In this work cadmium telluride thin film photovoltaic devices have successfully been produced using a novel closed-field magnetron sputtering technique. This technique offers the possibility of producing cells in an all-in-one vacuum process with the potential to provide a new lower cost production route. The sputtered cadmium telluride layers were characterised in detail using a range of advanced microscopy based techniques both in the as deposited and after the cadmium chloride treated state, a treatment that is necessary to produce a working cell. In the as deposited condition the cadmium telluride layer was seen to have a fine-grained columnar structure containing a high density of stacking faults. After the cadmium chloride treatment these grains recrystallized and the new grains were equiaxed with a much lower density of intragranular defects. Similar effects were also observed in samples prepared using close space sublimation. To understand this recrystallization behaviour during the cadmium chloride treatment, the key treatment parameters were systematically varied. Chemical analysis in Scanning Transmission Electron Microscopy (STEM) showed that chlorine travelled down the cadmium telluride grain boundaries and accumulated adjacent to the cadmium telluride/cadmium sulphide interface. This interface is where the cadmium telluride grains were found to recrystallise first during interrupted cadmium chloride treatments. The nature of the stacking faults was examined using High Resolution Transmission Electron Microscopy (HR-TEM). This showed that in localised regions up to one plane of atoms per sequence was missing based on the expected zinc blende structure. This changed the packing of the atoms such that a local change in crystal structure occurred. This local change in phase was successfully mapped using Electron Backscatter Diffraction in planar section produced using Focused Ion Beam milling. This was subsequently studied in more detail using Transmission Electron Backscatter Diffraction in the Scanning Electron Microscope, where the intra-granular arrangement of the phases was observed. HR-TEM was used to quantitatively measure the linear defects in the cadmium telluride layer after thermal annealing with and without the cadmium chloride present. This showed that annealing alone resulted in only a modest reduction in the density of linear defects and grain recrysallisation only occurred in the presence of cadmium chloride. Cadmium magnesium telluride (CMT) was successfully grown epitaxially onto the cadmium telluride as an electron reflector layer to improve cell performance. During deposition the cell experienced high temperatures and this caused the stacking faults to return in a cell that had been previously cadmium chloride treated. This resulted in a reduction in cell efficiency, providing another link between linear defects and a degradation in cell performance.

A novel probabilistic method has been developed for modelling the operation of energy storage in electricity systems with significant amounts of wind and solar powered generation. This method is based on a spectral analysis of the variations of wind speed and solar irradiance together with profiles of electrical demand. The method has been embodied in two Matlab computer programs: Wind power only: This program models wind power on any time scale from seconds to years, with limited modelling of demand profiles. This program is only capable of modelling stand-alone systems, or systems in which the electrical demand is replaced by a weak grid connection with limited export capacity. 24-hours: This program models wind power, solar PV power and electrical demand, including seasonal and diurnal effects of each. However, this program only models store cycle times (variations within a time scale) of 24 hours. This program is capable of modelling local electrical demand at the same time as a grid connection with import or export capacity and a backup generator. Each of these programs has been validated by comparing its results with those from a time step program, making four Matlab programs in total. All four programs calculate the power flows to and from the store, satisfied demand, unsatisfied demand and curtailed power. The programs also predict the fractions of time that the store spends full, empty, filling or emptying. The results obtained are promising. Probabilistic program results agree well with time step results over a wide range of input data and time scales. The probabilistic method needs further refinement, but can be used to perform initial modelling and feasibility studies for renewable energy systems. The probabilistic method has the advantage that the required input data is less, and the computer run time is reduced, compared to the time step method.

Solar photovoltaic modules provide clean electricity from sunlight but will not be able to compete on an open market until the cost of the electricity they produce is comparable to that produced by traditional methods. At present, modules based on crystalline silicon wafer solar cells account for nearly 90% of photovoltaic production capacity. However, it is anticipated that the ultimate cost reduction achievable for crystalline silicon solar cell production will be somewhat limited and that thin film solar cells may offer a cheaper alternative in the long term. The highest energy conversion efficiencies reported for thin film solar cells have been for devices based around chalcopyrite Cu(In, Ga)(Se, S)2 photovoltaic absorbers. The most efficient Cu(In, Ga)(Se, S)2 solar cells contain absorber layers deposited by vacuum co-evaporation of the elements. However, the cost of ownership of large area vacuum evaporation technology is high and may be a limiting factor in the cost reductions achievable for Cu(In, Ga)(Se, S)2 based solar cells. Therefore, many alternative deposition methods are under investigation. Despite almost thirty companies being in the process of commercialising these technologies there is no consensus as to which deposition method will lead to the most cost effective product. Non-vacuum deposition techniques involving powders and chemical solutions potentially offer significant reductions in the cost of Cu(In, Ga)(Se, S)2 absorber layer deposition as compared to their vacuum counterparts. A wide range of such approaches has been investigated for thirty years and the gap between the world record Cu(In, Ga)(Se, S)2 solar cell and the best devices containing non-vacuum deposited absorber layers has closed significantly in recent years. Nevertheless, no one technique has demonstrated its superiority and the best results are still achieved with some of the most complex approaches. The work presented here involved the development and investigation of a new process for performing one of the stages of non-vacuum deposition of Cu(In, Ga)(Se, S)2 absorber layers. The new process incorporates copper into an initial Group III-VI precursor layer, e.g. indium gallium selenide, through an ion exchange reaction performed in solution. The ion exchange reaction requires only very simple, low-cost equipment and proceeds at temperatures over 1000°C lower than required for the evaporation of Cu under vacuum. In the new process, indium (gallium) selenide initial precursor layers are immersed in solutions containing Cu ions. During immersion an exchange reaction occurs and Cu ions from the solution exchange places with Group III ions in the layer. This leads to the formation of an intimately bonded, laterally homogeneous copper selenide – indium (gallium) selenide modified precursor layer with the same morphology as the initial precursor. These modified precursor layers were converted to single phase chalcopyrite CuInSe2 and Cu(In, Ga)Se2 by annealing with Se in a tube furnace system. Investigation of the annealing treatment revealed that a series of phase transformations, beginning at low temperature, lead to chalcopyrite formation. Control of the timing of the Se supply was demonstrated to prevent reactions that were deemed detrimental to the morphology of the resulting chalcopyrite layers. When vacuum evaporated indium (gallium) selenide layers were used as initial precursors, solar cells produced from the absorber layers exhibited energy conversion efficiencies of up to 4%. While these results are considered promising, the devices were characterised by very low open circuit voltages and parallel resistances. Rapid thermal processing was applied to the modified precursor layers in an attempt to further improve their conversion into chalcopyrite material. Despite only a small number of solar cells being fabricated using rapid thermal processing, improvements in open circuit voltage of close to 150mV were achieved. However, due to increases in series resistance and reductions in current collection only small increases in solar cell efficiency were recorded. Rapid thermal processing was also used to demonstrate synthesis of single phase CuInS2 from modified precursor layers based on non-vacuum deposited indium sulphide. Non-vacuum deposition methods provide many opportunities for the incorporation of undesirable impurities into the deposited layers. Analysis of the precursor layers developed during this work revealed that alkali atoms from the complexant used in the ion exchange baths are incorporated into the precursor layers alongside the Cu. Alkali atoms exhibit pronounced electronic and structural effects on Cu(In, Ga)Se2 layers and are beneficial in low concentrations. However, excess alkali atoms are detrimental to Cu(In, Ga)Se2 solar cell performance and the problems encountered with cells produced here are consistent with the effects reported in the literature for excess alkali incorporation. It is therefore expected that further improvements in solar cell efficiency might be achieved following reformulation of the ion exchange bath chemistry.

This thesis describes studies on nanohybrid systems consisting of single-walled carbon nanotubes (SWNTs) with monolayer coatings of semiconducting polymers. Steady-state and time-resolved optical and high-resolution microscopy experiments were used to investigate the blends. These materials show promise for use in organic photovoltaics (OPVs) owing to the high carrier mobilities and large aspect ratios of SWNTs, the controllable solubilisation of tubes with various polymers and the broad light-harvesting abilities of organic polymers. Chapters 1 and 2 introduce the theory and background behind the work and present a literature review of previous work utilising carbon nanotubes in OPV devices, revealing poor performances to date. The experimental methods used during the thesis are detailed in Chapter 3 and the solution processing techniques used to prepare the polymer–nanotube blend samples are described in Chapter 4. Chapter 5 describes a study on a nanotube blend with a thiophene polymer, a system previously unsuccessfully implemented into OPV devices. Ultrafast spectroscopic measurements showed that electrons can transfer on a 400 fs time scale from the polymer to nanotubes and the conditions to allow long-lived free charges to be produced were found. The study is extended in Chapter 6 to show that nanostructures consisting of a nanotube coated in one polymer can then be coated by a second polymer and that these nano-engineered structures could be implemented into OPV devices. The use of a competition binding process to isolate purely semiconducting nanotubes dispersed with any desired polymer is then described in Chapter 7. Finally, Chapter 8 introduces systems consisting of chains of porphyrin units, nature’s light-harvesting systems, bound to nanotubes and the blends were found to exhibit the required electronic alignment for use in OPVs. The work described in this thesis provides an explanation for the poor device behaviour of nanotube–polymer blends to date and, in particular, demonstrates several nanohybrid systems that show particular promise for improved OPV applications.

In this thesis different methods of energy storage are evaluated for use in multifamily residential buildings in order to increase the self-consumption of self-generated photovoltaic electricity. The computational software MATLAB was used to simulate and study five different energy systems applied on two case studies. The five energy systems are; one reference system consisting of photovoltaics, one system with photovoltaics and a hydrogen storage system, and three systems consisting of photovoltaics and batteries using different management strategies. The different systems were compared based on their effect on the buildings self-consumption ratio and grid interaction as well as system costs and profitability. The battery systems successfully increased the self-consumption ratio and decreased grid interaction. Assuming a favourable development of market conditions, all systems containing batteries were paid back. The battery system that could reduce high consumption peaks during the entire year was the most profitable system as the buildings fixed grid fees could be lowered. The hydrogen storage system increased the self-consumption ratio to a small degree, as much of the electricity was lost in the conversion processes. Also, the components of the hydrogen system are very costly and the investment could therefore not be paid back within the 30 year life-time. Photovoltaics can be used to decrease variable electricity costs while energy storage can be used to decrease both variable and fixed electricity costs. The results suggest that focusing on handling power peaks and leveling grid interaction is more valuable than focusing on increasing self-consumption in multifamily residential buildings. The value of energy storage systems in multifamily residential buildings has been discussed with respect to technology development and changes in market conditions, the conclusion being that the value will most likely increase within the next decade and onward. It is believed that local energy storage systems have an important role to play in a power system with an increasing amount of renewable and intermittent power sources.

In Cu(In,Ga)Se2 (CIGS) solar cells the CIGS layer serves as the light absorber, growing naturally p-type. Together with an n-type buffer layer they form a p-n heterojunction. Typically, CdS is used as a buffer, although other, less toxic materials are investigated as alternatives. The intrinsic p-type doping of CIGS layers is the result of complex defect physics. Defect formation energies in CIGS are very low or even negative, which results in extremely high defect concentrations. This leads to many unusual electrical phenomena that can be observed in CIGS devices. This thesis mostly focuses on three of these phenomena: light-soaking, light-on-bias, and light-enhanced reverse breakdown. Light-soaking is a treatment that involves illuminating the investigated device for an extended period of time. In most CIGS solar cells it results in an improvement of open-circuit voltage, fill factor, and efficiency that can persist for hours, if not days. The interplay between light-soaking and the remaining two phenomena was studied. It was found that light-soaking has a strong effect on light-on-bias behavior, while the results for light-enhanced breakdown were inconclusive, suggesting little to no impact. Light-on-bias is a treatment which combines simultaneous illumination and application of reverse bias to the studied sample. Illuminating CdS-based samples with red light while applying a reverse bias results in a significant increase in capacitance due to filling of traps. In many cases, this is accompanied by a decrease in device performance under red illumination. Complete recovery is possible by illuminating the treated sample with blue light, which causes hole injection from the CdS buffer. In samples with alternative buffer layers, there is little distinction between red and blue illumination, and the increase in capacitance is milder. At the same time, there is little effect on device performance. Reverse breakdown can occur when a sufficiently large reverse bias is applied to a p-n junction, causing a large reverse current to flow through the device. In CIGS solar cells, the voltage at which breakdown occurs in darkness decreases in the presence of blue illumination. A model explaining the breakdown in darkness was proposed as a part of this thesis. The model assumes that all voltage drops on the buffer layer in darkness and on the CIGS layer under blue illumination. The high electric field in the buffer facilitates Poole-Frenkel conduction and Fowler-Nordheim tunneling between the absorber and the buffer.

Master of Science / Department of Chemistry / Jun Li / With the worldly consumption of energy continually increasing and the main source of this energy, fossil fuels, slowly being depleted, the need for alternate sources of energy is becoming more and more pertinent. One promising approach for an alternate method of producing energy is using solar cells to convert sunlight into electrical energy through photovoltaic processes. Currently, the most widely commercialized solar cell is based on a single p-n junction with silicon. Silicon solar cells are able to obtain high efficiencies but the downfall is, in order to achieve this performance, expensive fabrication techniques and high purity materials must be employed. An encouraging cheaper alternative to silicon solar cells is the dye-sensitized solar cell (DSSC) which is based on a wide band gap semiconductor sensitized with a visible light absorbing species. While DSSCs are less expensive, their efficiencies are still quite low compared to silicon. In this thesis, Grätzel cells (DSSCs based on TiO2 NPs) were fabricated and optimized to establish a reliable standard for further improvement. Optimized single layer GSCs and double layer GSCs showing efficiencies >4% and efficiencies of ~6%, respectively, were obtained. Recently, the incorporation of metallic nanoparticles into silicon solar cells has shown improved efficiency and lowered material cost. By utilizing their plasmonic properties, incident light can be scattered, concentrated, or trapped thereby increasing the effective path length of the cell and allowing the physical thickness of the cell to be reduced. This concept can also be applied to DSSCs, which are cheaper and easier to fabricate than Si based solar cells but are limited by lower efficiency. By incorporating 20 nm diameter Au nanoparticles (Au NPs) into DSSCs at the FTO/TiO2 interface as sub wavelength antennae, average photocurrent enhancements of 14% (maximum up to ~32%) and average efficiency enhancements of 13% (maximum up to ~23% ) were achieved with well dispersed, low surface coverages of nanoparticles. However the Au nanoparticle solar cell (AuNPSC) performance is very sensitive to the surface coverage, the extent of nanoparticle aggregation, and the electrolyte employed, all of which can lead to detrimental effects (decreased performances) on the devices.

Le dopage du silicium par implantation ionique pour le photovoltaïque est une application relativement récente dont l'essor se heurte encore aujourd'hui aux coûts élevés d'intégration au sein des lignes de fabrication des cellules solaires. L'implantation ionique par immersion plasma promet de répondre aux futures exigences du secteur en termes de coûts et de productivité.Ces travaux de thèse ont permis le développement de procédés d'implantation ionique par immersion plasma de l'équipement PULSION®, conçu par IBS, dédiés à la fabrication de cellules solaires en silicium monocristallin. Dans un premier temps, nous montrons qu'il permet la réalisation de profils de dopage d'émetteur de type n variés, répondant aux exigences des cellules solaires à haut rendement. Les émetteurs fabriqués sont caractérisés de manière chimique, physique et électrique afin de démontrer leur excellente qualité. L'intégration de l'implantation ionique des émetteurs au sein d'un processus de fabrication industriel et peu coûteux, développé par l'INES sur silicium monocristallin de type p, permet d'atteindre des rendements de conversion supérieurs à 19,3%, soit un gain de plus de 0,5% par rapport aux rendements obtenus avec des cellules usuelles à émetteurs dopés par diffusion POCl3.La réalisation d'émetteurs de type p est également étudiée dans ce mémoire afin de préparer la transition technologique vers les cellules solaires sur silicium monocristallin de type n. Confirmant les atouts et le potentiel de la technologie d'implantation ionique par immersion plasma, les travaux menés au cours de cette thèse débouchent sur la conception d'un prototype industriel PULSION® dédié au photovoltaïque. / Ion implantation is a major process technology for manufacturing integrated circuits. However, silicon doping by ion implantation for photovoltaics is a relatively recent application, and its growth still faces high costs of integration into solar cell production lines. Plasma-immersion ion implantation (PIII) promises to meet the future industry requirements in terms of costs and productivity.This thesis work has led to the development of processes dedicated to silicon-based solar cell manufacturing using the plasma-immersion ion implanter – PULSION® – designed by IBS. First, we show that PIII enables the realization of various doping profiles for phosphorus-doped emitters which fit the requirements of high-efficiency solar cells. Emitters thus fabricated are chemically, physically and electrically characterized to demonstrate their excellent quality. Those emitters, implanted through plasma immersion and integrated into a low cost solar cell manufacturing line from INES on monocrystalline silicon, enable to raise the conversion efficiency, obtained with conventional POCl3-diffused solar cells, by more than 0.5% absolute to reach efficiencies above 19.3%.Fabrication of p-type boron implanted emitters is also studied in order to improve conversion efficiencies of p-type silicon based solar cells, but also in order to anticipate the technological shift from p-type to n-type silicon material. Thanks to this thesis work, the strength and potential of PIII for photovoltaic applications have been proven and this has convinced IBS to design a PULSION® equipment dedicated to solar cell manufacturing.

Diploma thesis deals with current priorities of energy policy within EU region, where is a substantial emphasis placed on exploitation of renewable energy sources (RES). There is mentioned historical development in the first part as well as an actual approach to energy policy by EU. Further is evaluated exploitation of RES and their proprotion on electricity generation. I also provide analysis whether current energy objectives can be met. In the last part I deal with photovoltaic industry both in EU and Czechia. Energy extraction from sunshine is currently the most growing field industry all over the world and especially in EU.

L’objectif de la thèse consiste à développer une série des molécules d’architecture en haltère à base de phtalocyanine et à caractère donneur, pour l’élaboration de cellules solaires organiques. Plus particulièrement, les molécules sont des triades entièrement conjuguées, constituées de deux phtalocyanines de zinc séparés par un chromophore rigide de nature variable (un dérivé de benzothiadiazole, d’isoindigo ou de dikétopyrrolopyrrole). Dans ce travail, nous avons cherché à optimiser les modes de synthèse en utilisant différentes réactions de couplages catalysées. Nous avons également cherché à faire varier la nature du cœur et le nombre de chaînes ramifiées périphériques, afin d’étudier leur impact sur les niveaux d’énergie et les propriétés optiques, structurales, de transport de charge et enfin photovoltaïques. / This work reports a series of dumbbell-shaped molecules based on phthalocyanine with an electro-donating character, to be used in organic solar cells. More particularly, the molecules are fully-conjugated triads, made of two zinc phthalocyanine fragments separated by a rigid central dye of different nature (derivative of benzothiadiazole, isoindigo or diketopyrrolopyrrole). The synthesis of the materials was optimized by varying the type of the cross-coupling reactions. The properties of the molecules (absorption, energy levels, structure, charge transport and photovoltaic) were investigated as function of the nature of the central dye and the peripheral ramified chains on the phthalocyanine fragments.