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-SrTi03, n-WO3, n-ZnO, n-CdS, n-CdSe, n-Si, and n-Gap; Sn02 conducting glass). The spectral response of the sensitized photocurrent was generally the same as the absorption spectrum of the phthalocyanine. The rather thick (400 8, to 1 pm) 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 (Le., 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 a supersensitizer.