<p dir="ltr">Transitioning to a carbon-neutral future will require a broad portfolio of green energy generation and storage solutions. With the abundant availability of solar radiation across the Earth’s surface, energy generation from photovoltaics (PVs) will be an important part of this green energy portfolio. While silicon-based solar cells currently dominate the PV market, temperatures exceeding 1000 °C are needed for purification of silicon, and batch processing of silicon wafers limits how rapidly Si-based PV can be deployed. Furthermore, silicon’s indirect band gap necessitates absorber layers to exceed 100 µm thick, limiting its applications to rigid substrates.</p><p dir="ltr">Solution processed thin-film solar cells may allow for the realization of continuous, high-throughput manufacturing of PV modules. Thin-film absorber materials have direct band gaps, allowing them to absorb light more efficiently, and thus, they can be as thin as a few hundred nanometers and can be deposited on flexible substrates. Solution deposition of these absorber materials utilizing molecular precursor-based inks could be done in a roll-to-roll format, drastically increasing the throughput of PV manufacturing, and reducing installation costs. In this dissertation, solution processed synthesis and the characterization of two emerging direct band gap absorber materials consisting of earth abundant elements is discussed: the enargite phase of Cu₃AsS₄ and the distorted perovskite phase of BaZrS₃.</p><p dir="ltr">The enargite phase of Cu₃AsS₄ (ENG) is an emerging PV material with a 1.42 eV band gap, making it an ideal single-junction absorber material for photovoltaic applications. Unfortunately, ENG-based PV devices have historically been shown to have low power conversion efficiencies, potentially due to defects in the material. A combined computational and experimental study was completed where DFT-based calculations from collaborators were used inform synthesis strategies to improve the defect properties of ENG utilizing new synthesis techniques, including silver alloying, to reduce the density of harmful defects.</p><p dir="ltr">Chalcogenide perovskites are viewed as a stable alternative to halide perovskites, with BaZrS₃ being the most widely studied. With a band gap of 1.8 eV, BaZrS₃ could be an excellent wide-bandgap partner for a silicon-based tandem solar cell.Historically, sputtering, and solid-state approaches have been used to synthesize chalcogenide perovskites, but these methods require synthesis temperatures exceeding 800 °C, making them incompatible with the glass substrates and rear-contact layers required to create a PV device. In this dissertation, these high synthesis temperatures are bypassed through the development of a solution-processed deposition technique.A unique chemistry was developed to create fully soluble molecular precursor inks consisting of alkaline earth metal dithiocarboxylates and transition metal dithiocarbamates for direct-to-substrate synthesis of BaZrS₃ and BaHfS₃ at temperatures below 600 °C.</p><p dir="ltr">However, many challenges must be overcome before chalcogenide perovskites can be used for the creation of photovoltaic devices including oxide and Ruddlesden-Popper secondary phases, isolated grain growth, and deep level defects. Nevertheless, the development of a moderate temperature solution-based synthesis route makes chalcogenide perovskite research accessible to labs which do not have high temperature furnaces or sputtering equipment, further increasing research interest in this quickly developing absorber material.</p>

Light-harvesting devices made from lead sulfide quantum dot (QD) absorbers are one of the many promising technologies of third-generation photovoltaics. Their simple, solution-based fabrication, together with a highly tunable and broad light absorption makes their application in newly developed solar cells, particularly promising. In order to yield devices with reduced voltage and current losses, PbS QDs need to have strategically passivated surfaces, most commonly achieved through lead iodide and bromide passivation. The interdot spacing is then predominantly filled with residual amorphous lead halide species that remain from the ligand exchange, thus hindering efficient charge transport and reducing device stability. Herein, it is demonstrated that a post-treatment by iodide-based 2-phenylethlyammonium salts and intermediate 2D perovskite formation can be used to manage the lead halide excess in the PbS QD active layer. This treatment results in improved device performance and increased shelf-life stability, demonstrating the importance of interdot spacing management in PbS QD photovoltaics.

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<div> Porous lithium ion battery (LIB) electrodes are comprised of electrochemically active material particles that store lithium and a surrounding conductive binder, liquid electrolyte, carbon black mixture that facilitates ionic and electronic transport. Typically, lithium diffusivity is several orders of magnitude smaller in the active material as compared to the surrounding electrolyte, making the electrode microstructure a governing factor in determining the balance between its lithium storage capacity and transport rate. Here, the effects of microstructure on the performance of LIBs are systematically analyzed at three length scales - the single particle length scale, the spatially resolved multiple particle length scale, and the porous electrode layer (homogenized) length scale. At the single particle length scale, a thermodynamically consistent variational framework is presented to examine the effects of crystallographic anisotropy, crystallographic texture, grain size, and grain morphology on the LiNi_1/3Mn_1/3Co_1/3O₂ (NMC111) chemistry. The theory was extended to the spatially resolved multiple particle length scale and the porous electrode layer length scale to explain the microstructural origin of experimentally observed instances of apparent phase separation in NMC111. At the electrode length scale, a data driven framework is presented to evaluate the electrochemical performance of a wide range of particle morphologies and battery architectures. Specifically, microstructural characteristics of 53 356 microstructures are assessed, and strategies to optimize electrode design parameters such as active particle morphology, spatial orientation, electrode porosity, and cell thickness are presented.</div><p></p>

This project is a bachelor thesis and aims to study the integration of concentrator photovoltaics (CPV), reverse osmosis (RO) and membrane distillation (MD) for water desalination and purification. In this report, an introduction of the need for efficient water desalination is presented. Following the introduction, relevant literature has been reviewed to build up the fundamental understanding of CPV, RO and MD. A general classification of CPV subsequently introduced. In order to acquire a more comprehensive understanding of CPVs, two case studies were performed with two different types of CPV/T. The cost efficiency of each type of CPV was analysed when integrated with RO and MD systems. The result turns out to be that it was not economically beneficial to have MD in the integrated system. The reason behind is the extensive thermal energy demand of MD. Other affecting parameters, such as location and system types were also discussed. Lastly, improvements and suggestions for further studies were considered. / Detta projekt är en kandidatuppsats och syftar till att studera ett integrerande system bestående av koncentrerade solceller (CPV), omvänd osmos (RO) och membrandestillation (MD) för vattenavsaltning och rening. Rapporten börjar med en introduktion om behovet av effektiv avsaltning av vatten. Relevant litteratur har granskats för att bygga upp den grundläggande förståelsen för CPV, RO och MD. Därefter gjordes en klassificering av CPV. För att få en mer omfattande förståelse av CPV valdes två olika typer av CPV /T för en djupare undersökning. Kostnadseffektiviteten för varje CPV analyserades, när dessa var integrerade med RO- och MD-system. Resultatet visar sig att det tyvärr inte var ekonomiskt fördelaktigt att ha med MD i det integrerade systemet. Anledningen bakom detta var det omfattande termiska energibehovet för MD. Andra avgörande faktorer, såsom plats och systemtyp diskuterades tillika. Slutligen avslutades rapporten med förslag på förbättringar och områden för vidare studier.

<p>III-V nanowire (NW) ensemble devices were fabricated using novel approaches to address key NW optoelectronic issues concerning electrical contacts, doping, surface effects and underlying electrostatics physics.</p> <p>NWs were first embedded in a filling medium, thus achieving low sheet resistance front contacts while preventing shunts. Various filling materials were assessed for porosity, surface roughness and thermal stability, giving Cyclotene as an ideal filing material. Sonication was also introduced as a novel method to achieve perfect planarization.</p> <p>The presence of the Cyclotene also enabled the NWs to be characterized precisely and easily by secondary ion mass spectrometry (SIMS) to give the NW dopant concentration with excellent spatial resolution. Additionally, SIMS characterization demonstrated the ability to characterize the height uniformity of individual segments in a heterostructure NW ensemble.</p> <p>The focus of the work shifted towards surface effects on NW device performance. Therefore, Poisson's equation was solved to provide a comprehensive model of NW surface depletion as a function of interface state density, NW radius and doping density. Underlying physics was examined where surface depletion was found to significantly reduce the conductivity of thin NWs, leading to carrier inversion for some.</p> <p>This model was then applied in conjunction with a transport model to fit current-voltage curves of an AlInP-passivated GaAs NW ensemble device. A 55% decrease in surface state density was achieved upon passivation, corresponding to an impressive four order of magnitude increase in the effective carrier concentration. Additionally, conventional and time-resolved photoluminescence measurements showed intensity and carrier lifetime improvement greater than 20x upon passivation.</p> <p>Finally, the model was extended to describe radial pn junction NWs with surface depletion to give radial energy band profiles for any arbitrary set of NW parameters. Specific cases were analyzed to extract pertinent underlying physics, while the built-in potential was optimized for the design for an optimal device.</p> / Doctor of Philosophy (PhD)