Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Desing Strategies for Solar Car Parks: a Case Study for Iztech Library Parking Lot(Izmir Institute of Technology, 2020) Bursa, Enes; Sarı, Emre; Sarı, Emre; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe world’s need for renewable resources is growing as a result of the global climate crisis. In order to overcome this issue. The Paris Agreement was signed by the nations as a step for solution to this issue. In it, targets for future were set, and the nations pledged to meet these targets. Nowadays investments in energy production from renewable sources are increasing. When compared to 2019, the amount of energy produced from renewable sources grew by 12.5% in 2020. Photovoltaic systems are receiving more investment as a result of their growing efficiency. In 2020, photovoltaic system production climbed by 20.5 percent. Turkey is increasing their investment in photovoltaic systems. It is crucial for universities to be pioneers in energy production from renewable sources. The studies carried out by universities should be taken into account in terms of both increasing knowledge in this area and having people resource who are trained in it. In this study, the open parking area of the library building of the Izmir Institute of Technology were covered with a roof in order to simulate and analyze the installation of photovoltaic solar panels on the roof. These simulations and calculations were done using software called Enact Systems. PVWatts is utilized by Enact system for climate and photovoltaic calculations infrastructure. 560 panels have been installed on the 835 m2 covered parking lot. The installed power of the panels is 224 kW, and they can generate about 302 gWh of electricity annually. This amount is equal to 51% of library consumption. With this production, the amortization period of the investment is calculated as 8 years.Master Thesis Fabrication of Perovskite Solar Cells Using Ultrasonic Spray Coating(Izmir Institute of Technology, 2022) Ceyhan, Eray; Sarı, Emre; Sarı, Emre; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyPerovskite solar cells (PSCs) are one of the most prominent research field for the last decade in photovoltaic technology. From 3.8 percent in 2009 to 25.7 percent in 2021 in single-junction architectures, and to 29.8 percent in silicon-based tandem cells, solar cell efficiencies of laboratory-scale devices using these materials have increased, surpassing the maximum efficiency achieved in single-junction silicon solar cells. Therefore, as of now, perovskite solar cells represented the solar technology that was developing the fastest. Perovskite solar cells have gained commercial appeal thanks to their extremely low production costs and promise for even higher efficiency. Their short- and long-term stability are key issues and research topics. In this context, the development of scalable perovskite solar cell fabrication has become essential. A novel ultrasonic spray casting technique is employed by incorporating hot nitrogen gas blowing as a scalable deposition method. We tried to optimize the perovskite film crystallization by applying our technique. With the help of our hot nitrogen gas blowing pipe we are able to enhance the nucleation process and at a desired levels. These investigations are supported by characterization tools such as optical microscope, scanning tunneling microscope, and current-voltage measurement. MAPb(I1-xBrx)3 precursor solution containing DMF and DMSO as solvent was used in our experiments. We examined the effect on the surface roughness change by adjusting the DMF and DMSO ratios. Finally, we construct a device of FTO/ c-TiO2/ m-TiO2/ MAPb(I1-xBrx)3/Spiro-OMeTAD/Au architecture and able to investigate the electrical characteristic of under dark and illumination.Master Thesis Manufacturing and Characterization of Perovskite Thin Films Using Novel Methods(Izmir Institute of Technology, 2020) Tekin, Hüseyin Cumhur; Sarı, Emre; Sarı, Emre; Tekin, Hüseyin Cumhur; 03.01. Department of Bioengineering; 04.04. Department of Photonics; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of TechnologyPerovskite 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 Investigation of Photodetectors Using Graphene Field Effect Transistors Incombination With Functional Dyematerials(Izmir Institute of Technology, 2020) Balcı, Sinan; Şahin, Hasan; Şahin, Hasan; Balcı, Sinan; Şahin, Hasan; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyA J-aggregate dye is a type of water-soluble, functional dye, which has a sharp and narrow absorption peak after it self-assembles into a brick-wall structure at high concentrations. The absorption peak of the J-aggregates is sharp, narrow and shifted to longer wavelengths compared to their monomer form and it is in the visible or near infrared spectrum. Due to its very sharp and narrow absorption, it has been used in silver halide photography, non-linear optics, lasing and sensing applications. On the other hand, graphene is one atom layer thick, honeycomb lattice of carbon atoms. In the pure, freestanding form, the bands of its electronic structure touch at one point, making it a gapless semimetal. Due to this characteristic, it is possible to manipulate its optical and electronic properties by changing the Fermi energy of graphene. Therefore, graphene found applications in many fields such as light emitting diodes, photodetectors, Hall sensors, optical modulators and flexible optoelectronics. The functional dye materials have not been combined with graphene photodetectors even though they are highly sensitive to light, less toxic than their competitors and stable at room temperature. In this thesis, using a J-aggregate dye, which has a sharp absorption peak around 585 nm wavelength, a graphene phototransistor has been demonstrated. By changing the charge concentration on graphene, using the charge carriers that arise from the excitation of J-aggregate dye, reversible modulation of graphene Dirac point has been demonstrated. In addition, a novel thin film formation technique has been developed in this study. Porous polyethylene membrane has been used to create thin films of water-soluble materials, such as J-aggregates, on hydrophobic surfaces.Master Thesis Plasmonic Enhancement of Perovskite Photoluminescence(Izmir Institute of Technology, 2020) Sarı, Emre; Balcı, Sinan; Sarı, Emre; Balcı, Sinan; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyRecently emerged perovskite materials show superior features like high efficiency, defect tolerance, facile synthesis, bandgap tunability and wide color gamut over their rivals in photonics applications. On the other hand, metals have interesting characteristics as they go smaller in size. Their absorption and scattering properties are completely different as nanoparticles. Their confined electron oscillations bring peculiar consequences. Due to change in these features, metallic nanoparticles can enhance or quench fields around them. Light-matter interactions determine how we see the world. Understanding quantum nature of light and matter and their interactions can benefit higher efficiencies and can open paths for novel technologies. In accordance with this purpose, this thesis study involves synthesis of cesium lead halide perovskite emitters and investigation of their interactions with silver nanoisland films. It was concluded that direct contact between perovskite layer and nanoislands results in a fluorescence quenching where intensity average lifetime decreases below 1 ns. Separating these layers with an alumina dielectric layer increased photoluminescence intensity after 15 nm and the highest intensity was observed at 18 nm thickness with 78% of PL enhancement. With different spacer thickness values, we achieved to see the change in photoluminescence intensity.Master Thesis Experimental and Theoretical Investigation of Functionalized Perovskites(Izmir Institute of Technology, 2020) Şahin, Hasan; Balcı, Sinan; Şahin, Hasan; Balcı, Sinan; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe last decade witnessed the rapid increase in the interest of the cesium lead halide perovskites (Cs-LHPs) and their successful applications in optoelectronic devices and photovoltaics. Increasing interest in perovskites arises from their extraordinary features such as having a tunable bandgap, variety in the crystal structure and phases, high photoluminescence quantum yield, ease of synthesis, and wide range absorption spectrum. Desiring to go beyond the emerging findings, subsequent studies have focused on the functionalization of perovskite nanocrystals (PNCs) by dimensional modifications and doping. This thesis study focuses on the modification of characteristics of Cs-LHPs by doping scenarios and dimensional reduction. Firstly, we reveal the modifications originated from the intercalation of Cr+3 and Gd+3 dopants into the Cs-LHP crystal structures. Cr+3 doping process is performed by using room temperature anti-solvent crystallization method. It is observed that the doping process leads to the emergence of distinctive signals in the PL spectrum. We clarify the origin of each additional PL peaks by experimental measurements and theoretical calculations. Additionally, white light emission is also achieved by the Cr3+ doping process. On the other hand, by using the hot-injection method, we synthesized neat and Gd+3 doped ?-CsPbI3 NCs. The stability of ?-CsPbI3 NCs is increased by the intercalation of Gd3+ ions into the host lattice. Also, enhancement of PLQY and lifetime is achieved by Gd3+ doping. Besides, to understand the dopant-induced modifications in the electronic and optical characteristics of perovskites, we also performed ab-initio density functional theory (DFT) calculations. In addition, we study how the characteristic properties of Cs-LHPs are modified upon dimensional reduction. By introducing the electrospraying method we reduced the synthesis and coating processes into a single step. Two-dimensional perovskite nanoplatelets were synthesized by electrospraying. We tuned the emission wavelengths of nanoplatelets in the range of 100 nm by thickness modifications. Lastly, by using DFT, we investigated the effect of thickness-dependent modifications on the structural, electronic, and vibrational properties of the orthorhombic CsPbI3 structure. Phonon calculations show that two ultra-thin forms of bulk CsPbI3 are dynamically stable. Also, the increase in the bandgap energy of the CsPbI3 structure by a decrease in thickness is revealed by electronic band dispersion calculations.Master Thesis Functionalization and Thickness Dependent Properties of Single Layer Dichalcogenides(Izmir Institute of Technology, 2019) Kahraman, Zeynep; Akdoğan, Yaşar; Kahraman, Zeynep; Şahin, Hasan; Şahin, Hasan; Akdoğan, Yaşar; 03.09. Department of Materials Science and Engineering; 04.04. Department of Photonics; 03. Faculty of Engineering; 04. Faculty of Science; 01. Izmir Institute of TechnologyAfter successful isolation of graphene in 2004, it was found that the layered materials showed different properties when diluted to the monolayer. The layer dependent structural, electronic and vibrational properties of the 1T phase of two dimensional (2D) platinum diselenide are investigated by means of state-of-the-art first-principles calculations. In addition ultra-thin two-dimensional Janus type platinum dichalcogenide crystals formed by two different atoms at opposite surfaces are investigated by performing state-of-the-art density functional theory calculations. While all Janus structures are indirect band gap semiconductors as their binary analogs, their Raman spectra show distinctive features that stem from broken out-of-plane symmetry. Moreover, it was shown that vertically stacked van der Waals heterostructures of binary and ternary (Janus) platinum dichalcogenides offer wide-range electronic features by forming bilayer heterojunctions of type-I, type-II and type-III. On the other hands, Ab initio calculations are performed in order to investigate the structural, vibrational, electronic, and piezoelectric properties of both bare TaS2 and its functionalized structures. Furthermore, the elastic and piezoelectric properties of TaS2 and its derivatives are analyzed. It is revealed that the in-plane piezoelectricity of TaS2 can be enhanced via one-surface fluorination while an additional degree of freedom for the piezoelectricity can be added in all Janus structures due to the broken out-of-plane symmetry. This thesis provides some important results understanding of thickness and functionalization dependent mechanics, vibrational, electronic properties of 2D materials.Master Thesis Fabrication and Characterization of Graphene/Silicon Based Schottky Photodiode(Izmir Institute of Technology, 2019) Dönmez, Gülçin; Çelebi, Cem; Sarı, Emre; Çelebi, Cem; Sarı, Emre; 04.05. Department of Pyhsics; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThis thesis focused on fabrication and characterization of CVD grown p-type graphene and n-type Si Schottky junction photodiode with rectification behavior. The device operated at wavelength range between 390 and 1100 nm at self-powered mode. The device was encapsulated with Epoxy Resin to prevent graphene from atmospheric adsorbates. The electronic and optoelectronic characterizations of the devices were done before and after coating the devices with ER. By encapsulation stability of the device was enhanced in terms of photoresponsivity. The maximum obtained photoresponsivity value of the bare device was 0.56 A/W. Also, time-resolved photocurrent spectroscopy measurements showed that the devices exhibited enhanced photodetector performance in terms of photo-switching characteristics. Furthermore, electrical characteristics of Gr/n-Si Schottky photodiode under various illumination power densities with 850 nm wavelength were investigated. The short circuit current showed linear response to power density. However, open circuit voltage exhibited two phased slow and fast increment with increased power density. Hall effect measurements were conducted in order to investigate hole carrier concentration and mobility of the graphene on n-Si. With increasing the power density the carrier concentration increased and the mobility decreased. Besides, light induced manipulation of the Schottky barrier height of Gr/n-Si photodiode was studied. Schottky barrier height of the graphene measured by KPFM method as 0.4 eV. With increasing power density we found that Schottky barrier height of the device increased from 0.4 eV to 0.5 eV and showed similar trend with the change in open circuit voltage.Master Thesis Three-Photon Electromagnetically Induced Transparency in Rydberg Atoms(Izmir Institute of Technology, 2019) Oyun, Yağız; Çakır, Özgür; Sevinçli, Sevilay; Sevinçli, Sevilay; Çakır, Özgür; 04.04. Department of Photonics; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyElectromagnetically Induced Transparency (EIT) is a quantum coherence phe- nomenon, in which an atomic medium is rendered transperent via destructive interference of excitation pathways. EIT was first observed in a three-level lambda scheme where a modified optical response is achieved by the interference of light field induced atomic state coherences at the resonance of transition. An EIT system also produces important optical effects including giant Kerr non-linearity and slow light. Rydberg-EIT media have been used to study optical properties of atomic media, non-linear optical effects and to gain better understanding on interacting many-body systems due to the controllable in- teractions of Rydberg atoms. Recently EIT in a four-level ladder scheme was realized experimentally in a dressed-state manner with Cs atomic vapor, in which a strong dress- ing field allows for a transparency window to be opened for probe field. Rydberg EIT has potential applications in terahertz regime, electrometry, metrology and quantum in- formation science, but extensive studies on four-level Rydberg EIT schemes are scarce. In this thesis; three-photon EIT in a cold atomic ensemble that has a ladder type excita- tion scheme, in which the highest energy state is a Rydberg state is investigated. Atom- light interactions of a four-level ladder system is developed for non-interacting case, then extended to many-body case. Starting with the steady-state solutions without atomic in- teractions, Rydberg EIT system is analyzed using mean-field and rate equation methods, though due to inadequate computing power and lack of time we could not finalize the rate equation method. To understand effects of Rydberg-Rydberg interactions on these systems in detail, two-body case is investigated with mean-field method. Afterwards, to achieve more realistic results, a self-consistent mean-field method for larger systems is developed. It is observed that as the van der Waals interaction energy increases, Rydberg blockade becomes more prominent. Therefore induced transparency weakens, broadens and shifts away from the resonance as expected. This means that, controllable interac- tions in a Rydberg EIT medium enables to control and modify the optical response of the atomic medium.Master Thesis Dimension Dependent Optoelectronic Properties of Cesium Lead Halide Perovskites(Izmir Institute of Technology, 2019) Şahin, Hasan; Şahin, Hasan; Balcı, Sinan; Şahin, Hasan; Balcı, Sinan; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyAll-inorganic cesium lead halide perovskites (ILHPs), are gaining wide variety of role as strong contenders due to their extraordinary photovoltaic features in optoelectronic research with tunable band-gap, large absorption cross-section, long carrier lifetime, and high carrier mobility. Most of the initial studies focused on bulk-like perovskite materials, while the rapidly growing colloidal perovskite nanocrystals impress additional interest because of their unique properties. In this thesis, colloidal lead halide perovskite nanocrystals’ optoelectronic properties are investigated and associated with their size and dimensionality. The photoluminescence characteristics of colloidal lead halide perovskite nanocrystals can be tuned by reducing their dimensionality. Thin layer fabrication of CsPbBr3 films which consist of 2D lead halide perovskite nanoplatelets, is achived by a novel coating approach via electrospraying from precursor solution. Electrospraying method represents not only a new and fast perovskite film fabrication but also dimensional tunability by changing the amount of oleylamine which is intercalating agent. Moreover, thicknessdependence of the structural, electronic and vibrational properties of orthorhombic CsPbI3, which is one of the most stable phase at room temperature, is investigated by means of state-of-the-art first-principles calculations. It is also investigated that the electronic band gap increases with decrease in perovskite thickness due to quantum size effect. Lastly, it is investigated that water induced transition to form large bundles of CsPbBr3 nanowires show a a redshifted photoluminescence. Water molecule causes the detachment of ligands from the perovskite surface which leads to form bundles. In summary, this thesis provides an understanding of dimension dependent optoelectronic properties of lead halide perovskite.