GCRIS

Now showing 1 - 2 of 2

Magnetron Sputtering Growth of Azo/Zno Multilayers for Cu2znsns4 Thin Film Solar Cells: Material and Device Characterization
(Izmir Institute of Technology, 2017) Köseoğlu, Fulya; Özyüzer, Lütfi; Aygün Özyüzer, Gülnur
Cu2ZnSnS4 (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 such as CuInGa(S,Se)2 (CIGS) and CdTe. Although, CZTS studies have been newly started, recently 9.4 % efficiency has been achieved. In the present thesis, all layers used in the CZTS device structure were investigated using energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scanning electron microscopy (SEM), spectrophotometry and Raman spectroscopy. For CZTS absorber layer, CZTS films based on a stacked precursor (Cu/Sn/Zn/Cu) were prepared. 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. We addressed the importance of Cu layer thickness adjacent to Sn to avoid developing detrimental phases and to get complete formation of kesterite CZTS absorber layer. We also addressed the importance of sulfurization time to restrict the Sn and Zn losses, formation of oxides such as SnO2 and ZnO, formation of MoS2 and voids between Mo/CZTS interface. Effect of the sulfur concentration on the properties of Zn(O,S) thin films were investigated. We showed that key parameters such as energy gap and crystal structure of the Zn(O,S) thin films can be tuned by changing the sulfur concentrations of the films. We succeed substitute conventionally used CdS buffer layer with environmentally friendly alternative Zn(O,S) buffer layer in CZTS solar cells. Effect of substrate position and rotation speed during the deposition of AZO thin films were investigated. We addressed that stress on the films can be significantly reduced by off-center deposition and rotating the sample holder during the deposition. In this way, high transmission in the visible range and metal like resistivity were achieved simultaneously at room temperature. We observed strong dependence of device performances on both sulfurization time and the thickness of Cu layer adjacent to Sn in CZTS absorber. The best device was based on CZTS films sulfurized for 30 minutes and having thicker Cu layer adjacent to Sn layer in precursors.
Preparation and Characterization of Titania Based Powders and Suspensions for Photocatalytic Applications
(Izmir Institute of Technology, 2015) Yurtsever, Hüsnü Arda; Çiftçioğlu, Muhsin
Growing environmental concerns related to the extensive use of nonsustainable fossil fuels and increasing energy demand will force mankind, sooner or later, to tap into clean and sustainable sources of energy and artificial photosynthesis is being considered as a promising prospect for this concern. Photocatalysis is expected to make a great contribution to solutions for environmental problems and renewable energy generation. Titania based photocatalytic materials are one of the widely used materials in artificial photosynthesis research due to their unique chemical and optical properties. Recent research have shown that rare earth element (REE) doping improves the photocatalytic activity of TiO2 phases in the visible region. The effects of REE doping level and heat treatment temperature on the microstructure evolution, optical properties and the photocatalytic water splitting/CO2 photoreduction activities of mostly sol-gel derived titania powders were investigated in this thesis. The results of this thesis indicated that REE ions may enter the interstitial voids of TiO2 lattice or segregate on the grain boundaries of TiO2 as a separate phase and RE2Ti2O7 phases were formed for the REEs with relatively smaller ionic sizes. The experimental work conducted revealed the importance of surface area, crystallinity, light absorption, the presence of oxygen vacancies and structural defects in the efficiency of photocatalytic processes. Results have shown that REE doping improves the artificial photosynthesis activity of TiO2 at relatively low doping levels and 700oC heat treatment temperature as the production rate of H2 and CO/CH4 were significantly higher with REE doped TiO2 compared to pure TiO2.

Phd Degree / Doktora

Browse

Filters

Settings

Sort By

Results per page

Search Results