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 Materials Science and Engineering (MSMSE), Wright State University, 2018, Materials Science and Engineering

Solar technology has a long history of incremental improvements in cost, reliability and efficiency. However, solar cells based on lead halide perovskite films have made more rapid leaps forward in the past 10 years, making it the fastest growing solar technology in terms of efficiency. Leaders in academia and industry continue to find success in overcoming manufacturability and stability issues, but have not yet discovered a high-efficiency perovskite film without the use of toxic lead. Probing less toxic analogs to the highly efficient lead halide, a series of thin films with perovskite structures, i.e. A2BB'X6 where A = Cs or FA, B/B' = Sn, Bi, Sb, Ag, and/or In and X = I, are fabricated using a mixed metal approach. XRD patterns reveal the low dimensional A3Bi2I9 crystal. UV/Vis spectra results show that the bandgap of bismuth-based perovskites is finely tuned, which has potential applications in future solar cells.

Committee: Hong Huang Ph.D. (Advisor); Maher Amer Ph.D. (Committee Member); Suzanne Lunsford Ph.D. (Committee Member) Subjects: Materials Science

Doctor of Philosophy, University of Toledo, 2020, Physics

Photovoltaic (PV) solar cells have attracted great attention because of the demand for low cost renewable energy sources. Detailed information on electronic properties, such as doping, defects, gap states…etc, must be fully understood to develop the technology of solar cells. Here, we report the fundamental electronic properties of two distinct materials systems, one is based on polycrystalline cadmium telluride (CdTe) and the other is lead-halide perovskite solar cells. This investigation provides useful information to understand the fundamental nature of single junction solar cell device and material. First, we investigate the impact of back surface treatment method for cadmium sulfide (CdS)/CdTe solar cells using hydroiodic acid (HI) etching to provide an appropriate electrical back contact. The structural properties of CdTe films and electrical properties of the CdTe absorber and interfaces are characterized. Using capacitance-based techniques with the support of current–voltage measurements, we show that the barrier height of the back contact is reduced, apparent doping concentration is increased, and a defect level at 0.409eV is eliminated after the HI-treatment. More importantly, the CdTe device performance is improved. This improvement is still limited by many factors. One factor is the device window layer that limits the current generation. Therefore, we replaced CdS layer by wide bandgap material, ZnMgO (ZMO). We noticed that the electrical properties of CdS/CdTe and ZMO/CdTe solar cells depend on both buffer material and the fabrication atmosphere. Using capacitance spectroscopy-based techniques, we show that CdS/CdTe solar cells have negligible front contact barriers regardless of the fabrication atmospher, while ZMO/CdTe devices show obvious front barriers are dependent on the fabrication atmosphere. Both CdS/CdTe and ZMO/CdTe solar cells have significant back contact barriers. Additionally, we find that the energy level of defects in CdS/CdTe cells (open full item for complete abstract)

Committee: Yanfa Yan (Committee Chair); Jian Li (Committee Member); Jacques Amar (Committee Member); Xunming Deng (Committee Member); Nikolas Podraza (Committee Member) Subjects: Energy; Materials Science; Physics

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 Philosophy, University of Akron, 2024, Polymer Engineering

The increased use of solar energy for power is anticipated to lead to the shift from traditional power sources to renewable energy sources. Photovoltaic (PV) is a promising technology due to its ability to directly convert sunlight into electricity with no pollution. Solar cells, specifically those based on metal halide perovskites (MHPs) have gained popularity recently due to their power conversion efficiency (PCE) that have increased dramatically over the past 15 years, from 3.8% to more than 26 %. The rapid development in PCE is due to the advanced features that MHPs have such as cost-effective and easy processing, high absorption coefficient, large diffusion length, and low exciton binding energy. In particular, the purpose of this study is to develop solution-processed perovskite solar cells (PSCs) by tuning film morphology and optoelectronic properties of metal halide perovskites incorporated with processing additives, thereby optimizing the performance of PSCs. To maximize the potential of perovskite, controllable crystallization is crucial for producing high-quality perovskite thin films with fewer structural defects and additive engineering is a facile and effective method among other techniques. We mainly investigated the effects of various processing additives on the MHPs based on MAPbI3 perovskite (where MA is CH3NH3) and correlate PCE in term of film morphology, crystallinity, photocurrent hysteresis, optoelectronic properties, device performance and stability of PSCs.

Committee: Xiong Gong (Advisor); Fardin Khabaz (Committee Chair); Mark D. Soucek (Committee Member); Mesfin Tsige (Committee Member); Jie Zheng (Committee Member) Subjects: Energy; Engineering; Materials Science; Nanotechnology

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

In the past 10 years, perovskite solar cells (PSCs) have drawn great attention in both academic and industrial sectors. Over 25.5% power conversion efficiency (PCE) has been reported from PSCs by three-dimensional (3D) methylammonium lead iodide (CH3NH3PbI3 or MAPbI3). However, the previous studies have indicated that PSCs exhibited poor stability. Thus, to commercialize PSCs, the development of efficient and stable PSCs is required. In this study, we reported two approaches to develop efficient and stable PSCs. One was to develop novel all-inorganic perovskites, where Pb2+ was partially heterovalently substituted Nd3+. Another was to develop PSCs with a bulk heterojunction (BHJ) device structure. In the first approach, it was found that the CsPbI2Br:xNd3+ thin films possess enhanced charge carrier mobilities, superior crystallinity, and enlarged crystal sizes, but with enlarged optical bandgaps. As a result, PSCs by the CsPbI2Br:xNd3+ thin films exhibit more than 20% enhanced PCEs and boosted stability compared to those by pristine CsPbI2Br thin film. To further boost the device performance of PSCs, solution-processed 4-lithium styrenesulfonic acid/styrene copolymer (LiSPS) is utilized as the passivation layer. PSCs by the CsPbI2Br:xNd3+/LiSPS bilayer thin film possesses reduced charge extraction lifetime and suppressed charge carrier recombination, resulting in 17.05% PCE and dramatically boosted stability compared to that without the LiSPS passivation layer. All these results indicate that we develop a facile way to approach high-performance PSCs by all-inorganic perovskite materials. In the second approach, we found that all-inorganic perovskite incorporated with low bandgap conjugated polymers, forming BHJ composite thin film possesses balanced and enhanced charge mobilities, superior film morphology with enlarged crystal sizes, and suppressed trap density As a result, BHJ PSCs exhibited a 21.08% PCEs, which is more than 16% enhancement compared to that wit (open full item for complete abstract)

Committee: Xiong Gong (Advisor); Mark D. Soucek (Committee Chair); Junpeng Wang (Committee Member) Subjects: Chemical Engineering; Energy; Materials Science

Doctor of Philosophy, The Ohio State University, 2021, Nuclear Engineering

Semiconductor gamma ray detectors are highly demanded in numerical fields of applications, such as homeland security, industry, medical imaging and academic research. As the golden standard of gamma spectroscopy, the High Purity Germanium (HPGe) detector has an energy resolution of less than 0.5% Full-Width-Half-Maximum (FWHM) at 662 keV. However, HPGe detector needs liquid nitrogen cooling due to its small energy bandgap. As the only commercially available room temperature gamma ray detector, the Cadmium-Zinc-Telluride (CdZnTe) detector achieves an energy resolution of less than 1% FWHM at 662 keV. Nevertheless, the growth issues and the associated high cost of the CdZnTe detectors continue to drive the search for alternative radiation detection materials featuring low-cost growth methods. Recently, the lead (Pb) halide perovskites emerged as a promising candidate for hard radiation detection due to their favorable properties, such as high atomic number, large mobility-lifetime product, wide and tunable energy bandgap. In this research, we evaluated the performance of perovskite gamma ray and X-ray detectors, especially the inorganic CsPbBr3 single crystals made from low-cost solution grown method. The design principles of a gamma ray detector architecture were studied. The leakage current reduction performance of different detector structures, that is, Ohmic-Ohmic, Schottky-Ohmic, Schottky-Schottky, were compared theoretically. The role of Electron/Hole Transport Layers in a gamma ray detector was discussed. Processing sequences for CsPbBr3 detector fabrication were developed. Through well controlled surface processing, the leakage current as low as less than 5 nA at -200 V was consistently achieved, which is comparable to a CdZnTe detector. The investigation of perovskite detector architecture and development of detector processing sequences pave the way of effective design and fabrication of CsPbBr3 detector with consistent performance. The X-ray and alpha part (open full item for complete abstract)

Committee: Lei Cao (Advisor) Subjects: Nuclear Engineering

Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2020, Materials Science and Engineering

Hybrid organic-inorganic perovskite solar cell is an emerging technology which has shown the fastest advancement in power conversion efficiency within a few years since introduction, thus making it one of the clean energy breakthroughs. These cells are based on thin-film technology which makes them suitable to manufacture using low-cost solution processing methods. As these types of cells are easily tunable with the selection of different materials, interfacial engineering is an important approach to increasing their efficiency. One of the main hurdles in this regard is the loss caused by the recombination of separated charges. An approach to tackle these issues is to incorporate organic monolayers between the charge (electron/hole) transport layers and the perovskite active layer. Such interface engineering has experimentally shown to improve the overall efficiency and stability of the cell. The current research focuses on the study of TiO2/HOOC-Ph-SH interface in order to understand the improved efficiency. Using ab initio quantum mechanical approach, we investigate the monolayer (HOOC-Ph-SH) adsorption onto the TiO2 surface to determine structural and electronic properties of the interface and discuss the connection of the results to solar cell performance.

Committee: Amit A. Farajian Ph.D. (Advisor); Raghavan Srinivasan Ph.D., P.E. (Committee Member); James A. Menart Ph.D. (Committee Member) Subjects: Chemistry; Materials Science; Physics; Quantum Physics

Doctor of Philosophy, University of Toledo, 2020, Physics

Organic-inorganic metal halide perovskite ABX3 (A: methylammonium-MA, formamidinium-FA, cesium-Cs; B: lead-Pb, tin-Sn; X: iodine-I, bromine-Br, chlorine-Cl) based photovoltaics (PV) is one the most promising candidates for generation of low-cost clean energy. Perovskite-based PV yield, commonly quantified as power conversion efficiency (PCE), largely depends upon the characteristics of component layers including that of perovskite absorber layer and the interfaces between the layers. This dissertation presents the wide range of studies performed on the morphology and optoelectronic properties of perovskite solar cell component layers using spectroscopic ellipsometry (SE) and photothermal deflection spectroscopy (PDS). The amount of defect induced sub-gap absorption in perovskite absorber layers as a function of perovskite composition and laboratory ambient exposure level are studied and their effect on the PCE of solar cells are discussed. In addition, this dissertation presents the study of electronic loss arising from defects in perovskite absorber layers and parasitic optical absorption loss in non-active component layers in several perovskite solar cells. Optical response ε in the terms of near infrared to ultraviolet complex dielectric function (ε = ε1 + iε2) spectra of varying Cs-to-FA ratios in solution processed FA1-xCsxPbI3 perovskite thin films are studied. Analysis of these ε spectra track changes in the positions of critical point (CP) energies, including bandgaps and above bandgap transitions, with varying Cs contents. Bandgap values are identified as the lowest energy CP, with additional sub-gap features attributed to the presence of defects. Absorption onset values, for which absorption coefficient (α) = 4000 cm1, are extracted, with FA0.8Cs0.2PbI3 showing the sharpest absorption edge and the least contribution to absorption from defects below the bandgap. External quantum efficiency (EQE) simulations of solar cells using ε spectra and layer thick (open full item for complete abstract)

Committee: Nikolas J. Podraza (Committee Chair); Robert W. Collins (Committee Member); Yanfa Yan (Committee Member); Richard Irving (Committee Member); Terry Bigioni (Committee Member) Subjects: Materials Science; Optics; Physics

Master of Science, The Ohio State University, 2020, Chemistry

Organic-inorganic hybrid perovskites have emerged in recent years as one of the most promising materials for solution-processed electronics and optoelectronics including solar cells, light-emitting diodes (LED) and field-effect transistors (FET). Combining the rigid inorganic framework with soft organic materials, these hybrid perovskites provide the opportunity for investigating organic-inorganic interactions at the molecular scale. This MS thesis summarizes studies on organic-inorganic hybrid lead halide perovskites to date, explores PSCs device fabrications and then conducts the synthesis targeting at a new lower-dimensional perovskite incorporating azobenzene. This thesis is organized by exploring the functions of organic cations ranging from structural building block (chapter 2), PSCs device fabrication progress (chapter 3) to the synthesis of azobenzene perovskite (chapter 4). To start the work, experiments were first repeated following established procedure. Then based on these practices, efforts were contributed to new material synthesis. In this process, challenges and problems were tried to be solved and rationalized by various techniques. Finally, synthetic strategy was proposed and conducted based on the rationalized motivation, proposing potential solutions or producing new chemical compounds for found problems.

Committee: Yiying Wu Dr. (Advisor); Patrick Woodward Dr. (Committee Member) Subjects: Chemistry; Electrical Engineering

Doctor of Philosophy, Case Western Reserve University, 2019, EMC - Mechanical Engineering

Perovskite solar cells (PSCs) have attracted enormous attention in recent years due to their high theoretical power conversion efficiencies (PCEs) and relatively low cost. The outstanding performance is attributed to the unique physical parameters of perovskite materials, and these physical parameters were analyzed by mathematic models in this study. Although PSCs have exceptional performance, their environmental sustainability causes grave concerns due to the lead material contained in the perovskite dyes and material- and energy-intensive processes involved in the manufacturing process. The cradle-to-gate environmental impacts of a liquid-state titania nanotube (TNT)-based PSCs were evaluated by using an attributional life cycle assessment (LCA) method, and it has been found that the lead production was not a major contributor to the human toxicity potential (HTP), which only takes up less than 0.3% of HTP in the life cycle. Particle size and distribution of nano-wastes and nano-emissions generated from the TNT film fabrication were also characterized in the study. With the development of perovskite PV technologies, different types of solid-state PSCs were developed to enhance the power conversion efficiency (PCE), stability, and environmental performance. The cradle-to-grave environmental impacts of five representative PSCs were evaluated and compared by building LCA models. The solvent usage was identified to be the main reason for the various LCA results among different systems, and the replacement of fresh organic solvents with recycled organic solvents results in more than 26% of GWP reduction in all systems. Currently, PSCs are expected to be scaled up to fulfill commercial demands. The most promising manufacturing methods to fabricate the large-scale perovskite PV systems were identified, and their environmental impacts were evaluated and compared based on their LCA models. The greenhouse gas emissions generated from producing 1 kWh of electricity (open full item for complete abstract)

Committee: Chris Yuan (Advisor); Yue Li (Committee Member); Roger French (Committee Member); Chirag Kharangate (Committee Member); Bo Li (Committee Member) Subjects: Environmental Engineering; Mechanical Engineering

Master of Science (MS), Ohio University, 2018, Electrical Engineering (Engineering and Technology)

Perovskite solar cells have become the fastest advancing solar technology to date. With only a few years of comprehensive research, laboratory demonstrations have shown power conversions above 20% efficiencies. Various methods for printing perovskite solar cells exist. This thesis explores the microplot method of printing using the novel Sonoplot Microplotter II instrument. The focus of the thesis is on utilizing the combinatorial approach to systematically investigate the experimental parameters including, substrate properties and temperature, humidity, printing speed, feature width, and annealing which greatly affect the printing process outcomes critical for the resulting solar cells performance. It was found that printing parameters had significant impact on the film thickness and edge qualities such as higher printing speeds and larger feature widths created a more uniform film. The annealing parameters impacted the crystal growth and density in such a way that higher annealing temperatures created more dense films and resulted in films with larger crystal sizes.

Committee: Wojciech Jadwisienczak (Advisor); Savas Kaya (Committee Member); Harsha Chenji (Committee Member); Jixin Chen (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, Case Western Reserve University, 2018, Physics

Understanding the transport properties of semiconductor materials has been a key to the discovery of various intriguing quantum phenomena in condensed matter physics and the development of new semiconductor technologies. In this dissertation, electronic transport properties of the 2D hole system at the GaAs/AlGaAs heterointerface, the exceptional thermoelectric material SnSe and the emerging solar cell material lead halide perovskite are investigated.

Committee: Xuan Gao (Advisor); Walter Lambrecht (Committee Member); Jesse Berezovsky (Committee Member); Geneviève Sauvé (Committee Member) Subjects: Condensed Matter Physics; Low Temperature Physics; Physics

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

Despite the impressive success of perovskite-based hybrid solar cells, their widespread usage has been limited partially owing to stability issues under working environmental conditions. Among these, the effects of humidity are some of the most significant. Water intercalation generally degrades the material, shortens its useful life, and reduces the efficiency of photovoltaic energy conversion. Understanding the reasons for these effects can be achieved through detailed and accurate atomic-scale analysis. Here, we study water intercalation at the interfaces of perovskite-based hybrid solar cell material and TiO2 electrode. Accurate ab initio computer simulations are used to obtain structural and electronic properties. We systematically investigate interfacial geometry and determine the most stable configurations for different orientations of TiO2 (001) surface and different layers of hybrid organic-inorganic tetragonal perovskite lead Iodide. We also determine water adsorption characteristic on reconstructed TiO2 and hybrid perovskite surfaces. These are then used to obtain the most stable interfacial configurations upon water intercalation. Based on the obtained electronic properties we compare interface functionality with and without water and discuss consequent effects on solar cell performance.

Committee: Amir Farajian Ph.D. (Advisor); Hong Huang Ph.D. (Committee Member); Nikolai Priezjev 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

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

Doctor of Philosophy, University of Toledo, 2017, Physics

The world energy consumption has increased rigorously in recent years due to the rapid economic development and the massive global population expansion. Today the world energy supply relies heavily on fossil fuels, known as non-renewable energy resources, which have limited reserves on Earth and do not form or replenish in a short period of time. Burning fossil fuels not only brings environmental pollutions but also results in carbon dioxide and other greenhouse gases, which are to blame for global warming. Therefore, to build a more sustainable and greener future, we have to develop alternative renewable energy resources. Photovoltaic (PV) cell, also commonly known as solar cell, is a very promising renewable energy technology. Here in this dissertation, we have studied two emerging PV materials with earth abundant elements, i.e. copper zinc tin sulfide (CZTS) and organic-inorganic hybrid halide perovskite. Having earth abundant elements means that the raw materials have rich reserves on Earth and the costs are relatively low. It also means that the materials have the potential capability to be produced in large scales in industry. We first explored two different deposition methods for preparing CZTS thin films. In the first method, the CZTS was fabricated by a solution based method with diethyl sulfoxide (DMSO) as the solvent and the effect of spin speed on the properties of CZTS thin films was studied. The results indicated that a higher spin speed was more favorable for attaining a more densely packed and pinhole-free film while no crystallographic differences were observed. In the second method, CZTS was fabricated using sputtered metal precursors followed by a closed-space sulfurization (CSS) technique, which had high manufacturing compatibility and could be applied in industry. After exploring different sulfurization conditions, including temperatures and time, the champion cell was obtained at 590ºC for 30min, with a maximum power conversion efficiency ( (open full item for complete abstract)

Committee: Yanfa Yan (Committee Chair); Randy Ellingson (Committee Member); Nikolas Podraza (Committee Member); Jacques Amar (Committee Member); Dean Giolando (Committee Member) Subjects: Materials Science; Physics

Master of Science in Polymer Engineering, University of Akron, 2017, Polymer Engineering

Perovskite hybrid solar cells (Pero-HSCs) are rising stars in the nowadays photovoltaic(PV) technology. Within couple of years, the efficiency of perovskite solar cells has evolutionarily reach 22%, which override other types of solar cell by its low cost and ease to assemble. In theory, the Pero-HSCs has an upper conversion efficiency as 31%, therefore there are huge potential to be fulfilled in the near future research. In this work, we mainly focused on strengthening the electron extraction and transportation in the lead methylammonium tri-iodide(MAPbI3) perovskite solar cells. After a brief introduction on the origins and working principles of perovskite solar cells (Chapter ¿), the optimization of the cathode interface layer is addressed (Chapter ¿). Followed, a bulk heterojunction perovskite device was assembled by asserting n-type nanoparticles into perovskite layer for the first time (Chapter ¿). Last, the significance of this work and outlook was analyzed in Chapter ¿. Interfacial engineering of conventional perovskite solar cell is investigated by adopting a ternary metal oxide, Zn2SnO4 (ZSO), as electron extraction layer(EEL). Compared with generally used ZnO (ZO), thin film of ZSO nanoparticles(NPs) possess higher transparency over the entire visible wavelength, and is low temperature (=100 oC) annealed. Combined with more favorable energy level for electron extraction as cathode interface layer and higher electron conductivity, a dramatically boost in short circuit current density (JSC) and accordingly higher power conversion efficiency(PCE) were observed. Device engineering of inverted structured perovskite solar cells by incorporating either ZO NPs or ZSO NPs into the perovskite layer to form bulk heterojunction is discussed. Owning to the improved carrier mobility and much more balanced e-h transport, charge recombination was largely suppressed, the enlarged VOC, JSC and fill factor(FF) was obtained, corresponding to a 25% augment in PCE co (open full item for complete abstract)

Committee: Xiong Gong (Advisor); Thein Kyu (Committee Chair); Zhenmeng Peng (Committee Member) Subjects: Energy; Engineering; Materials Science; Polymers

Doctor of Philosophy, Case Western Reserve University, 2017, Macromolecular Science and Engineering

Since CH3NH3PbI3 based perovskites were discovered as viable active materials for the next generation photovoltaic devices, their instability in different environmental conditions has been a constant challenge. In pursuit of a better understanding of the degradation mechanisms, perovskite solar cells have been fabricated and investigated by scientists in order to find correlations between the solar cell characteristics/performance and the interface variation. In this thesis, the perovskite reactivity to humidity is studied by exposing samples to D2O environment for different durations. The degradation process of CH3NH3PbI3 perovskite is examined in-situ by using time-of-flight secondary ion mass spectrometry (ToF-SIMS). 3D images are constructed through the layer-by-layer spatially resolved elemental distribution analysis and the D2O moisture penetration through the sample. The intermediate products of interaction with moisture are analyzed by ToF-SIMS and X-ray photoelectron spectroscopy (XPS). We also investigated the electrical operation-induced degradation on CH3NH3PbI3 perovskite solar cells. Upon exposure to electrical current, the structure and composition were examined by combining depth-resolved imaging with ToF-SIMS, XPS and field-emission scanning electron microscopy (FE-SEM). The results show that the interface of the perovskite and the meso-porous TiO2 intermix into each other during the initial operations of solar cell. This intermixing turns the efficiency upward and improves the power conversion efficiency (PCE) up to ~50%. Both depth profiles and SEM images proved that operating devices undergo irreversible changes in thickness, which results in a dramatic performance loss eventually. In addition to studying the degradation process of the perovskite, a new formation method was developed to achieve complete conversion of PbI2 to CH3NH3I3 on FTO/Compact TiO2 substrate by employing a quaternary ammonium salt as an additive in the PbI2 solution. Thi (open full item for complete abstract)

Committee: Clemens Burda (Advisor); David Schiraldi (Committee Chair); Alex Jamieson (Committee Member); Chung-Chiun Liu (Committee Member); Xuan Gao (Committee Member) Subjects: Chemistry; Materials Science; Molecular Chemistry; Organic Chemistry; Polymer Chemistry

Doctor of Philosophy, University of Toledo, 2016, Physics

Photovoltaic (PV) devices are becoming more important due to a number of economic and environmental factors. PV research relies on the ability to quickly fabricate and characterize these devices. While there are a number of deposition methods that are available in a laboratory setting, they are not necessarily able to be scaled to provide high throughput in a commercial setting. A close-space sublimation (CSS) system was developed to provide a means of depositing thin films in a very controlled and scalable manner. Its viability was explored by using it to deposit the absorber layer in Zn3P2 and CdTe solar cell devices. Excellent control over morphology and growth conditions and a high level of repeatability was demonstrated in the study of textured Zn3P2 thin films. However, some limitations imposed by the structure of Zn3P2-based PV devices showed that CSS may not be the best approach for depositing Zn3P2 thin films. Despite the inability to make Zn3P2 solar cell devices, high efficiency CdTe solar cells were fabricated using CSS. With the introduction of Perovskite-based solar cell devices, the viability of data collected from conventional J-V measurements was questioned due to the J-V hysteresis that Perovskite devices exhibited. New methods of solar cell characterization were developed in order to accurately and quickly assess the performance of hysteretic PV devices. Both J-V measurements and steady-state efficiency measurements are prone to errors due to hysteresis and maximum power point drift. To resolve both of these issues, a maximum power point tracking (MPPT) system was developed with two algorithms: a simple algorithm and a predictive algorithm. The predictive algorithm showed increased resistance to the effects of hysteresis because of its ability to predict the steady-state current after a bias step with a double exponential decay model fit. Some publications have attempted to quantify the degree of J-V hysteresis present in fabricated Perovski (open full item for complete abstract)

Committee: Yanfa Yan PhD (Advisor); Jon Bjorkman PhD (Committee Member); Bo Gao PhD (Committee Member); Dean Giolando PhD (Committee Member); Cora Lind-Kovacs PhD (Committee Member); Nikolas Podraza PhD (Committee Member) Subjects: Solid State Physics

Master of Science, The Ohio State University, 2016, Chemistry

Understanding and application of nanostructure metal oxide semiconductor is fundamentally significant in science and technology field. With further investigation of the chemical and physical characteristics of metal oxide semiconductor, we are able to more precisely control and strengthen the relation between the synthesis and application. This focus of this dissertation is on the understanding of correlation between the size and coloration of a p-type wide band gap Cu-based delafossite semiconductor and its application in perovskite solar cell. The copper gallium oxide (CuGaO2 or CGO) was synthesized by hydrothermal method and further characterized via X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron spectroscopy and etc. It turns out the coloration of CuGaO2 comes from the Cu(II) spices by oxygen interstitial doping. As a result, with higher doping level, the flat band potential is more positive in yellow CuGaO2 than grey CuGaO2. In addition, the size can be independently controlled from the coloration by different synthesis conditions. With deeper exploration of the intrinsic difference in various CuGaO2, the fact revealed on this delafossite material could be the stepping stone for the further application in catalysis or photovoltaics. Organic Inorganic hybrid perovskite as a narrow band-gap semiconductor has become a hot topic in photovoltaic area. It rapidly affects and strikes the development of the emerging solar cells. With knowing the advantages and disadvantages of perovskite in its solar cell application, we introduced the p-type CuGaO2 as hole transport material in the perovskite solar cell structure. Due to the decreased hole transfer resistance, the short circuit current density was improved as well as the power conversion efficiency compared to hole material free cells.

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