Semiconductor electrodes. 30. Spectral sensitization of the semiconductors titanium oxide (n-TiO2) and tungsten oxide (n-WO3) with metal phthalocyanines

Thin films (100-250 A) of several phthalocyanines (MgPc, ZnPc, AICIPc, TiOPc, CoPc, FePc, H2Pc) were investigated as sensitizers for photoelectrochemical processes at n-type Ti02 and W 0 3 single crystal electrodes in aqueous solution. The sensitized oxidation of several solution species (I-, Fe(CN)64-, hydroquinone, Fe(I1)-EDTA) occurred with photocurrents proportional to light intensity and spectral responses characteristic of the metal phthalocyanine (MPc) films. At negative electrode potentials cathodic photocurrents for the reduction of benzoquinone, 02, and Fe(II1)-EDTA were observed, consistent with the p-type behavior of the phthalocyanines themselves. The photoelectrochemical behavior is rationalized from the energy levels of the semiconductors, solution couples, and MPc. The surface ionization potentials were found to yield better estimates of the phthalocyanine levels than the redox potentials of the MPc couples (measured in N,N-dimethylacetamide solutions).