The Optimization Of Mesoporous TiO-₂ Thin Film Electrodes And Study On Electron Transport Performance In Dye Sensitized Solar Cells

Dye-sensitized solar cell(DSC) based on mesoporous TiO2 thin film electrodes was took as the research object in this paper. Mesoporous TiO2 thin film electrodes with different composition and microstructure were designed and prepared through the optimization of thin film electrodes. DSCs were fabricated by combining with dye C106, and were comparative evaluated the photoelectric properties parameters of them. The light harvesting capacities of photoanodes were researched by UV-vis absorption spectra. It is important that the micro kinetics mechanism of the charge separation, recombination, and charge transport, collection on Ti O2/electrolyte interface in DSC were further studied though the transient photocurrent voltage decay and electrochemical impedance technique. The thesis consists of the following two parts:(1) Anatase TiO2 nanoparticals with an average size of 12 nm were synthesized by combining sol-gel method and hydrothermal crystallization technology. DSCs based on different thickness of mesoporous TiO2 thin film electrodes were fabricated. The results indicated that when the film thickness was in the range of 2.1~9.8 ?m, the dye molecules adsorption amount increased with the increase of film thickness, thus increasing the light harvesting capacity. Although the open circuit photovoltage decreased, the short circuit current density, the electron lifetimes and electron diffusion coefficient increased, which made the overall conversion efficiency of DSCs improved. But when the film thickness was further increased over 9.8 ?m, the path of electron transport and the kinetic parameters of the density of states and recombination rate increased with the thickness increasing, resulting in the decrease of electron transport and collection performance, which influenced the photoelectric properties of DSCs.(2) The one-dimensional TiO2-B nanotubes that inner diameter is about 5 nm, outer diameter is about 8 nm and the length is in the range of 200~400 nm were prepared by the hydrothermal synthesis method. The TiO2-B nanotubes with different proportion and TiO2 nanoparticles were fabricated the nanotube/nanoparticle composite thin film electrodes of DSCs. The role of one-dimensional nanotube structures in DSC had been systematically investigated. Compared with DSC based on the pure TiO2 nanocrystalline electrode, DSC based on the nanotube/nanoparticle composite thin film electrode had both the rapid electron transport of TiO2-B nanotubes and the high surface area of TiO2 nanoparticles. DSC with adding one-dimensional nanotubes remained the short-circuit current density larger, while improved the open circuit voltage. The one-dimensional nanotube structure can provide direct paths for electron transport, and reduce the charge recombination rate on Ti O2/electrolyte interface, resulting in prolonging electron life and increasing the diffusion length, which effectively promoted the electron transport performance and improved photoelectric properties of DSCs.