Sharif Digital Repository

This research is focused on fabrication of TiO2 layers by electrophoretic deposition (EPD) for application as photoanode in Dye Sensitized Solar Cell (DSC). DSCs are third generation of solar cells, also known as the Grätzel cell, after its inventor Michael Grätzel. A DSC is composed of a porous layer of wide band gap semiconductor such as TiO2 and ZnO, covered with a molecular dye that absorbs sunlight, and a counter electrode contacted by a liquid redox electrolyte. Dye Sensitized semiconductor (photoanode) has important role in conversion of photon to electricity. To achieve higher efficiency, preparation of photoanode with high surface area resulted to enough dye adsorption is necessary.... 

In this thesis, the goal is to improve the efficiency of quantum and solar cell. The effect of quantum wells was simulated by Silvaco. Initially, the quantum well has been adjusted to a cell junction GaAs. Then, using quantum wells in cell junction towing and three, improving short-circuit, the returns will be 53.79% and 54.33%. This efficiency is about 10% more than the triple-junction solar cells. To improve the efficiency effects of layer thicknesses, parameters, and the number of quantum wells were studied.Tandem cell is 〖In〗_0.51 〖Ga〗_0.49 P/GaAs, and triple is 〖In〗_0.51 〖Ga〗_0.49 P/GaAs/〖In〗_0.28 〖Ga〗_0.72 As. By adjusting the quantum well and sandwiching the well layers staggered by... 

This thesis demonstrate a new hybrid Plasma Electrolytic Oxidation (PEO)-Hydrothermal method to produce a nano-structured TiO2 layer over a titanium substrate. Microstructural characterization was carried out by using a FE-SEM to explore nano scale structural changes due to hydrothermal treatment. More over EDS was used to analyse elements of the coating. The FE-SEM images confirmed formation of a 3D network consisting “nano flakes+nano fibers”after 6 or 12 hours and a ”sea urchin like nanostructure+nano fibers” after 24 hour. To improve the performance of nano-structured photoelectrodes, different electrolytes were studied to achieve maximum amount of anatase phase. the best results was... 

In the present work, one dimensional ZnO nanostructures were grown by seed-assisted hydrothermal method. Hydrothermal processing parameters were controlled to obtain ZnO nanorods with diameter lower than 120 nm. The products were characterized by FE-SEM, EDAX, XRD, PL, and ATR-FTIR analyses. ZnO nanoparticles were also synthesized via a simple solvothermal method and their photo peropeties were compared with onedimensional nanostructures. Thereafter dye-sensitized solar cells based on TiO2-ZnO double layer nanostructured film were fabricated. It was observed that DSSC efficiency increased with decreasing the thickness of the film. The highest efficiency of 2.41% was obtained  

In recent years, thin-film photovoltaic cells with thicknesses of less than 1-2 µm have been developed with potentially lower production costs. Due to the small thickness of the absorbing semiconductor in these cells, the absorption is inevitably low at energies close to the electronic band gap of the semiconductor. This is particularly a problem for thin-film devices. Recently، periodic metallic nanostructures supporting surface plasmons have been introduced as alternative solutions to achieve light trapping in thin-film solar cells.Full numerical methods are usually used for the analysis of these periodic structures. The main drawback of these methods is that they are time-consuming and... 

In the current research, Anatase-Rutile Titania hollow spheres were synthesized using hydrothermally prepared carbon spheres as template. Different calcination temperatures were used to remove carbon template and crysalized Titania. The characterizations for the physicochemical properties of prepared samples were carried out by XRD, FESEM, XPS, DRS, UV-Vis and FTIR.It is found that doping of carbon in the crystal structure of Titania hollow sphere, cause red shift in band gap wavelenght and the absorption wavelength edge was expanded to the visible light region and the additional diffusive electronic states were observed on the valence band spectra of samples.The photoelectric conversion... 

Different types of morphologies and phase structures of crystalline TiO2 were synthesized by hydrothermal methods. For the first time, dandelion-like rutile TiO2 powder composed of numerous single crystalline nanorods was synthesized using TiCl4 as the main precursor. TiO2 Nanoparticles were produced using TTIP and 2-propanol, as precursor and solvent, respectively. Field emission scanning electron microscopy analyses revealed that the synthesized TiO2 nanoparticles had average crystallite size in the range 21–70 nm, whereas dandelion-like TiO2 showed diameter in the range 2-10 µm. According to the significant refractive index of TiO2, in particular rutile phase, it can be used in the... 

The photovoltaic (PV) industry is in rapid growth and a large supply of PV feedstock materials must be provided to maintain this growth. Since silicon is still the dominant material for the fabrication of solar cells, low-cost solar-grade silicon (SoG-Si) feedstock is demanded. The most cost-effective and direct approach for producing SoG-Si is to purify and upgrade metallurgical-grade silicon. The major impurities in silicon are Al, Fe and Ca. other impurities present are Cu, Ti , Zn, Ni, Cr, Mn, Cd, B and P. In this study The effects of the acid leaching process parameters, including the particle size of silicon, the acid type (HCl, HNO3, H2SO4, and their combination), tmepreture and the... 

Many efforts have been put into increasing the efficiency of dye-sensitized solar cells that part of it has been devoted to structure and chemical composition of photoanode electrode. In this thesis, the effect of changes in the composition and its influence on light scattering ability in photoanode of dye sensitized solar cells was studied.First, the nanoparticles of titanium dioxide powder through solvothermal method as well as spherical particle and barium titanate powder by sol-gel method were synthesized. XRD and FE-SEM analyses indicated that synthesized powders are in good size and morphology regarding the intended chemical composition. Optical properties of TiO2 particles were... 

By using Mie theory and experimental data for complex refractive index of Au and Ag nanoparticles, the scattering and absorption efficiency of these nanoparticles in silicon medium (crystalline, Polycrystalline and amorphous silicon) was investigated. It was shown that Ag and Au nanoparticles can be used for confine the light, in desired wavelength band, inside the solar cell.The optimum nanoparticle size for using in this kind of solar cells was about 70-80 nm. In amorphous silicon confined photons cannot participate in electron-hole generation so the application of these metal nanoparticles in this kind of solar cells cannot be useful. Also the complex refractive index for equivalent... 

Dye-sensitized solar cell (DSSCS) is the third-generation of solar cells based on semiconductors formed between a photo sensitized anode and counter cathode which make a photo electrochemical system. They haven’t been commercially marketed due to their lower efficiency than the previous generations. In order to achieve the higher efficiency, the electron injection and light absorption must be increased. One way to increase electron injection is doping the semiconductor with an external ion to reduce lattice band gap. In this work, we made powder and Nano-structured film of titanium dioxide doped with various molar ratios of Mg by the sol-gel process. The effect of Mg:Ti molar ratio on... 

Solar cells are one of the most promising clean and readily available energy sources. Organic solar cells as a new generation of solar cells, have attracted strong attention in recent years, due to the advantages of flexibility, thinness, and simple manufacturing process. This work focuses on the electrical processes in organic solar cells and approaches for enhancing the efficiency of solar cell by employing two-dimensional drift-diffusion model. At the first step. We investigate the role of different parameters such as mobility (considering different recombination mechanisms), active layer thickness, light intensity, barrier injections and energetic disorder on the performance of single... 

Structure and morphology of titanium dioxide have an excessive effect on the photovoltaic properties of dye-sensitized solar cells (DSCs). Different approaches have been used to improve the efficiency of these cells. One is using a scattering layer. Studies have been shown that properties of scattering layer such as composition and morphology have great effect on photovoltaic properties of solar cell. In this project, the effect of cubic morphology of TiO2 as a scattering agent in photoanode of DSCs is studied. Titanium dioxide with various morphologies including nanoparticles, solid and hollow cubic structures have been synthesized by solvothermal and hydrothermal methods, respectively. The... 

In this project single sided dye sensitized solar cell is introduced as a new design that has both of electrodes in one side. These electrodes can be separated vertically by a thin insulator layer such as SiO2 or horizontally by lithographic method. First a metallic thin film is patterned by lithography, and then thickened by electrochemical deposition of Chromium. Platinum is electrodeposited on the substrate of counter electrode and a thin spacer layer is deposited on Platinum layer to separate it from Titanium dioxide layer.
In Chapters 1, 2 & 3 basic science and methods which are needed for doing this project is introduced. In chapter 1 material for making a standard dye sensitized... 

In this study, transparent conductive thin film of Aluminum doped ZnO (ZnO:Al) have been fabricated thorough RF sputtering. The main goal of fabrication of these layers is achieving thin films with minimum resistivity and maximum optical transparency in visible range of spectrum employing as transparent electrodes and buffer layer at the entirely oxidized solar cells. To achieve the suitable structure, various parameters including pressure, power and the thickness of the deposition and annealing on morphologies of thin film has been investigated. According to these results, thin film of ZnO:Al has the transparency of 80% in the visible light range . Doping of ZnO with Aluminum caused... 

Dye-sensitized solar cells (DSSCs) have been intensively studied duringthe last decade as a promising third solar cellgeneration due to their potential low-cost manufacturingprocess. DSSCsare based on a semiconductor (i.e., TiO2), formed between a photo-sensitized anode and an electrolyte. In order to reach high conversion efficiencies, it isimportant to increase the electron injection and opticalabsorption. One promising solution to increase the electroninjection is to decrease the large band gap of TiO2 bydoping a foreign ion into TiO2 lattice.
In the present study, Ag- doped TiO2 powders and films with different Ag:Ti molar ratios are reported. The effect of dopant at.%, annealing... 

In this thesis, we focus on studying and fabrication of doped titanium dioxide electrodes and their application in nanostructured dye sensitized solar cells (DSSCs). For this purpose, non-metallic nitrogen (N) and metallic neodymium (Nd) elements were selected. N-doped titanium dioxide nanoparticles were synthesized via solvothermal method and their structural and optoelectrical properties were investigated in comparison to undoped titanium dioxide synthesized by the same method. Based on the obtained results, doping of titanium dioxide by nitrogen resulted in shifting the Fermi level up-ward, increase in charge carriers density, shift of optical absorbance to higher wavelength, and decrease... 

The efficiencies of perovskite solar cells have increased rapidly in recent years and reached about 22%. Which hopes to make this type of solar cell more functional. In the normal structure of perovskite solar cells, the presence of mesoporous TiO2 mesoporous layer has increased sustainability and efficiency. To create this layer, a common method is placing the sample in a furnace for 30 minutes at 450°C-500°C. Using the furnace, in addition to being time consuming, has a high energy consumption. In this study, we tried to create a TiO2 mesoporous layer with the help of lighting. To create TiO2 mesoporous layer, What causes porosity in the layer is the removal of ethyl cellulose and create... 

Perovskite solar cells are the new generation of solar cells, and are mainly introduced in two types of structures.1) planer and 2) mesoscopic structure. The difference between these two structures derives from the absence of mesoporous layer in the planer structures. The mesoporous layer acts as an electron transporting layer, and is mainly a titanium dioxide semiconductor. To apply the mesoporous layer, the preparation of the TiO2 paste is needed.The synthesis of titanium dioxide nanopowder for the preparation of TiO2 paste requires high temperature heat treatment and is not desirable in terms of energy consumption.Another weakness of this layer is the presence of surface defects, which... 

Solar cells, as a part of photovoltaics (PV) industry, have a significant share in the renewable energy market. Perovskite solar cells (PSCs) and thin film solar cells (TFSCs) achieved 23% and 22% power conversion efficiencies (PCEs) respectively. However, the PV industry still faces challenges like “high manufacturing costs” and “stability”. Among the strategies to overcome these challenges are substitution of the costly materials with cheaper, more abundant ingredients along with utilizing inexpensive deposition methods like printing rather than vacuum-based methods such as evaporation and sputtering. Carbon materials attract more attention in the solar cell research community for their...