Synthesis Of Three-dimensional （3D） Hierarchical Structure TiO₂and Its Application On Dye-sensitized Solar Cells

Dye-sensitized solar cells (DSSC) as a new generation photovoltaic device, has been studied extensively because of its integration of high efficiency, low cost and facile fabrication. The photoanode is the heart part of DSSC. In general, high specific surface area, fast electron transport and large light scattering ability are desirable properties for a well performing photoanode. However, the porous photoanode fabricated from anatase TiO2nanoparticles is usually rather transparent. Moreover, the electrons produced from the dye molecules have to pass through numerous grain boundaries in order to get transparent conductive-oxide (TCO) electrode. Recently, in order to improve the efficiency of DSSC, many efforts have been devoted to improve the electron transport ability, dye adsorption ability and light scattering ability of photoanode through tailoring the micro-morphology and microstructure of TiO2particles.In this paper, mesoporous TiO2microspheres and flower-like TiO2microspheres with hierarchical structure were successfully synthesized by hydrothermal method. The samples were characterized by XRD, FESEM, TEM and surface area analyzer. The as-synthesized mesoporous TiO2microspheres and flower-like TiO2microspheres were used to prepare the photoanode of DSSC. The photovoltaic performances of DSSCs assembled with different photoanodes were measured by electrochemical workstation and IPCE measurement system. The experiment content and results are as follows:(1) Mesoporous TiO2microspheres with high surface areas were prepared by hydrothermal method using titanium sulfate as raw materials in the presence of urea. The particle size, surface area, pore size and pore volume of the mesoporous TiO2microspheres can be tailored by adjusting the amount of urea. The DSSC fabricated with TiO2microspheres synthesized with1.2g urea shows the highest light-to-electric energy conversion efficiency of6.2%under illumination of simulated AM1.5G solar light (100mW/cm2), which is much higher compared with a commercial Degussa P25TiO2nanocrystals photoelectrode (4.24%). The photoanode made of TiO2microspheres was modified with different concentration of TiO2solution. The result show that photoanode treated with low concentration TiO2solution can effectively improve the efficiency of DSSC, but with the concentration increaseing, the efficiency of DSSC decreases.(2) A double layered photoanode for dye sensitized solar cells (DSSCs) using TiO2nanocrystals as underlayer and mesoporous TiO2microspheres as scattering layer was fabricated. Owing to its large light scattering ability, strong dye adsorption ability and good electronic transfer capability, a high light-to-electricity conversion efficiency of7.78%for the DSSC with this novel double layered photoanode was achieved under illumination of simulated AM1.5G solar light (100mW/cm2), indicating50%,19%and25%increase in the conversion efficiency compared to the single layered nanocrystalline TiO2photoanode, double layered nanocrystalline TiO2photoanode and mesoporous TiO2microspheres photoanode respectively.(3) Flower-like TiO2were successfully synthesized by hydrothermal method using Ti powders as raw materials. A bilayer-structured photoanode made of TiO2nanoparticles and flower-like TiO2was fabricated by a doctor-blade method. A relatively high light-to-electricity conversion efficiency of7.75%for the DSSC assembled with this bilayer-structured photoanode was achieved under illumination of simulated AM1.5G solar light (100mW/cm2), which is much higher than that of the DSSCs assembled with nanocrystalline TiO2photoanode (6.45%) and flower-like TiO2photoanode (3.89%).