Study On Preparation And Photoelectric Performance Of Amorphous TiO₂ Mesoporous Film

Dye-sensitized solar cell (DSC) has a good prospect for application of solar conversion devices because of its lower-cost than the conventional semiconductor solar cells and environment friendliness. Although the overall light-to-electricity efficiency of DSC is not high enough compared to the silicon solar cells, DSC can be used as the effective large area solar conversion device for the application in architecture, such as the external wall, the roof, the window and the curtain wall, since it is inexpensive to manufacture.TiO₂ mesoporous film, the most widely used photoelectrode material of DSC, is the key componet of DSC because it adsorbs dye and serves as both electron acceptor and transport layer. There are several problems for TiO₂ mesoporous film to realize the industrial development: (1) the fabrication method still needs to be improved with more controllable and simpler process; (2) the fluctuated efficiency of TiO₂ film photoelectrode needs to be improved; (3) the overall light-to-electricity efficiency of TiO₂ film photoelectrode needs to be enhanced. An amorphous TiO₂ mesoporous film is used as photoelectrode of DSC to resolve these problems.The spherical TiO₂ particles with an average size of 20nm were synthesized by the Tetrahydrofuran modified reverse microemulsion method under atmospheric pressure and the temperature of 50⁶0℃. The resulting colloid was coated straight on the FTO conducting glass, fllowing by drying and sintering processes, to form an amorphous TiO₂ film with homogeneous mesoporous inner structure of interconnected spherical particles. The method makes the synthesis conditions for TiO₂ nano-particles much lower than for the TiO₂ nanocrystallines attributing to no demand of crystallization and growth for amorphous TiO₂. The method also makes preparing process much simpler owing to supporting to coat the colloid straight on the substrate to form a homogeneous mesoporous TiO₂ film.Under the same conditions, the dye-adsorption amount and performances, such as short circuit photocurrent (Isc), open circuit photovoltage (Voc), fill factor (ff) and the overall light-to-electricity efficiency (η), of the amorphous TiO₂ mesoporous film were measured and compared with those of the anatase nanocrystalline mesoporous film prepared by P25. The experimental results shows that the dye-adsorption amounts of the amorphous TiO₂ film are 1.18～5.76×10-8mol/cm2 less than those of the anatase nanocrystalline film when the film thicknesses vary from 3μm to 16μm. However, with much less dye-adsorption amout, the amorphous TiO₂ film photoelectrode generates equivalent Isc, higher Voc and ff comparing with the anatase nanocrystalline film photoelectrod, hence higherη. The maximum ofηis 5.37% for the amorphous TiO₂ film based DSC and 4.69% for the anatase nanocrystalline film based DSC.The electrical and optical properties of the amorphous TiO₂ mesoporous film were measured and compared with those of the anatase nanocrystalline mesoporous film prepared by P25. It was found that the amorphous TiO₂ mesoporous film had high light scattering ability, which enhanced the light utilization of dye molecules in the film, while CM-TiO₂ film had poor light scattering. In addition, the resistances of TiO₂ films were tested by using two sheets of FTO conducting glass serving as electrical contact material with TiO₂ film, which allowed the irradiation of light and accorded with the practical electrical contact situation of TiO₂ film with FTO conducting glass substrate in DSC. Under irradiation, the resistance of dye-loaded or -unloaded amorphous TiO₂ film is about one order of magnitude lower than that of anatase nanocrystalline film. It indicates that the photo-electrons transport through AM-TiO₂ film more efficiently than it does through CM-TiO₂ film.Based on the especial electrical and optical properties of the amorphous TiO₂ mesoporous film and the high ability of adsorbing dye of the anatase nanocrystalline mesoporous film, the DSC based on the composite TiO₂ film with the double layered structure of the two kinds of TiO₂ films obtainedηof 6.89%, which was 28% higher than that obtained neither by the DSC based on the pure amorphous TiO₂ film or the DSC based on the anatase nanocrystalline film.