In the heterojunction system, SnS was used as the absorption layer of solar cells. In this work, Cd-free ZnS material was selected as the window layer. SnS and ZnS were prepared by vacuum evaporation. Annealing plays a considerable role in the process which will affect the crystal structure and composition of the film. In this experiment, the films were annealed at temperature 300°C, 400°C and 500°C in N2 atmosphere. In XRD diagram, two strong diffraction peaks at 29.2° and 32.2° were observed, corresponding to β-ZnS (111) and SnS (111), respectively. SEM images show that average grain size of the film is about 50 nm. Noticeable increase of grain size and clear boundaries between grains were found after annealing. The electrical properties of the SnS thin films were changed through varying annealing processes. All the results indicate that ZnS/SnS structure is a good choice of SnS solar cells.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.