Self-oriented TiO2 nanosheets in films for enhancement of electron transport in nanoporous semiconductor networks

Self-oriented anisotropic nanoparticles in nanoporous films were obtained by controlling the surface functionality induced by the organic amino acid derivatives adsorbed onto TiO2 nanosheets. In particular, tyrosine-functionalized TiO2 nanosheets were self-oriented in a nonparallel orientation with respect to the substrate plane owing to the following surface properties: (1) the z-potential, (2) hydrogen bonding, and (3) hydrophobicity due to the collaborative effects of segregative interactions from hydrophilic surroundings, i.e., water and oxide substrates. Although nanoporous films with both parallel and nonparallel orientations of TiO2 nanosheets with respect to the substrate plane exhibited a similar internal surface area and porosity, evaluation of the electrochemical properties of TiO2 films with non-parallel orientation showed a significant improvement in electron transport through the TiO2 nanoporous network, as demonstrated in dye-sensitized solar cell devices.