Ordered porous TiO2 films obtained by freezing and the application in dye sensitized solar cells

• Ordered porous TiO2 films were achieved by freezing.
• Enlarged film thickness is beneficial for ice crystal growth.
• Prolonged freezing time is helpful for ice crystal growth.
• Light scattering is enhanced by ordered porous films.
• Light scattering is beneficial to performance of DSSCs.

TiO2 films with ordered porous structure were prepared by freezing. By simply freezing wet TiO2 film on a cold copper plate, ice crystals could grow from bottom of film. Removing such ice crystals then led to ordered, micro-sized pores in the films. With assistance of scanning electron microscopy and N2 adsorption–desorption isotherms, micro-structural properties of the films were studied. Coarsening behavior of ice crystals was analyzed based on evolvement of the micro-structure. It was found that, both larger film thickness and longer freezing time were beneficial for the formation of ordered porous structure, which was caused by enhanced ice crystals growth. The films were then used to fabricate photoanode of dye sensitized solar cells, of which the photo-to-electric power conversion efficiency was evaluated. It was observed that, solar cell made of ordered porous TiO2 film came out with 13% larger photo-current density comparing to that made of conventional doctor blading method, which is due to the enhanced light scattering by the ordered porous structure.