Semiconductor electrodes, 26: Spectral sensitization of semiconductors with phthalocyanine

Spectral sensitization by metal-free phthalocyanine (H2Pc) films was observed on various semiconductor electrodes (single crystal n-TiO2, n-SrTiO3, n-WO3, n-ZnO, n-CdS, n-CdSe, n0Si, and n-GaP; SnO2 conducting glass). The spectral response of the sensitized photocurrent was generally the same as the absorption spectrum of the phthalocyanine. The rather thick (400 A to 1 micron H2Pc films showed both anodic and cathodic photocurrents depending upon the applied potential. The anodic photocurrents represented the usual sensitization of the n-type semiconductor, while the cathodic photocurrents were attributed to p-type behavior of the phthalocyanine itself. The current-potential curves of the semiconductor electrodes depended on the nature of the H2Pc film, the presence of a redox couple (i.e., p-hydroquinone/p-benzoquinone) in solution and the wavelength of the irradiating light. The magnitude of the steady state sensitized photocurrent was linear with light intensity and was strongly affected by the addition of the supersensitizer.