TiO ₂ Film Preparation And Properties Of Dye-sensitized Solar Cells Based Optimization

Dye-sensitized solar cells (DSSCs) have attracted worldwide attention because they are made of low-cost materials with simple inexpensive manufacturing procedures. Although the achieved energy conversion efficiency in DSSCs is low, it has improved quickly in the last years. Improvement of conversion efficiency and fabrication cost for the dye-sensitized solar cell are the necessary problems that must be resolved before the practical use of DSSCs. In this paper, we optimized the morphology and structure of TiO2photoelectrode and adopted new carbon counterelectrode aimed at improving the conversion efficiency as well as the fabrication cost of DSSCs. The researches in this thesis mainly focus on:(1)The optimization of the structure and performance of TiO2nanotube anode materials;(2) The fabrication of light scattering layer and its application in DSSCs;(3) Preparation and study on DSSCs based on carbon counterelectrode. The major results obtained are listed as follows:Highly ordered free-standing TiO2nanotube thin films were prepared by a modified secondary anodization method, and the front-side illuminated DSSCs were assembled. Due to a lower loss of light, front-side illuminated DSSCs had a higher energy conversion efficiency compared to the back-illuminated DSSCs with TiO2nanotube arrays attached to the opaque Ti foil. The influence of the secondary anodization voltage on the morphology, crystalline phase and photovoltaic performance of the as-fabricated samples has been investigated. Results show that the side wall of TiO2nanotubes becomes obviously thin as the secondary anodization voltage increases and leads to crack when the voltage reaches25V. XRD pattern shows that the mass fraction of the anatase reduces by the increase of the secondary anodization voltage. Furthermore, the dye-sensitized solar cells (DSSCs) based on TiO2nanotube arrays with different secondary anodization voltage have been assembled. The highest energy conversion efficiency was obtained from the cell with TiO2nanotube membrane re-anodizad at15V, as high as10.6%.TiO2hollow microspheres with hiberarchy structure were prepared by a simple hydrothermal method using Ti(SO4)2as titanium source. The influence of the concentration of NH4F on the morphology and structure was studied, then a preliminary discussion of the formation mechanism of the TiO2hollow sphere was presented. TiO2microspheres with good morphology and structure were obtained by adding a certain volume of alcohol in the reaction solution. The results displayed that the addition of alcohol could change the polarity of reaction solution, improving the surface activity of TiO2hollow microspheres, and promoting the growth of them. Furthermore, the addition of alcohol could also have influence on the nucleation、growth、and crystallization of TiO2hollow microsphere. An appropriate addition of ethanol would promote the nucleation and crystallization of TiO2hollow microspheres. DSSCs with a highest monochromatic incident photon-to-electron conversion efficiency (TPCE) of85% were obtained which were based on TiO2hollow microsphere as the scattering layer.A new type of counter electrode was fabricated with a method of doctor-blade method using a viscous conductive carbon paste (C-Liet) as a binder and carbon black as a catalyst. Film adhesion test and electrochemical impedance spectroscopy (EIS) were taken to test the physical and electrochemical properties. Results show that the addition of the conductive carbon paste (C-Liet) can greatly improve the adhesion between carbon material and the conductive substrate (FTO), as well as the conductivity and catalytic activity of the carbon counter electrode. Experiment results displayed that when the mass ratio of carbon black:C-Liet was5:2, the dye-sensitized solar cell (DSSCs) based on this "carbon-C-Liet" counter electrode yielded a optimal conversion efficiency, This provides a new way for DSSCs to reduce fabrication cost in practical application.