WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 24Citation - Scopus: 23Photovoltaic Performance of Magnetron Sputtered Antimony Selenide Thin Film Solar Cells Buffered by Cadmium Sulfide and Cadmium Sulfide /Zinc Sulfide(Elsevier B.V., 2023) Cantas, A.; Gundogan, S.H.; Turkoglu, F.; Koseoglu, H.; Aygun, G.; Ozyuzer, L.Antimony selenide (Sb2Se3)-based thin-film solar cells have recently attracted worldwide attention as an abundant, low-cost, and efficient photovoltaic technology. The highest efficiencies recorded for Sb2Se3 solar cells have been obtained using cadmium sulfide (CdS) as a buffer layer. The Cd-included hybrid buffer layers could be one option to increase device efficiency through more effective usage of light. Therefore, in this work, the effect of single CdS and hybrid CdS/zinc sulfide (ZnS) buffer layers on the photovoltaic performance of Sb2Se3 thin-film solar cells has been investigated in detail. Sb2Se3 thin films have been deposited on molybdenum (Mo)-coated soda-lime glass (SLG) substrates by radio frequency magnetron sputtering technique followed by a post-heat treatment process. The morphological, and structural properties of Sb2Se3 thin films have been investigated by X-Ray Diffraction and Scanning Electron Microscopy. To compare the device performances of single CdS and hybrid CdS/ZnS buffered Sb2Se3 thin-film solar cells, SLG/Mo/Sb2Se3/CdS/ZnS/indium tin oxide (ITO) and SLG/Mo/Sb2Se3/CdS/ITO structures have been fabricated. The findings of this study have revealed a reduction in solar cells’ performance from η=3.93% for CdS buffer to η=0.13% for CdS/ZnS hybrid buffer. The change in the solar cell performance using the CdS/ZnS hybrid buffer has been discussed in detail. © 2023 Elsevier B.V.Article Citation - WoS: 21Citation - Scopus: 24Effect of Defects and Secondary Phases in Cu2znsns4 Absorber Material on the Performance of Zn(o,s) Buffered Devices(Elsevier Ltd., 2019) Türkoğlu, Fulya; Köseoğlu, Hasan; Cantaş, Ayten; Akça, Fatime Gülşah; Meriç, Ece; Buldu, Dilara Gökçen; Aygün, GülnurCopper zinc fin sulfide (CZTS) absorber layer attracts so much attention in photovoltaic industry since it contains earth abundant, low cost and non-toxic elements contrary to other chalcogenide based solar cells. In the present work, CZTS absorber layers were prepared following a two-stage process: firstly, a stack of metal precursors (Copper (Cu)/Tin (Sn)/Zinc (Zn)/Copper (Cu)) were deposited on molybdenum (Mo) substrate by magnetron sputtering, then this stack was annealed under S atmosphere inside a tubular furnace. CZTS thin films were investigated using energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy and Raman spectroscopy. The effect of sulfurization time and the thickness of top and bottom Cu layer in precursors on the properties of CZTS thin films were investigated. The importance of Cu thickness adjacent to Sn to avoid detrimental phases was addressed. The significance of sulfurization time to restrict the Sn and Zn losses, formation of oxides such as fin dioxide and zinc oxide, and formation of molybdenum disulfide and voids between Mo/CZTS interface was also addressed. Moreover, cadmium sulfide buffer layer, which is conventionally used in CZTS solar cells, is replaced by an environmentally friendly alternative zinc oxysulfide buffer layer.Article Citation - WoS: 33Citation - Scopus: 33Characterization of Thin Film Li0.5la0.5ti1-Xalxo3 Electrolyte for All-Solid Li-Ion Batteries(Elsevier, 2018) Ulusoy, Seda; Gülen, Sena; Aygün, Gülnur; Özyüzer, Lütfi; Özdemir, MehtapSince addition of Al in Li0.5La0.5TiO3 has enhanced ionic conductivity in bulk materials, it is important to apply this material on all solid state thin film batteries. Because some of the good ionic conductors such as Lithium Phosphorus Oxynitride (LiPON) are sensitive to oxygen and moisture and their application is limited, so amorphous Li0.5La0.5Ti1−xAlxO3 (LLTAlO) is a most promising candidate because of its stability. In this study, the crystalline LLTAlO targets were prepared changing the amount of x content by conventional solid state reactions. Using these targets, lithium lanthanum titanium oxide (LLTO) thin film electrolytes were deposited on ITO/SLG substrates by radio frequency magnetron sputtering system in Ar atmosphere. The structural and compositional properties of targets and thin films were characterized by SEM, XRD, Raman spectroscopy and XPS. It was found that all targets are crystalline while the thin films are amorphous. To understand the effect of Al doping on ionic conductivity, electrical measurements were done at room temperature by AC impedance spectroscopy forming ITO/LLTAlO/Al structure like capacitor. Highest ionic conductivity result, 0.96 × 10−6 S·cm−1, is obtained from the nominal thin film composition of Li0.5La0.5Ti1−xAlxO3 (x = 0.05) at room temperature measurements. Heat treatment is also conducted to investigate to understand its effect on ionic conductivity and the structure of the thin films. It is found that ionic conductivity enhances with annealing. Also, temperature dependent ionic conductivity measurements from 298 K to 385 K are taken in order to evaluate activation energy for Li-ion conduction.Article Citation - WoS: 35Citation - Scopus: 38Influence of Sulfurization Temperature on Cu2znsns4 Absorber Layer on Flexible Titanium Substrates for Thin Film Solar Cells(IOP Publishing Ltd., 2018) Buldu, Dilara Gökçen; Cantaş, Ayten; Türkoğlu, Fulya; Akça, Fatime Gülşah; Meriç, Ece; Özdemir, Mehtap; Tarhan, Enver; Özyüzer, Lütfi; Aygün, GülnurIn this study, the effect of sulfurization temperature on the morphology, composition and structure of Cu2ZnSnS4 (CZTS) thin films grown on titanium (Ti) substrates has been investigated. Since Ti foils are flexible, they were preferred as a substrate. As a result of their flexibility, they allow large area manufacturing and roll-to-roll processes. To understand the effects of sulfurization temperature on the CZTS formation on Ti foils, CZTS films fabricated with various sulfurization temperatures were investigated with several analyses including x-ray diffraction (XRD), scanning electron microscopy (SEM), x-ray photoelectron spectroscopy and Raman scattering. XRD measurements showed a sharp and intense peak coming from the (112) planes of the kesterite type lattice structure (KS), which is strong evidence for good crystallinity. The surface morphologies of our thin films were investigated using SEM. Electron dispersive spectroscopy was also used for the compositional analysis of the thin films. According to these analysis, it is observed that Ti foils were suitable as substrates for the growth of CZTS thin films with desired properties and the sulfurization temperature plays a crucial role for producing good quality CZTS thin films on Ti foil substrates.Article Citation - WoS: 42Citation - Scopus: 46Importance of Cds Buffer Layer Thickness on Cu2znsns4-Based Solar Cell Efficiency(IOP Publishing Ltd., 2018) Cantaş, Ayten; Türkoğlu, Fulya; Meriç, Ece; Akça, Fatime Gülşah; Özdemir, Mehtap; Tarhan, Enver; Özyüzer, Lütfi; Özyüzer, Gülnur AygünCu2ZnSnS4 (CZTS) thin films were grown on Mo-coated soda lime glass (SLG) substrates by the sulfurization of DC magnetron-sputtered Zn, Sn and Cu metallic precursors under a sulfur atmosphere at 550 °C for 45 min. Understanding the composition and structure of the CZTS absorber layer is necessary to obtain efficient solar cells. With this aim, x-ray diffractometry, Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy and x-ray photoelectron spectroscopy were used to investigate the CZTS absorber layers. CZTS absorber films were obtained and found to be Cu-poor and Zn-rich in composition, which are both qualities desired for efficient solar cells. CdS was used as a buffer layer and was grown by the chemical bath deposition technique. The optical properties of CdS films on SLG were searched for using a spectroscopic ellipsometer and the results revealed that the bandgap increases with film thickness increment. CZTS-based solar cells with different CdS buffer layer thicknesses were prepared using a SLG/Mo/CZTS/CdS/ZnO/AZO solar cell configuration. The influence of the CdS buffer layer thickness on the performance of the CZTS solar cells was investigated. Device analysis showed that electrical characteristics of solar cells strongly depend on the buffer layer's thickness. Highly pronounced changes in V OC, fill factor and J SC parameters, which are the main efficiency limiting factors, with changing buffer layer thicknesses were observed. Our experiments confirmed that decreasing the CdS thickness improved the efficiency of CZTS solar cells down to the lowest thickness limit.Article Citation - WoS: 21Citation - Scopus: 22Investigation of Electron Beam Lithography Effects on Metal-Insulator Transition Behavior of Vanadium Dioxide(IOP Publishing Ltd., 2017) Yüce, Hürriyet; Alaboz, Hakan; Demirhan, Yasemin; Özdemir, M.; Özyüzer, Lütfi; Aygün, GülnurVanadium dioxide (VO2) shows metal-insulator phase transition at nearly 68 °C. This metal-insulator transition (MIT) in VO2 leads to a significant change in near-infrared transmittance and an abrupt change in the resistivity of VO2. Due to these characteristics, VO2 plays an important role on optic and electronic devices, such as thermochromic windows, meta-materials with tunable frequency, uncooled bolometers and switching devices. In this work, VO2 thin films were fabricated by reactive direct current magnetron sputtering in O2/Ar atmosphere on sapphire substrates without any further post annealing processes. The effect of sputtering parameters on optical characteristics and structural properties of grown thin films was investigated by SEM, XRD, Raman and UV/VIS spectrophotometer measurements. Patterning process of VO2 thin films was realized by e-beam lithography technique to monitor the temperature dependent electrical characterization. Electrical properties of VO2 samples were characterized using microprobe station in a vacuum system. MIT with hysteresis behavior was observed for the unpatterned square samples at around 68 °C. By four orders of magnitude of resistivity change was measured for the deposited VO2 thin films at transition temperature. After e-beam lithography process, substantial results in patterned VO2 thin films were observed. In this stage, for patterned VO2 thin films as stripes, the change in resistivity of VO2 was reduced by a factor of 10. As a consequence of electrical resistivity measurements, MIT temperature was shifted from 68 °C to 50 °C. The influence of e-beam process on the properties of VO2 thin films and the mechanism of the effects are discussed. The presented results contribute to the achievement of VO2 based thermochromic windows and bolometer applications.Article Citation - WoS: 7Citation - Scopus: 7Comparative Study of Annealing and Gold Dopant Effect on Dc Sputtered Vanadium Oxide Films for Bolometer Applications(Springer Verlag, 2017) Alaboz, Hakan; Demirhan, Yasemin; Yüce, Hürriyet; Aygün, Gülnur; Özyüzer, LütfiVanadium oxide (VOx) thin film has been widely used for IR detectors and it is one of the promising materials for THz detectors due to its high temperature coefficient of resistance (TCR) values. VOx films with proper TCR values have also high resistance and it restricts bolometer performance especially for uncooled bolometers. To overcome this problem, deposition at elevated temperatures or annealing approach has been accepted and used but gold co-deposition approach has been proposed recently. In this study, vanadium oxide films were fabricated on high resistivity silicon substrates by reactive direct current magnetron sputtering in different O2/Ar atmosphere at room temperature. We investigated influence of oxygen partial pressure during deposition process and fabricated VOx thin films with sufficient TCR values for bolometer applications. In order to decrease resistivity of the deposited films, post annealing and gold doping approaches were performed separately. Effect of both post annealing process and gold doping process on structural and electrical properties of VOx thin films deposited at room temperature were investigated and detailed comparison between these methods were presented. We obtained the best possible approach to obtain optimum conditions for the highly reproducible VOx thin films which have the best resistivity and suitable TCR value for bolometer applications.Article Citation - WoS: 10Citation - Scopus: 10In-Situ Spectroscopic Ellipsometry and Structural Study of Hfo2 Thin Films Deposited by Radio Frequency Magnetron Sputtering(American Institute of Physics, 2014) Cantaş, Ayten; Özyüzer, Gülnur Aygün; Basa, Deepak KumarWe have investigated the reduction of unwanted interfacial SiO2 layer at HfO2/Si interface brought about by the deposition of thin Hf metal buffer layer on Si substrate prior to the deposition of HfO2 thin films for possible direct contact between HfO2 thin film and Si substrate, necessary for the future generation devices based on high-κ HfO2 gate dielectrics. Reactive rf magnetron sputtering system along with the attached in-situ spectroscopic ellipsometry (SE) was used to predeposit Hf metal buffer layer as well as to grow HfO2 thin films and also to undertake the in-situ characterization of the high-κ HfO2 thin films deposited on n-type 〈100〉 crystalline silicon substrate. The formation of the unwanted interfacial SiO2 layer and its reduction due to the predeposited Hf metal buffer layer as well as the depth profiling and also structure of HfO2 thin films were investigated by in-situ SE, Fourier Transform Infrared spectroscopy, and Grazing Incidence X-ray Diffraction. The study demonstrates that the predeposited Hf metal buffer layer has played a crucial role in eliminating the formation of unwanted interfacial layer and that the deposited high-κ HfO2 thin films are crystalline although they were deposited at room temperature.Article Citation - WoS: 10Citation - Scopus: 10Morphology, Order, Light Transmittance, and Water Vapor Permeability of Aluminum-Coated Polypropylene Zeolite Composite Films(John Wiley and Sons Inc., 2011) Balköse, Devrim; Oğuz, Kaan; Özyüzer, Lütfi; Tarı, Süleyman; Arkış, Esen; Özmıhçı Ömürlü, FilizIn this study, the polypropylene-zeolite composite films having 2-6 wt % natural zeolite were coated with a thin film of aluminum (Al) by magnetron sputtering, and the contribution of the Al coating on film properties was investigated. The samples were characterized by EDX, X-ray diffraction, SEM, AFM, UV-visible spectroscopy, and water vapor permeation analyses. The surface of the films coated with a smooth Al film having 98-131 nm thickness. EDX revealed that Al percentage on the surface appeared to be as 8-10 wt % indicating contribution of polymer surface under Al film to analysis. XRD analysis showed that the grain size of Al at the surface was 22-29 nm. The surface roughness increased after Al-coating process. The transmission of coated films was very low for both UV and visible regions of the light spectrum. Permeation analysis indicated that water vapor permeation was lower for Al-coated material.Article Citation - WoS: 3Citation - Scopus: 3Mgb2 Superconducting Thin Films Grown by Magnetron Sputtering(National Institute of Optoelectronics, 2007) Ulucan, Savaş; Özyüzer, Lütfi; Okur, SalihIn this study, we report the growth and properties of MgB2 thin films on polycrystalline Al2O3 substrates. A composite MgB2 target was produced by MgB2 and Mg powder mixing, using a hot pressing technique. MgB2 thin films were grown on Al 2O3 substrates by d.c. magnetron sputtering, without heating the substrate. To enhance the superconducting properties of the as-grown films and to increase the crystal quality, an ex-situ anneal process was applied. The crystal structure of the thin films was determined by X-ray diffraction. The resistivity versus temperature of the deposited MgB2 thin films was studied to examine the transition temperatures of the films under various magnetic fields. The effects of the annealing temperature and annealing time on the electrical properties of MgB2 thin films are revealed.