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 TiO2 microspheres are synthesized at low temperature.
• The TiO2 microsphere film can improve carrier transport efficiency of DSSC.
• The interface optimization of the TiO2 microsphere film is studied.
• The Mg2+ modified TiCl4 treatment can optimize the performance of scattering layer.
• DSSC based on the bi-layer anode gets an optimized efficiency of 9.12%.

Size controllable anatase TiO2 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 TiO2 microsphere films are built on the top of TiO2 nanoparticle underlayer to prepare a type of bi-layer anodes. It is illustrated that this type of TiO2 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 TiO2 microspheres. Then we further optimize the interface of TiO2 microsphere scattering layer through TiCl4 treatment and Mg2+ modified TiCl4 treatment. TiCl4 treatment can improve the dye adsorption and connections between the TiO2 microspheres. However, it also generates more surface defects in the meantime. And through the Mg2+ modified TiCl4 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%.