intégré des NSs au sein d'un empilement transparent et conducteur de type oxyde/métal/oxyde, dans le but de remplacer l'électrode classique en oxyde d'indium et d'étain d'une CSO. Le rôle de chaque couche de l'empilement sur le comportement optique de l'électrode est discuté. Les épaisseurs des couches d'une électrode de type ZnO/Ag/ZnO ont été optimisées. / Thin-film solar cells are able to produce low-cost energy without greenhouse gas emissions. In order to increase devices performance, we investigate the impact of metallic nanostructures (NSs) integrated in organic solar cells (OSC). These NSs can generate scattering effects and surface plasmon resonances. Using FDTD modeling, we demonstrate that plasmon engineering can be used to increase light absorption in a photoactive material while minimizing the energy lost as heat in the NSs. The influence of opto-geometrical parameters of plasmonic structures in organic material is investigated (diameter, position of particles in the layer and period of spherical particles array). Experimentally, silver NSs are deposited by evaporation and incorporated into an organic layer. We measured an optical absorption enhancement in the spectral range useful for photo-conversion. Three different architectures of plasmonic OSC are fabricated and characterized by SEM, TEM and ToF-SIMS, then modeled, allowing us to identify some technological obstacles and to propose possible improvements. We also integrated NSs inside a transparent and conductive multilayer stack composed of oxide/metal/oxide, in the aim of replacing the traditional indium tin oxide electrode of a OSC. The role of each layer of the stack on the electrode optical behavior is discussed. Layers thicknesses of a ZnO/Ag/ZnO electrode were optimized.

A direct “green” aqueous synthesis of mercapto acetate-stabilized copper indium sulfide (CIS) nanoparticles (NPs) and core/shell CIS@ZnS NPs of a varied composition under ambient conditions and a temperature lower than 100 °C is reported. The CIS@ZnS NPs can be anchored to the surface of nanocrystalline FTO/TiO2 films without additional purification or ligand exchange steps yielding visible-light-sensitive heterostructures ready for using as photoanodes in the liquid-junction solar cells. The highest photoelectrochemical activity in a three-electrode cell was demonstrated by a TiO2/CIS@ZnS heterostructure with atomic Cu : In : S and Zn : Cu ratios of 1 : 5 : 10 and 1 : 1. The optimized TiO2/CIS@ZnS photoanodes were tested in two-electrode solar cells with aqueous polysulfide electrolyte and TiO2/Cu2S heterostructures produced by a photo-assisted method as counter-electrodes. Under illumination by a 30 mW cm−2 xenon lamp, the optimized cells showed the average light conversion efficiency of 8.15%, the average open-circuit voltage of −0.6 V and the average fill factor of 0.42. The cells revealed excellent stability and reproducibility of photoelectrochemical parameters with around one percent variation of the light conversion efficiency around an average value for six identical solar cells. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

L'une des approches pour améliorer les performances des cellules solaires organiques, sans augmenter l'épaisseur de la couche photoactive, consiste à incorporer des nanoparticules (NPs) métalliques dans cette couche ou à proximité pour bénéficier de la diffusion de la lumière incidente ou de résonances de plasmons de surface localisés. Cependant, ces NPs métalliques peuvent engendrer des recombinaisons des porteurs de charges électriques, créer des court-circuits ou favoriser l'extinction des excitons au contact du métal. Une solution est alors de protéger ces NPs métalliques par un revêtement diélectrique (coquille ou couche fine). L'objectif de cette thèse est d'étudier l'influence de nanostructures de type cœur–coquille (métal-diélectrique) sur les performances optiques et photoélectriques de cellules solaires organiques, à l'aide de modélisations numériques et de réalisations expérimentales. Dans un premier temps, une étude numérique prédictive, basée sur une modélisation par méthode FDTD, nous a permis d'analyser l'influence de paramètres architecturaux et opto-géométriques sur les propriétés optiques de cellules solaires plasmoniques. Par la suite, nous avons synthétisé et caractérisé des nanosphères (NSs) avec un cœur métallique en argent ou en or recouverts d'une fine coquille de silice. L'incorporation de NSs Ag@SiO2 synthétisées (voie humide) ou de NPs Ag/SiO2 déposées par évaporation (voie sèche) dans des cellules solaires à architecture inverse ont permis d'augmenter le photocourant de 12% ou de 18% respectivement par rapport à la cellule de référence (sans NSs). / One of the approaches to improve the organic solar cells performance without increasing the thickness of the photoactive layer is to incorporate metallic nanoparticles (NPs) in this layer or in its proximity to have benefited from light scattering or localized surface plasmon resonance effects. However, these NPs can generate charge carriers recombination, short circuits or exciton quenching due to the contact with the metal. A solution is then to coat these MNPs with a dielectric (thin shell or layer) to protect them. The objective of this thesis is to study the influence of metal­dielectric core­shell nanostructures on the optical and photoelectric performances of organic solar cells, by using numerical modeling and experiments. First, a predictive numerical analysis by FDTD modeling allowed us to optimize the influence of architectural and optogeometric parameters on optical properties of plasmonic organic solar cells. Silver or gold core nanospheres (NSs) coated with a thin silica shell were synthesized and characterized. Finally, the integration of chemically synthesized Ag@SiO 2 NSs (wet process) or Ag/SiO 2 NPs deposited by evaporation (dry process) in inverted organic solar cells has increased the photocurrent by 12% or 18%, respectively, compared to the reference cell(without NSs).

Nesta tese visamos o entendimento aprofundado dos processos e mecanismos que influenciam a performance de células solares sensibilizadas por corante (DSCs), particularmente a influência das interfaces TiO2/corante, TiO2/eletrólito e rutilo/anatase, assim contribuindo para obter dispositivos eficientes. Nesse sentido, foi investigada a influência das propriedades eletrônicas do novo corante [Ru(dcbpyH2)2(tmtH2)]Cl associadas às transições de transferência de carga MLCT e LMCT sobre a eficiência de fotoinjeção e fotoconversão de energia solar nas DSCs. Por meio da aplicação das espécies isoladas (Bu4N)3[Ru(dcbpy)2(tmtH2)], (Bu4N)4[Ru(dcbpy)2(tmtH)] e (Bu4N)5[Ru(dcbpy)2(tmt)] em DSCs, foram demonstradas as contribuições de duas bandas MLCTs e uma LMCT para a fotoconversão de energia, que foram reveladas por deconvolução dos espectros de fotoação. Além disso, aquelas espécies apresentaram valores de eficiência global corrigidos pela quantidade de corante adsorvido no TiO2 maiores do que o corante N719, indicando que os novos corantes de rutênio têm potencial de aplicação como fotossensibilizadores de células solares. Também foi investigado o mecanismo do efeito sinérgico observado em misturas de rutilo e de anatase por meio do estudo das contribuições dos processos de recombinação e de difusão de elétrons nos filmes mesoporosos mistos de TiO2 sobre a performance das DSCs, em função da distribuição daqueles nanocristais em diferentes proporções, confirmadas por microscopia Raman confocal. A impedância das interfaces/junções presentes nas DSCs foi caracterizada por espectroscopia de impedância eletroquímica (EIS) para determinação de parâmetros fundamentais como capacitância química, resistência de difusão, resistências de recombinação, coeficiente de difusão, tempo de vida e comprimento de difusão dos elétrons dos filmes mistos de TiO2. As características I x V das células solares, ou seja, os parâmetros de eficiência global (η), densidade de corrente de curto-circuito (Jsc), voltagem de circuito-aberto (Voc) e fator de preenchimento (FF) foram relacionados com os parâmetros de impedância e o grau de homogeneidade das misturas de nanopartículas de rutilo e de anatase. Em particular, foi demonstrado o papel fundamental das propriedades de difusão de elétrons nos filmes mistos de TiO2 para o aumento da performance das DSCs. Os estudos de simulação dos espectros de impedância de filmes mistos não homogêneos de TiO2 comercial Aldrich mostraram que o coeficiente de difusão de elétrons desses materiais apresenta um máximo na região de 15% de rutilo e 85% anatase, coincidindo com o máximo de eficiência das DSCs de mesma composição. De fato, diferenças sutis nas contribuições da capacitância química e resistência de difusão foram responsáveis pelo aumento do coeficiente de difusão das DSCs baseadas em filmes mistos não homogêneos de TiO2. Por outro lado, quando foi aumentada a área de contato entre as nanopartículas de anatase e de rutilo, foi observado um aumento da capacitância química e tempo de vida dos elétrons nos filmes mistos homogêneos de TiO2. Estes foram atribuídos ao aumento da eficiência de transferência de elétrons entre os nanocristais de rutilo e de anatase, que diminuiram a recombinação de elétrons e promoveram a estabilização de cargas na banda de condução do TiO2. / The understanding of the detailed mechanism and processes that influence the performance of dye-sensitized solar cells (DSCs), particularly the influence of TiO2/dye, TiO2/electrolyte and rutile/anatase interfaces, thus contributing to increase the efficiency of that devices, is the main goal of this thesis. Accordingly, we investigated the influence of the electronic properties of the new dye [Ru(dcbpyH2)2(tmtH2)]Cl associated the MLCT and LMCT charge transfer transitions on the efficiency of photoinjection and solar energy photoconversion in DSCs. The species (Bu4N)3[Ru(dcbpy)2(tmtH2)], (Bu4N)4[Ru(dcbpy)2(tmtH)] and (Bu4N)5[Ru(dcbpy)2(tmt)] were isolated and used in DSCs, revealing the contributions of two MLCTs and a LMCT band for energy conversion by deconvolution of the photoaction spectra. Interestingly, these new ruthenium dyes presented overall efficiency normalized by the amount of dye adsorbed on TiO2 larger than for the N719 dye, indicating a potential for application as photosensitizers. The mechanism of the synergistic effect observed in blends of rutile and anatase was investigated studying the contributions of the recombination and electron diffusion processes in mesoporous mixed TiO2 films on the performance of DSCs, as a function of the distribution of those nanocrystals in different proportions, as confirmed by Raman microscopy (Confocal). The impedance of interfaces/junctions present in the DSCs was carefully characterized by electrochemical impedance spectroscopy (EIS) to determine key parameters such as chemical capacitance, diffusion resistance, recombination resistance, diffusion coefficient, lifetime and the electron diffusion length in mixed TiO2 films. The I x V characteristics, i.e. the overall efficiency parameter (η), density of short circuit current (Jsc), open-circuit voltage (Voc) and fill factor (FF) of solar cells were correlated with the impedance parameters and the degree of homogeneity of mixtures of rutile and anatase nanoparticles. In fact, the essential role of electron diffusion properties in the mixed TiO2 films on the performance of DSCs was demonstrated. Impedance studies of low homogeneity mixed films prepared with commercial TiO2 (Aldrich) by fitting the experimental spectra with a suitable equivalent circuit revealed that the electron diffusion coefficient of these materials exhibits a maximum at 15% rutile and 85% anatase, as expected based on the synergic effect in DSCs. In fact, subtle differences in the contributions of chemical capacitance and diffusion resistance were responsible for the increase of the electron diffusion coefficient in low homogeneity mixed TiO2 films. On the other hand, an increase in the anatase and rutile nanoparticles contact area reflected positively in the chemical capacitance and electron lifetime, as expected for an enhanced electron transfer efficiency between the rutile and anatase nanocrystals, thus decreasing the electron recombination and increasing the stability of the photoinjected charge on the TiO2 conduction band.

Hybride Nanostrukturen verbinden die Vorzüge von individuellen Materialien, die neue Eigenschaften hervorrufen können. In dieser Arbeit wurden verschiedene Metal Nanostrukturen synthetisiert und deren optische Eigenschaften analysiert. Die Herstellung eines Spasers oder Lichteinfang in Solarzellen wurde untersucht. Der Einfluß von Größe, Form und Brechungsindex auf die Metal-Plasmonen wurde erforscht. Die gewonnen Erkenntnisse genutzt um Metal Nanopartikel mit gezielten Eigenschaften herzustellen. Hybride Gold Nanostrukturen (funktionalisiert mit Farbstoffen oder Quantenpunkten) wurden hergestellt und Energie-Transfereffekte untersucht. Diese hybriden Nanostrukturen wurden optisch gepumpt um Spasing zu erreichen. Allerdings wurde festgestellt, dass eine unrealistisch hohe Verstärkung benötigen wird, um die charakteristischen Verluste im Metal zu überwinden. Silber und Gold Nanopartikel wurden synthetisiert um diese in Dünnschichtsolarzellen einzusetzen. Es konnte gezeigt werden, dass Silber chemisch instabil ist und, wenn oxidiert, hohe Absorption auftritt. Durch hohe Temperaturen konnte die Oxidschicht auf den Silberpartikeln reduziert werden und damit auch die Verluste. Stabilere Gold Partikel wurden in Perovskit-Solarzellen eingebaut, wodurch die Effizienz einer solch modifizierten Solarzelle um ~40% gesteigert werden konnte. Dies wurde durch eine erhöhte Anzahl an generierten Ladungsträgern mittels metallischen Lichtfallen erreicht. Zusätzlich wurden anisotrope Janus Trägerpartikel synthetisiert und mit Metal Nano-partikeln funktionalisiert. Gold Nanopartikel wurden abgeschieden und zu einer Gold Hülle gewachsen. Dies erfolgte entweder gleichförmig über das gesamte Hantel-Trägerpartikel oder einseitig unter Ausnutzung der chemischen Anisotropie. Desweiteren wurden Platin Nano-partikel einseitig abgeschieden und in Wasserstoffperoxid Lösung gegeben. Die Partikel wurden daraufhin mittels dynamischer Lichtstreuung auf Selbstvortrieb untersucht. / Hybrid nanostructures combine the assets of the individual materials with a vast amount of new properties. In this work various metal nanoparticles have been synthesized and investigated on their optical properties. The synthesized metal nanoparticles have been implemented for potential applications, e.g. fabrication of a spaser or in solar cells. At first, the size, shape and refractive index effects of gold and silver nanoparticles have been investigated. The insight gained helps to optimize the synthesis of metal nanoparticles with specific optical properties needed for further applications. Optimized hybrid gold nanostructures have been synthesized and functionalized with dye molecules or quantum dots to investigate energy transfer effects. These hybrid structures have been optically pumped to achieve spasing. However, comparison with a theory showed that such metal nanostructures need unrealistic high gain to overcome the inherent losses and achieve spasing. Silver and gold nanoparticles have been synthesized for applications in thin film solar cells. It has been shown that silver lacks chemical stability and thus, if oxidized, the nanoparticles exhibit weak scattering and strong Ohmic losses. The oxide layer of silver nano-spheres could be via annealing. By contrast, gold nanoparticles, known for their higher stability, have been implemented in a perovskite solar cell. Such a modified solar cell showed an increase in efficiency by ~40% through increased generation of carriers. Anisotropic Janus carrier systems have been synthesized and functionalized with metal nanoparticles. Gold nanoparticles have been deposited either uniformly or on one lobe only of the dumbbell-shaped carrier system by using its chemical anisotropy. These gold nano¬particles have been grown to a gold shell. Platinum nanoparticles have been deposited on a single lobe and its self-propelling ability in a chemical fuel was investigated by means of dynamic light scattering.

This Master thesis, in collaboration with Morgonsol Väst AB, was completed as a part of the Solar Energy engineering program at Dalarna University. It analyses the electrical and thermal performance of a prototype PVT collector developed by Morgonsol Väst AB. By following the standards EN 12975 and EN ISO 9806 as guides, the thermal tests of the collector were completed at the facility in Borlänge. The electrical performance of the PVT collector was evaluated by comparing it to a reference PV panel fitted next to it. The result from the tests shows an improved electrical performance of the PVT collector caused by the cooling and a thermal performance described by the linear efficiency curve ηth=0.53-21.6(Tm-Ta/G). The experimental work in this thesis is an initial study of the prototype PVT collector that will supply Morgonsol Väst with important data for future development and research of the product.

Hybridsolarzellen werden sowohl aus ZnO-Schichten als auch ZnO-Nanostrukturen und Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b'']dithiophen)-alt-4,7(2,1,3-benzothiadiazol)] (PCPDTBT) hergestellt. Das Wachstum der ZnO-Schichten und Nanostrukturen wird mittels gepulster Laserdeposition (PLD) auf Saphirsubstraten durchgeführt. Die Schichten weisen eine c-Achsenorientierung auf. Die Polarität einer ZnO-Schicht bestimmt die Morphologie der nachfolgend gewachsenen ZnO-Nanostrukturen. Dabei kann die Morphologie kontrolliert zwischen Nanostäbchen auf einer O-terminierten ZnO-Schicht und Nanowänden auf einer Zn-terminierten ZnO-Schicht eingestellt werden. Untersuchungen mittels konvergenter Elektronenbeugung zeigen, dass die Nanostrukturen immer Zn-terminiert sind. Die Grenzfläche zwischen ZnO und PCPDTBT wird mit Photoelektronenspektroskopie untersucht und ergibt eine Vakuumniveauangleichung zwischen beiden Materialien. Prinzipiell ist der Übergang für photovoltaische Aktivität geeignet, jedoch sind die erzielten Wirkungsgrade sehr niedrig. Die Ursache ist eine niedrige Exzitonendissoziationseffizienz, die durch die Benutzung von sol-gel ZnO, kleinen organischen Molekülen und einer niedrigeren Leitfähigkeit vom PLD-ZnO verbessert werden kann. Dennoch beträgt der maximale Wirkungsgrad der Hybridsolarzellen nur 0,21 %. / Hybrid solar cells are built from ZnO layers and ZnO nanostructures and Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b'']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT). The growth of the ZnO layers and nanostructures is performed with pulsed laser deposition (PLD) on sapphire substrates. The samples exhibit a c-axis orientation. The polarity of a ZnO layer determines the morphology of subsequently grown ZnO nanostructures. One can control the morphology between ZnO nanorods on an O-terminated layer and nanowalls on a Zn-terminated layer. Studies with convergent electron beam diffraction reveals that the ZnO nanostructures are always Zn-terminated. The interface between ZnO and PCPDTBT is studied with photoelectron spectroscopy and shows a vacuum level alignment between both materials. In principle, the interface is suitable for photovoltaic activity, however, the achieved power conversion efficiencies are very low. This is due to a low exciton dissociation efficiency, which can be improved by the use of sol-gel ZnO, small organic molecules, and a lower conductivity of the PLD ZnO. Nevertheless, the maximum power conversion efficiency amounts to 0.21 %, only.

Diese Dissertation leistet einen Beitrag zum Verständnis des Energie- und Elektronentransfers innerhalb von neuartigen supramolekularen Strukturen, die aus einem zentralen Phthalocyanin und zwei axial angekoppelten Porphyrinen bestehen. Zwei solcher Trimere, welche die koordinative Ankopplung von Porphyrinen über ein Silizium-Zentralatom des Phthalocyanins nutzen, wurden im Rahmen der Arbeit zum ersten Mal quantitativ bezüglich auftretender innermolekularer Transferprozesse charakterisiert. Ziel war die Beantwortung der Frage, ob diese Substanzklasse die wunschgemässe Vereinigung von Lichtsammlung und Ladungstrennung ermöglicht. Aus der Kombination der Messdaten, aufgenommen mit einer Vielzahl von Messverfahren, konnten für die beiden untersuchten Trimere in zwei unterschiedlich polaren Lösungsmitteln die Ratenkonstanten der Energie- und Ladungstransferkanäle ermittelt werden. In allen Fällen findet ein effizienter Ladungstransfer von den Porphyrinen zum Phthalocyanin und ein Lochtransfer vom Phthalocyanin zu einem der beiden Porphyrine statt. Dieses Ergebnis bestätigt die Erwartung, dass Lichtsammlung und Ladungstrennung in diesem Molekül vereint auftreten. Zusätzlich zu den beiden oben erwähnten Prozessen findet je nach Lösungmittelpolarität und Struktur der Porphyrine ein dem Energietransfer paralleler Elektronentransfer und ein Ladungsrücktransfer statt. Allerdings zerfällt der ladungsseparierte Zustand zu schnell, was eine praktische Nutzung der untersuchten Verbindungen in Solarzellen noch verhindert und ihre Weiterentwicklung erfordert. / This thesis contributes to the comprehension of energy and electron transfer within novel supra-molecular structures, denominated triads, consisting of a central phthalocyanine axially-coupled to two porphyrins. In the course of this thesis, two of the trimers, were quantitatively characterized regarding their intramolecular transfer processes. Both feature a dative bond between the porphyrins and the phthalocyanine via the central silicium atom of the latter. These investigations aimed at answering whether this class of compounds allows the desired combination of light harvesting and charge separation. The rate constants of both investigated trimers in two solvents with different polarity were determined by the combination of data from a variety of measurement methods. An efficient charge transfer from the porphyrins to the phthalocyanine and a hole transfer from the phthalocyanine to one of the porphyrins occurs in all investigated cases. This result confirms the prospect that light harvesting and charge separation can occur combined in one molecule. Depending on solvent polarity and the structure of the porphyrines, electron transfer parallel to the energy transfer and a charge back transfer takes place in addition to both above-mentioned processes. However, the charge-separated state of the investigated substances decays to fast, still preventing a practical utilization of these compounds in solar cells and necessitating further developments.