Dye-sensitization of n-TiO2 single-crystal electrodes with vapor-deposited oxometal phthalocyanines

Abstract Photoelectrochemical dye-sensitization of n-type titanium dioxide (n-TiO2) was investigated using thin films of oxometal phthalocyanines (MOPc's) vapor-deposited on rutile (001) surface. Their dye-sensitizing effects were affected by the morphology of deposited MOPc's which depended on substrate temperatures during deposition. At low temperature of 20°C, MOPc's grew in a thin layer composed of small grains, while the molecules deposited at 200°C aggregated to form heterogeneous island-like crystallites. The n-TiO2 electrodes the surface of which was all covered by the thin layers of both titanyl Pc (TiOPc) and vanadyl Pc (VOPc) yielded photoreduction currents under excitation at their visible absorption bands, based on p-type organic semiconducting properties of MOPc's. On the other hand, the island-like crystallites of TiOPC dye-sensitized the photoelectrochemical oxidation of the bare n-TiO2 surface due to its heterogeneous structure. The VOPc islands were not capable of dye-sensitization because of its lower energy level of the excited state