Synthesis and characterization of CuInS2 thin film structures

CuInS2 is a promising semiconductor material for solar cell applications. Here we use a mild solvothermal synthesis route to prepare CuInS2 films with different thicknesses and morphologies on fluorine-doped tin oxide coated glass. The microstructure of the films is studied in detail by scanning electron microscopy and transmission electron microscopy (TEM) and associated analytical techniques. For further characterization, we apply X-ray diffraction and UV/Vis absorption spectroscopy. Two different films are synthesized using different reagent stoichiometries and thermal treatments. The thicker film (25 mu m) consists of three different regions. Close to the substrate a 600 nm thick densely packed layer occurs, on which a 1 mu m thick flaky structure is found. On top of this structure, microspheres are located which possess a size of about 3 mu m and are composed of numerous flakes. The thinner film consists of a 200 nm thick densely packed layer and a net-like structure built of individual flakes as well. In both films, TEM reveals that the flakes are adjacent to 10 nm thin branch-like rods. Energy dispersive X-ray spectroscopy of the densely packed layers indicates a Cu-rich composition which suggests them to be a p-type semiconductor. The rods and the flakes show a stoichiometric composition. Due to its high surface area, the thinner film offers a promising morphology for solar cell applications based on the large available area for the separation of electron-hole pairs, when the material is combined with a suitable electron conductor.