Extending charge separation lifetime and distance in patterned dye-sensitized SnO₂-TiO₂ μm-thin films

A simple method for the preparation of patterned dye-sensitized SnO₂-TiO₂ thin films, designed to prolong the lifetime of the interfacial charge separated state is presented. Using microfluidic technology, the thin films were sensitized with the organic sensitizer D35 such that they contain SnO₂-TiO₂ areas with dye and SnO₂ dye-free areas at which injected electrons can be accumulated. Single wavelength transient absorption spectroscopy confirmed significantly extended charge separation lifetime at the dye-semiconductor interface. Sufficiently high density of injected electrons results in substantial decrease of charge recombination rate constants (k_cr); a factor of ∼50 compared to dye-sensitized TiO₂ thin films and a factor of ∼2000 compared to dye-sensitized SnO₂ thin films. Furthermore, the potential of this approach was confirmed by photoinduced conduction band mediated electron transfer from the dye to a model electron acceptor, Co protoporphyrin IX, which was adsorbed to the SnO₂-only regions.