Preparation And Application Of TiO₂Nanotubes-based Photoanode For Dye Sensitized Solar Cells

Dye-sensitized solar cell （DSSC） has been widely studied due to the simplepreparation process, low cost, environment friendly and abundant materials. Theconversion efficiency of DSSC has exceeded12%, however, it is still lower comparedwith the traditional silicon solar cell. The composite of one-dimensional nanostructure andnanoparticle, which could take advantage of both large surface area and efficient electrontransfer, is regarded as an effective way to improve the efficiency of DSSC. In addition,quantum dot sensitization instead of the poor stability and expensive dye is anotherimportant research field. Therefore, we mainly studied the preparation process of TiO₂nanotubes, the composite photoanode of TiO₂nanotubes/nanoparticles （TNT/TP） and CdSsensitized TiO₂nanotube.（1） The highly ordered TiO₂nanotube arrays （TNT） were fabricated by anodizationof Ti foil in ethylene glycol electrolyte containing0.5wt%ammonium fluoride. Theinfluence of anodization parameters on the morphology of TiO₂nanotubes wasinvestigated to find out the optimum process parameters for TiO₂nanotube fabrication.The results show that the diameter and wall thickness of TiO₂nanotubes increases with theanodization voltage. At the beginning of the reaction, the length of the nanotubes increaseslinearly with anodization time, then the rate of increase slows down and finally the lengthremains unchanged. The diameter of TiO₂nanotubes under anodization at30V is about110nm with the length up to10μm. After sintered at450oC, TiO₂nanotubes aretransformed into homogenous anatase phase, which is suitable for follow-up experiments.（2） TiO₂nanopartciles （TP） are printed on the as-synthesized TiO₂nanotubes to formthe composite photoanode with TiO₂nanotubes/nanoparticles through screen-printing. Thephotoanode with TiO₂nanotubes or TiO₂nanoparticles are also prepared for comparison.The results indicate that the TNT/TP samples have the advantages of large surface area,fast electron transport, superior electron recombination restraint characteristics and highlight scattering. DSSCs with as-synthesized photoanode were fabricated and thephotoelectric performance was measured. The results confirm that the efficiency ofTNT/TP cell is higher than the TNT cell and TP cell significantly. A relatively high conversion efficiency of6.43%was obtained at5μm thick TiO₂nanotubes and14μmthick TiO₂nanoparticles.（3） TiO₂nanotubes were decorated by CdS quantum dots through successive ioniclayer adsorption in CdCl2and Na2S solution. The results show that CdS quantum dotscover the TiO₂nanotubes completely. The amount of deposition can be controlled by thenumber of cycle. CdS sensitization is an effective way to extend the optical absorption ofphotoanode into visible region. The sonication treatment can uniform the distribution ofCdS and improve the crystallization properties. After15cycle deposition under sonication,the conversion efficiency of DSSC was0.23%.