Titanium Dioxide Nanotube Arrays In Dye-sensitized Solar Cells, Optical And Electrical Properties

As a wide band gap semiconductor with innocuity, stabilization and cheapness, TiO2 is one of the best materials for preparing the anodes of DSSC. Nanotube arrays has a larger surface area, higher surface energy,it's better than pure powders and nano-films.It's expected to improve the photoelectric conversion efficiency of DSSC.DSSCs were fabricted by dye-sensitized TiO2 nanotube arrays which prepared by HF and NaF electrolyte system. The surface morphology, crystal structure and elemental composition were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and studied the formation mechanism of nanotube arrays. The optical properties of DSSCs were characterized by solar energy detector, the influence of the calcination temperature, anodization time, different electrolyte system and acid treatment were analyzed.The formation mechanism of nanotube arrays was studied, which including the following process:at first, the dense titanium oxide film was rapidly formed, whose formation at the same time with its dissolution, but it's pre-generation rate faster than dissolution rate; Secondly the nanotubes was formed, which beginning with the formation of oxide film surface with pores caused by electrode/solution interface of double electron layer structure (close layer/dispersed layer), whose adjacent pores together grew bigger, then forming a small tubes, small tubes furthered into the larger tube, to enter the stable growth phase until reaching to the maximum aperture, and the length of nanotubes will continue to increase. Finally the high-density nanotube arrays was formed with regular and orderly structure.According to the SEM graph analysis shows:TiO2 nanotube arrays can be prepared by HF and NaF Electrolyte system. The tubes length between 450-550nm, tubes diameter between 45-65nm by HF Electrolyte system, The tubes length between 2.5～3μm, tube diameter between 30-45nm by NaF Electrolyte system. As the calcination temperature, the nanotube arrays appearance had little change under 500℃, the nanotube arrays morphology was gradually changed more than 500℃. According to EDS, XRD diagram analysis shows:the oxides obtained after ignition was TiO2·After 500℃calcination treatment, amorphous TiO2 nanotube arrays formed in the anatase phase, after 600℃calcination treatment, TiO2 nanotube arrays formed anatase and rutile mixed crystal.The main factors of DSSC optical properties included: nanotube length, diameter of the nanotube, TiO2 crystal. The proper concentration of acid could enhance the surface active sites on TiO2 nanotube arrays and improve the pre-dye adsorption, thus improved photoelectric conversion efficiency of DSSC.In NaF electrolyte system,30min treated by 0.1mol/L HCL solution,the photoelectric conversion efficiency of DSSC reached a maximum in this experiment,was 2.63%.