Preparation of hierarchical TiO2 films with uniformly or gradually changed pore size for use as photoelectrodes in dye-sensitized solar cells

The TiO2 photoelectrode containing pores of different sizes was fabricated by adding various amounts of polystyrene microspheres (188 nm) into the TiO2 paste, which was used as template agent during the sintering process. On the one hand, it was found that the photoelectrode with appropriate size of pores was beneficial for the enhancement of photovoltaic performance of the corresponding dye-sensitized solar cells (DSSCs) via efficient utilization of incident light. On the other hand, the presence of large pores would also tend to reduce the amount of dye-uptake resulting in the decrease of cell performance. Furthermore, a multi-layered stacking architecture of TiO2 nanoporous film with pore size gradually increased from bottom FTO glass to the top of the film was developed and used as photoelectrode in DSSCs with N719 as the sensitizer. The photoelectric conversion efficiency of 7.80% was realized which is 17.6% higher than that obtained for DSSCs containing TiO2 nanoporous films with uniform size of pores. UV-vis spectra measurement and electrochemical impedance spectroscopy analysis were carried out for further studying the effect of the pore size and the stacking pattern on the photoelctronic and electrochemical properties of the resultant DSSCs. (C) 2013 Elsevier Ltd. All rights reserved.