abstract: The deposition of airborne dust, especially in desert conditions, is very problematic as it leads to significant loss of power of photovoltaic (PV) modules on a daily basis during the dry period. As such, PV testing laboratories around the world have been trying to set up soil deposition stations to artificially deposit soil layers and to simulate outdoor soiling conditions in an accelerated manner. This thesis is a part of a twin thesis. The first thesis, authored by Shanmukha Mantha, is associated with the designing of an artificial soiling station. The second thesis (this thesis), authored by Darshan Choudhary, is associated with the characterization of the deposited soil layers. The soil layers deposited on glass coupons and one-cell laminates are characterized and presented in this thesis. This thesis focuses on the characterizations of the soil layers obtained in several soiling cycles using various techniques including current-voltage (I-V), quantum efficiency (QE), compositional analysis and optical profilometry. The I-V characterization was carried out to determine the impact of soil layer on current and other performance parameters of PV devices. The QE characterization was carried out to determine the impact of wavelength dependent influence of soil type and thickness on the QE curves. The soil type was determined using the compositional analysis. The compositional data of the soil is critical to determine the adhesion properties of the soil layers on the surface of PV modules. The optical profilometry was obtained to determine the particle size and distribution. The soil layers deposited using two different deposition techniques were characterized. The two deposition techniques are designated as “dew” technique and “humidity” technique. For the same deposition time, the humidity method was determined to deposit the soil layer at lower rates as compared to the dew method. Two types of deposited soil layers were characterized. The first type layer was deposited using a reference soil called Arizona (AZ) dust. The second type layer was deposited using the soil which was collected from the surface of the modules installed outdoor in Arizona. The density of the layers deposited using the surface collected soil was determined to be lower than AZ dust based layers for the same number of deposition cycles. / Dissertation/Thesis / Masters Thesis Engineering 2016

Since a superconductor has no resistance below a certain temperature and can therefore save a large amount of energy dissipated, it is a 'green' material by saving energy loss and hence reducing carbon emissions. Recently the massive manufacture of high-temperature superconducting (HTS) materials has enabled superconductivity to become a preferred candidate to help generation and transportation of cleaner energy. One of the most promising applications of superconductors is Superconducting Magnetic Energy Storage (SMES) systems, which are becoming the enabling engine for improving the capacity, efficiency, and reliability of the electric system. SMES systems store energy in the magnetic field created by the flow of direct current in a superconducting coil. SMES systems have many advantages compared to other energy storage systems: high cyclic efficiency, fast response time, deep discharge and recharge ability, and a good balance between power density and energy density. Based on these advantages, SMES systems will play an indispensable role in improving power qualities, integrating renewable energy sources and energizing transportation systems. This thesis describes an intensive study of superconducting pancake coils wound using second-generation(2G) HTS materials and their application in SMES systems. The specific contribution of this thesis includes an innovative design of the SMES system, an easily calculated, but theoretically advanced numerical model to analyse the system, extensive experiments to validate the design and model, and a complete demonstration experiment of the prototype SMES system. This thesis begins with literature review which includes the introduction of the background theory of superconductivity and development of SMES systems. Following the literature review is the theoretical work. A prototype SMES system design, which provides the maximum stored energy for a particular length of conductors, has been investigated. Furthermore, a new numerical model, which can predict all necessary operation parameters, including the critical current and AC losses of the system, is presented. This model has been extended to analyse superconducting coils in different situations as well. To validate the theoretical design and model, several superconducting coils, which are essential parts of the prototype SMES system, together with an experimental measurement set-up have been built. The coils have been energized to test their energy storage capability. The operation parameters including the critical current and AC losses have been measured. The results are consistent with the theoretical predictions. Finally the control system is developed and studied. A power electronics control circuit of the prototype SMES system has been designed and simulated. This control circuit can energize or discharge the SMES system dynamically and robustly. During a voltage sag compensation experiment, this SMES prototype monitored the power system and successfully compensated the voltage sag when required. By investigating the process of building a complete system from the initial design to the final experiment, the concept of a prototype SMES system using newly available 2G HTS tapes was validated. This prototype SMES system is the first step towards the implementation of future indsutrial SMES systems with bigger capacities, and the knowledge obtained through this research provides a comprehensive overview of the design of complete SMES systems.

The diploma thesis deals with the study of perovskite solar cells with a regular n-i-p architecture. The theoretical part of this work is mainly focused on the stability of perovskite solar cells, i.e. thermal stability and the influence of UV radiation on final perovskite solar cell stability. Furthermore, the deposition methods, the architecture of solar cells and the materials used for the preparation of electron and hole transport layers were described in more detail. The experimental part deals with the optimization of the preparation of perovskite solar cells (especially in terms of resulting photovoltaic conversion efficiency), with a description of the structure preparation process of the final photovoltaic cell and the interpretation of the measured results.

This thesis is focused on the photochromic molecule of spiropyran, which changes its structure as well as physical and chemical properties after UV irradiation. These changes are reversible, the molecule thermally restore its initial structure. For the study, the molecule SP1 with the systematic name 1',3'-dihydro-1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-(2H)-indole] was used. This molecule was incorporated within polymers PVK, Tg PPV, PCBTDPP and PCDTBT and the method of UV-VIS spectroscopy was used to observe the photochromic activity within these matrices. The influence of matrices to the ability to undergo UV induced photochromic conversion as well as to the reverse conversion to the initial structure induced by heat was monitored. Furthermore, the influence of spiropyran to the electrical properties of individual matrices was studied. The effect of photochromic conversion to both, the mobility of charge carriers and to the photogeneration was observed. For this purpose, the method of current-voltage measurement was used.

Electrical transport in materials is typically diffusive, due to dominant momentum-relaxing scattering of carriers with the phonons or defects. In ultraclean material systems such as GaAs/AlGaAs or graphene/hBN heterostructures, momentum-relaxing can be suppressed, leading to the onset of non-diffusive transport regimes, where Ohm's law is no longer valid. Within these non-diffusive regimes, the hydrodynamic regime occurs when momentum-conserving electron-electron scattering length scale is smaller than the device length scale (usually at intermediate temperatures). On the other hand, weak electron-electron scattering (at low temperatures) results in ballistic transport, commonly understood using the familiar single-particle framework of injected carriers travelling in straight line trajectories with intermittent reflections off device boundaries. Both the ballistic and hydrodynamic regimes can exhibit a emph{negative} nonlocal resistance, and collective behaviour such as the formation of current vortices. In this work, we study nonlocal current-voltage characteristics in mesoscopic devices fabricated from a GaAs/AlGaAs heterostructure that hosts a two-dimensional electron system in a GaAs quantum well. First, we report a quadratic non-linearity in the nonlocal current-voltage characteristics that manifests in any device where a nonlocal voltage measurement is possible. Using measurements at low temperatures ($sim$ 4 K) across multiple devices and considering various contact configurations for each device, we show that the non-linearity is universal. We apply the non-linearity to rectification and frequency multiplication. We also report on a periodic peaks in the nonlocal voltage vs. magnetic field, in an enclosed mesoscopic geometry in which transverse magnetic focusing (TMF) is typically studied. These peaks occur at weak magnetic fields, are independent of the source-detector separation and are distinct from TMF. Our experimental findings are backed by an extensive set of simulations using in both the semiclassical as well as quantum-coherent transport models. / Master of Science / Current is made up of charged particles such as electrons moving through a material. Typically, current is proportional to the applied voltage and flows from higher to lower potential within the device with the potential decreasing monotonically as we move from the source contact to the drain contact irrespective of the path taken through the device. This is commonly known as Ohm's law, and is followed in most materials we come across. The motion of electrons carrying this current is akin to the motion of balls inside a pinball machine, their momentum randomized by intermittent collisions due to lattice vibrations, defects and impurities present in the material. In ultraclean two-dimensional materials at low-intermediate temperatures (where lattice vibration is weak), these collisions become sparse. Collisions of electrons with other electrons now become important. When electron-electron collisions are frequent, the electrons collectively behave like a fluid, giving rise to so called hydrodynamic transport. On the other hand, when electron-electron collisions are sparse as well, electrons move unhindered in ballistic straight line trajectories until they reflect off the device boundaries. This is known as ballistic transport. Under both these transport regimes, Ohm's law breaks down, leading to interesting physical phenomena such as the formation of current whirlpools. In this work, we study the voltage measured at a point in the device which is distinct from the point where current is injected or extracted. This is commonly known as the nonlocal voltage. We explore the relationship between the nonlocal voltage and the injected current and find it to be significantly different from predictions made by Ohm's law. We use this novel current-voltage relationship to build a rectifier and frequency multiplier - two devices commonly used in high-frequency detection, radar systems and telecommunications. We also report previously unseen periodic oscillations in the nonlocal voltage when the magnetic field perpendicular to the device is varied. Using high-resolution simulations, we show the these oscillations can not be explained by looking at individual electron paths, and arise due to contribution from all electrons that travel through the device.

The aim of this project is to model current volt-age characteristic curves for different plasma conditions (i.eelectron density, electron temperature, ion temperature andplasma potential) that can be found in active auroras. This isdone by simulating the charging of a FFU with a connectedLangmuir probe in the software SPIS. These I-V curves wereused to determine the plasma properties of the auroras in whichthe sounding rockets SPIDER-1 and SPIDER-2 were launched.Through the simulations it was also studied how the differentparameters effects the I-V curves.The results showed that the plasma SPIDER-1 was launchedin most likely had properties close to nominal conditions and forSPIDER-2 there was colder electrons in the plasma. A conclusionthat only the electron temperature affects the shape of the I-Vcurves for the values simulated in this project can be drawnas well as the conclusion that the geometry of the probe doesnot affect the shape of the I-V curves. Another result showsthat electron temperature also affect how the hull of the FFUcharges. A higher electron temperature gives the hull a morenegative charge. / Syftet med detta projekt är att modellera ström-pänningskaraktäristisk kurvor för olika plasmatillstånd som finns i aktiva auroror. Detta görs genom att simulera laddning på en FFU med en ansluten Langmuir-prob i SPIS. Dessa I-V-kurvor används för att bestämma plasma egenskaperna för aurororna sondraketerna SPIDER-1 och SPIDER- 2 skjöts upp i. I-V kurvorna används också för att bestämma hur plasma parametrarna elektron temperatur, jon temperatur och elektrondensitet samt hur probens geometri påverkar I-V- kurvornas utseende. Resultaten visade att den plasma SPIDER-1 blev uppskjuten i troligen hade nominella förhållanden och att den SPIDER-2 blev uppskjuten i troligtvis hade kallare elektroner. En slutsats om att endast elektron temperaturen påverkar formen på IV- kurvorna kan dras, såväl som slutsatsen att probens geometri inte påverkar formen på IV-kurvorna. Ett annat resultat visar att elektron temperaturen också påverkar ytpotentialen på FFUn. En högre elektron temperatur ger FFUn en mer negativ laddning. / Kandidatexjobb i elektroteknik 2020, KTH, Stockholm

The overall aim of the present thesis is to clarify the control of intracellular chloride homeostasis in central neurons, because of the critical role of chloride ions (Cl–) for neuronal function. Normal function of the central nervous system (CNS) depends on a delicate balance between neuronal excitation and inhibition. Inhibition is, in the adult brain, most often mediated by the neurotransmitter γ-aminobutyric acid (GABA). GABA may, however, in some cases cause excitation. GABA acts by activating GABA type A receptors (GABAARs), which are ion channels largely permeable to Cl–. The effect of GABAAR-mediated neuronal signaling - inhibitory or excitatory - is therefore mainly determined by the Cl– gradient across the membrane. This gradient varies with neuronal activity and may be altered in pathological conditions. Thus, understanding Cl– regulation is important to comprehend neuronal function. This thesis is an attempt to clarify several unknown aspects of neuronal Cl– regulation. For such clarification, a sufficiently sensitive method for measuring the intracellular Cl– concentration, [Cl–]i, is necessary. In the first study of this thesis, we examined two electrophysiological methods commonly used to estimate [Cl–]i. Both methods, here called the interpolation and the voltage-ramp method, depend on an estimate of the Cl– equilibrium potential from the current-voltage relation of GABA- or glycine-evoked Cl– currents. Both methods also provide an estimate of the membrane Cl– conductance, gCl. With a combination of computational and electrophysiological techniques, we showed that the most common (interpolation) method failed to detect changes in [Cl–]i and gCl during prolonged GABA application, whereas the voltage-ramp method accurately detected such changes. Our analysis also provided an explanation as to why the two methods differ. In a second study, we clarified the role of the extracellular matrix (ECM) for the distribution of Cl– across the cell membrane of neurons from rat brain. It was recently proposed that immobile charges located within the ECM, rather than as previously thought cation-chloride transporter proteins, determine the low [Cl–]i which is critical to GABAAR-mediated inhibition. By using electrophysiological techniques to measure [Cl–]i, we showed that digestion of the ECM decreases the expression and function of the neuron-specific K+ Cl– cotransporter 2 (KCC2), which normally extrudes Cl- from the neuron, thus causing an increase in resting [Cl–]i. As a result of ECM degradation, the action of GABA may be transformed from inhibitory to excitatory. In a third study, we developed a method for quantifying the largely unknown resting Cl– (leak) conductance, gCl, and examined the role of gCl for the neuronal Cl– homeostasis. In isolated preoptic neurons from rat, resting gCl was about 6 % of total resting conductance, to a major part due to spontaneously open GABAARs and played an important role for recovery after a high Cl– load. We also showed that spontaneous, impulse-independent GABA release can significantly enhance recovery when the GABA responses are potentiated by the neurosteroid allopregnanolone. In a final commentary, we formulated the mathematical relation between Cl– conductance, KCC2-mediated Cl– extrusion capacity and steady-state [Cl–]i. In summary, the present thesis (i) clarifies how well common electrophysiological methods describe [Cl–]i and gCl, (ii) provides a novel method for quantifying gCl in cell membranes and (iii) clarifies the roles of the ECM, ion channels and ion transporters in the control of [Cl–]i homeostasis and GABAAR-mediated signaling in central neurons.

Cette thèse porte sur la dynamique quantique dans un dcSQUID inductif. Ce dispositif est une boucle supraconductrice interrompue par deux jonctions Josephson. Sa dynamique est analogue à celle d'une particule massive évoluant dans un potentiel bidimensionnel. Dans la limite quantique, le dcSQUID se comporte comme un atome artificiel à deux degrés de liberté, contrôlé par le courant et le flux de polarisation. Dans la limite où l'inductance de la boucle est petite devant celle des jonctions, celles-ci sont fortement couplées. La dynamique du circuit est alors celle d'un oscillateur anharmonique quantique unidimensionnel. Dans la limite des deux premiers niveaux d'énergie, ce circuit est un qubit de phase. Jusqu'alors la décohérence dans ce circuit était dominée par le bruit en courant. Nous montrons, par des mesures de spectroscopie et d'oscillations cohérentes, que l'effet du bruit en courant s'annule à courant de polarisation nul, permettant une augmentation des temps de cohérence. Dans la limite où l'inductance de la boucle est grande devant celle des jonctions, la dynamique devient bidimensionnelle. Le circuit exhibe alors un spectre d'énergie riche qui peut être décrit comme celui de deux oscillateurs anharmoniques couplés, correspondant aux modes d'oscillations symétrique et antisymétrique des phases des deux jonctions. Nous mettons en évidence ce spectre par des mesures de spectroscopie et nous démontrons la manipulation cohérente des états quantiques de chaque mode. En particulier nous mettons en évidence un couplage non-linéaire entre les deux modes, dans une limite de couplage fort. Ce couplage nous permet alors d'observer des oscillations cohérentes entre les deux modes internes de cet atome artificiel. De plus, dans ce manuscrit, nous présentons une technique innovante de fabrication de jonctions métalliques par évaporations sous angles qui n'a pas recours à un pont de résine suspendu. Finalement nous proposons un modèle simple basé sur les effets de chauffage qui explique pour la première fois une anomalie récurrente observée dans les caractéristiques courant-tension des dcSQUID. / This thesis focuses on the quantum dynamics in inductive dcSQUID. This device is a superconducting loop interrupted by two Josephson junctions. Its dynamics can be described as a massive fictitious particle in a two dimensional potential. A dcSQUID behaves as an artificial atom with two degrees of freedom, controlled by current and flux bias. When the loop inductance is smaller than the Josephson inductance, the junctions are strongly coupled. The device is then described as a one dimensional quantum anharmonic oscillator. In the limit of the two lowest energy levels, a dcSQUID is a phase qubit. Until now decoherence was dominated by the current noise. We show by spectroscopic measurement and coherent oscillations measurement that the effect of the current noise vanishes at zero current bias, enabling longer coherence times. When the loop inductance is larger than the Josephson inductance, the dynamics becomes two dimensional. The device exhibits a rich energy spectrum which can be describe as the one of two coupled anharmonic oscillators, corresponding to symmetric and antisymmetric oscillations modes of the phases across each junctions. We present spectroscopic measurement of this spectrum. We demonstrate the coherent manipulation of the quantum states of each mode. We show evidence of non linear coupling between the modes, in the strong coupling regime. This coupling enables the measurement of coherent oscillations between the internal modes of this artificial atom. In addition we present a novel fabrication technique that allows metallic junction fabrication by angle evaporation without the use of suspended bridge of resist. We propose also a simple model based on heating effects that explain for the first time a frequent anomaly in the IV characteristic of dcSQUID.

Currently organic-inorganic hybrid perovskite solar cells (PSCs) is one kind of promising photovoltaic technology due to low production cost, easy fabrication method and high power conversion efficiency. Charge transport layers are found to be critical for device performance and stability. A traditional electron transport layer (ETL), such as TiO2 (Titanium dioxide), is not very efficient for charge extraction at the interface. Compared with TiO2, SnO2 (Tin (IV) Oxide) possesses several advantages such as higher mobility and better energy level alignment. In addition, PSCs with planar structure can be processed at lower temperature compared to PSCs with other structures. In this thesis, planar-structure perovskite solar cells with SnO2 as the electron transport layer are fabricated. The one-step spin-coating method is employed for the fabrication. Several issues are studied such as annealing the samples in ambient air or glovebox, different concentration of solution used for the samples, the impact of using filter for solutions on samples. Finally, a reproducible fabrication procedure for planer-structure perovskite solar cells with an average power conversion efficiency of 16.8%, and a maximum power conversion efficiency of 18.1% is provided.

The Master’s Thesis deals with supercapacitators based on principle of eletrical double layer. At the outset there is an explanation of supercapacitor working principal. We discussed advantages and disavantages supercapacitators compared with other related elements in electrotechnics. Materials based on carbon and their structure for production supercapacitators are described too. In next part of Thesis we mention different methods and techniques for the measurement and the evaluation of supercapacitators‘s capacities. Optimal materials for production supercapacitators are presented in conclusion.