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In the last decade, photovoltaics (PV) has experienced an important transformation. Traditional solar cells formed by compact semiconductor layers have been joined by new kinds of cells that are constituted by a complex mixture of organic, inorganic and solid or liquid electrolyte materials, and rely on charge separation at the nanoscale. Recently, metal organic halide perovskites have appeared in the photovoltaic landscape showing large conversion efficiencies, and they may share characteristics of the two former types. In this paper we provide a general description of the photovoltaic mechanisms of the single absorber solar cell types, combining all-inorganic and hybrid and organic cells into a single framework. The operation of the solar cell relies on a number of internal processes that exploit internal charge separation and overall charge collection minimizing recombination. There are two main effects to achieve the required efficiency, first to exploit kinetics at interfaces, favouring the required forward process, and second to take advantage of internal electrical fields caused by a built-in voltage and by the distribution of photogenerated charges. These principles represented by selective contacts, interfaces and the main energy diagram, form a solid base for the discussion of the operation of future types of solar cells. Additional effects based on ferroelectric polarization and ionic drift provide interesting prospects for investigating new PV effects mainly in the perovskite materials. This work was supported by MINECO of Spain under a project (MAT2013-47192-C3-1-R), and the Helmholtz-Energy-Alliance ‘‘Hybrid-Photovoltaics’’.

Fatigued state of the Pt-PZT-Pt system is studied by means of low-temperature conduction measurements. It is shown that the conduction in the temperature interval of 100-140 degrees K is determined by the cold field emission of electrons (tunneling conduction mechanism). The Fowler-Nordheim equation describes well the observed current-voltage relations for reasonable values of the system parameters. The conduction measurements in this regime show that the strong fatigue of the switching polarization provokes a substantial increase of the cold-field-emission-controlled current. The decrease of the switching polarization from 60 to 15 mu C/cm(2) due to fatigue results in a shift of the I-V characteristic towards the lower fields by some 500 kV/cm. Partial. rejuvenation of the sample by short-time beating to 490 degrees K results in a complete restoring of the initial current-voltage characteristic. It is shown that the fatigue-induced increase of the conduction can be modeled by the charging of the interfacial layers of thickness comparable with the tunneling length. This interpretation is consistent with the fatigue scenario related to the space charge-assisted blocking of the centers of the domain nucleation suggested earlier.

A new class of conducting discotic liquid crystals is identified in recently synthesized derivatives of heptacyclic triindole, which combine the hole transport properties of the carbazole unit with...

A grain growth anomaly in Ti-rich strontium titanate ceramics is reported. Here we show that three discontinuities on the temperature dependence of grain growth take place with drops in the grain size at temperatures around 1500, 1550, and 1605 degrees C. We also show that similar discontinuities can be observed in the dependence of the grain boundary activation energy for conductivity and in the grain boundary thickness, assessed by impedance spectroscopy (IS). These notable coincidences are reported for the first time and strongly support the formation of different grain boundary complexions in polycrystalline oxides with transitions in between the observed grain growth regimens, which may be correlated to different grain boundary mobility and dielectric properties. These results call into question the discussion on the role of nonstoichiometry of SrTiO3 and complexions on the microstructure development and open opportunities to design properties of functional materials.

In our contribution we will present a transparent photoconductive sensor based on organic materials. The performance of the photoconductive sensor will be demonstrated by electrical and spectral response measurements. The existence of a high-field space charge region near the cathode will be shown by means of local illumination measurements.

EDELWEISS is a direct non-baryonic cold dark matter detection experiment in the form of weakly interacting massive particles (also known as WIMPs), which currently constitute the most popular candidates to account for the missing mass in the Universe. To this purpose, EDELWEISS uses germanium bolometers at cryogenic temperature (20 mK approximately) in the Underground Laboratory of Modane (LSM) at the French-Italian border. Since 2008, a new type of detector is operated, equipped with concentric electrodes to optimize the rejection of surface events (coplanar-grid detectors). This thesis work is divided into several research orientations. First, we carried out measurements concerning charge collection in the crystals. The velocity laws of the carriers (electrons and holes) have been determined in germanium at 20 mK in the orientation, and a complete study of charge sharing has been done, including an evaluation of the transport anisotropy and of the straggling of the carriers. These results lead to a better understanding of the inner properties of the EDELWEISS detectors. Then, studies relating to the improvement of the performances were carried out. In particular, we have optimized the space-charge cancellation procedure in the crystals and improved the passive rejection of surface events (β). The fiducial volume of the detectors has been evaluated using two X-ray lines from cosmically activated radionuclides: 68Ge and 65Zn. Lastly, an exhaustive study of the low energy spectra has been carried out, which makes it possible to develop a systematic analysis method for the search of low-mass WIMPs in EDELWEISS.; EDELWEISS est une expérience de détection directe de matière noire froide non-baryonique sous forme de particules massives et faiblement interagissantes (connues sous l'acronyme de WIMPs), qui constituent actuellement les candidats les plus populaires pour rendre compte de la masse manquante de l'Univers. Dans ce but, EDELWEISS utilise des bolomètres de germanium opérés à température cryogénique (20 mK environ) dans le Laboratoire Souterrain de Modane (LSM) à la frontière franco-italienne. En particulier, depuis 2008, un nouveau type de détecteur est en fonctionnement, équipé d'électrodes concentriques pour optimiser le rejet des évènements de surface (détecteurs à grilles coplanaires). Cette thèse se décompose en plusieurs axes de recherche. Tout d'abord, nous avons réalisé des mesures concernant la collecte des charges dans les cristaux. Les lois de vitesse des porteurs (électrons et trous) ont été déterminées dans le germanium à 20 mK dans la direction , et une étude complète de la répartition des charges a été menée, avec une évaluation de l'anisotropie du transport et de la diffusion transverse des porteurs. Ces résultats permettent d'avoir une meilleure compréhension du fonctionnement interne des détecteurs d'Edelweiss. Ensuite, des études portant sur l'amélioration des performances ont été effectuées. Nous avons en particulier permis d'optimiser la procédure de régénération des cristaux et améliorer le rejet passif des évènements de surface (β). Le volume utile de détection des détecteurs a été évalué en utilisant les raies de deux radio-isotopes activés cosmiquement, le 68Ge et le 65Zn. Enfin, une étude exhaustive portant sur l'étude des spectres à basse énergie a été menée, ce qui permet de mettre au point une méthode d'analyse systématique pour la recherche de WIMPs de basse masse dans EDELWEISS.

EDELWEISS is a direct non-baryonic cold dark matter detection experiment in the form of weakly interacting massive particles (also known as WIMPs), which currently constitute the most popular candidates to account for the missing mass in the Universe. To this purpose, EDELWEISS uses germanium bolometers at cryogenic temperature (20 mK approximately) in the Underground Laboratory of Modane (LSM) at the French-Italian border. Since 2008, a new type of detector is operated, equipped with concentric electrodes to optimize the rejection of surface events (coplanar-grid detectors). This thesis work is divided into several research orientations. First, we carried out measurements concerning charge collection in the crystals. The velocity laws of the carriers (electrons and holes) have been determined in germanium at 20 mK in the orientation, and a complete study of charge sharing has been done, including an evaluation of the transport anisotropy and of the straggling of the carriers. These results lead to a better understanding of the inner properties of the EDELWEISS detectors. Then, studies relating to the improvement of the performances were carried out. In particular, we have optimized the space-charge cancellation procedure in the crystals and improved the passive rejection of surface events (β). The fiducial volume of the detectors has been evaluated using two X-ray lines from cosmically activated radionuclides: 68Ge and 65Zn. Lastly, an exhaustive study of the low energy spectra has been carried out, which makes it possible to develop a systematic analysis method for the search of low-mass WIMPs in EDELWEISS.; EDELWEISS est une expérience de détection directe de matière noire froide non-baryonique sous forme de particules massives et faiblement interagissantes (connues sous l'acronyme de WIMPs), qui constituent actuellement les candidats les plus populaires pour rendre compte de la masse manquante de l'Univers. Dans ce but, EDELWEISS utilise des bolomètres de germanium opérés à température cryogénique (20 mK environ) dans le Laboratoire Souterrain de Modane (LSM) à la frontière franco-italienne. En particulier, depuis 2008, un nouveau type de détecteur est en fonctionnement, équipé d'électrodes concentriques pour optimiser le rejet des évènements de surface (détecteurs à grilles coplanaires). Cette thèse se décompose en plusieurs axes de recherche. Tout d'abord, nous avons réalisé des mesures concernant la collecte des charges dans les cristaux. Les lois de vitesse des porteurs (électrons et trous) ont été déterminées dans le germanium à 20 mK dans la direction , et une étude complète de la répartition des charges a été menée, avec une évaluation de l'anisotropie du transport et de la diffusion transverse des porteurs. Ces résultats permettent d'avoir une meilleure compréhension du fonctionnement interne des détecteurs d'Edelweiss. Ensuite, des études portant sur l'amélioration des performances ont été effectuées. Nous avons en particulier permis d'optimiser la procédure de régénération des cristaux et améliorer le rejet passif des évènements de surface (β). Le volume utile de détection des détecteurs a été évalué en utilisant les raies de deux radio-isotopes activés cosmiquement, le 68Ge et le 65Zn. Enfin, une étude exhaustive portant sur l'étude des spectres à basse énergie a été menée, ce qui permet de mettre au point une méthode d'analyse systématique pour la recherche de WIMPs de basse masse dans EDELWEISS.

The synthesis, structural and mesomorphic properties of five tetrabenzopentaphene derivatives are presented. All the compounds exhibit columnar mesophases which have been characterized by optical microscopy, differential scanning calorimetry and X-ray diffraction. The thermogravimetric analysis of the ester derivatives reveals that they suffer a decomposition process to the anhydride derivative at temperatures above 200 °C. The influence of the length of the terminal alkyl chains on the mesomorphic behaviour of the compounds has been studied. The structural characterization of the compounds has been completed with the study of their aggregation in solution by means of NMR. The fluorescent properties of the compounds are reported as well as a preliminary study of the photoconductivity of one of them.

Die Isoliereigenschaften von Schwefelhexafluorid sind ein wichtiges Kriterium für die Auslegung von gekapselten gasisolierten Schaltanlagen. Bei langsam ansteigenden Spannungen können sich positive Raumladungen vor eventuell auftretenden Defekten bilden und die weitere Entladungsentwicklung hemmen, was zu einer signifikanten Erhöhung der resultierenden Durchschlagspannung führt. Durch zahlreiche durchgeführte Experimente konnte ein grundlegendes Driftmodell zur Abschätzung des Bereiches aktiver Koronastabilisierung gefunden werden, welches auf einer Modellierung der im Gasraum vor der Störstelle ablaufenden Driftvorgänge der positiven Ladungsträger beruht. Durch Integration dieses einfachen Driftmodells in eine dreidimensionale elektrostatische Feldberechnung konnte die Größe der vor der Störstelle entstehenden Raumladungszone abgeschätzt werden. The insulation properties of sulphur-hexafluoride are essential for the design of metal encapsulated switchgear. With decreasing steepness of the applied test voltage an increasing number of positive ions will move to the outer streamer region and build up a positive space-charge cloud in front of the protrusion. The space-charge reduces the electric field near the rod, further ionization processes are stopped and thus an increased voltage level is needed to initiate the leader process, leading to higher breakdown voltages. The results found during the numerous experiments lead to considerations for a fundamental simulation modell. It is assumed that space-charge-stabilization only occurs if the velocity of the streamer growth is lower than the drift velocity of the positive ions. By implementing this model in a 3-dimensional electrostatical field calculation the size of the space-charge cloud could be estimated.

The deposition of unipolarly charged aerosol particles by simultaneous Brownian diffusion and electrostatic dispersion (spacecharge) in laminar flow tubes has been modelled in two different ways. In the first approach, the rigorous transport equation has been solved numerically under the restriction of negligible axial components of the particle Brownian motion and of the space-charge electric field. The thus calculated theoretical penetrations agree satisfactorily with the experimental results obtained for air ions. Second, the system has also been modelled from a phenomenological point of view, based on the fact that deposition by diffusion and space-charge follows first- and second-order kinetics, respectively. The latter approach yields a simple and practical equation correlating particle penetration with tube geometry, aerosol flow rate, and particle mobility and concentration.

Resume Le projet de transport par câble extrude a courant continu connait actuellement un regain d’interet au niveau industriel mondial. Aussi les etudes sur la fiabilite de telles installations se poursuivent aussi bien dans les laboratoires universitaires qu’industriels. Parmi ces etudes figurent les travaux sur l’apparition et l’evolution de la charge d’espace dans les isolants synthetiques. Plusieurs methodes ont ete mises au point afin d’en etudier la distribution sur des echantillons plans ayant subit un vieillissement accelere, c’est a dire en appliquant de fortes contraintes electriques et thermiques. Pour des raisons evidentes d’apprehension des phenomenes pouvant intervenir sur un câble en fonctionnement, il est essentiel de pouvoir effectuer des mesures du champ electrique total sur des câbles en conditions de service. De recents developpements de la Methode de l’Onde Thermique (MOT) ont permis de mettre au point un outil plus adapte a cette exigence industrielle.

The EDELWEISS experiment is aiming at the detection of Weakly Interactive Massive Particles (WIMPs), today's most favoured candidates for solving the dark matter issue. Background ionising particles are identified thanks to the simultaneous measurement of heat and ionisation in the detectors. The main limitation to this method is coming from the ionisation measurement, charge collection being less efficient in some part of the detectors known as «dead» areas. The specificity of the measurement is due to the use of very low temperatures and low collection fields. This thesis is dedicated to the study of carrier trapping. It involves time-resolved charge measurements as well as a simulation code adapted to the specific physical conditions. We first present results concerning charge trapping at the free surfaces of the detectors. Our method allows to build a surface-charge in a controlled manner by irradiation with a strong radioactive source. This charge is then caracterised with a weaker source which acts as a probe. In a second part of the work, bulk-trapping characteristics are deduced from charge collection efficiency measurements, and by an original method based on event localisation in the detector. The results show that a large proportion of the doping impurities are ionised, as indicated independently by the study of degradation by space-charge build-up. In this last part, near-electrodes areas are found to contain large densities of charged trapping centres, in connection with dead-layer effects.; Le but de l'expérience EDELWEISS est la détection de particules massives très faiblement interagissantes, candidats actuellement majeurs pour résoudre le problème de la matière noire. On identifie les particules ionisantes du fond grâce à la mesure simultanée de chaleur et d'ionisation dans les détecteurs. La principale limitation à cette méthode provient de la mesure d'ionisation, la collecte de charges étant altérée dans certaines zones dites «mortes» du détecteur. La spécificité de la mesure tient à l'emploi de très basses températures et de faibles champs de collecte. Cette thèse est consacrée à l'étude du piégeage de porteurs, par l'utilisation conjointe de mesures résolues en temps et d'un code de simulation adapté à ces conditions physiques particulières. On présente tout d'abord les résultats concernant le piégeage sur les surfaces libres des détecteurs. Notre méthode permet de constituer une charge surfacique de manière contrôlée sous irradiation par une source de forte activité, pour ensuite la caractériser à l'aide d'une source plus faible utilisée comme une sonde. Dans une deuxième étude, les caractéristiques du piégeage en volume sont déduites de mesures du rendement de collecte, ainsi que par une méthode originale utilisant la localisation des évènements dans le détecteur. Les résultats montrent qu'une proportion importante des impuretés dopantes sont chargées, comme l'indique de manière indépendante l'étude concernant les phénomènes de dégradation liés à la constitution d'une charge d'espace. Ce dernier volet met également en évidence la présence de nombreux pièges chargés sous les électrodes, et leur lien avec les effets de zone morte.

One of the most studied systems in the field of organic photovoltaic devices are bulk heterojunction solar cells based on poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) as electron donor and methano[60] fullerene [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as electron acceptor. A striking feature of these types of solar cells is that at the optimal device thickness of typically 100 nm only 60% of the incident light is absorbed. It is evident that the absorption can be enhanced by increasing the thickness of the active layer. However, in spite of an increased absorption the overall power conversion efficiency shows a negative trend when increasing the device thickness beyond 100nm. From device point of view the reduced performance with increasing thickness mainly originates from a decrease of the fill factor. We demonstrate that this fill factor decrease is a result of the formation of space-charges in thick devices and charge recombination.

The EDELWEISS experiment is aiming at the detection of Weakly Interactive Massive Particles (WIMPs), today's most favoured candidates for solving the dark matter issue. Background ionising particles are identified thanks to the simultaneous measurement of heat and ionisation in the detectors. The main limitation to this method is coming from the ionisation measurement, charge collection being less efficient in some part of the detectors known as «dead» areas. The specificity of the measurement is due to the use of very low temperatures and low collection fields. This thesis is dedicated to the study of carrier trapping. It involves time-resolved charge measurements as well as a simulation code adapted to the specific physical conditions. We first present results concerning charge trapping at the free surfaces of the detectors. Our method allows to build a surface-charge in a controlled manner by irradiation with a strong radioactive source. This charge is then caracterised with a weaker source which acts as a probe. In a second part of the work, bulk-trapping characteristics are deduced from charge collection efficiency measurements, and by an original method based on event localisation in the detector. The results show that a large proportion of the doping impurities are ionised, as indicated independently by the study of degradation by space-charge build-up. In this last part, near-electrodes areas are found to contain large densities of charged trapping centres, in connection with dead-layer effects., Le but de l'expérience EDELWEISS est la détection de particules massives très faiblement interagissantes, candidats actuellement majeurs pour résoudre le problème de la matière noire. On identifie les particules ionisantes du fond grâce à la mesure simultanée de chaleur et d'ionisation dans les détecteurs. La principale limitation à cette méthode provient de la mesure d'ionisation, la collecte de charges étant altérée dans certaines zones dites «mortes» du détecteur. La spécificité de la mesure tient à l'emploi de très basses températures et de faibles champs de collecte. Cette thèse est consacrée à l'étude du piégeage de porteurs, par l'utilisation conjointe de mesures résolues en temps et d'un code de simulation adapté à ces conditions physiques particulières. On présente tout d'abord les résultats concernant le piégeage sur les surfaces libres des détecteurs. Notre méthode permet de constituer une charge surfacique de manière contrôlée sous irradiation par une source de forte activité, pour ensuite la caractériser à l'aide d'une source plus faible utilisée comme une sonde. Dans une deuxième étude, les caractéristiques du piégeage en volume sont déduites de mesures du rendement de collecte, ainsi que par une méthode originale utilisant la localisation des évènements dans le détecteur. Les résultats montrent qu'une proportion importante des impuretés dopantes sont chargées, comme l'indique de manière indépendante l'étude concernant les phénomènes de dégradation liés à la constitution d'une charge d'espace. Ce dernier volet met également en évidence la présence de nombreux pièges chargés sous les électrodes, et leur lien avec les effets de zone morte.

International audience; In order to improve the knowledge of dielectric properties of insulators, we have imagined an original method of characterization of the charge buildup. Electrons of an electron beam are implanted through a metallic ball directly in contact with the insulator in a scanning electron microscope. By calculating and modeling the capacitance and the electrostatic force between the ball and the insulator plane, it has been possible to determine the relationship between the injected charges in the metallic ball and its surface potential. The major role of the dielectric thickness has been evidenced when the insulator is placed on a grounded metallic plane. At high potential values, a dielectric breakdown of the medium surrounding the sphere occurs and electrical charges are transferred from the ball to the dielectric sample. This transfer has been evidenced and quantified in the case of sapphire and quartz. Analytical calculations and numerical simulations using the finite-element method have been performed for interpreting these experimental results.

The detection of fundamental components of light red-green-blue is based on transient behavior of a np silicon photodiode. Applied small voltage step to a photodiode illuminated with constant visible light, instntaneously changes the space-charge charge and quasi-neutral charges. The instantaneous changes of charge corresponds to dark current and photocurrent. The photocurrent is wavelenght-dependent. Therefore, bias voltage switching simulation under different monochromatic and chromatic illumination condition are carried out to investigate the transient behavior. The Fast Fourier Transform (FFT) is used to characterize the wavelenght-dependent capacitance. The simulation results will be compared with experimental one obtained with amorphous silicon (a-Si:H) n-i-p photodiode. The obtained results demonstrate that the one-terminal standard devices wavelenght dependent capacitance can be used for color detection.

A minimal two-field fluid approach is followed to describe the radio-frequency (RF) wave propagation in the bounded scrape-off layer plasma of magnetic fusion devices self-consistently with direct current (DC) biasing of this plasma. The RF and DC parts are coupled by non-linear RF and DC sheath boundary conditions at both ends of open magnetic field lines. The physical model is studied within a simplified framework featuring slow wave (SW) only and lateral walls normal to the straight confinement magnetic field. The possibility is however kept to excite the system by any realistic 2D RF field map imposed at the outer boundary of the simulation domain. The self-consistent RF + DC system is solved explicitly in the asymptotic limit when the width of the sheaths gets very large, for several configurations of the RF excitation and of the target plasma. In the case of 3D parallelepipedic geometry, semi-analytical results are proposed in terms of asymptotic waveguide eigenmodes that can easily be implemented n...

Three-dimensional (3D) laser cooling method of fast stored ion beams based on linear coupling mechanism is explored. We employ the tracking code "SAD", showing that resonant coupling remarkably enhances transverse cooling rates. Molecular dynamics (MD) code "SOLID" is also employed to study the effect of space charges and the possibility of beam crystallization.

Leakage conduction of Pt-Pb(ZrXTi:(1-X))O-3-Pt capacitors is studied by means of different measuring techniques and analyzed in terms of semiconductor properties of the system. Based on the experimental data, it is concluded that two different regimes of carrier injection (with the critical electric field of the crossover between these regimes being independent of the measuring technique) are responsible for true leakage conduction in Pt-Pb(ZrXTi1-X)O-3-Pt films. For interpretation of the experimental results a Space-Charge-Influenced-Injection model which takes into account both role of charge of depletion in the bulk of the film and injection through the blocking contact is proposed. This model describes well the main features of the observed current-voltage characteristics and provides a reasonable fit for the current-voltage curves measured at elevated temperatures, the values of the fitting parameters being in a good agreement with the results of other studies. The presented study provides insight in me physical nature of leakage conduction of Pt-Pb(ZrXTi1-X)O-3-Pt system and suggests a method for analyzing its semiconductor parameters by means of conduction measurements.

La masiva producción de neumáticos, así como su posterioralmacenamiento después de su utilización constituye un grave problema medioambiental al que se pretende dar salida con diversas soluciones. Una de ellas pasa por mezclar estos neumáticos reutilizados (Ground Tire Rubber GTR) con diversos polímeros termoplásticos, siendo esta opción la analizada en el presente trabajo, el cual tiene como objetivo obtener materiales aislantes adecuados para la industria eléctrica a partir de la mezcla del Etil-vínil Acetato (EVA) con neumáticos fuera de uso. Como exigencia principal se ha partido de unos costes mínimos de reciclado, es decir, mediante el uso del GTR sin desvulcanizary sin ningún pretratamiento previo con ácidos, pero en cambio actuando sobre la concentración y tamaños de las partículas del GTR, la cual se ha conseguido de una forma sencilla y económica como es el tamizado. Con este fin se han realizado análisis dieléctricos, mecánicos y térmicos de un gran número de compuestos obtenidos a partir de los tres tamaños de partículas del GTR (p500μm), y las siete concentraciones con las que se han formado los compuestos (0%, 5%, 10%, 20%, 40%, 50% y 70% en GTR). Todos estos datos han permitido una caracterización precisa de las propiedades de los nuevos compuestos y, de acuerdo con estos resultados y las Normativas vigentes, se han determinadoposibles aplicaciones eléctricas de los compuestos.

The applicability of extremely thin non-electroneutral membranes for ion-selective electrodes (ISEs) is investigated. A theoretical treatment of potential and concentration profiles in space-charge membranes of <