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A comprehensive model involving both photochemical and electrochemical steps has been constructed for photoelectrochemical cells comprising identical, inert metal electrodes immersed in a solution containing a fluorescent dye and a nonphotosensitive redox couple. The model allows for the possibility of electrodic electron transfer to or from dye photolysis products formed in the bulk of the electrolyte as well as at the electrode surface. Steady-state analyses on the model lead to complicated relationships between open-circuit photovoltage, V,,, irradiance, E, the dark concentrations of the various species, and the various rate constants. When the photolytic concentration perturbation and the open-circuit photovoltage are small, these relationships simplify to V,, = (RT/F) In (1 + KIE), where K1 is a function of the dark concentrations of the various species and of the rate constants for excitation, fluorescence emission, intersystem crossing, photochemical reaction, and the various types of quenching, diffusion, and electron transfer. When the further and not necessarily identical assumption of low irradiance is made, the logarithmic relationship simplifies to the linear form V, = (RT/F)KIE.

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