Low-temperature synthesis of size-controllable anatase TiO2 microspheres and interface optimization of bi-layer anodes for high efficiency dye sensitized solar cells

Size controllable anatase TiO 2 microspheres with compact nano-aggregate structures are synthesized via a facile and low-temperature solvothermal treatment. The diameters of as-prepared products can be controlled to vary from 250 to 1100   nm. Different kinds of TiO 2 microsphere films are built on the top of TiO 2 nanoparticle underlayer to prepare a type of bi-layer anodes. It is illustrated that this type of TiO 2 microsphere scattering layer can not only increase the absorption of light, but also improve the carrier transport and charge collection efficiency of dye sensitized solar cell (DSSC). Therefore, an optimized efficiency of 8.20% is achieved for DSSC with a scattering layer consisted of 500   nm TiO 2 microspheres. Then we further optimize the interface of TiO 2 microsphere scattering layer through TiCl 4 treatment and Mg 2+ modified TiCl 4 treatment. TiCl 4 treatment can improve the dye adsorption and connections between the TiO 2 microspheres. However, it also generates more surface defects in the meantime. And through the Mg 2+ modified TiCl 4 treatment, we can increase the dye adsorption density and retard the interfacial charge recombination and decrease the surface defects, simultaneously. As a result, the efficiency of DSSC based on bi-layer anode is enhanced from 8.20% to 9.12%.