Sensitization of Photoconductivity in Cadmium Sulfide*

The photoconductivity of cadmium sulfide in the red and near infrared can be enhanced by sensitization with cyanine dyes. There is general qualitative agreement between the results of sensitization with pinacyanole, dicyanine-A, kryptocyanine, and neocyanine, and those obtained when these dyes are used as optical sensitizers in photography, so that the two effects may be considered to be similar.Cells have been made in the form: metal electrode || dye || cadmium sulfide || metal electrode, which upon illumination show a photo-emf and steady current, the dye being positive with respect to the cadmium sulfide. A simple explanation is proposed which relates this emf to the energy difference between the conduction bands of dye and cadmium sulfide. On the basis of this picture, and assuming electron conduction in both, the conduction band of the dye must lie above that of the cadmium sulfide, and the condition for sensitization by charge carrier transfer according to the original proposal of Gurney and Mott is satisfied.