In this paper, photoexcitation processes in the bilayer devices based on inorganic materials and poly(N-vinylcarbazole) (PVK) were investigated. In order to clarify the roles of inorganic materials in photoconductive properties of bilayer devices, TiO2 and ZnS were chosen to combine with PVK. A model for generation of photocurrent (Iph) in single layer device of PVK was obtained. It is deduced that the recombination rate constant (Pcomb) and the ionization rate constant (γ) of excitons should be considered as the most important factors forIph. For inorganic materials (TiO2 or ZnS)/PVK bilayer devices, in reverse bias of -4 V, the photocurrent of 115 mA/cm2 in the TiO2/PVK device was observed, but the photocurrent in the ZnS/PVK device was only 10 mA/cm2 under the illumination light of 340 nm and the light intensity of 14.2 mW/cm2.The weaker photocurrent is attributed to the absorption of ZnS within UV region and the energy offset at the interface between PVK and ZnS, which impedes the transport of charge carriers.