Thin films of tri-oligo(phenylene-vinylene) end terminated by di-butyl-thiole (tOPV) were thermally deposited in UHV on the surface of CdS film. The surface potential variation and the formation of the structure of unoccupied electron states (DOUS) located 0-20 eV above the vacuum level were monitored during organic film deposition using low-energy total current spectroscopy (TCS). Migration of substrate atomic components (Cd and S) into the deposited organic film was observed and its influence on the interface DOUS formation was discussed. Photovoltage sensitivity in the tOPV/CdS heterojunction was discovered and the photovoltage transient characteristics as well as the spectral distributions were measured.