Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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  • Master Thesis
    Experimental Investigation of a Photovoltaic Thermal System With Phase Change Material
    (01. Izmir Institute of Technology, 2024) Çetkin, Erdal; Çetkin, Erdal; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    Çevre dostu enerji kaynakları arasında güneş enerjisi en yaygın kullanılanlardan biridir. Fotovoltaik sistemler, güneş ışığını elektrik enerjisine dönüştürerek bu enerji kaynağını kullanmanın temel yolunu oluşturur. Ancak, PV sistemlerin verimliliği, sıcaklık artışlarıyla azalır. Bu çalışma, PV panellerin performansını artırmak için faz değiştiren malzemeler ve su soğutmalı fotovoltaik termal sistemlerin entegrasyonunu araştırmaktadır. Çalışma iki aşamadan oluşmaktadır ve her iki deney de Antalya'da gerçekleştirilmiştir. İlk aşamada, erime noktaları 25°C ve 35°C olan faz değiştiren malzemelerle entegre edilmiş PV panellerin performansı, standart PV panellerle karşılaştırılmıştır. Sonuçlar, faz değiştiren malzeme entegrasyonunun termal yönetimi iyileştirdiğini ve elektriksel verimliliği artırdığını göstermektedir. PV-PCM35 sistemi, yüksek sıcaklık koşullarında panel sıcaklığını 21.3°C oranında düşürerek, ortalama %2.16 ve maksimum %3.72 oranında verimlilik artışı sağlamıştır. İkinci aşamada, faz değiştiren malzeme ile entegre edilmiş su soğutmalı bir PV/T sistemin performansı, geleneksel PV sistemlerle karşılaştırılmıştır. Bulgular, PV/T-PCM sisteminin elektriksel verimlilikte önemli iyileştirmeler sağladığını ortaya koymaktadır. Su soğutma mekanizması, ısıyı etkili bir şekilde dağıtarak panel sıcaklıklarının düşük kalmasını sağlamış ve verimliliği artırmıştır. PV/T-PCM sistemi, maksimum elektriksel verimlilikte %3.79 ve termal verimlilikte %62.74 artış göstermiştir. Bu sonuçlar, PV/T-PCM sistemlerinin özellikle Antalya gibi yüksek sıcaklıklara sahip bölgelerde daha verimli enerji üretme potansiyeline sahip olduğunu göstermektedir.
  • 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 Science
    Thin-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
    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, Mehmet; Güneş, Mehmet; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    Hydrogenated 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.