Dye Sensitization of n and p Type Gallium Phosphide Photoelectrodes

A series of organic dyes, employed as visible light sensitizers, were found to generate anodic and cathodic photocurrent for both n- and p-type GaP (100) single crystal electrodes respectively. The cathodic photocurrent spectra, produced by hole injection at sensitized p-type GaP electrodes, matched well with the UV-Vis absorbance spectra of the adsorbed dye film, however the anodic photocurrent spectra generated at sensitized n-type GaP was dominated by bathochromically shifted sensitizing species. The standard sensitization mechanism of n-type semiconductors, where a molecular excited state transfers an electron to the conduction band, should not be operative in this system since the dye excited state energy is well below the energy of the conduction band minimum. Numerous mechanisms were investigated to elucidate the origin of anodic sensitized photocurrents. Sensitized photoanodic decomposition appears to be the most likely mechanism. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.005211jes] All rights reserved.