Master of Science in Electrical Engineering, University of Toledo, 2011, College of Engineering

In this project, we studied Bi-Ge-Se and Zn-Ge-Se chalcogenide glass films as potential materials for novel, Junctionless nanodipole photovoltaic (PV) applications. The principle of operation of junctionless nanodipole PV devices is based on the use of nanocrystals, with uncompensated electric dipole moments, which are dispersed in a photoconductive host medium. The electric field of these nanodipoles serves to separate the photogenerated electron-hole pairs and thus generate photocurrent. Bulk samples of these chalcogenide materials were prepared using a conventional melt quench technique, and thin films were then deposited by a thermal evaporation technique under high vacuum condition from the prepared bulk samples. The thin films were characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-Ray diffraction (XRD) and Raman spectroscopy. Both types of glasses are based on the Ge-Se binary glass system. The as-deposited thin films prepared were amorphous, or glassy, in nature and had chemical compositions that were close to what is considered intermediate-phase Ge-Se glass with additions of small amounts of Bi or Zn. The glass transitions and the crystallization tendency of both the bulk materials and the thin films were studied by DSC. In an effort to induce the formation of a crystalline, and preferably, a nano-crystalline phase, in the glass, glass samples were annealed at several different temperatures in the vicinity of their measured glass transition temperatures. The results from our XRD and Raman spectroscopy measurements indicated that upon annealing of Bi-Ge-Se films at 210°C, nanocrystals of Bi2Se3 are formed in the Bi-Ge-Se glass. At higher temperatures, c-GeSe and c-GeSe2 formed as well and the glass material crystallizes too much for the purposes of nanodipole PV. The Bi2Se3 crystallites formed by disturbing the Ge-Se and Se chain structure are observed in the Raman spectra of the films. Thus we are confident we (open full item for complete abstract)

Committee: Daniel Georgiev PhD (Advisor); Anthony Johnson PhD (Committee Member); Yong Gan PhD (Committee Member) Subjects: Electrical Engineering; Engineering; Materials Science; Physics

Doctor of Philosophy, Case Western Reserve University, 2013, Physics

The optical properties of one-dimensional layered materials provides a wealth of interesting phenomena. Fine control of the optical properties of the constituent materials and the thicknesses of each layer allows for sophisticated design of useful optical devices. Optical devices based on one-dimensional layered structures may have significant contributions in solving some of society's greatest problems in the coming century. The first of these challenges is to transition from fossil fuel energy generation to low-carbon, renewable energy replacements. Among the many proposed solutions is solar photovoltaic energy capture. In solar photovoltaics, light is converted to electric current by generating charge carriers in semiconductors. These charge carriers are then moved to opposing electrodes generating an electric current. These components: semiconductor, electrodes, and a supporting substrate form a layered optical system that can be studied. The interaction between absorbing material and the weak optical cavity formed by these electrodes causes enhanced absorption. By carefully designing the layer thicknesses, the absorption in the semiconductor layer can be tuned. In addition, the total absorbed solar photons vary as functions of the layer thicknesses requiring optimization by calculation and experiment. The second challenge is to store digital data for several decades at low-cost and with minimal use of power-consuming magnetic hard drive disks. Using scalable polymer processing techniques, it is possible to fabricate a multilayer optical data storage medium that satisfies the need for low-cost, scalable storage capacity. With a large number of physical layers, only small changes are needed to optical read/write hardware avoiding the pitfalls encountered with holographic and other exotic optical data storage technologies. The design and optimization of solar photovoltaic and optical data storage devices is considered. In addition, characterization of (open full item for complete abstract)

Committee: Kenneth Singer (Advisor); Rigoberto Advincula (Committee Member); Rolfe Petschek (Committee Member); Jie Shan (Committee Member) Subjects: Optics; Physics

Master of Engineering, Case Western Reserve University, 2025, EMC - Aerospace Engineering

Analysis of three missions has been carried out with a set of three power and three propulsion systems to determine system synergy as well as to find an optimal system for each mission. The three missions are GTO to LLO, LMO, and Titan flyby. The three propulsion systems of analysis are Hall Effect Thrusters, Magnetoplasmadynamic Thrusters, and VASIMR Thrusters. The three power systems of analysis are Silicon photovoltaics, multi-junction photovoltaics, and nuclear reactors. The mission to Low Lunar Orbit has a maximum trip time of 8 weeks, and four systems are capable of achieving this result. Those systems are Hall-Nuclear, MPDNuclear, VASIMR-MJ, and VASIMR-Nuclear, the last of which achieves the target in just 26 days. The VASIMR-Nuclear system is also capable of bringing the most passengers with a total capacity of 255 people. The mission to LMO was limited to a maximum trip time of 9 months, and 1 system is capable of achieving this result. This system is again VASIMR-Nuclear, capable of bringing 31 people the LMO in 241 days, or about 8 months. The mission to Titan flyby using the VASIMR-Nuclear system is capable of bringing 54500 kg of dry mass to Titan flyby at 1000 km at 3.13 km/s relative to the planet.

Committee: Paul Barnhart (Advisor); Majid Rashidi (Committee Member); Richard Bachmann (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, University of Akron, 2024, Polymer Engineering

Metal halide perovskites, as an emerging and promising photovoltaic material, have drawn great concentrations in both academia and industry in the past decade. Compared to the most common silicon-based solar cells, perovskite solar cells have many advantages, such as the easy-processing and environmentally friendly manufacture. Recently, 26.7% efficiency has been certified by the National Renewable Energy Laboratory. Although this efficiency is still lower than the certified record of Si-based solar cells (27.6%), the theoretically highest efficiency of perovskite solar cells (33.7%) is higher than that of Si-based solar cells (29.4%), which indicates the huge potential of perovskite solar cells. However, there are still many issues that limit the application of perovskite solar cells, such as the stability of perovskite solar cells. Moreover, for the perovskite material itself, the severe photocurrent hysteresis and unbalanced charge carrier mobility will influence the device performance of perovskite solar cells. To solve these issues, many efforts have been made to boost the devices performance and improve the stability of perovskite solar cells. For example, the additives and surface modifications were widely reported to address stability issues. The unbalanced charge carrier mobility could be tuned by either optimizing the perovskite formula or blending other p-type/n-type materials. Furthermore, according to recent research, the main reason for the hysteresis of perovskite solar cells is the counterion migration of perovskite materials. Therefore, some organic molecules with special function groups, such as carboxyl and hydroxyl, were applied to interact with the counterions of perovskites to suppress the migration of counterions. In my research projects, my works are mainly focused on enhancing the stability and device performance of perovskite solar cells. Meanwhile, look for novel metal halide perovskite composites to reduce the photocurrent hysteresis and (open full item for complete abstract)

Committee: Xiong Gong (Advisor); Fardin Khabaz (Committee Chair); Jie Zheng (Committee Member); Junpeng Wang (Committee Member); Toshikazu Miyoshi (Committee Member) Subjects: Energy; Engineering; Materials Science

Master of Sciences (Engineering), Case Western Reserve University, 2025, EECS - Computer and Information Sciences

Ontologies have become increasingly popular in the scientific community as a way to standardize terminologies and concepts in metadata. While various groups within the scientific community have established frameworks and rules for creating ontologies, there are significant variations and diverse approaches in the development of Materials and Applied Data Science ontologies. Our goal is to provide the research community with guidance on developing these ontologies through a unified automated framework, called the MDS-Onto Framework. A key component of the MDS-Onto Framework is a bilingual package named \emph{FAIRmaterials}, which simplifies the process of creating sound ontologies. To demonstrate the practical capabilities and implementation steps of FAIRmaterials needed to create and merge ontologies, we present two exemplar cases: X-Ray Diffraction and Photovoltaics, both highlighting the feasibility and efficiency of the proposed framework.

Committee: Roger French (Committee Chair); Erika Barcelos (Advisor); Yinghui Wu (Committee Member); Jing Ma (Committee Member) Subjects: Computer Science; Philosophy

Master of Science (MS), Bowling Green State University, 2024, Physics

Various types of polycrystalline solar cells are significant in both scientific research and commercial renewable energy production, but they tend to perform worse than their crystalline counterparts (e.g., Silicon) due to a variety of reasons, including low minority carrier lifetimes, although they show promise to be cost effective. Identifying the critical recombination mechanisms and locations within the solar cell (i.e., bulk or interfaces) where they occur is a challenge. Time resolved photoluminescence (TRPL) is one technique used for diagnosing these issues. TRPL is a commonly used characterization tool for semiconductors, providing information on minority carrier lifetime and other transport properties. This thesis will review the basic concepts of TRPL in general and specific examples of how it is applied to thin-film Cd(Se,Te) solar cells. TRPL measured lifetimes can be a result of several, coupled underlying mechanisms that are difficult to deconvolute, such as radiative and non-radiative recombination in the bulk semiconductor and at the interfaces. In this work, numerical simulation of TRPL is employed for hypothesis testing of possible mechanisms. Simulations entail the time-dependent solutions of the semiconductor transport equations by employing the finite element method. Inspired by recent data from the National Renewable Energy Laboratory, simulations were conducted over a broad parameter space of film thickness, laser pulse intensity, and key recombination variables in the bulk semiconductor and at interfaces. Key findings indicate that bulk and interface recombination can only be distinguished when one or the other dominates significantly. Regions of applicability are numerically delineated. It is also found that Se depth grading further complicates data interpretation. These results suggest that additional characterization techniques that are complimentary to TRPL should be conducted in parallel to quantify dominant recombination mechanis (open full item for complete abstract)

Committee: Marco Nardone Ph.D. (Committee Chair); Mikhail Zamkov Ph.D. (Committee Member); Alexey Zayak Ph.D. (Committee Member) Subjects: Physics

Master of Science (M.S.), University of Dayton, 2024, Chemical Engineering

There is a continuous thrust for cleaner and more sustainable alternatives for energy conversion with the increasing global energy demand. Among them, photovoltaics, specifically thin film solar cells are highly promising and are one of the fastest growing clean energy technologies in the United States. This research presents the synthesis and characterization of a set of novel multinary copper chalcogenide semiconductor nanocrystals (NCs), CuZn2ASxSe4-x consisting primarily of earth-abundant elements for applications in photovoltaic devices. A modified hot-injection method was used to synthesize these semiconductor NCs containing both S and Se chalcogens. The novelty of the new semiconductor NCs lies in the incorporation of multiple cations as well as two different chalcogen anions within the crystal lattice, which is an achievement from the materials synthesis aspect. The composition-controlled optical and photoluminescence properties of the CuZn2ASxSe4-x NCs were investigated via multi-modal material characterization including x-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, and photoluminescence spectroscopy (PL). The crystal structure, as determined from the XRD primarily consisted of the metastable wurtzite (P63mc) phase. The NCs exhibited direct band gap in the visible range that could be tuned both by varying the group III cation within the composition as well as the ratio of S/Se, based on the Tauc plot obtained from the UV-vis characterization. This work lays the groundwork for future investigations into the practical applications of copper chalcogenide NCs in solar energy conversion.

Committee: Soubantika Palchoudhury (Committee Chair); Guru Subramanyam (Committee Member); Robert Wilkens (Committee Member); Robert Wilkens (Committee Member); Guru Subramanyam (Committee Member); Kevin Myers (Advisor); Soubantika Palchoudhury (Committee Chair) Subjects: Aerospace Materials; Alternative Energy; Analytical Chemistry; Biochemistry; Chemical Engineering; Chemistry; Energy; Engineering; Environmental Science; Industrial Engineering; Information Science; Inorganic Chemistry; Materials Science; Nanoscience; Nanotechnology; Nuclear Chemistry; Nuclear Engineering

Master of Science, University of Akron, 2023, Polymer Science

In the realm of perovskite solar cells, there has been a substantial rise in research focusing on organic-inorganic halide perovskites (OIHPs) in recent years. This is owing to remarkable progress in single junction OIHPs' power conversion efficiency (PCE), which has improved from 3.8% in the initial prototype built in 2009 to a current state-of-the-art value of approaching 26%. However, the weak bonding of the organic components in the hybrid crystal structure has made the OIHPs chemically unstable and susceptible to degradation caused by humidity, ultraviolet light, and heat. This is a major challenge that must be addressed for them to be suitable for industrial-scale production. In response to this challenge, alternative materials, such as inorganic cesium-based metal halide perovskites (CsPbX3, X = I, Br, or mixed), have attracted significant interest. These materials have shown great promise in terms of their power conversion efficiency (PCE), with some achieving PCE values exceeding 20%. Among these inorganic materials, CsPbI2Br stands out as a promising candidate due to its suitable bandgap and stable phase under operation conditions. However, the significant voltage deficit in inorganic CsPbI2Br-based PSCs, particularly in the inverted structure, remains a challenge for further PCE enhancement. This study presents a simple and effective approach to improve the performance of inverted all-inorganic CsPbI2Br-based PSCs by leveraging unreacted metal halide (PbI2) to passivate grain boundaries in the bulk perovskite film. The CsPbI2Br solar cells with an optimized excess of PbI2 exhibit reduced voltage deficits, boosting the open-circuit voltage from 1.04 V to 1.18 V, resulting in a PCE of 13.19% for inverted CsPbI2Br PSCs. Furthermore, the devices demonstrate improved long-term and thermal stability compared to the pristine devices. This approach holds promise for the development of inorganic perovskite solar cells with superior performance and stability, circu (open full item for complete abstract)

Committee: Mark Soucek (Advisor); Xiong Gong (Committee Member) Subjects: Chemistry; Condensed Matter Physics; Electrical Engineering; Engineering; Nanotechnology; Physics; Solid State Physics

Master of Science in Engineering, Youngstown State University, 2023, Department of Electrical and Computer Engineering

The use of renewable and sustainable energy sources such as solar cells have been increasing slowly and gradually. With the rapid increase and growth of solar photovoltaics (PV) production, approximately 22% from 2010 to 2020, high number of PV cells are being manufactured annually. Solar cells have been proven to be an efficient source of renewable energy because of their availability, installation, and affordability. Among all the different types of solar cells, thin-film PV has several advantages over other technologies because of its need for relatively fewer resources, ability to fully automate fabrication process, and the option to fabricate on a more affordable substrate. Nevertheless, the manufacturing process of these thin-film solar cells still involves several critical steps. For example, they still rely on conventional method of laser scribing techniques which in addition to being time consuming, has several reliability issues as well. In this project, the theory of threshold switching method is experimentally verified on Cadmium Telluride (CdTe) PV. The study was conducted by applying different voltage bias configurations to the sample. A drastic decrease in the resistance was observed. The time lapse study of decreased resistance was conducted, which proved that the resistance change is indeed a permanent phenomenon. Our experimental results of threshold switching indicates that this could potentially lead to a scribe-less technology in manufacturing of solar cells which may potentially lead to an increase in manufacturing reliability and efficiency.

Committee: Vamsi Borra PhD (Advisor); Daniel Georgiev PhD (Committee Member); Victor Karpov PhD (Committee Member); Ghassan Salim MS (Committee Member) Subjects: Aerospace Materials; Electrical Engineering; Materials Science; Nanotechnology

Master of Science (MS), Bowling Green State University, 2022, Physics

While Silicon photovoltaic (PV) cells have been the workhorse of solar power generation, many different PV technologies will need to be employed to achieve a greener energy future. One promising emerging technology is Perovskite solar cells, which have demonstrated >25% power conversion efficiency (PCE) with only a decade of research. It has been found that this material also has desirable properties for another emerging technology: All-Back-Contact (ABC) thin-film PV devices. This work investigates Perovskite absorbers in two different ABC designs: Quasi-Interdigitated Back Contact (QIBC) and Metasurface Lattice Back Contact (MSLBC) consisting of a periodic array of photo-absorbing cylinders. Due to the similarity to MSLBC designs, a Metasurface Perfect Absorber (MSPA) was also investigated. The optoelectronic performance of these devices was simulated using COMSOL Multiphysics®, which uses the finite element method to solve sets partial differential equations. It was found that a textured front surface for the QIBC device provides superior optical absorption over a flat front surface at higher wavelengths due to light trapping and optical resonance. Despite the inferior optical performance, the flat front surface QIBC design was shown to achieve a PCE >23%. The MSPA design was found to have high absorption for a wide range of incident angles due to Mie resonance within the periodic cylindrical structures. Strong absorption was also observed in the MSLBC device due again to Mie resonance. The PCE of this device was found to be superior under bottom illumination with room for improvement. Optimization of this design was performed by targeting the cylinder diameter and cylinder height. By comparing the optical and electronic performance for a wide range of these parameters, optimal values were found. The bifacial performance of this device was then examined and it showed little improvement over single-side illumination.

Committee: Marco Nardone Ph.D. (Committee Chair); Alexey Zayak Ph.D. (Committee Member); Haowen Xi Ph.D. (Committee Member) Subjects: Physics

Master of Science (M.S.), University of Dayton, 2021, Mechanical Engineering

As global energy demand increases so does the need for renewable energy. Solar energy will play a major role in the fight against climate change and meeting the worlds increasing energy demand. Therefore, it is important to study how solar photovoltaic (PV) production can be optimized. Studies have shown different methods for determining the optimal tilt angle for a fixed PV array all around the world, however the United States remains largely unexplored in this regard. This thesis aims to find the optimal tilt and maximum energy output of PV arrays for every county in the United States. By simulating energy production through the use of open-source material, the results show that states in the southwestern region of the United States produce the most amount of energy annually and have the lowest optimal tilt angles. Tilt angles in this region can be as low as 24 degrees, while states in the northern region of the United States had the highest optimal tilt angles, which could be as high as 42 degrees. This thesis provides the applications used for finding the optimal tilt and energy output. Another important consideration for increasing PV panel energy production is the use of tracking arrays. Tracking arrays dynamically track the sun throughout the course of the day, but tracking technology includes additional capital costs and is not affordable for residential systems. This thesis explores the use of a bi-annual fixed tilt array, where the tilt angle of the fixed array is changed at two times in the year to better capture the seasonal variation in solar irradiation. Optimization techniques are used to resolve the ideal tilt angles as well as the optimal time to change between these two angles for every state in the continental United States. Biannual arrays are then compared to fixed tilt and 1D tracking arrays while examining local weather variations and their effect on the optimal PV tilt angle and solar PV production. In general, PV panels with a fixed tilt in (open full item for complete abstract)

Committee: Rydge Mulford (Committee Chair) Subjects: Energy; Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2021, Chemistry

Metal halide materials encompass a wide range of compounds with many interesting structural and optoelectronic characteristics; the most ubiquitous of these materials are the halide perovskites. The ability to utilize a large number of elements in these compounds makes the possible compositions nearly endless. Herein, we discuss the synthesis and characterization of five new metal halide systems. In Chapter 2, the halide double perovskite solid solution, Cs2AgBiBr6–xClx, is characterized via diffraction and optical absorption techniques, and it is shown that a complete solid solution forms. The ability to engineer the band gap via halide exchange is a powerful tool towards rational material design. In Chapters 3 and 4, exploration of the pseudo-ternary CH3NH3X-AgX-MX3 [M = Sb3+, Bi3+; X = Br–, I–] phase diagrams results in three new phases that have lower dimensionality than the 3-D halide double perovskites. Chapter 3 focuses on AgSbI4, a 2-D layered semiconductor that exhibits significant thermochromism near room temperature as a result of a high degree of electron-phonon coupling. Chapter 4 centers on understanding silver bonding with the heavier halides [Br– and I–]. CH3NH3AgBr2, and CH3NH3Ag2I3 are both synthesized and their 1-D chained structures characterized via a combination of single crystal and synchrotron diffraction. A combination of bond valence sum calculations and literature analysis show that silver has a preference for four-coordinate environment with halide ions, and for the iodides, almost never forms octahedra. Chapters 5 and 6 explore photoluminescence in a pair of halide double perovskite systems: Cs2NaInCl6:Sb3+ and Cs2AgIn1–xBixCl6. The former is a dopant induced phosphor, with bright blue emission (PLQY ≈ 79%) and high thermal stability. The latter, a phosphor based on self-trapped excitonic emission, has one of the most red-shifted excitation profiles of the halide double perovskite phosphors. When coupled with a standard 400 nm light emit (open full item for complete abstract)

Committee: Patrick Woodward (Advisor); Christine Thomas (Committee Member); Yiying Wu (Committee Member) Subjects: Chemistry

Master of Science in Engineering, University of Akron, 2021, Polymer Engineering

In recent years, the world storage of coal, oil, natural gas, and other sources of nonrenewable energy is becoming less and less, meanwhile the problem of energy shortage is becoming more and more emergent which will restrict the development of the international economy. Under this background, most countries begin to develop solar energy, which promotes the development of solar cells. As we know, solar cells can straightforwardly transform light into electricity through the photovoltaic effect, and currently silicon solar cell is the most sophisticated technology in commercialization. Nevertheless, because of the complexity of the fabrication technique and the high cost of silicon materials, it is not easy to cut its price substantially. Therefore, finding new materials and new methods to fabricate economic solar cells is necessary. Right now, the hot research topic in this field is perovskite solar cells (PSCs). This kind of solar cell has a special light-absorbing active layer, which is called organic inorganic hybrid perovskite (OIHP), the most common is methylammonium lead iodide (CH3NH3PbI3 or MAPbI3). This kind of PSC can be easily solution-processed, and the raw materials are less expensive, both make it cheap to process and simple to fabricate. Previous studies have shown that perovskite like MAPbI3 with a three-dimensional (3D) structure are highly efficient. But the poor stability limits its application. Thus, it is urgent to develop a novel kind of PSCs with both high efficiency and good stability. Here, we present two feasible methods, compositional engineering and interfacial engineering, to fabricate 2D:3D mixed PSCs and 2D/3D bilayer PSCs for achieving the goal of high-performance photovoltaics. In the first method, with the help of 4-fluoro-phenethylammonium (4F-PEA) organic spacer, the corresponding champion PSC can obtain a better device performance with a power convention efficiency (PCE) over 20%, as well as a better stability for 3000 (open full item for complete abstract)

Committee: Xiong Gong (Advisor); Weinan Xu (Committee Chair); Chunming Liu (Committee Member) Subjects: Chemical Engineering; Energy; Materials Science

Doctor of Philosophy, The Ohio State University, 2020, Materials Science and Engineering

III-V/Si multijunction photovoltaics possess the potential for high power conversion efficiencies (surpassing the single-junction limit) at low cost by leveraging the inexpensive and scalable Si platform. Both space and terrestrial markets can benefit from this technology; however, multiple materials-related obstacles must first be overcome in order to truly demonstrate this potential and enable adoption of this new technology. For terrestrial usage, low-cost III-V deposition techniques are necessary to remain cost competitive with current photovoltaics. Given a Si bottom cell, the optimal series-connected dual-junction photovoltaic efficiency for both space and terrestrial solar spectra is achieved with a 1.7-1.8 eV top cell, which is most conveniently provided by GaAsyP1-y (y ~0.7-0.8) at around 3% lattice mismatch to the Si substrate. While epitaxial integration of GaAsyP1-y alloys on Si is favorable over high-cost and non-scalable wafer bonding or stacking techniques, controlling (minimizing) dislocation content within the strain-relaxed metamorphic materials, and/or minimizing its impact on top cell performance via careful device design, is key to achieving optimal performance. Materials challenges related to the heterovalent, lattice-mismatched GaP/Si interface and the thermal expansion coefficient mismatch of GaAsyP1-y to Si all complicate the production of low-defect density GaAsyP1-y materials. To this end, we have undertaken metalorganic chemical vapor deposition (MOCVD) growth studies of GaP/Si nucleation layers and GaAsyP1-y step-graded buffers, demonstrating substantial progress by reducing defect densities by over an order of magnitude in the course of this recent work. These efforts have largely been enabled via rapid feedback regarding crystalline defect populations obtained from electron channeling contrast imaging (ECCI). From these experimental studies, a deeper understanding of dislocation dynamics in these metamorphic materials is reac (open full item for complete abstract)

Committee: Tyler Grassman (Advisor); Suliman Dregia (Committee Member); Michael Mills (Committee Member); Roberto Myers (Committee Member) Subjects: Materials Science

Doctor of Philosophy, University of Toledo, 2020, Physics

Energy is considered one of the top problems facing humanity, and climate change clearly require3s growth in the fraction of energy provided by renewable sources in order to minimize the use of fossil fuels. Solar energy is an environmentally friendly technology which avoids nearly all generation of greenhouse gases. It is more available than hydro, wind, and other renewable energy sources. As science and technology advance, various types of solar cells are being produced to harvest solar energy. Silicon technology dominates the photovoltaic (PV) industry. Thin film solar electric technologies are evolving to reduce the cost of energy ($/Watt). Cadmium telluriude (CdTe) is one of the leading thin film technologies with a reduced energy cost and the shortest energy payback time. CdTe is a direct band gap II-VI material and has been investigated for decades to improve device performance, stability, and conversion efficiency. However, the open-circuit voltage (VOC) of CdTe devices is lower than for GaAs solar cells, despite having similar energy band gaps. Simulation and theoretical study show that the voltage deficit can be improved by making an ohmic contact to CdTe, or by reducing the back-contact potential barrier and increasing the doping level of CdTe. In this dissertation, I report on nanomaterials-based back contact interface layers, surface etching, the doping of CdTe using copper (II) chloride (CuCl2), and on the opto-electronic properties of CdTe double heterostructure samples. Nanocrystals (NCs) of FeSe2, FeTe2, NixFe1-xS2, and CuFeS2 were synthesized using hot injection colloidal methods. These materials were then characterized using X-ray diffraction, electron microscopy, Raman and UV-Vis-NIR spectroscopies. The charge transport properties of these nanomaterial-based thin films were tested in CdTe photovoltaics. Nickel iron pyrite (NixFe1-xS2) NCs showed composition-controlled conductivity, and where x = 0.05 (5%), they showed optimal device performanc (open full item for complete abstract)

Committee: Randy Ellingson (Committee Chair); Michael Heben (Committee Member); Robert Collins (Committee Member); S. Thomas Megeath (Committee Member); Mikhail Zamkov (Committee Member) Subjects: Nanoscience; Nanotechnology; Physical Chemistry; Physics

Doctor of Philosophy, Case Western Reserve University, 2020, Macromolecular Science and Engineering

The global photovoltaic (PV) industry has seen a rapid increase in installed capacity in recent years. As of 2019, the cumulative installed capacity of PV reached 627 GW, and the need to decrease levelized cost of energy (LCOE) initiated the pursuit to extend the lifetime of PV modules. The degradation of polymeric PV packaging materials is a crucial factor in determining the power loss rate and lifetime of real-world PV system. Two of the PET based backsheets contain a fluoropolymer outer layer, and the other one contains a thermoplastic polyolefin (TPO) inner layer. Indoor accelerated testing on two sets of samples was used to isolate the degradation mechanism induced by humidity and UV. This testing included damp heat (DH) exposure (85 C, 85 % relative humidity) and QUV exposure (1.55 W/m2 at 340 nm, black panel temperature 70 C). In DH testing, yellowing induced by antioxidant hydrolysis and additive migration can be observed. Hydrolysis is evident in EVA, whereas POE is relatively stable in DH. Physical degradation of backsheet materials induced by damp heat, including the phase transition of polyvinylidene fluoride (PVDF) and increase of crystallinity of PET, exposed potentialities for backsheet failure. In QUV exposure, chain scission of both encapsulants were confirm by indentation on multi-layer polymeric systems, and by Fourier transform infrared (FTIR) spectroscopy. In both DH and QUV exposures, POE exhibited better stability compared to EVA. The all-PET and PET + PVDF backsheets shows comparable performance, whereas the TPO + PET + PVDF backsheet shows the worst chemical and mechanical stability. A statistical tool, Analytic Suns-Voc, was developed to connect indoor polymer degradation under accelerated testing to large-scale, outdoor power loss of PV systems. Through the different time-series power loss modes obtained with Analytic Suns-Voc, the fielded PV modules can be viewed as sensors, and the degradation status of polymeric packaging materials ca (open full item for complete abstract)

Committee: Roger French (Committee Chair); Hatsuo Ishida (Committee Member); Ica Manas-Zloczower (Committee Member); Laura Bruckman (Committee Member); Jennifer Braid (Committee Member) Subjects: Materials Science; Polymers

Master of Science (MS), Bowling Green State University, 2020, Physics

Multiple exciton (MX) generation has been a significant part of the success of many semiconductor applications such as photoinduced energy conversion, stimulated emission and carrier multiplication. Generally, in small size semiconductor nanocrystals, MX processes are enhanced through quantum confinement of photoinduced charges. Unfortunately, the small particle volume of these semiconductor nanocrystals can also drive non-radiative Auger decay of multiple excitons reducing the MX feasibility in nanocrystal-based laser, photovoltaic and photoelectrochemical devices. Here, we reveal such Auger decay of biexcitons can be restrained with the utilization of quantum-well (QW) nanoshell heterostructures. The reported architecture reduces the Coulomb interactions between photoinduced charges which leads to enhanced biexciton lifetimes. Transient absorption measurements were used to demonstrate the increased biexciton lifetimes which revealed the cadmium based QW nanoshells (CdS/CdSe/CdS) increased the biexciton lifetime by more than 30 times compared to zero-dimensional CdSe nanocrystals. Suppression of Auger decay was attributed to the substantial confinement volume of the QW nanoshell architecture.

Committee: Mikhail Zamkov Prof. (Advisor); Marco Nardone Prof. (Committee Member); Alexey Zayak Prof. (Committee Member) Subjects: Materials Science; Physics

Master of Sciences, Case Western Reserve University, 2020, EECS - Computer and Information Sciences

Linear Performance Loss Rate (PLR) has been widely used in the photovoltaic (PV) community as a tool for modeling the degradation of PV modules over time. In the real-world commercial deployment of solar power, PV modules are manufactured by different companies to varying degrees of quality, deployed in a wide variety of locations, and undergo system damage and degradation. Since factors such as these will affect the performance of PV modules in different ways after data is already recorded, a linear model would not be fully able to effectively capture their lifetime performances. Many tools and models have been developed for specific lab tested PV systems, but have failed to generalize to large quantities of commercial powerplants. In this work, we introduce a new solar power plant analysis tool that uses a non-linear PLR method that better models the degradation of PV modules over their lifetime, and we will be testing our model on a population of 1100 commercial PV systems that have been operating for up to 6 years. In this dataset, the median adjusted R2 value of the Linear PLR method is 0.03, while the median adjusted R2 of a Segmented method is increased at 0.21. Decomposition by season can further increase the performance of both linear and segmented methods to median adjusted R2 values of 0.19 and 0.28, respectively. Comparing the metadata factors to the calculated PLR values can lead to insights regarding which factors contribute to the greatest change in PLR and degradation of PV systems.

Committee: Roger French (Advisor); Xusheng Xiao (Committee Chair); Koyuturk Mehmet (Committee Member) Subjects: Computer Science

Doctor of Philosophy, University of Akron, 2020, Chemistry

The great potential for the myriad applications of porphyrin-based nanostructures with different morphologies originates from the idea that porphyrins have highly tunable photophysical and photochemical properties. Potential applications of these types of materials include catalysis, molecular sensing, and energy conversion and storage, all of which depend on the electronic structures and morphologies of porphyrin nanoassemblies. These properties are in turn governed by peripheral substituents of the porphyrin ring, central metal ion or solvent. However, the self-assembly into various morphologies is challenging, and has attracted significant recent attention. The self-assembly of porphyrins using non-covalent interactions such as π-π stacking, electrostatic interactions and hydrogen bonding into well-defined supramolecular nanostructures represents an attractive alternative from classic synthetic approaches toward generating highly ordered nanostructures. In this dissertation, the synthesis and characterization of the self-assembled structure(s) of a porphyrin bearing guanidinium salts 1 (5,15-bis(4-guanidiniumphenyl)-10,20-diphenylporphyrin) in the presence of pyrophosphate (PPi), adenosine diphosphate (ADP) and adenosine triphosphate (ATP) in MeOH and H2O was studied. The electrostatic attraction of the phosphate anions and the positive guanidinium salts, as well as π-stacking interactions between porphyrin chromophores is suggested to drive the self-assembly into the formation of nanorods, nanofibers, and nanosheets. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) results reveal the formation of nanorods with length from 266 nm and diameters of 11.3 - 22.5 nm and nanosheets that ~0.354 – 0.537 μm wide. Spectroscopically, the absorption spectra of porphyrin 1 in 1:1 MeOH/H2O solution with increasing concentrations of the phosphates resulted in the decrease and broadening in the Soret band centered at 415 nm, as well as the growth of a (open full item for complete abstract)

Committee: David Modarelli (Advisor); Tessier Claire (Committee Member); Chrys Wesdemiotis (Committee Member); Youngs Wiley (Committee Member); Yu Zhu (Committee Member) Subjects: Chemistry

Doctor of Philosophy, University of Toledo, 2019, Physics

With growing energy demands, renewable energy technologies, and particularly photovoltaics (PV), are becoming more relevant for future large-scale deployment. While the current stage of PV field is growing at the highest pace with respect to other forms of energy resources, the quest to achieve higher solar power conversion efficiencies (PCE) at lower cost is still continuing. To this end, the search for PV technologies and structures that are robust, efficient and cost effective have brought the field of emerging PV to respond to shortcomings of Si based and also the 2nd generation PV technologies (e.g. CdTe or CuInGaSe2 (CIGS)). One of the most successful forms of emerging or 3rd generation PV has been demonstrations of metal halide perovskite PV. While perovskites have been remarkable in achieving high PCEs (< 25%) in the span of one decade, they possess properties that allow for more novel approaches in structures and fabrication. The potential to reduce costs further with roll to roll manufacturing, due to solution processability of perovskites, raises the possibility of fabrication on flexible substrates or semitransparent devices. All of these contribute to potential of these devices for variety of applications. In the meantime, the possibility of bandgap engineering in perovskites without significant compromise in PCE has brought up another field of possibility which involves the applications of perovskites in multijunction or tandem structures. Demonstrations of tandem devices with perovskite subcells have been made by pairing these devices with CIGS, Si and other prominent PV technologies. To further understand the limitation of device performances particularly from the prospect of optics, in this thesis, a model based on transfer matrix method was developed. Using this approach, the optics of multi-layer stack in the structure of tandem device is analyzed and clear recipes on the bandgap and thickness of perovskite subcell to maximize the performance of (open full item for complete abstract)

Committee: Michael Heben PhD (Advisor); Robert Collins PhD (Committee Member); Yanfa Yan PhD (Committee Member); Sanjay Khare PhD (Committee Member); Glenn Lipscomb PhD (Committee Member) Subjects: Condensed Matter Physics; Energy; Materials Science; Optics; Physics