Doctor of Philosophy, Case Western Reserve University, 2014, Chemistry

Core-substituted naphthalenediimides (core-substituted NDIs) were incorporated into rod-like molecules and oligomers through reaction at the imide nitrogen positions. N,N'-Di(4-bromophenyl)-2,6-di(N-alkylamino)-1,4,5,8-naphthalenetetracarboxydiimide was synthesized in only three steps, and used as a versatile platform to prepare extended structures by reaction with thiophene substrates using Suzuki-coupling conditions. The optoelectronic properties of the new compounds were examined by UV/vis absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry and theoretical calculations. The imide substituents had little effect on the optical and electrochemical properties of core-substituted NDIs in solution. A bathochromic shift of the absorption was observed upon film formation, accompanied by quenching of fluorescence. These observations are consistent with increased inter-molecular interactions between core-substituted NDI moieties in the solid state. All compounds were tested in organic solar cells by blending with poly(3-hexylthiophene) (P3HT), and several showed a photovoltaic effect, demonstrating their potential as electron acceptors in organic solar cell. The best solar cell was observed for core-substituted NDI with 4-(thiophen-2-yl)phenyl imide substituents (5a), showing a power conversion efficiency of 0.57% and a large open circuit voltage of 0.87 V. This approach allows new structure-property relationship studies of non-fullerene acceptors in organic solar cells, where one can vary the imide substituent to optimize photovoltaic parameters while keeping the optical and electrochemical properties constant. To study the structure-property relationships of core-substituted NDIs as acceptors for organic solar cells, a series of 2,6-dialkylamino NDI compounds with various substituents were synthesized, characterized and tested in bulk heterojunction solar cells by blending with P3HT. The imide substituents consisted of a linker connected to a thioph (open full item for complete abstract)

Committee: Geneviève Sauvé (Advisor); John Protasiewicz (Committee Chair); Thomas Gray (Committee Member); Carlos Crespo (Committee Member) Subjects: Alternative Energy; Chemistry; Energy; Materials Science; Molecular Chemistry; Molecules; Morphology; Organic Chemistry; Physical Chemistry

Doctor of Philosophy, Case Western Reserve University, 2014, Chemistry

Organic photovoltaic is a promising technology for solar energy harvesting. The power conversion efficiency (PCE) of solution-processed bulk heterojunction (BHJ) cells has reached over ~10%. Fullerene and its derivatives have been the most investigated acceptor. However, fullerene derivatives have disadvantages: (i) weak absorption in visible and near-IR range, (ii) limited energy tunability. Promising alternative non-fullerene acceptors are limited, and the best efficiency achieved so far is ~5%. In this study, we used azadipyrromethene (ADP) as the building block to synthesize a series of electron acceptors. ADP derivatives are strong chromophores with strong absorption around ~ 600 nm. They are electro-active materials with two reduction peaks. Their optoelectronic properties can be tuned upon structural modifications. In this work, we synthesized a series of 3-dimensional (3D) conjugated homoleptic Zn(II) complexes of ADP dyes. The degree of conjugation in ADP was extended by installing phenylacetylene, ethynylthiophene and thiophene groups at the pyrrolic positions of the ADP core using Stille coupling. 3D structures of these molecules were synthesized by chelating with Zn(II). These new molecules showed broad intense red to near-IR absorption with onsets around 800 nm. The estimated LUMO energy level of Zn(II) complexes ranged from -3.60 to -3.85 eV. Their strong acceptor properties were demonstrated by fluorescence quenching experiments using poly(3-hexylthiophene) as the donor. These metal complexes quenched the fluorescence efficiently in both solutions and film. DFT calculations showed that all the metal complexes have distorted tetrahedral structures, with additional conjugated `arms' extending in 3 dimensions. A unique feature of these complexes is that the two ADP ligands are p-stacked with each other, with frontier molecular orbitals delocalized over the two ligands. These complexes can therefore easily accept electrons, delocalize the negative char (open full item for complete abstract)

Committee: Geneviève Sauvé (Advisor); Anna Samia (Committee Chair); Clemens Burda (Committee Member); Robert Dunbar (Committee Member) Subjects: Alternative Energy; Chemistry; Energy; Molecular Chemistry; Molecular Physics; Molecules; Morphology; Organic Chemistry; Physical Chemistry

Master of Science in Chemistry, Youngstown State University, 2021, Department of Biological Sciences and Chemistry

The semiconductor cadmium telluride (CdTe) has become the leading material for thin-film photovoltaic applications. Among the many techniques for preparing these thin films, electroless deposition, commonly known as chemical bath deposition, deserves special focus since it has been shown to be a pollution-free, low-temperature and inexpensive method. In this project, CdTe thin films were deposited on stainless steel 304 by the electroless deposition method using cadmium acetate and tellurium oxide dissolved in pH 12.5 NH3(aq). The deposition was based on the gradual release of cadmium ions (Cd2+) and the gradual addition of tellurium as TeO3 2- and their subsequent reduction in a hot aqueous alkaline chemical bath at 70 °C. This was attained by adding a complexing agent such as ammonia and a chemical reducing agent. Using triethanolamine as a complexing agent produced similar results. The following reducing agents were used: aluminum, sodium hypophosphite, formaldehyde, sodium borohydride and hydrazine. All of them deposited a film on stainless steel containing Cd and Te, but formaldehyde produced the best films in terms of uniform thickness, photosensitivity, and rapid growth rate. Electroless deposition of a thin Pt layer on top of the CdTe film improved the cathodic CdTe polarization for hydrogen evolution. The structural and morphological properties of the resulting films were characterized using X-ray diffraction (XRD), stylus profilometry, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) while the light/dark voltametric methods were used to determine the films' photosensitivity.

Committee: Clovis Linkous PhD (Advisor); Timothy Wagner PhD (Committee Member); Christopher Arnsten PhD (Committee Member) Subjects: Chemistry; Energy; Experiments; Materials Science

Master of Science in Chemistry, Youngstown State University, 2018, Department of Chemistry

The energy we get from the sun is a key factor in electric power production on earth and in space applications. The development of photovoltaic cells has enabled a new direct method for solar electricity. However, the manufacturing cost of photovoltaic cells must be lowered to have widespread implementation. Among the leading candidates CdTe, is used for photovoltaic applications, since it has optimum band gap energy for the efficient conversion of solar energy into electricity. It is produced by a series of vacuum procedures, which is a significant part of its fabrication cost. In this work, cadmium telluride (CdTe) thin films were electrodeposited on stainless steel 304 substrates using a three-electrode system at a negative potential. Cadmium sulfate and tellurium dioxide in pH 1.8 H2SO4 were used as the cadmium and tellurium sources, respectively. Deposition conditions were adjusted to codeposit Cd and Te at the same rate. Films were deposited on stainless steel 304 as a relatively inexpensive substrate. However, to obtain a proper ohmic contact between CdTe and the steel, it was necessary to electrodeposit a thin interlayer of pure Te to achieve an ohmic contact. Electrodeposition of a thin Pt layer on top of the CdTe served to greatly increase the rate of H2 evolution. The structural and morphological properties of the resulting films were characterized using light/dark voltammetric methods, X-ray diffraction (XRD), Profilometry, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS).

Committee: Clovis Linkous PhD (Advisor); Tom Order PhD (Committee Member); Timothy Wagner PhD (Committee Member) Subjects: Analytical Chemistry; Chemistry; Condensed Matter Physics

Master of Science in Renewable and Clean Energy Engineering (MSRCE), Wright State University, 2017, Renewable and Clean Energy

Hybrid perovskite photovoltaic materials are currently the most promising functional materials for solar cell applications with efficiency reaching to those of more conventional materials such as silicon. Using self-assembled monolayers between photovoltaic materials and electrodes is a method for improving the stability and functionality. Recent experiments have shown that using 4-mercaptobenzoic acid and pentafluorobenzenethiol monolayers bridging lead iodide hybrid perovskite photovoltaic materials and electrodes result in improved stability and efficiency. The details of monolayer assembly, molecular adsorption configuration, and resulting modification of electronic properties are important characteristics related to solar cell performance. These characteristics can be obtained through accurate computer stimulations. Here we use ab initio computer stimulations to model adsorption characteristics of this monolayers. First we determine the structure of bulk and reconstructed surfaces of hybrid perovskite. Next we use several initial adsorption configurations to optimize the molecules attachments to reconstructed surfaces and find the most stable geometries. These are than used to determine electronic properties including charge accumulation, Electrostatic potential, and density of states at different interfaces. The effects of different monolayers and different hybrid perovskite surfaces on interfacial electronic properties are compared and discussed.

Committee: Amir Farajian Ph.D. (Advisor); James Menart Ph.D. (Committee Member); Allen Jackson Ph.D. (Committee Member) Subjects: Mechanical Engineering

Master of Science in Renewable and Clean Energy Engineering (MSRCE), Wright State University, 2017, Renewable and Clean Energy

A third-generation of solar cell is based on organic-inorganic hybrid perovskite materials. These have reached up to 22.1% conversion efficiency through exponential growth just within the last decade, compared to much longer improvement times for other photovoltaic technologies. Lead halide perovskites are among the most commonly used materials in this context. Despite the relatively large number of available works on some of these materials, in particular CH3NH3PbI3, others are less investigated. Here, we focused on CH3NH3PbCl3, CH3NH3PbBr3 and CH3NH3PbI3 for assessing structure stability and optical response. Using quantum-mechanics-based first principles approaches, we calculated the optimized structures of these three materials in their cubic phase, followed by their optical response. Structure characteristics including geometrical features, energetics and phonon dispersions were presented and analyzed. Electronic structure calculations and resultant optical characteristics including real and imaginary dielectric constants, refractive index and absorption coefficient were calculated and discussed. Our results showed different stability characteristics for the three structures inferred from cohesive energy and phonon dispersion. The bromide and chloride materials showed narrower ranges of functional optical frequencies compared to iodide one. However, the former two materials showed increased dielectric constant, refractive index and absorption at lower wavelength compared to those of the latter, indicating possibly better photovoltaic performance at those wavelengths. The results could be useful in feasibility assessments of lead halide hybrid perovskite photovoltaic materials.

Committee: Amir Farajian Ph.D. (Advisor); James Menart Ph.D. (Committee Member); Allen Jackson Ph.D. (Committee Member) Subjects: Energy; Engineering; Materials Science; Quantum Physics; Sustainability

Doctor of Engineering, Cleveland State University, 2017, Washkewicz College of Engineering

High Intensity Laser Power Beaming is a wireless power transmission technology developed at the Industrial Space Systems Laboratory from 2005 through 2010, in collaboration with the Air Force Research Laboratory to enable remote optical `refueling' of airborne electric micro unmanned air vehicles. Continuous tracking of these air vehicles with high intensity lasers while in-flight for tens of minutes to recharge the on-board battery system is not operationally practical; hence the recharge time must be minimized. This dissertation presents the development and system design optimization of a hybrid electrical energy storage system as a solution to this practical limitation. The solution is based on the development of a high energy density integrated system to capture and store pulsed energy. The system makes use of ultracapacitors to capture the energy at rapid charge rates, while lithium-ion batteries provide the long-term energy density, in order to maximize the duration of operations and minimize the mass requirements. A design tool employing a genetic algorithm global optimizer was developed to select the front-end ultracapacitor elements. The simulation model and results demonstrate the feasibility of the solution. The hybrid energy storage system is also optimized at the system-level for maximum end-to-end power transfer efficiency. System response optimization results and corresponding sensitivity analysis results are presented. Lastly, the ultrafast supply/extended energy storage system is generalized for other applications such as high-power commercial, industrial, and aerospace applications.

Committee: Hanz Richter Ph.D. (Committee Chair); Taysir Nayfeh Ph.D. (Committee Member); Lili Dong Ph.D. (Committee Member); Majid Rashidi Ph.D. (Committee Member); Petru Fodor Ph.D. (Committee Member) Subjects: Electrical Engineering

Master of Science, University of Akron, 2014, Physics

Thin film organic semiconductors have applications in electronic devices such as tran- sistors, light emitting diodes, and organic solar cells. The performance of such devices depends on the mobility of the charge carriers which is strongly affected by the mor- phology of the material. In this work, we perform Monte Carlo simulations to study charge transport in lattice models of homogeneous and heterogeneous materials. The model device consists of a layer of the material between two electrodes at different potentials. Charge carriers are injected from the electrodes and move by hopping un- der the influence of the electric field and Coulomb interactions. To model the effect of polymer chain connectivity on charge transport we include an energetic barrier to hopping between sites on different chains. We measure current-voltage (I - V ) characteristics of model devices and de- termine the mobility of the charge carriers from the slope of the I - V curves in the ohmic regime. We validate our algorithms with simulations of simple devices consist- ing of two parallel layers of donor and acceptor materials between the electrodes. To study the effect of ordered domains in polymeric semiconductors we simulate charge transport in a recently developed lattice model for polymers that undergo an order- disorder transition. We find that ordering in the material leads to strong anisotropies with increased mobility for transport parallel to the ordered domains and reduced mobility for perpendicular transport.

Committee: Jutta Luettmer-Strathmann Dr. (Advisor); Yu-Kuang Hu Dr. (Committee Member); Robert Mallik Dr. (Committee Member) Subjects: Physics; Polymer Chemistry; Polymers

Master of Science, University of Toledo, 2013, Physics

In order to make photovoltaic power generation a sustainable venture, it is necessary to use cost-effective materials in the manufacture of solar cells. In this regard, AZO (Aluminum doped Zinc Oxide) and CZTS (Copper Zinc Tin Sulfide) have been studied for their application in thin film solar cells. While AZO is a transparent conducting oxide, CZTS is a photovoltaic absorber. Both AZO and CZTS consist of earth abundant elements and are non-toxic in nature. Highly transparent and conductive AZO thin films were grown using RF sputtering. The influence of deposition parameters such as working pressure, RF power, substrate temperature and flow rate on the film characteristics was investigated. The as-grown films had a high degree of preferred orientation along the (002) direction which enhanced at lower working pressures, higher RF powers and lower substrate temperatures. Williamson-Hall analysis on the films revealed that as the working pressure was increased, the nature of stress and strain gradually changed from being compressive to tensile. The fall in optical transmission of the films was a consequence of free carrier absorption resulting from enhanced carrier density due to incorporation of Al atoms or oxygen vacancies. The optical and electrical properties of the films were described well by the Burstein-Moss effect. CZTS absorber layers were grown using ultrasonic spray pyrolysis at a deposition temperature of 350 C and subsequently annealed in a sulfurization furnace. Measurements from XRD and Raman spectra confirmed the presence of pure single phase Cu2ZnSnS4 . Texture analysis of as-deposited and annealed CZTS films indicated that the (112) plane which is characteristic of the kesterite phase was preferred. The grain size increased from 50 nm to 100 nm on conducting post-deposition annealing. CZTS films with stoichiometric composition yielded a band gap of 1.5 eV, which is optimal for solar energy conversion. The variation of tin in the film changed it (open full item for complete abstract)

Committee: Yanfa Yan (Committee Chair); Victor Karpov (Committee Co-Chair); Alvin Compaan (Committee Co-Chair) Subjects: Condensed Matter Physics; Electrical Engineering; Energy; Engineering; Experiments; Materials Science; Morphology; Nanotechnology; Physics; Plasma Physics; Solid State Physics; Sustainability; Technology; Theoretical Physics

Doctor of Philosophy, University of Akron, 2013, Chemistry

Pure, sulfur rich and wurtzite phase CdS nanoparticles with average size ~4.7 nm were prepared in aqueous solution using thioglycerol as a capping ligand. Approximately 542 molecules of thioglycerol molecules were present on the surface of each CdS-TG nanoparticle. CdS-TG nanoparticles can trap a large amount of water molecules and the chemical shift of the trapped water molecules are dependent on the environment and the amount of water trapped. The presence of sodium ions in CdS-TG increases the order of thioglycerol molecules due to the interaction with ions. Relaxation values indicated the interaction between TSLi molecule and thioglycerol. Formation of the hydrophobic monolayer of TSLi on the outer surface of CdS-TG nanoparticles were confirmed by 2D-HETCOR studies. At the interface, cations are far from the aromatic ring and thioglycerol molecules and remain in water pockets with some motions. Pure, sulfur rich, wurtzite phase CdS-TEG nanoparticles with average size of ~4.5 nm were prepared using 2-mercaptoethanol (also known as thioethyleneglycol, TEG) as a capping ligand. Grafting of aromatic ring containing sulfonyl chloride with CdS-TEG nanoparticles through sulfonate ester was studied using benzene sulfonyl chloride in the basic aqueous medium. NMR studies confirmed the feasibility of the reaction and indicated that the rate of esterification reaction increased with increase in concentration of benzene sulfonyl chloride. Naphthalene sulfonyl chloride with CdS-TEG nanoparticles were used to study the photoluminescence behavior before and after the reaction. Quenching of the light observed in the naphthalene rings bonded to the nanoparticles and confirmed that electron or energy transfer took place easily in covalently bonded aromatic rings and nanoparticles. Grafting of polystyrene chain was done by changing polystyrene sulfonic acid to the polystyrene sulfonyl chloride. Some aromatic rings in polymer were bonded with nanoparticles through ester bo (open full item for complete abstract)

Committee: David Modarelli Dr. (Advisor); Matthew Espe Dr. (Committee Member); Claire Tessier Dr. (Committee Member); Thomas Leeper Dr. (Committee Member); Hendrik Heinz Dr. (Committee Member) Subjects: Chemistry

Master of Science (MS), Ohio University, 1997, Electrical Engineering & Computer Science (Engineering and Technology)

Quantum efficiency measurements of a-C:H based photovoltaic cells

Committee: Henryk Lozykowski (Advisor) Subjects: