Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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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 Ionic Conductivity of Li0.5la0.5ti1-Xalxo3 Electrolytelayer for Thin Film Batteries(Izmir Institute of Technology, 2016) Ulusoy, Seda; Özyüzer, Lütfi; Aral, GürcanIn this study, crystalline lithium lanthanum titanium (aluminum) oxide Li0.5La0.5Ti1-xAlxO3 (LLTO) powder targets with different Aluminum (x) content were prepared by conventional solid state reactions as Li0.5La0.5TiO3, Li0.5La0.5Ti0.99Al0.01O3, Li0.5La0.5Ti0.95Al0.05O3, Li0.5La0.5Ti0.90Al0.10O3 and Li0.5La0.5Ti0.85Al0.15O3 compositions. Then, after a couple of calcination processes with regrinding of the prepared stoichiometric powder batch, it is placed into Cu-base plate to be pressed in order to provide a compact, dense and smooth target surface for the thin film deposition. For the thin film fabrication, radio frequency (RF) magnetron sputtering technique is used to sputter the dielectric target. Thin films were deposited on soda-lime glass (SLG) and 256 nm thick indium tin oxide (ITO) layer grown on soda-lime glass (SLG) substrates. For the electrical measurements of LLTO thin film, it was fundamental to have ITO as conducting layer electrode. Targets with various Al (x) compositions were deposited for the investigation of Ti substitution with Al on structural and electrical properties. Besides, crystalline structure of the targets was characterized by X-ray powder diffraction (XRPD) and Raman Spectroscopy analysis while structural, morphological and compositional properties of the thin films were determined by x-ray diffraction (XRD), scanning electron microscope (SEM) and x-ray photoelectron spectroscopy (XPS) respectively. Moreover, in order to understand the effect of Al doping on ionic conductivity, electrical measurements were performed at room temperature by AC impedance spectroscopy forming ITO/LLTO/Al capacitor like structure. Maximum ionic conductivity result is obtained for Li0.5La0.5Ti0.95Al0.05O3 thin film composition. Also, temperature dependent ionic conductivity measurements were performed from 298 K to 373 K to evaluate activation energy for the Li-ion conduction. Keywords: Ionic conductivity, Li0.5La0.5Ti1-xAlxO3, electrolyte, thin film, activation energy, RF magnetron sputteringMaster Thesis Indium Tin Oxide (ito) Coating on Cylindricalsurfaces: Electrical and Structural Characterization(Izmir Institute of Technology, 2015) Arslan, Halil; Aral, Gürcan; Özyüzer, Lütfi; Özyüzer, Lütfi; Aral, GürcanOptical transparent conductive oxides (TCOs) which were discovered in the first quarter of twentieth century, and which belong to the class of semiconductor elements, are the constituent of today’s and future technology thanks to the high optical transparency ( ≥ % 85) they have in the visible region (390- 700 nm), and to the low electrical resistivity they have (10-4 ohm.cm). One of the most common usage of optical transparent conductive oxides; which have a quite extensive application area from transistors to solar panels, from flexible screens to OLEDs; is the textile materials known as smart clothes. The use of TCOs in textile materials, generally occurs by means of electrochromic structures that have the feature of changing color. In the most general sense, electrochromic structures can be defined as the materials that change their colors, which they gain thanks to reduction and oxidation reactions under a low potential difference of 1.5 – 5V, as a transition from one color state to another or from colorless state to color state. Even though they differ according to their area of utilization, electrochromic structures are generally consisted of seven layers as; Surface / conductive thin film (TCO) / Electrolyte film / Ionic conductive layer / Opposite electrolyte film / Conductive thin film (TCO) / and Surface. Electrical conductor and optical transparent indium doped tin oxide (ITO) film that are of vital importance in electrochromic fiber structures, were deposited on the fiber surface along with the specially-designed magnetic sputter in order to coat the cylindrical surfaces within the scope of the thesis. Film deposition was repeated by replacing the ionizing gas (Ar) flow rate and the energy applied. While the structural characterization of thin films was carried out by means of optical microscope and scanning electron microscope (SEM), electrical characterization of deposited thin film, was carried out by a multi-meter (Ohm meter). In addition, the thickness of thin film that was magnified on the surface of the fiber, was calculated by SEM particularly, and also by different methods. As a result of the analyzes carried out, it was observed that ~ 40 sccm ionizing gas flow rate, 90 W applied energy, and 119 cm/min fiber feed rate increased the quality of the thin film acquired.