فهرست مطالب لیلی متولی زاده

In the present work, yellow apple's skin, red apple's skin and Cercis siliquastrum’s petals have been used as pigments in dye-sensitized solar cells based on TiO2 nanoparticles. These pigments were extracted by a simple heat treatment method. In order to measure the absorption characteristics of pigments, ultraviolet-visible spectroscopy (Uv-Vis) analysis was used. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate the structural characteristics and morphology of nanoparticles, respectively. The I-V curves of solar cells were drawn under standard conditions in light and dark states. The results show that the cells made using dyes extracted from yellow and red apple's skins and Cercis siliquastrum’s petals have short circuit currents of 27.49 μA, 58.50 μA and 173.85 μA, respectively, and their open circuit voltages are 0.53V, 0.53V and 0.55V, respectively. Their fill factors are equal to 0.56, 0.65 and 0.68 respectively and their efficiencies are 0.04%, 0.08% and 0.27% respectively.

In this research, zinc oxide thin films with gallium impurity have been deposited using the spray pyrolysis technique. The structural and optical properties of these films are investigated as a function of gallium doping concentrations. The ZnO and ZnO:Ga  films grown at a substrate temperature of 350 ºC with gallium doping concentrations from 1.0 to 5.0.%. The XRD analysis indicated that ZnO films have nanocrystalline wurzite structure with (002) preferential orientation and grain size varied from 39.1 to 16.1 nm. The optical properties of the thin films have been performed using UV-Vis spectrophotometer and band gap energy values are determined. The results show that the transmittance of these films was higher than 90% in the visible region and by adding Ga up to 5.0%, band gap films have been increased.

SnO2 nanoparticles have been synthesized via sol-gel method in different annealing temperatures. TEM, FESEM and XRD techniques have been used to investigate the structure and morphology of SnO2 nanoparticles. The XRD pattern analysis shows all samples are single phase. XRD patterns show as the annealing temperature increases, the peaks become sharper which is related to the increase in the crystallite size of nanoparticles and enhancing the crystalline order and reducing lattice strain. The Williamson-Hall analysis and Halder-Wagner method were used to study the individual contributions of crystallite sizes and lattice strain to the peak broadening of nanoparticles. The physical parameters such as strain, stress and energy density values were calculated for three major reflection peaks of XRD patterns. Williamson-Hall analysis of XRD patterns show that increasing the annealing temperature causes the crystallite size to increase and to reduce lattice strain. TEM and FESEM images showed that by increasing temperature, nanoparticle size increases.

SnO2 nanotubes have been synthesized via sol-gel template method using alumina membrane. Synthesis parameters, such as sol preparation conditions, the required time of immersion and annealing conditions, were optimized to obtain the SnO2 nanotubes with well defined composition. Transmission electron microscopy (TEM) and X-ray diffraction techniques have been used to investigate the structure and morphology of SnO2 nanotubes. TEM image showed that the nanotubes have been obtained. The diameter of the obtained nanotubes were approximately 200 nm, were consistent by the pore size of alumina template. The optical transmittance and absorption spectra show that the nanotubes are semi-transparent against visible spectra whereas they absorb the ultraviolet waves. The optical bandgap were measured (3.56 eV) very close to that of the bulk materials.