L’objectif de cette thèse était de concevoir denouveaux matériaux polymères hydrophobes pour la protectionde composants semi-conducteurs, résistants à hautetempérature, aux forts champs électriques et aux atmosphèresagressives. Dans ce contexte, les polyimides d’addition sontapparus comme la famille de polymères la mieux adaptée pourl’application envisagée. La synthèse de l’encapsulant étantréalisée directement dans les boîtiers des modules, elle ne peutdonc pas contenir de solvant organique exogène. Ainsi, nousavons développé de nouvelles voies de synthèse sans solvantde poly(aminobismaléimide)s et de poly(bismaléimide)s.Dans un premier temps, différentes diamines aliphatiques ontété utilisées comme solvant réactif lors de la synthèse depoly(aminobismaléimide)s à une température bien inférieure à latempérature de fusion du bismaléimide utilisé (Tf > 300 °C). Unepremière série de 3 nouveaux poly(aminobismaléimide)sréticulés de 70 à 95 % a ainsi été réalisée. A partir de cespremières synthèses, 10 nouveaux poly(aminobismaléimide)sont été élaborés. Pour 9 d’entre eux, des diamines aromatiquesont été utilisées et, pour le dernier, une diamine siloxane. Cesrésultats démontrent la possibilité de généraliser ce procédé desynthèse.Dans un second temps, des poly(bismaléimide)s ont étésynthétisés, toujours sans solvant. Pour cela, les synthèses dequatre nouveaux bismaléimides liquides à température ambianteont été mises au point. Ces composés ont une structurealiphatique ou siloxane dans laquelle un motif pyroméllitique aété, ou pas, introduit. Leur polymérisation amorcée avecl’amorceur radicalaire ad hoc, conduit à la formation desmatériaux sans l’usage de solvant.Selon le choix des réactifs, des matériaux thermodurcissablesou élastomères sont obtenus. Ces derniers semblent mieuxadaptés à l’application souhaitée car, d’une part, la faibleviscosité des mélanges réactionnels permet leur applicationsans difficulté dans un module de puissance et, d’autre part, leurcaractère hydrophobe est plus marqué. L’un d’eux présente unestabilité thermique à 250 °C particulièrement intéressante et unetempérature de relaxation mécanique quasi hors gamme detempérature de fonctionnement. Ce matériau peut doncvraisemblablement être utilisé comme encapsulant. / The aim of this work is to develop new hydrophobicpolymeric materials for the protection of semi-conductorcomponents. These materials must withstand high temperature,strong electric fields and aggressive atmospheres such asmoisture. In this context, addition polyimides emerged as themost suitable polymers for the intended application. Thesynthesis of the encapsulant being made directly in the powermodules, it must be solvent free. Thus, we have developed newsolvent free synthesis routes of poly(aminobismaleimide)s andpoly(bismaleimide)s.First of all, different aliphatic diamines were used as a reactivesolvent in the synthesis of poly(aminobismaleimide)s to atemperature well below the melting point of the usedbismaleimide (m.p. > 300 °C). A first series of 3 newpoly(aminobismaleimide)s, crosslinked from 70 to 95 %, hasthus been made. From these first syntheses, 10 newpoly(aminobismaleimide)s have been developed. For 9 of them,aromatic diamines were used and, for the latter, a siloxanediamine. These results demonstrate that this process can begeneralized.Secondly, poly(bismaleimide)s were synthesized, still withoutany solvent. In order to do so, the syntheses of four newbismaleimides, liquid at room temperature, have beendeveloped. These compounds have an aliphatic or siloxanestructure in which a pyromellitic pattern has been or notintroduced. Their polymerization initiated with the suitable radicalinitiator leads to the formation of materials without the use of anysolvent.Depending on the choice of reagents, thermosetting materials orelastomers are obtained. These latter seem more suitable for thedesired application because, on one hand, the low viscosity ofthe reaction mixtures enables their application in a powermodule without any difficulty and, on the other hand, theirhydrophobic behaviour is stronger. One of them has aparticularly attractive thermal stability at 250 ° C and amechanical relaxation temperature almost out of the workingtemperature range. Therefore, this material may be used asencapsulant.

abstract: Photovoltaic (PV) module degradation is a well-known issue, however understanding the mechanistic pathways in which modules degrade is still a major task for the PV industry. In order to study the mechanisms responsible for PV module degradation, the effects of these degradation mechanisms must be quantitatively measured to determine the severity of each degradation mode. In this thesis multiple modules from three climate zones (Arizona, California and Colorado) were investigated for a single module glass/polymer construction (Siemens M55) to determine the degree to which they had degraded, and the main factors that contributed to that degradation. To explain the loss in power, various nondestructive and destructive techniques were used to indicate possible causes of loss in performance. This is a two-part thesis. Part 1 presents non-destructive test results and analysis and Part 2 presents destructive test results and analysis. / Dissertation/Thesis / Masters Thesis Engineering 2015

Les cellules photovoltaïques (PV) des modules ou panneaux solaires, sont protégées des agressions extérieures par des résines polymères encapsulantes qui, pour la plupart, sont des matériaux élastomériques réticulés. L’optimisation et le contrôle de l’étape d’encapsulation peut permettre un gain de productivité et augmenter la durée de vie des modules, ce qui réduit les coûts de l’électricité générée. Deux voies ont ainsi été explorées dans ce travail : 1) La première concerne l’étude de l’état de réticulation de l’encapsulant majoritairement utilisé actuellement, un copolymère d’éthylène et d’acétate de vinyle connu sous le nom d’EVA ; celui-ci est mis en œuvre sous forme de feuilles ou films. Une faible réticulation de l’encapsulant peut mener, entre autre, à son fluage lors de son utilisation, impactant directement la durée de vie du module. Il est donc important de suivre le niveau de réticulation de l’encapsulant lors des opérations de contrôle. La comparaison de différentes méthodes d’évaluation du degré de réticulation ont donc été menées ; 2) La deuxième voie concerne des études autour d’un nouveau procédé d’encapsulation. En effet, le procédé industriel actuel, inclut une étape dite de « lamination », pendant laquelle l’encapsulant est fondu et réticulé autour des cellules. Cette étape relativement longue crée des contraintes thermomécaniques pouvant limiter la durée de vie des modules PV. Le développement d’un nouveau procédé d’encapsulation où l’encapsulant en film est remplacé par un encapsulant liquide photopolymérisable permettrait de diminuer les coûts de production tout en augmentant potentiellement la durée de vie des modules. Les propriétés rhéologiques et la cinétique de polymérisation de ce nouvel encapsulant sont ainsi étudiées. Enfin les deux voies d’encapsulation sont comparées. Il a été montré que d’un point de vue des performances électriques le nouveau procédé présente un avantage potentiel et que d’un point de vue de la tenue au vieillissement il est équivalent au procédé industriel actuel / Photovoltaic (PV) cells, for solar modules or panels, are protected from environmental stresses by polymeric encapsulants, which are mostly crosslinked elastomers. The optimization and the control of the encapsulation step have a twofold interest by increasing PV module lifetime and productivity, thus leading to a decrease of the cost of generated electricity. Two main directions have been investigated in this work: 1) The first one is related to the study of the crosslinking degree of the main industrial PV polyolefin encapsulant, EVA, which is a copolymer composed of ethylene and vinyl acetate, used currently in film form. Indeed, poor crosslinking level can lead to its creep, impacting directly the module lifetime. To overcome this problem, the quality control needs to be improved, by the evaluation of the crosslinking degree obtained while using the conventional encapsulation process (through lamination of encapsulant foils). Thus, the comparison of several methods to evaluate this degree are led ;2) The second direction concerns the study of a new encapsulation process. Indeed, the conventional lamination process potentially creates mechanical stresses in the PV cells, which as a consequence may limit the PV module lifetime. Moreover, lamination requires a relatively long processing time. To overcome this problem, the development of a new encapsulation process using a photopolymerizable encapsulant, initially liquid, decreases the production costs of PV modules and potentially increases their lifetime. The rheology properties and the polymerization kinetics of the new encapsulant are studied. At the end of the present work, both encapsulation processes are compared. Electrical performances of PV cells are measured before and after encapsulation as well as before and after ageing cycles. It has been revealed that the new encapsulation process presents at least as good, if not better performances than the standard process, thus highlighting its big potential for the manufacturing of PV modules

abstract: Ethylene vinyl acetate (EVA) is the most commonly used encapsulant in photovoltaic modules. However, EVA degrades over time and causes performance losses in PV system. Therefore, EVA degradation is a matter of concern from a durability point of view. This work compares EVA encapsulant degradation in glass/backsheet and glass/glass field-aged PV modules. EVA was extracted from three field-aged modules (two glass/backsheet and one glass/glass modules) from three different manufacturers from various regions (cell edges, cell centers, and non-cell region) from each module based on their visual and UV Fluorescence images. Characterization techniques such as I-V measurements, Colorimetry, Different Scanning Calorimetry, Thermogravimetric Analysis, Raman spectroscopy, and Fourier Transform Infrared Spectroscopy were performed on EVA samples. The intensity of EVA discoloration was quantified using colorimetric measurements. Module performance parameters like Isc and Pmax degradation rates were calculated from I-V measurements. Properties such as degree of crystallinity, vinyl acetate content and degree of crosslinking were calculated from DSC, TGA, and Raman measurements, respectively. Polyenes responsible for EVA browning were identified in FTIR spectra. The results from the characterization techniques confirmed that when EVA undergoes degradation, crosslinking in EVA increases beyond 90% causing a decrease in the degree of crystallinity and an increase in vinyl acetate content of EVA. Presence of polyenes in FTIR spectra of degraded EVA confirmed the occurrence of Norrish II reaction. However, photobleaching occurred in glass/backsheet modules due to the breathable backsheet whereas no photobleaching occurred in glass/glass modules because they were hermetically sealed. Hence, the yellowness index along with the Isc and Pmax degradation rates of EVA in glass/glass module is higher than that in glass/backsheet modules. The results implied that more acetic acid was produced in the non-cell region due to its double layer of EVA compared to the front EVA from cell region. But, since glass/glass module is hermetically sealed, acetic acid gets entrapped inside the module further accelerating EVA degradation whereas it diffuses out through backsheet in glass/backsheet modules. Hence, it can be said that EVA might be a good encapsulant for glass/backsheet modules, but the same cannot be said for glass/glass modules. / Dissertation/Thesis / Masters Thesis Chemical Engineering 2018

Les dispositifs médicaux miniaturisés sont de plus en plus répandus dans le monde médical, car ils offrent de nouvelles opportunités de traitement et de surveillance. La miniaturisation des systèmes permet notamment une chirurgie minimalement invasive, une portabilité améliorée et une facilité d'utilisation. Parmi les exemples on peut mentionner les micro-stimulateurs cardiaques, les micro-implants cochléaires et les micro-capteurs ex-situ de glucose. Cependant, les micro-dispositifs implantables qui utilisent des technologies d'assemblage autres que les boîtiers métalliques sont encore à découvrir. La surveillance de paramètres physiologiques à l'aide de capteurs in-situ de pression et BioMEMS pourraient bénéficier des progrès faits sur les études d'encapsulation en couche mince destinées à protéger les micro-dispositifs de silicium contre la corrosion. En effet, une barrière qui empêche la diffusion et la pénétration des substances nocives est indispensable pour protéger à la fois le patient et le micro-dispositif. Les couches minces céramiques déposées par des procédés chimiques en phase vapeur sont de bons candidats grâce à leurs faibles perméabilités aux gazes, faibles réactivités chimique et conformités de dépôt élevées. Cependant, dans des milieux biologiques représentatifs du corps humain, peu d'études ont été réalisées dans le domaine de la protection des dispositifs microélectroniques contre la corrosion.Au cours de cette thèse, dix matériaux, choisis à l'issue d'une étude bibliographique, ont été étudiés: Al2O3, BN, DLC, HfO2, SiC, SiN, SiO2, SiOC, TiO2 et ZnO. Des couches ultrafines de ces matériaux (de 5 à 100 nm) ont été déposées par voie chimique en phase vapeur assisté par plasma (PECVD) ou par couches atomiques (ALD) sur des substrats silicium recouverts de matériaux généralement présents dans des dispositifs microélectroniques tels que le silicium cristallin, le cuivre, le tungstène nitrure et le poly-imide. Des mesures de cytotoxicité ont été réalisées et des tests de vieillissement ont été effectués pendant plusieurs semaines à des températures différentes dans une solution saline phosphatée (PBS) mais aussi dans une solution à base de sérum de veau fœtale (NaCl/SVF). Les changements dans la composition chimique et l'épaisseur ont été suivies par VASE, XPS et spectroscopie de masse d'ions secondaires à temps de vol (TOF-SIMS). Il a été montré que les couches de SiO2 et de SiN (généralement utilisées pour la protection dans l'industrie de la microélectronique) n'étaient pas stables dans le PBS et le NaCl/SVF à 37°C, même si en revanche elles offraient une bonne barrière aux gazes. L'Al2O3 a lui montré une très bonne tenu en milieu salin et une remarquable herméticité mais en revanche, il s'est corrodé rapidement dans le NaCl/SVF. Les couches de DLC, SiOC et TiO2 ont donné les meilleurs résultats de stabilité dans le PBS et le sérum de veau. Enfin, il a aussi été montré dans cette thèse que l'empilement TiO2 sur Al2O3 offrait la meilleure efficacité comme barrière hermétique et diffusive pour la protection des microsystèmes de silicium contre la corrosion dans les milieux salins. / Miniaturized medical devices are becoming increasingly adopted by doctors and patients because they enable new treatment and monitoring capabilities, minimally invasive surgery, improved portability and ease of use. Recent examples include micro pacemakers, micro cochlear implants and ex-situ micro glucose sensors. However, implantable micro devices employing packaging technologies other than metallic enclosures are yet to be seen. Physiological monitors such as in-situ pressure sensors and BioMEMS could profit significantly from advances in thin barrier films for corrosion protection of silicon micro devices. Coating films that stop the diffusion and permeation of harmful substances are necessary to protect both the patient and the micro device. Ceramic films deposited by chemical vapor deposition techniques are good candidates for this task due to their low permeability to gases, low chemical reactivity and high conformality. However, few studies are available about the corrosion protection offered by biocompatible coatings to microelectronic devices in representative biological environments.Ten materials were selected in this thesis after a bibliographic study: Al2O3, BN, DLC, HfO2, SiC, SiN, SiO2, SiOC, TiO2 and ZnO. Ultra-thin films of these materials (5-100 nm) were deposited by plasma enhanced chemical vapor deposition (PECVD) or atomic layer deposition (ALD) on substrates commonly found in electronic micro devices: crystalline silicon, copper, tungsten nitride and polyimide. In vitro cytotoxicity tests and degradation tests were performed for several weeks at different temperatures in Phosphate Buffer Saline (PBS) and NaCl supplemented with 10% Fetal Bovine Serum (NaCl/FBS). Changes in thickness and chemical composition were monitored by VASE, XPS and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). It was found that SiO2 and SiN films (generally used for protection in the microelectronics industry) are not stable in PBS and NaCl/FBS at 37°C, even though they act as good hermetic barriers. Al2O3 showed very good stability in saline solution and excellent behavior as gas barrier, but it was rapidly dissolved in NaCl/FBS.In contrast, films of DLC, SiOC and TiO2 showed very low chemical reactivity in both mediums. Finally, it was shown that multilayers of TiO2 on Al2O3 offer the best performance as hermetic and diffusion barriers for corrosion protection of silicon micro systems in saline environments.

abstract: The popularity of solar photovoltaic (PV) energy is growing across the globe with more than 500 GW installed in 2018 with a capacity of 640 GW in 2019. Improved PV module reliability minimizes the levelized cost of energy. Studying and accelerating encapsulant browning and solder bond degradation—two of the most commonly observed degradation modes in the field—in a lab requires replicating the stress conditions that induce the same field degradation modes in a controlled accelerated environment to reduce testing time. Accelerated testing is vital in learning about the reliability of solar PV modules. The unique streamlined approach taken saves time and resources with a statistically significant number of samples being tested in one chamber under multiple experimental stress conditions that closely mirror field conditions that induce encapsulant browning and solder bond degradation. With short circuit current (Isc) and series resistance (Rs) degradation data sets at multiple temperatures, the activation energies (Ea) for encapsulant browning and solder bond degradation was calculated. Regular degradation was replaced by the wear-out stages of encapsulant browning and solder bond degradation by subjecting two types of field-aged modules to further accelerated testing. For browning, the Ea calculated through the Arrhenius model was 0.37 ± 0.17 eV and 0.71 ± 0.07 eV. For solder bond degradation, the Arrhenius model was used to calculate an Ea of 0.12 ± 0.05 eV for solder with 2wt% Ag and 0.35 ± 0.04 eV for Sn60Pb40 solder. To study the effect of types of encapsulant, backsheet, and solder on encapsulant browning and solder bond degradation, 9-cut-cell samples maximizing available data points while minimizing resources underwent accelerated tests described for modules. A ring-like browning feature was observed in samples with UV pass EVA above and UV cut EVA below the cells. The backsheet permeability influences the extent of oxygen photo-bleaching. In samples with solder bond degradation, increased bright spots and cell darkening resulted in increased Rs. Combining image processing with fluorescence imaging and electroluminescence imaging would yield great insight into the two degradation modes. / Dissertation/Thesis / Doctoral Dissertation Systems Engineering 2020

abstract: Encapsulant is a key packaging component of photovoltaic (PV) modules, which protects the solar cell from physical, environmental and electrical damages. Ethylene-vinyl acetate (EVA) is one of the major encapsulant materials used in the PV industry. This work focuses on indoor accelerated ultraviolet (UV) stress testing and characterization to investigate the EVA discoloration and delamination in PV modules by using various non-destructive characterization techniques, including current-voltage (IV) measurements, UV fluorescence (UVf) and colorimetry measurements. Mini-modules with glass/EVA/cell/EVA/backsheet construction were fabricated in the laboratory with two types of EVA, UV-cut EVA (UVC) and UV-pass EVA (UVP). The accelerated UV testing was performed in a UV chamber equipped with UV lights at an ambient temperature of 50°C, little or no humidity and total UV dosage of 400 kWh/m2. The mini-modules were maintained at three different temperatures through UV light heating by placing different thickness of thermal insulation sheets over the backsheet. Also, prior to thermal insulation sheet placement, the backsheet and laminate edges were fully covered with aluminum tape to prevent oxygen diffusion into the module and hence the photobleaching reaction. The characterization results showed that mini-modules with UV-cut EVA suffered from discoloration while the modules with UV-pass EVA suffered from delamination. UVf imaging technique has the capability to identify the discoloration region in the UVC modules in the very early stage when the discoloration is not visible to the naked eyes, whereas Isc measurement is unable to measure the performance loss until the color becomes visibly darker. YI also provides the direct evidence of yellowing in the encapsulant. As expected, the extent of degradation due to discoloration increases with the increase in module temperature. The Isc loss is dictated by both the regions – discolored area at the center and non-discolored area at the cell edges, whereas the YI is only determined at the discolored region due to low probe area. This led to the limited correlation between Isc and YI in UVC modules. In case of UVP modules, UV radiation has caused an adverse impact on the interfacial adhesion between the EVA and solar cell, which was detected from UVf images and severe Isc loss. No change in YI confirms that the reason for Isc loss is not due to yellowing but the delamination. Further, the activation energy of encapsulant discoloration was estimated by using Arrhenius model on two types of data, %Isc drop and ΔYI. The Ea determined from the change in YI data for the EVA encapsulant discoloration reaction without the influence of oxygen and humidity is 0.61 eV. Based on the activation energy determined in this work and hourly weather data of any site, the degradation rate for the encaspulant browning mode can be estimated. / Dissertation/Thesis / Masters Thesis Chemical Engineering 2018

This work developed a process to provide physical, electrical, and environmental protection to the electrical lead system of an optical switch device. A literature review was conducted to find materials and processes suitable to the stress-sensitive, high voltage characteristics of many optical switch devices. An automatic dispensing dam and fill process, and three candidate materials (two epoxy and one silicone) were selected for investigation. Experimental and analytical techniques were used to evaluate the materials. Methods applied included interferometric die warpage measurements, electrochemical migration resistance tests (ECMT), thermal cycling, and finite element analysis. The silicone dam and fill system was selected based upon the results of die warpage and electrochemical migration resistance tests. A modified, selective dam and fill process was developed and preliminary reliability testing was performed. The paper provides detailed instructions for successful encapsulation of the optical switch's lead system.

Present day advanced technologies heavily rely on one particular class of matter, i.e. the crystals. It is the periodic nature of the atoms and the properties arising due to the periodicity in crystals that is exploited to meet various technological feats. The technological revolutions in the semiconductor, optics and communication industries are the examples. The anisotropy in the crystals gives them enhanced properties as required in the field of non-linear optics. The field of non-linear optics became practically a reality after the invention of lasers. The coherent and monochromatic optical beams in the visible and ultraviolet ranges are in high demand due to their application in the fields like material processing, semiconductor lithography, laser micromachining, laser spectroscopy, photochemical synthesis, inertial confinement fusion and other basic scientific studies. In this thesis, work on the growth and characterization of two technologically important non-linear optical crystals has been carried out after developing the necessary instrumentation and some novel techniques for synthesis and growth. Also, studies on the glassy nature of one of the crystals have been carried out. This thesis consists of seven chapters. The first chapter gives a brief introduction to the nonlinear optical phenomenon, crystal growth and glassy state. Instrumentation is the backbone of crystal research technology. Without precision growth equipments large size crystals cannot be grown and without precision characterization instrumentation no conclusion regarding the quality and usefulness of the grown material can be drawn. The work reported in Chapter 2 describes the instrumentation developed for the growth, processing and characterization of crystals grown by solution and melt growth techniques. In low temperature solution growth, crystal growth workstations have been developed using tanks (made of acrylic), heating elements, and stirring propellers. Cooling coils have been inserted into the designed water bath to grow crystals below ambient also. This bath has an advantage to work over a wide range of temperatures, so that maximum retrieval of the material is possible. The growth of large crystals is usually hindered due to spurious nucleation precipitating during the growth process. A novel nucleation-trap crystallizer has been designed and developed that facilitates the continuation of the growth run in spite of extra nucleation precipitating after seeding. In this crystallizer, the spurious nuclei and any other particles generated after the filtration are forced into a well, and the growth of spurious nuclei is arrested by manipulating the temperature of this trap. Achieving adequate heat flow and mass flow profiles is of vital importance for growing good quality crystals. An optimized stirring procedure for the solution or melt is needed for ensuring the desired supply of growth units to the crystal-nutrient interface, and for transporting away any debris of the crystal-growth process. An ACRT set up has been designed and developed. For the growth of crystals by the flux technique and from direct melt, a crystal puller has been designed and developed. The crystal puller consists of a crystal rotation unit, slow and fast pulling mechanisms and a control unit. The pulling assembly is protected from damage caused by possible human errors through interlock mechanisms. The vibration at the shaft of the seed rotation assembly has been minimized by using a dc motor for rotation. A versatile triangular / square wave oscillator has been designed for developing a dc motor control. By implementing this control, the speed of the motor does not vary with supply-voltage variations. A quarter-step switching logic sequence is introduced for stepper motors, which is used for the slow UP/DOWN movement of the puller. This puller can be controlled locally by a control panel provided with the puller, or through a PC remotely by bypassing the local control. Additionally, for the processing and characterization of the grown DKDP crystals, a closed-loop thread-cutter, a ferroelectric loop tracer, and a computer-controlled system for measuring the half-wave voltage have been developed. A novel mercury encapsulant seeding technique that facilitates the processing of solution with immersed seed is invented and has been described in Chapter 3. This technique allows processing of solution with the seed inside the growth chamber, and still avoids contamination of the solution and formation of crystal clusters that are normally generated when seed is inserted after processing of the solution. DKDP and KAP crystal seeds have been used to check the dissolution of seeds, if any, when immersed in pure water for several hours and at high temperatures after introducing the seal. It has been observed that the mercury seal does not allow creeping of water into the seed holder, and there is no dissolution of the seed. This technique has been practically implemented for the growth of crystals from aqueous solution and its usefulness has been demonstrated by growing ammonium acid phthalate, potassium acid phthalate and potassium di-deuterium phosphate crystals. Nonlinear-optical crystals find major use in inertial-confinement fusion (ICF) experiments. For such applications, nonlinear crystals with very large damage-resistance are needed. Alternatively, crystals with moderate damage resistance but large size can be used for frequency-conversion for efficient plasma experiments. Potassium di-hydrogen phosphate, KH2PO4 (KDP) and its deuterated analog, K(DxH1-x)2PO4 (DKDP) are at present the only nonlinear optical crystals which can be grown to large sizes and are suitable for ICF studies. Also, solid-state light valves, light deflectors, and laser communication devices require large and perfect tetragonal DKDP crystals, with high deuterium concentration for easier operation. Chapter 4 describes the growth and characterization of DKDP crystals. DKDP crystals have been grown by all the three techniques i.e. conventional, platform and novel mercury encapsulant seeding techniques. Details about a new approach for the synthesis of DKDP solution have been given. A comparative study of the grown crystals by mercury-encapsulant technique and other techniques is described. Habit modification was observed due to the placement of seed crystals at an off-centre position and orientation in mercury encapsulant seeding technique and has been discussed. The grown crystals have been characterized for homogeneity, dislocations, transmission, DSC, rockng curve, etc. Due to the higher photon energies and the ability to be more tightly focused, coherent radiations of shorter wavelength (deep-UV) are in demand. The photon energies in this region are sufficient for bond-breaking processes in many materials, and find applications in fields like material processing, semiconductor lithography, laser micromachining, laser spectroscopy, photochemical synthesis, etc. Although excimer lasers (XeCl, KrF, ArF etc.) produce significant power in the deep-UV region, these laser systems involve corrosive gases, and are bulky, apart from requiring regular maintenance. A maintenance-free, compact, solid-state laser is preferable. But this, in turn, requires an efficient NLO crystal in that region. CLBO is one such crystal. Growth of CLBO crystals has been carried out by the flux-growth technique using B2O3-deficient flux, as well as from stoichiometric melt and has been discussed in Chapter 5. It was observed that the nucleation of material on platinum wire or spontaneous nucleation was difficult to achieve in spite of high supercooling. After forcing cracks into the mass deposited on platinum wire nucleation could be achieved. The growth of crystals was carried out on seeds with different orientations. Transmission studies, etch-pit studies and harmonic-generation experiments were performed on the grown crystals. The glass-forming tendency of CLBO has been studied and reported in Chapter 6. DTA experiments show that CLBO melt generally transforms to glass on cooling. Even at a cooling rate as low as 1°C/min, the material does not crystallize but transforms into glass. Ergodicity making and glass transition temperatures were determined for glassy CLBO. Since neither the crystallization peak nor the melting peak was observed in DTA experiments during the heating part of thermal cycle for glassy CLBO, a new approach of seeded crystallization was adopted in the calorimetric experiments to achieve crystallization. Since the size of added nuclei is already above the critical radius, the onset of crystallization peaks is independent of the critical-radius energy barrier. Kissenger method was applied to determine the activation energy of seeded- crystallization process. The transformation of glass CLBO to the crystalline phase is mediated by dendrites. Possibility of bulk crystal growth from the glassy state has been discussed, and a novel idea of surface crystallization is proposed. Chapter 7 summarizes the work carried out and projects the scope for future work.

abstract: In recent years, solar photovoltaic (PV) industry has seen lots of improvements in technology and of growth in market with crystalline silicon PV modules being the most widely used technology. Plant inspections are gaining much importance to identify and quantitatively determine the impacts of various visual defects on performance. There are about 86 different types of defects found in the PV modules installed in various climates and most of them can be visually observed. However, a quantitative determination of impact or risk of each of identified defect on performance is challenging. Thus, it is utmost important to quantify the risk for each of the visual defects without any human subjectivity. The best way to quantify the risk of each defect is to perform current-voltage measurements of the defective modules installed in the plant but it requires disruption of plant operation, expensive measuring equipment and intensive human resources. One of the most riskiest and dominant visual defects is encapsulant browning which affects the PV module performance in the form of current degradation. The present study deals with developing an automated image processing tool which can address the issues of human subjectivity on browning level impacting performance. The image processing tool developed in this work can be directly used to quantify the impact of browning on performance without intrusively disconnecting the modules from the plant. In this work, the quantified browning level impact on performance has also been experimentally validated through a correlation study using short-circuit current and reflectance/transmittance measurements of browned PV modules retrieved from aged plants/systems installed in diverse climatic conditions. The primary goal of the image processing tool developed in this work is to determine the performance impact of encapsulant browning without interrupting the plant operation for I-V measurements. The use of image processing tool provides a single numerical value, called browning index (BI), which can accurately quantify browning levels on modules and also correlate with the performance and reflectance/transmittance parameters of the modules. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2016