Synthesis of hierarchically organized nanostructured TiO2 by pulsed laser deposition and its application to dye-sensitized solar cells

Hierarchically organized TiO₂ nanostructures were synthesized on fluorine-doped SnO₂(FTO)/glass substrate at room temperature under various oxygen pressures using pulsed laser deposition (PLD). The microstructures of the obtained TiO₂ nanostructures were changed sensitively as oxygen pressure. A fully dense structure could be achieved below oxygen pressure of 50 mTorr. However, ultrafine nanoparticles (5~15 nm) were produced over 50 mTorr and they assembled hierarchically in ordered forest consisted of characteristic tree-shaped structures. The hierarchical assemblies were gradually to be porous and finally the tree shape was disappeared and the assemblies were disordered with increasing oxygen pressure. The synthesized TiO₂ nanostructures were changed from amorphous to anatase phase without morphological changes after air annealing at 450°C for 1 hour. The anatase nanostructures were applied to dye-sensitized solar cells (DSSCs). Cell performance and electron diffusion characteristics of the hierarchical anatase assemble prepared by PLD as photoelectrode were investigated in DSSCs. Optimal TiO₂ nanostructure synthesized by PLD for photoelectrode in DSSCs was discussed in terms of electron transport and dye absorption.