Dye-sensitizing effect of TiOPc thin film on n-TiO2 (001) surface

Dye-sensitization processes for the (001) surface of n-type titanium oxide (n-TiO2) single crystal coated with vacuum-deposited titanylphthalocyanine (TiOPc) were investigated by means of photoelectrochemical measurements and X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS). The electrode of n-TiO2 coated with TiOPc exhibited two photooxidation current bands in an aqueous electrolyte including hydroquinone (H(2)Q), due to direct excitation of n-TiO2 below 420 nm and electron transfer from TiOPc to n-TiO2 under the Q-band absorption of TiOPc at 600-800 nm, respectively, The former photocurrent process due to n-TiO2 excitation was remarkably decreased by presence of surface states, which originated from defects of oxygen induced by Ar ion bombardment of the n-TiO2 surface. The photooxidation process sensitized by the latter was evaluated from the determined energy levels of electronic bands for n-TiO2 and TiOPc. The LUMO level of TiOPc was located 0.3 eV above that of n-TiO2, which enabled electrons to transfer from TiOPc to n-TiO2. The excited state of TiOPc was not quenched by the surface states of n-TiO2 but was efficiently transferred to n-TiO2 at the n-TiO2/TiOPc interface.