Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Sb2se3 Absorber Layered Solar Cell Fabrication and Characterization(01. Izmir Institute of Technology, 2021) Kurtuldu, Seher Hazal; Aygün, Gülnur; Tarhan, Enver; Tarhan, Enver; Aygün Özyüzer, Gülnur; Tarhan, Enver; 01. Izmir Institute of Technology; 04.05. Department of Pyhsics; 04. Faculty of ScienceThin-film antimony selenide (Sb2Se3) solar cells have gained attention as a high-potential photovoltaic technology around the world. Outstanding features like a high absorption coefficient, a suitable direct bandgap, and good hole mobility make Sb2Se3 a promising absorber material for solar cell applications. It has demonstrated a very rapid growth reaching 9.2% power conversion efficiency (PCE) in only 7 years after intensive studies. In the present thesis, first of all Sb2Se3 thin films were deposited on soda lime glasses (SLGs) and investigated using energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scanning electron microscopy (SEM), spectrophotometry and Raman spectroscopy. Structural and optical studies were carried out depending on the thickness, used argon (Ar) gas flow rate and post-annealing temperature of the Sb2Se3 films in order to optimize the absorber layer to be used in solar cell. This study revealed that key parameters such as band gap energy and crystal structure of the Sb2Se3 thin films affected by the thickness, Ar gas flow rate during deposition and post-annealing temperature. In addition, oxide phase formation was also found to be related to these growth parameters. Finally, SLG/ITO/Zn(O,S)/Sb2Se3/Ag for superstrate configuration and both SLG/Mo/Sb2Se3/CdS/ITO and SLG/Mo/Sb2Se3/CdS/ZnS/ITO devices fabricated for substrate configuration solar cells. Since Zn(O,S)/Sb2Se3 heterojunction has not been studied before in the literature, this study will be the first. At the end of the electrical analysis, the best conversion efficiency of 3.9% was achieved by the solar cell with the substrate configuration.Master Thesis Growth and Characterization of Znsno Thin Films on Polymers for Oleds(Izmir Institute of Technology, 2019) Ekmekçioğlu, Merve; Aygün, Gülnur; Aygün Özyüzer, Gülnur; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe use of flexible organic light-emitting diodes (OLEDs) in smartphones and televisions with inclined screen shows significant improvements in commercial applications. Recently, flexible OLEDs have been used in lightweight, portable, wearable and even deformable screens, sensors as well as solid-state lighting applications. Under favour of these applications, remarkable developments are observed in the production of flexible electronics. The advantages of OLEDs according to the existing liquid crystal display (LCD) technology are self-emission capability, wide viewing angle, fast response time, simple structure, and low driving voltage. Highly conductive and transparent anodes are required for efficiency and uniform light emission in OLEDs. Indium tin oxide (ITO) which is one of the most promising anodes among transparent conductive oxides (TCO), has superior electrical and optical properties such as ~85% high transmittance at the visible region and ~104 Ω−1 cm−1good conductivity. The reason is due to the bandgap range of about 3.70 eV. Zinc tin oxide (ZnSnO or ZTO) is another TCO commonly used for many applications in the literature. Alternative anodes eliminate the use of ITO due to the absence of indium element so that highly desirable. In this thesis, ZTO is used as anode instead of ITO thin film and the eligibility of ZTO as an anode in OLED production is explored. The advantages of the optimized ZTO thin film according to the ITO are that is abundant on earth, has better performance, has low surface resistance, has less surface roughness, is capable of being produced as an anode in OLEDs. In this thesis to be successful, at the first stage ZTO thin films have grown on soda lime glass by magnetron sputtering, then ZTO and ZTO/Ag/ZTO multilayer thin films respectively have been deposited on flexible Polyethylene terephthalate (PET) and Polyimide (PI) substrates by magnetron sputtering method. In this way, the best coated thin films have been investigated using spectrophotometry, energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), Xray diffraction (XRD) and Raman spectroscopy.Master Thesis Improvement of Transparent Conductive Hybrid Ito/Ag Electrodes by Electro-Annealing(Izmir Institute of Technology, 2019) Uyanık, Zemzem; Uyanık, Zemzem; Aygün, Gülnur; Aygün Özyüzer, Gülnur; 04.05. Department of Pyhsics; 01. Izmir Institute of Technology; 04. Faculty of ScienceHibrit ITO/Ag/ITO (IAI) ince film tabaka yapılarının optik ve elektriksel performansları, ITO ve Ag katmanı kalınlığının fonksiyonu olarak incelenmiştir. Hibrit IAI ince filmleri borosilikat cam üzerine oda sıcaklığında yüksek vakum altında dc mıknatıssal saçtırma yöntemi ile üretilmiştir. Hibrit yapıdaki ITO, Ag, ITO filmlerin kalınlığı düşük tabaka direncine ve yüksek optik geçirgenliğe sahip olacak şekilde ayarlanmıştır. ITO katmanları arasındaki gömülü metal Ag katmanı, 10 nm ile 25 nm arasında değişen kalınlıklarda kullanılmıştır. IAI tabakası analiz edildikten sonra IAI ince filmlerin kristalliğini iyileştirmek için elektro-tavlama uygulanmıştır ve elektrik akımının IAI ince filmler üzerindeki etkisinin araştırılmasıyla elektronik cihaz ömrünün arttırılması amaçlanmıştır. Elektro-tavlamanın endüstriyel uygulamalar için daha uygun bir teknik olduğu sonucuna varılmıştır. IAI ince filmin yüzey direnci elektro-tavlama işleminden sonra 8.7 Ω/□ olarak bulunmuştur en yüksek geçirgenliğe ise 88.9% da ulaşılmıştır. Hibrit IAI ince filmlerin optoelektronik özellikleri, ITO film kristalliğini etkileyen ara katman olan metal Ag kalınlığına bağlıdır. Hibrit IAI ince filmlerinin yapısal özellikleri, CuK����� radyasyonuna sahip (�����=0.154 nm) X-ışını kırınımı (XRD) (Philips X'Pert Pro) ile tavlama sıcaklığının fonksiyonu olarak karakterize edilmiştir. IAI ince filmlerinin morfolojisi hakkında bilgi taramalı elektron mikroskobu (SEM) ile elde edilmiştir. IAI ince filmin optik geçirgenliği 200-2600 nm dalga boyu aralığına sahip PerkinElmerLambda 950 UV/Vis/NIR Spektrofotometre ile ölçülmüştür. Yüzey direnci ölçümleri için Keithley 2424 kaynak metrisi kullanılarak dört nokta yöntemi uygulanmıştır.Master Thesis Investigation of Sulfurization Temperature Effects on Cu2znsns4 Thin Flims Prepared by Magnetron Sputtering Method on Flexible Titanium Foil Substrates for Thin Flim Solar Cells(Izmir Institute of Technology, 2017) Buldu, Dilara Gökçen; Aygün, Gülnur; Aygün Özyüzer, Gülnur; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThis thesis presents the effect of sulfurization temperature on Cu2ZnSnS4 (CZTS) thin films on flexible titanium (Ti) foil substrates. The CZTS films was produced by using a two-stage method. In the first step, the metallic precursor layers Cu/Sn/Zn/Substrate were deposited on Ti foil substrate by using DC magnetron sputtering method. In the second step, the deposited metal precursors were sulfurized in a graphite box under Argon (Ar) ambient inside a tubular furnace under a definite temperature. To understand the effects of temperature on the formation of the CZTS structure several analyses were performed. Our samples, each with a different sulfurization temperature; ranging from 530 to 580 oC, were carried out and the structural properties of the absorber layer was determined. XRD measurements showed a sharp and intense peak coming from the (112) planes which was a strong evidence for good crystallinity. The intensity of (112) plane became a sharp and intense with increasing sulfurization temperature. Raman spectroscopy of the sulfurized thin films revealed that, the kesterite structure CZTS thin film were obtained with increasing sulfurization temperature. Electron Dispersive Spectroscopy (EDS) was also used for the compositional analysis of the thin films. EDS analysis showed that the films were grown with a Cu-poor Zn-rich composition. From these analyses we conclude that no interface formation occurred between the substrate and the CZTS thin films, hence, a buffer layer was not required. It was also seen that Ti foil was suitable as substrate for the growth of CZTS thin films with desired properties. We also conclude that the sulfurization temperature plays a crucial role for producing good quality CZTS thin films on Ti foil substrate.Master Thesis Temperature Dependence of Resistivity and Hall Coefficient in Cu2znsns4 Absorbers for Thin Film Solar Cells(Izmir Institute of Technology, 2017) Akça, Fatime Gülşah; Aygün, Gülnur; Özyüzer, Lütfi; Aygün Özyüzer, Gülnur; Özyüzer, Lütfi; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technologyenergy is the most powerful clean energy source to act on the current energy needing all over the world. The utilization of green energy systems should be promoted since these energy systems benefit consumers, industry and the environment effectively for the developing countries. This advancement can be solely achieved if renewable energy sources become more accessible. It means that not only cheaper but also handy clean energy systems are needed. In spite of relatively high efficiency obtained by using c-Si, Si solar modules require high budget for manufacturing. The high production cost of c-Si, PV industry is lead to search for cheaper candidate materials like Cu2ZnSnS4 (CZTS) as absorber layer in solar cells. The aim of the thesis is to investigate electrical properties of CZTS p-type intrinsic semiconductor compound on soda lime glass substrates, including the temperature dependent electrical conductivity, carrier concentrations and mobility extracted from Hall Effect measurements. Firstly, the metal precursor films were fabricated in multi-target sputtering system, then they were sulfurized inside the tubular furnace in order to obtain the CZTS compound. X-ray diffraction and Raman spectroscopy measurements revealed the formation of kesterite structure. A good crystallinity and grain compactness of the films were determined by scanning electron microscopy (SEM). Electrical properties were measured by van der Pauw techniques. Hall effect measurements showed the p-type semiconductor behavior for all samples at room temperature. Also, optical properties including absorption coefficient, spectral transmission, and optical band gap were determined to characterize CZTS thin films.Master Thesis Properties of Thin Film Lixlaytio3 Electrolyte for All-Solid State Li-On Batteries(Izmir Institute of Technology, 2016) Gülen, Sena; Aygün, Gülnur; Aygün Özyüzer, Gülnur; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyOne of the requirements of daily life, the most preferred rechargeable batteries are Li-ion batteries because of high energy, long life cycle and eco-friendly properties. Having high energy density, no memory effect and slow energy losses, these batteries have applications in portable electronic devices, power source for space vehicles, electric cars etc. Furthermore, there is a strong interest in all solid-state rechargeable lithium-ion battery research, because these batteries will replace the conventional liquid electrolyte Li-ion batteries due to use of non-combustible inorganic solid electrolyte, which has high safety and reliability. While the bulk ionic conductivity of La0.5Li0.5TiO3 (LLTO) produced by solid-state reaction is 10-3 S/cm, the total ionic conductivity of LLTO is 10-5 S/cm. Another way to increase ionic property is to dope the solid electrolyte with transition metals. The substitution of transition metal leads to decrease of the lattice parameter because of reduced average ionic radius. This causes increase of Li-ion content and also ionic conductivity. In this study, initially pure and Al doped targets were fabricated by using solid-state reaction after that the available targets are placed to the sputtering gun. When the all optimizations of the system were completed, pure and Al doped LLTO thin films were deposited by RF (radio frequency) magnetron sputtering technique on ITO coated soda lime glass substrates. While the thin film was been deposited, the substrate was heated at approximately 220 oC. For ionic conductivity measurement of the Al doped LLTO electrolyte, small circular Al contact regions were created on Al doped LLTO thin films by thermal evaporation system. Afterword the impedance spectra of the sandwich structure in a frequency range of 1 Hz - 200 MHz was recorded by using probe station. Thickness, the crystal structure, optical transmission, chemical compositions, surfaces and porosity of the thin films are investigated by surface profilometer, XRD, UV-Visible Spectroscopy, XPS, and Raman Spectroscopy respectively.Master Thesis Fabrication and Characterization of Superconducting Bi2212 Bolometer for the Detection of Thz Waves(Izmir Institute of Technology, 2014) Kurt, Metin; Özyüzer, Lütfi; Aygün, Gülnur; Kurt, Metin; Aygün Özyüzer, Gülnur; Özyüzer, Lütfi; 01. Izmir Institute of Technology; 04.05. Department of Pyhsics; 04. Faculty of ScienceSince terahertz (THz) waves can pass through materials like clothing, plastic, wood, ceramic, leather and without harm to the body, it can be used for characterization, detection and 3D imaging of these materials. THz application area expands day by day such as high-speed wireless communications, medical imaging, security in airports and shopping centres and detection of chemical and biological materials. Rapidly increasing applications of the electromagnetic waves (EM) in the under developed terahertz frequency (0.1-10 THz) range requires a well understandings of efficient terahertz wave detection. An intense, coherent and continuous electromagnetic wave source is obtained by High-Tc superconductor Bi2Sr2CaCu2O8+δ (Bi2212) single crystal. At the same time Bi2212 single crystal can detect THz waves in suitable conditions. Nowadays, different types of bolometers are used for detection of THz waves. But they have many limitations like slow response time which is the most significant problem and costly cryogenic spending. In this study, single crystal of Bi2212 is cleaved to layer by layer by scotch tape until the necessary is reached thickness. Afterwards, it is pasted on a sapphire substrate and the scotch tape is etched with the aid of chloroform solution and ultrasonic cleaner. After the crystal fabrication, the exact thickness of the crystal were obtained using atomic force microscopy. Then, the samples were annealed at 400oC for 1 hour in order to adjust the oxygen doping level and then deposited with 150 nm Au layer by thermal evaporation. Afterwards they were annealed again at 425oC for 30 minutes to decrease the contact resistivity. After clean room process, our log-periodic antenna design was formed on the crystal by using e-beam lithography and Ar-ion beam etching step by step. Finally, four probe wires were connected to the two contact paths and log-periodic antenna by silver epoxy. The temperature dependence of a-b axis resistivity (R-T) for Bi2212 single crystals were performed.Master Thesis Growth of Cu2znsns4 Absorber Layer on Flexible Metallic Substrates for Thin Film Solar Cell Applications(Izmir Institute of Technology, 2014) Yazıcı, Şebnem; Aygün, Gülnur; Aygün Özyüzer, Gülnur; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThis thesis presents the results of the fabrication and investigation of Cu2ZnSnS4 (CZTS) p-type semiconducting compound on rigid and flexible substrates, such as soda lime glass, ceramics and metallic foil substrates. The CZTS material was obtained by using a two-stage method. In the first stage, the metallic precursor was deposited by using DC magnetron sputtering technique then, the sulfurization process followed it. The particular emphasis has been placed on the distinctive substrate behavior in the growth procedure, including the microstructural characterization of the CZTS structure and the investigations of the back contact/CZTS interface. Additionally, the effect of the high temperature sulfur treatment on the formation mechanism of CZTS structure inves-tigated elaborately. Moreover, electrical properties including the temperature dependent electrical conductivity, carrier concentrations and mobility extracted from Hall Effect measurements, and optical properties including absorption coefficient, spectral transmis-sion, and optical band gap have been determined to characterize CZTS thin films. Raman spectroscopy and XPS analysis of the sulfurized thin films revealed that, except for the presence of Sn-based secondary phases, nearly pure CZTS thin films were obtained. Additionally, the intense and sharp XRD diffraction peak from the (112) plane provided evidence of good crystallinity. EDS analysis indicated sufficient sulfur content but poor Zn atomic weight percentage in the films. Absorption and band-gap energy analysis were carried out to confirm the suitability of CZTS thin films for the usage as the absorber layer in solar cell applications. Finally, Hall Effect measurements showed the p-type semiconductor behavior of the CZTS samples. We aimed to investi-gate the role of the flexible titanium and molybdenum foil substrates in the growth mechanism of CZTS thin films. The crack formation in the CZTS layer on the Mo foils were detected, which is an indication of the incompatible thermal expansion coefficient of Mo with the CZTS structure.Master Thesis Co Gas Sensor Applications of Fe Doped Calix[4] Arene Molecules(Izmir Institute of Technology, 2013) Özbek, Cebrail; Aygün, Gülnur; Aygün Özyüzer, Gülnur; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyInvisible and odourless carbon monoxide (CO) is one of the most toxic gas for respiratory systems. Therefore, the concentration level of carbon monoxide in the environment is extremely vital. In this thesis study, Calixarene molecules have been synthesized and the carbon monoxide selectivity and sensitivity of bare and iron doped calixarene molecules were measured by quartz crystal microbalance QCM technique and interdigitated electrodes with 3 ï m spacing. Calixarenes are promising compounds for sensing studies due to the well-designed cyclic structure, easily derivatization at both p- position of phenolic ring (upper rim) and phenolic-O (lower rim) as well as having diversely cavities which are a straightforward platform to form complex with molecules and ions. Quartz Crystal Microbalance is a powerful technique for nano scale determining the sorption properties of materials. According to Sauerbrey relation, the mass change on quartz crystal electrode cause a certain shift in the resonant frequency of vibrating crystal oscillator. This shift can be monitored using QCM method. In this study, a computer controlled QCM measurement system was developed for toxic gas detection. Iron doped calixarene based sensors were fabricated using drop-casting method on an AT-cut QCM gold electrode and interdigitated gold electrodes. The sensitivity and reproducible detection performances of prepared calixarene-iron doped calixarene thin films were measured under exposure of varying carbon monoxide for nitrogen and dry air used as desorption gas, respectively. The analysis of carbon monoxide sensitivity of iron doped calixarene is a new study for literature. This thesis study will guide future studies on this topic.Master Thesis Production and Characterization of Hfo2 High-K Dielectric Layers by Sputtering Technique(Izmir Institute of Technology, 2010) Cantaş, Ayten; Aygün, Gülnur; Aygün Özyüzer, Gülnur; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyHfO2 thin films have been deposited on Si by in-situ spectroscopic ellipsometric sputtering technique. The grown films have been examined by various diagnostic and analysis techniques (Spectroscopic Ellipsometer (SE), FTIR, XRD, XPS). The optimization of in-situ SE sputtering system has been processed according to the measurement results of the grown HfO2 films. From the measurements simultaneously taken by using SE, film thickness, refractive index and real part of dielectric function have been examined as a function of deposition time. It was found that the thickness changes linearly with deposition time. The formation of undesired SiO2 interfacial layer has been tried to be prevented and searched by using FTIR. MOS capacitors from the oxides having best qualities have been produced to obtain electrical properties of grown oxides. The process of production-characterization and development of oxidation conditions have been achieved and the following results have been obtained: (a) Low O2/Ar gas ratio and 30-40 watt power have been considered as the most convenient oxidation parameters. (b) The formation of SiO2 interface has not been prevented but formation of HfxSiOy has been obtained. (c) The refractive index value (n.2.1) of bulk HfO2 at 632 nm has been obtained.