Abstract Photoconductive couples in which a ZnO thin film is placed in surface contact with a layer of aggregated organic dye have been investigated under low-intensity illumination and with flash lamp methods. For the dyes studied (crystal violet, methylene blue, eosin- Y, and acridine orange) it was found that the photoresponse at visible wavelengths varies with the square-root of the incident light intensity, linearly with the dark current, and builds-up and decays via exponential processes. Measurements made during the formation of the couples show that ZnO conduction electrons are transferred to the dye in the dark and return when the dye layer is illuminated. A Schottky barrier model is proposed, in which ZnO conduction electrons are trapped in interfacial levels close in energy to the dye ground state. The theory indicates that the fraction of ZnO conduction electrons ( Δn n 0 ) transferred in the dark is approximately related to the ZnO thermoelectric work function (Φ) and the dye photoelectric work function (φ) by: φ≅ Φ + A( Δn n 0) 2 , where A is a constant determined by ZnO parameters. The data for the different dyes studied are in reasonable agreement with this result. A detailed analysis of the model leads to predictions of the kinetic processes in agreement with experiment.