The sensitization photocurrent at single crystalline ZnO electrodes in contact with an aqueous solution of crystal violet has been investigated during excitation by a 1 msec laser pulse. The photocurrent shows relaxation phenomena which can be explained by an involvement of “surface states. They capture electrons from the excited dye molecules followed by electron injection into the conduction band or recombination” with the oxidized dye molecules. – The quantum yield for the electron injection is in the order of 2%. This relatively low value a high efficiency of the recombination via surface states. – In the presence of hydroquinone, a slight increase of the quantum observed which is attributed to a photoreduction of the excited dye molecules. The reduced crystal violet molecule can inject an electron into the conduction band from its ground state.
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Yamase et al. (1978) studied this question.