Solar cooling research center is being developed on CSEM-UAE outdoor research facility in RAK/UAE.  The research center is capable to test system from 1 TR cooling capacity to 10 TR cooling capacity. The source of heat is solar radiation and heat pipe type evacuated tube solar collectors are used to collect the solar energy. Solar station controls and circulates water in solar collectors and helps charge the hot water stratified tank. While in operation of the solar cooling facility, circulation pumps for hot water, chilled water and rejection circuit have to be continuously operated along with fan coil units, solar station, chiller and cooling tower. These all components require continuous electrical power. Currently, the entire electrical power requirement is supplied by a diesel generator. Since the center is for research activities, most of the time solar cooling center is on no load condition. Thus solar collectors are subjected to saturation. To prevent heat collection during no load conditions solar collectors are covered. Research project carried out to design of the renewable energy powered system to ensure the electricity availability for all the components so that the facility can be operated continuously without fossil fuel. UAE climate is sunny throughout the year thus Photovoltaic will be most prominent as a renewable source in generating electrical power. The PV is subjected to UAE harsh hot and dust environment which affect the performance of the PV. Thus the performance variations of PV due to dust deposition and temperature have analyzed. A matlab simulink model has developed to analyze the energy generation in UAE environment with available weather data. Technical and economical analysis has done for different PV technologies and find out the optimum PV design for the solar cooling center. To prevent the saturation of the solar collectors, a heat rejection unit have designed and installed. The control system for the automatic operation also implemented.

>Magister Scientiae - MSc / Tin dioxide (SnO2) thin films are a worthy candidate for an electron transport layer (ETL) in perovskite solar cells, due to its suitable energy level, high electron mobility of 240 cm2 v-1 s- 1, desirable band gap of 3.6 - 4.0 eV, and ultimately proves to be suited for a low temperature thermal oxidation technique for ETL production. A variety of methods are available to prepare SnO2 thin films such as spin and dip coating and chemical bath deposition. However, the customary solid-state method, which incorporates thermal decomposition and oxidation of a metallic Sn precursor compound in an oxygen abundant atmosphere prevails to be low in cost, is repeatable and allows for large-scale processing.

Cette thèse se focalise sur les propriétés passivantes octroyées par des couches minces d’Al2O3 déposées par Atomic Layer Deposition (ALD) à partir de TMA et H2O pour les cellules photovoltaïques en silicium ayant des températures de fabrication inférieures à 400 °C. La première partie de ce travail de doctorat vise à identifier les mécanismes de formation des charges électrostatiques négatives présentes dans l’oxyde d’aluminium. Pour ce faire, les effets de l’illumination post-dépôt (à savoir le flux et l’énergie des photons), ainsi que la température du substrat ont été étudiés. Il a été constaté qu’au moins 70 % de ce qu’on appelle généralement les « charges fixes » sont en fait des charges piégées résultant de l’injection d’électrons du substrat de silicium dans l’oxyde d’aluminium. Par la suite, nous avons étudié l’influence des paramètres de dépôt de l’Al2O3 ainsi que l’impact des traitements post-dépôt sur le piégeage des charges et donc sur les performances passivantes qui en résulte au sein d’un empilement Al2O3/a-SiNX:H déposé sur du silicium cristallin de type p. Les liens entre l’épaisseur de l’Al2O3, la qualité et la durabilité de la passivation ont pu être établis. Le meilleur compromis s’est avéré être aux alentours 60 cycles ALD (~ 6 nm), permettant une durée de vie des porteurs de charges minoritaires allant jusqu’à 4500 μs. La deuxième partie de ce travail doctoral porte sur les mécanismes de dégradation de la passivation. La formation de cloques à l’interface c-Si/Al2O3 est le premier mécanisme de dégradation étudié. Grâce à la microscopie acoustique colorée, la dégradation de l’interface Al2O3/c-Si lors de l’épaississement de l’Al2O3 a été confirmée, mais également lors la réduction de sa température de dépôt, c’est-à-dire en augmentant sa teneur en hydrogène. Une dérive thermique pendant l’ALD (TD-ALD) a été utilisée pour résoudre ce problème de cloquage. L’augmentation continue de la température du substrat pendant le dépôt favorise la libération de l’hydrogène à partir de l’interface c-Si/Al2O3. Pour 60 cycles ALD, le TD-ALD a permis d’augmenter la durée de vie des porteurs de charges jusqu’à 5500 μs. Enfin, l’affaiblissement de la passivation par effet de champ résultant des charges positives dans la couche de protection a-SiNX:H a été mis en évidence par simulation numérique. Les propriétés du a-SiNX:H ont été expérimentalement optimisée grâce à une approche par plan d’expérience. Une nouvelle couche mince d’a-SiNX: H contenant 50 % de charges fixes positives en moins a permis d’obtenir une durée de vie des porteurs de charges de 8800 μs pour 60 cycles de TD-ALD, c’est-à-dire une vitesse de recombinaison de surface exceptionnelle basse de 0,8 cm.s-1. / This thesis focuses on the passivation properties provided by thin Al2O3 films grown by atomic layer deposition (ALD) from TMA and H2O for silicon solar cells having process temperatures lower than 400 °C. The first part of this doctoral work aims at identifying the formation mechanisms of negative electrostatic charges in aluminium oxide. Thus, the effects of post-deposition illumination (namely photon flux and photon energy), as well as substrate temperature were investigated. It was found that at least 70 % of what are generally named “fixed charges” are in fact trapped charges resulting from the injection of carriers from the silicon substrate into the aluminium oxide. From this result, we studied the influence of Al2O3 deposition parameters and post-deposition treatments on charge trapping and resulting passivation performances within an Al2O3/a-SiNX:H stack on p-type c-Si. The dependence of passivation performance (and stability) on Al2O3 thickness has been highlighted. Best compromise has been found to be around 60 ALD cycles (~6 nm), providing a lifetime up to 4500 µs. The second part of this PhD deals with the degradation mechanisms of passivation. Blistering at the c-Si/Al2O3 interface is the first studied degradation mechanism. Thanks to coloured picosecond acoustic microscopy, the Al2O3/c-Si adhesion has been confirmed to be reduced by Al2O3 thickening but also by the reduction of its deposition temperature, i.e. an increase of hydrogen content. A thermal drift during ALD (TD-ALD) has been used to solve this blistering issue. Gradual increase of the substrate temperature during the growth favours the release of hydrogen from the wafer/Al2O3 interface. For 60 ALD cycles, TD-ALD increased the lifetime up 5500 µs. Finally, the weakening of the electrostatic passivation arising from the positive charges in a-SiNX:H capping layer has been underlined by finite element simulations. The a-SiNX:H properties have been experimentally tuned thanks to a design of experiment approach. New a-SiNX:H capping containing 50 % less positive fixed charges resulted in a lifetime of 8800 µs for 60 TD-ALD cycles, i.e. an outstanding surface recombination velocity of 0.8 cm.s-1.

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Self-catalyzed GaAs nanowires (NWs) are grown epitaxially on Si(111) substrates using molecular beam epitaxy (MBE). The dynamics of the droplet are examined to improve NW yield and to control NW morphology. Control and understanding of the NW diameter via droplet dynamics is applied to NW photovoltaics and to novel corrugated NW distributed Bragg reflectors (DBRs). At the beginning of the MBE growth, a Ga pre-deposition step, between 0 s and 500 s in duration, is introduced to improve the yield of the NW arrays. The effect of the pre-deposition time was examined for five different hole diameters and yield was increased to nearly 100% for the appropriate combination of hole diameter and pre-deposition time. Two models were used to model the NW growth progression under different atomic flux ratios. The first model considers the contributions from direct and diffusion fluxes to the droplet and solves coupled equations for the droplet contact angle and the NW radius. The second model treats the contact angle as constant. Both models explained the accompanying experimental observations. Both models could be used to model future NW growths and the choice between the two would depend on the availability of contact angle data and whether the crystal phase must be considered. Absorption in NWs is determined by the diameter and the HE1n modes. The effectiveness of a linearly tapered inverted conical NW is demonstrated using finite element simulations. The photocurrent of an optimized inverted conical NW array is found and shown to be similar to that achieved by optical nanocones and nanowires. Diameter modulations can also be introduced into NW structures periodically to produce corrugated NW distributed Bragg reflectors (DBRs). The tunability of the reflectance peaks is demonstrated and explained by changes to the effective refractive index of the structure. / Thesis / Doctor of Philosophy (PhD) / This thesis seeks to understand the growth processes behind self-catalyzed nanowire growth. Nanowires (NWs) are very thin, vertical columns of semiconducting material. Self-catalyzed growth is a method of producing these structures that uses a droplet at the top of the structure to add material to the structure over time. These structures have numerous applications. This thesis focuses on solar cells and distributed Bragg reflectors (DBRs). Experiments show how control over the droplet can improve NW yield and give significant control of the NW diameter. These experiments are supported by mathematical models. Control over the diameter is important for the applications discussed. Using numerical simulations, it is shown how control over the diameter of the structure can lead to improvements in light absorption in NW solar cells. Additionally, periodic changes to the diameter can be used to create novel NW structures such as DBRs, which is a promising new application.

Metal halide perovskite semiconductors offers bright future for optoelectronic applications due to their excellent optical and electrical properties and their low-cost solution-based facile fabrication. The most of the perovskite application are based on the defective polycrystalline films and they offer inadequate moisture/thermal chemical stability. Therefore, this dissertation is dedicated to find new strategies to deploy the single-crystal perovskites to photovoltaics and new methods to reduce the moisture/thermal instability of inorganic perovskite light-emitters. In first part of this dissertation, we aimed to reveal the potential of the single crystal in photovoltaics. Single-crystal semiconductors can outperforms their polycrystalline forms in terms of photovoltaic performance due to their better structural quality and less electronic traps. However, the most efficient perovskite solar cells are based on polycrystalline films. While single crystals can perform beyond the limits of polycrystalline films, their synthesis and device integration are complex. Therefore, we aimed to create new synthetic methods to unveil the potential of the single-crystal perovskites in photovoltaics. We developed new strategies leading the perovskite single crystals to go beyond 20% power conversion efficiency in Chapter 2. Also fundamental limits of the perovskite single crystals are investigated in Chapter 3 by fabricating single crystal cells with varying thicknesses, and the electron diffusion length is calculated to be 520 μm. In Chapter 4, we propose surface modification and compositional engineering techniques to bring the perovskite single crystal photovoltaic one step beyond of the previous point by reaching 21.9% and 22.8% efficiencies, respectively. In the second part of this dissertation (Chapter 5), a novel synthetic method is offered to achieve highly stable light-emitting perovskite-related materials since the fast degradation of perovskites in the presence of water and moisture is a challenge for perovskite-based technologies and hinders the material’s potential. We demonstrated that these a direct transformation of 3D CsPbBr3 films to CsPb2Br5 exhibiting excellent stability against humidity and heat while keeping the high photoluminescence quantum yield. We believe the strategies offered in this dissertation will open an avenue in photovoltaic and light emitting applications, and can be utilized in new optoelectronic applications in future.

An existing water filtration system at the Channel Islands Marine & Wildlife Institute (CIMWI) wastes approximately 25 gallons of water per day rinsing out solid waste under light load. To reduce CIMWI’s water and energy consumption, an automated system was designed and built to recover the rinse water and return it to the existing filtration loop. Models for fluid system requirements, basic energy needs, and photo- voltaic energy generation were created to aid in component selection. Basic sensors and electronics were programmed in Python for use with a Raspberry Pi single board computer to collect and process water recovery data over time. Pump automation and data acquisition energy needs were met with a 100W photovoltaic module, pulse width modulation (PWM) charge controller, and an absorbed glass mat (AGM) battery. A prototype system, $732 in total cost, was installed and was found to recover 19 gallons of water over the initial 30-hour testing period under light load. Models and software developed for this project could be adapted to aid in the creation of similar water recovery systems.

As the Internet-of-everything continues diversifying, wireless nods sensors, wearables, and smart-objects will require mature technologies to harvest energy from the environment in which they are installed. Out of the many energy forms, solar and artificial light are constantly present and the utilization solar technologies including organic photovoltaics can provide advantages including flexibility, semitransparency, and lightweight. Additionally, the incredibly low environmental footprint and reduced manufacturing costs associated with solution processing can provide an edge for entry into the industrial and consumer markets. While the utilization of conjugated polymers and nonfullerenes elevated the efficiencies of organic photovoltaic for commercialization, increasing the technological readiness level requires the development of protocols to translate lab performance of state-the-art-materials to scalable manufacturing techniques that can be adapted for roll-to-roll processing. This dissertation demonstrates the full fabrication of high-performance OPV devices through techniques such as inkjet printing and slot-die coating. The development of ink formulation frameworks based on solvent engineering, rheological and interface properties, and solubility parameters sets the base for standardized high-yield processes with reduced environmental footprint in line with circular carbon initiatives. Moreover, the utilization of engineering strategies involving intrinsic properties of materials, device architectures, and integration enables the development of complex energy harvesting and sensing devices for potential utilization in agrivoltaics and biosensing.

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