Dependence of electron transport in nanocrystalline TiO2 films sensitized with [NBu4]2[Ru(Htcterpy)(NCS)3] ([NBu4]+ = tetrabutylammonium cation; H3tcterpy = 4,4′,4″-tricarboxy-2,4:2′,4′:2″-terpyridine) on the properties of TiO2 nanoparticles

Nanocrystalline TiO2 colloids were prepared by hydrothermalization. The porosity and the size distribution of the particles increase with a longer hydrothermalization reaction period. The particle size decreases with lower reaction temperature. Electron transport in nanocrystalline TiO2 film electrodes sensitized with [NBu4]2[Ru(Htcterpy)(NCS)3] ([NBu4]+ = tetrabutylammonium cation; H3tcterpy = 4,4′,4″-tricarboxy-2,4:2′,4′:2″-terpyridine) (black dye) was investigated from the standpoint of TiO2 particle properties such as particle size, size distribution, and porosity. When the size distribution and the porosity were comparable, the electron lifetime (τrec) increased and the electron diffusion coefficient (D) decreased at smaller particle sizes. The value of D   decreased when the porosity increased. Large differences in the diffusion length (L=Dτrec) among the TiO2 films were observed. However, Jsc did not depend on L. Thus, we conclude that the Jsc values were more effectively influenced by the absorption coefficient (α) than by L.