Preparation And Properties Of Dye Sensitized Solar Cells Fabricated Via Liquid Phase Deposition

Dye-sensitized solar cells (DSSCs) have attracted great interest in academic research and industrial applications because of the high conversion efficiency, low cost and simple fabrication processes. In order to broaden the application areas of dye-sensitized solar cells and get early access to the industrial production, scientists have been trying to use more convenient, energy saving and efficient method for preparing DSSCs. Efforts have been also spared to use lightweight bendable, flexible conductive substrate instead of the big weight, easy broken expensive indium tin plated conductive layer of metal oxide glass to prepare flexible DSSCs. Up to now, screen-printing and doctor-blade method are the most commonly used ways to fabricate the photoanodes. In details, the porous TiO2film is coated via doctor-blade or screen-printing with a polymer-dispersed TiO2paste on a conductive substrate, followed by calcination to remove the polymer binder, which results in the poor connection between the TiO2films. Since the poor connectivity of the TiO2film will finally result in an increase of resistance of the DSSCs, a modification process via TiCl4dilute solution is needed as well as a second calcination to improve the connectivity between the conductive substrate and the porous TiO2film, and the TiO2grains.This thesis presents a method of liquid phase deposition to fabricate the photoanodes of DSSCs, which is to soak the conductive substrate in a Ti solution with heating to accelerate the hydrolysis so that the TiO2film will be directly deposited on the substrate to form a photoanode of DSSCs. (1) TiO2porous films with particle size ranges300-400nm, specific surface area of152m2g-1, are directly grown on the FTO glass via liquid phase deposition at60℃, followed by a sintering process at high temperature, and then sensitized to use as the photoanode of a DSSC. The results of different substrate pretreatment show that the spin-coated FTO glass with TiO2sol as a seed layer followed by calcination, presents a highest photo-to-electric conversion efficiency of4.39%.(2) In order to improve the photoelectric performance, a gradient structure is designed, including a film I with larger particle sizes and pore sizes, lower specific surface area, and a film II with smaller particle sizes and pore sizes, higher specific surface area. The deposite temperature is firstly adjusted to80℃to obtain film I and then adjusted to60℃to obtain film II, a TiO2sol spin-coated FTO glass followed by calcination is used as the substrate. A gradient photophotoanode is thus fabricated after sintering and sensitizing before assembly, which finally presents an average photo-to-electric conversion efficiency of6.35%and a maximum of6.51%.(3) Titanium foil is treated by anodization to form a three-dimensional porous structure on the surface before deposition. Gradient TiO2film is deposited at80℃first and subsequently at60℃, followed by calcination and sensitizing before assembly into a sandwiched DSSCs. Also a study of different pretreatment is carried out in this thesis. The result shows that the titanium foil with a three-dimensional network structure on the surface presents a photo-to-electric conversion efficiency of2.56%with the non-gradient photoanode while the gradient photoanode achieves a maximum photo-to-electric conversion efficiency of3.09%.