Fabrication Of Ordered TiO₂Nanotubes Array Photoanode For Dye-sensitized Solar Cells

Due to the low-cost and easy fabrication process, dye-sensitized nanocrystallinesolar cells （DSSCs） has made great progress in recent years. As the core component,photo-anode material has great impact to the power conversion efficiency of DSSCs.Nowadays the most commonly used photo-anode material is porous TiO₂nanoparticles.However, the light-induced electrons and holes are easy to recombine due to the largegrain boundary between the particles, thus greatly limits the conversion efficiency. Oneeffective way to solve this problem is to introduce the so-called1-D nanostructures suchas nanorods, nanowires and nanotubes array. Among these1-D array structures,nanotubes array is more preferred due to the larger surface area and superior electronstransport properties. It is believed that the conversion efficiency of DSSCs would befurther improved with TiO₂nanotubes array as the photo-anode materials.Currently, there are several methods to fabricate TiO₂nanotubes array film such asthe template way, hydrothermal method and anodization. Among these methods,anodization has been widely used due to the simple process and accessibility to controlthe morphology of nanotubes array by adjusting reaction parameters. In this thesis,anodization has been employed to fabricate TiO₂nanotubes array films, and thesenanotubes array films were assembled into DSSCs as photo-anodes. The main researchwork is focused on the following aspects:（1） A5cm×5cm big scale TiO₂nanotubes array film has been fabricated byanodization. The anodizing duration played a vital role in controlling the length and themorphology of the nanotubes array film. Moreover, the as-fabricated TiO₂nanotubesarray is tightly sticking to the Ti substrate. Several ways have been tried to separate thenanotube array film. It was found that immersing the resulted sample into a saturatedHgCl2aqueous solution was an effective way to separate the nanotubes array from the Ti substrate, and a5cm×5cm large scale and unbroken film was obtained.（2） TiO₂nanotubes array films with both ends opened has been prepared. By commonanodization, the bottom of the fabricated tubes array is closed, however both ends opennanotubes are more preferable in many cases such as DSSCs and QDSSC （quantum dotdye-sensitized solar cell）. In this thesis, after anodization at60V, post-treatments byincreasing the voltage and changing the Pt counter electrode with Ti foil are added toobtain the nanotubes array with both ends opened. It is found that only by enhancingboth the reaction voltage and current density can we obtain the both ends openednanotube array.（3） Assembly and photovoltaic test of DSSC with TiO₂nanotubes array as thephoto-anode material based on the fluorine doped tin oxide （FTO） glass substrate.Transfer the resulted nanotubes array to FTO glass with adhesive of different componentratio （which will result in different thickness of TiO₂nanoparticles layer）. The preparedsamples which serve as the anode materials are assembled into DSSCs. Afterphotovoltaic test, it is found that as the thickness of the nanoparticles layer decrease s, theconversion efficiency increases.（4） Assembly and photovoltaic test of DSSC with TiO₂nanotubes array as thephoto-anode material based on the Ti foil substrate. Since the TiO₂nanotube array film isfragile during the transferred process and easy to break off after sintering, the structure ofTiO₂nanotube array tightly stick to the Ti substrate was adopted to assemble the DSSC.During the fabrication process, the effect of vacuum absorption is being studied. Theresult suggests that after vacuum absorption, the conversion efficiency is significantlyincreased.