Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Manufacturing and Characterization of Perovskite Thin Films Using Novel Methods(Izmir Institute of Technology, 2020) Bıyıklı, Ozan; Sarı, Emre; Tekin, Hüseyin CumhurPerovskite photovoltaics is a promising technology due to its low-cost fabrication and high efficiency. Since their first demonstration in 2009, efficiencies of perovskite solar cells (PSCs) increased unprecedently fast from 3.81% to 25.2% in 10 years. The most common method for the deposition of the absorber layer of the perovskite solar cells is the spin-coating method, which is not a scalable method, and this method is an obstacle to their commercialization. Efficiencies obtained with scalable methods are currently lower than that of the spin-coating method. In this thesis, among the scalable deposition methods, a novel ultrasonic spray-coating was used by adding antisolvent vapor to the system. The antisolvent quenching technique, that is commonly used to improve the crystalline quality of the film by spin-coating was successfully adapted for ultrasonic spray coating. The interaction between diethyl ether (DE) vapor, which is used as an antisolvent, and MAPb(I(3-x)Brx)3 precursor solution (where the solvent is DMF:DMSO, 4:1) was utilized to improve the crystalline quality of the perovskite film. As a result of this interaction, the intermediate phase was observed. The transition to the intermediate phase is supported by data from characterization methods such as optical microscopy, scanning electron microscopy (SEM), X-Ray diffraction (XRD), and current-voltage measurement. Furthermore, n-i-p devices with the FTO/c-TiO2/m-TiO2/MAPb(I(1-x)Brx)3/Spiro-OMeTAD architecture were produced with different antisolvent vapors and their efficiencies was compared. It was observed that devices using DE vapor reach higher efficiencies than devices without any antisolvent vapor.Master Thesis Anti-Reflective and Optical Transparent Coatings for Thin Film Solar Cells and Glasses(Izmir Institute of Technology, 2020) Kamolov, Shukrullo; Özyüzer, Lütfi; Özyüzer, LütfiAntireflective coatings in some implementation necessary for the decreasing surface reflection, but in some applications also for increasing transmittance. Incident radiation on the surface of the optical material is divided into transmitted, reflected, scattered, and absorbed proportions, and the proportion of current energy that deployed among them is defined by RI (refraction indices). Solar panels made from crystalline or polycrystalline silicon, but another type of solar panel is a thin-film solar panel. Thin-film technology has several advantages, such as low material consumption, which leads to cost savings to production, the ability to absorb diffused solar radiation, a relatively high efficiency (up to 20%), long service life (efficiency decreases by 10-15% of the initial efficiency). For all types of photovoltaic devices, energy loss is an important issue. Single-layer and two-layer antireflection coatings with a low refractive index, coated and uncoated (SiO2) thin-film with the sol-gel method were prepared and compared in terms of performance and continuity. The photocatalytic performance of (SiO2) thin films in 1, 2, 3, 4, 5 and 24 hours was defined with methylene blue dye solution (20 mL) under UV source and was illuminated by it. The I-V characteristics curve of solar cells for small and large area was learned and increasing efficiency was observed. Adhesion tests in this study was applied by tape tests on substrates of glass. As a result, the field tests of small and large area glasses coated solar panels were realized, the low reflectance and high efficiency were obtained.Master Thesis Efficiency Studies of Cu2znsns2 Thin Film Solar Cell(Izmir Institute of Technology, 2018) Meriç, Ece; Özyüzer, Lütfi; Aral, GürcanCu2ZnSnS4 (CZTS) is a promising candidate as an absorber layer for thin film solar cells due to not only its low cost but also nontoxic properties contrary to alternative materials such as CdTe and Cu(In,Ge)Se2 (CIGS). Recently, CZTS and similar chalcogenides have attracted remarkable attention because of their suitable properties. In my thesis; I studied the efficiency of Cu2ZnSnS4 thin film solar cells for various stoichiometric cases. Besides, the effect of back contact, buffer layer thickness and sulfurization time were investigated. CZTS thin films were fabricated by DC magnetron sputtering method on Molybdenum (Mo) coated Soda Lime Glass (SLG) and Ti foil substrates. Cu, Sn, Zn, Cu layers were, respectively, deposited on the substrates, and then sulfurization process was followed as the second step in the growth process to obtain a desirable CZTS formation. The as grown CZTS structure was investigated using Raman and X-Ray Diffraction (XRD) spectroscopies. Scanning electron microscopy (SEM) was used to investigate the surface morphology of the films. Energy dispersive spectroscopy (EDS) was used to define the chemical structure of the surface of the films. Next, a CdS buffer layer was deposited on CZTS absorber layer using CBD method at 85oC for varying times (60, 75 and 90 min). Then, ZnO and Al doped ZnO (AZO) layers were deposited on CdS. J-V curves were obtained for SLG/Mo/CZTS/CdS/ZnO/AZO solar cell structure. The photovoltaic characteristic of solar cells was studied and their dependence on CdS deposition time were found. Among all the device we produced, the highest efficiency was obtained for the device with the lowest CdS deposition time. In addition; effect of sulfurization time on the solar cell conversion efficiency was studied.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 Özyüzer, GülnurThis 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 Investigation of the Electronic Structure of the Ruthenium Dyes Used in Solar Cells by Combining Hartree-Fock Theory With the Quantum Monte Carlo Technique(Izmir Institute of Technology, 2015) Berkman, Irmak Çağlar; Bulut, NejatThe Haldane-Anderson model is constructed to describe the electronic properties of a system where a transition-metal impurity atom is added into a semiconductor host material. The electric and magnetic properties of the ruthenium-based dyes are investigated by using Haldane-Anderson model in this study. Because ruthenium-based dyes are semiconductor and ruthenium atom is a transition metal and its 4d orbitals are considered as impurities for dye molecules. Density Functional Theory (DFT) and Hartree-Fock Theory (HF) was used to obtain the Haldane-Anderson model parameters of the ruthenium-based dyes. Multi-orbital Hirsch-Fye Quantum Monte Carlo (HFQMC) algorithm was used to investigate effect of onsite Coulomb interactions of impurity 4d orbitals. Firstly, the Anderson model parameters are calculated by using Hartree-Fock and Density Functional Theory. After that, the occupation numbers of 4d orbitals and the all orbital occupancies of the dye molecules are obtained by using the Hirsch-Fye Quantum Monte Carlo algorithm and the magnetization of 4d orbitals are calculated. Finally, physical meaning of our results are discussed.Master Thesis Hydrogen Production From Water Using Solar Cells Powered Nafion Membrane Electrolyzers(Izmir Institute of Technology, 2007) Aksakal, Ziya Can; Şeker, ErolThe aims of this thesis are two folds; to construct single and multi cell proton exchange membrane electrolyzers and to evaluate the performance of these electrolyzers powered by solar panels on Iztech campus. All other parts, except the purchased membrane electrode assemblies, were designed, manufactured and assembled in our labs.In the construction of single and multiple cell proton exchange membrane electrolyzers, Nafion-117 based membrane electrode assemblies were used. Graphite bipolar plates, end plates, current collectors and gaskets were machined on institute.s computer numerical controlled lathe. In the first stage, a single cell electrolyzer with 20cm2 available electrolysis surface areas was examined with a direct current power supply by varying current density (0-500mAmp/cm2), water flow rate (0.05 to 0.5g/cm2min), and temperature (30-50oC). It was found that average cell voltage decreases from 2.18V at 30oC to 1.97V at 50oC when the current density is 500mAmp/cm2. Since cell gaskets were softened and stick to the membrane above 50oC of operating temperature, temperatures higher than 50 oC could not be tested. Five cell electrolyzer stack was constructed according to the final single cell design. It was observed that the stack could generate 388ml/min hydrogen under 500mAmp/cm2 and 10.09V of the operating condition at 41.5oC. When the stack was directly coupled with a solar array, voltage of the stack was found to vary from 7.5V to 12.5V and the current density changes from 0 to 1000mAmp/cm2 with respect to the solar radiance of the day. This results in a voltage efficiency ranging from 98.7% to 60% based on the higher heating value of hydrogen. Electrolyzer powered by solar cells can generate up to 750ml/min hydrogen and total daily production could be as high as 350L per day but weather condition greatly affects the production rate. Together with the losses inside the electrolyzer, another important energy loss is due to voltage mismatches between PV array and electrolyzer in low solar irradiance during sunrise and sunset.Master Thesis The Effects of Native and Light Induced Defects in the Optical and Electronic Properties of Hydrogenated Amorphous Silicon Germanium (a-Sige:h) Alloy Thin Films(Izmir Institute of Technology, 2005) Dönertaş Yavaş, Medine Elif; Güneş, MehmetHydrogenated amorphous silicon-germanium alloy thin films (a-SiGe:H) of various germanium concentrations, are potential candidates meeting the requirements of high efficiency stacked solar cells and optoelectronic devices where a certain bandgap is necessary. In this thesis to obtain reliable information about the native and light induced defect states present in a-SiGe:H alloy thin films of various germanium concentrations SSPC, DBP, transmission spectroscopy and PDS techniques have been used. A procedure based on Ritter Weiser optical formulation has been applied to calculate fringe free absolute absorption coefficient spectra of a-SiGe:H alloy thin films of various Ge% from the yield DBP and simultaneously measured transmission signals for the first time. The results have been compared with those independently measured by PDS method.In the annealed state the effects of native defect states in a-SiGe:H alloy thin films of various Ge% have been investigated. For the a-SiGe:H alloy films with Ge concentration in the range of 10% to 30%, hntn-products for the photogenerated free electrons is the highest, therefore they serve as the best photoconductive absorber layer in the multijunction solar cells. The effect of Ge content in amorphous silicon network clearly indicates a systematic decrease in the bandgap with increasing Ge content. The E0v values are almost constant around 55meV for alloying up to 40% Ge. Finally the changes in the defect density present in the bandgap of alloy films are inferred from the α(1.0eV) measured by both PDS and low bias light DBP spectrum. The difference between PDS and low bias DBP spectra is attributed to the underlying physics of these methods. The best film with lowest defect density can be prepared with alloying Ge in the range from 10% to 40% Ge.In the light soaked state, samples were left under white light illumination (15 suns) for determined time intervals. SSPC measurements indicate that all samples exhibit certain degree of degradation in the magnitude of sph and hntn products. The rate of α(1.0 eV) decreases as Ge% increases in the light soaked state. Higher Ge content films (50%, 75%) show almost no degradation in sub-bandgap absorption. As the degradation slope of α(hν) and 1/η nτn product are not same for all samples it can be inferred that subgap absorption and photoconductivity measurements are not controlled by the same set of defects present in the bandgap.