Crystalline phase evolution in nanostructured copper sulfide thin films prepared by spray pyrolysis method: the effect of annealing

In this study, physical properties of copper sulfide thin films deposited on glass substrates by spray pyrolysis method at different temperatures (260 °C, 285 °C and 310 °C) were investigated. The influence of annealing time on the physical properties of grown layers was also studied. According to FESEM images, the sizes of the compact copper sulfide grains were varied from about 100 nm to 60 nm. Hall effect and resistivity measurements confirmed that all samples had p-type conductivity. The XRD patterns showed that, together with the dominant digenite phase (Cu_1.8S) in all samples, the copper-rich phases also appeared as a result of increasing substrate temperature. The optical UV-Vis spectra analysis showed that due to increasing the substrate temperature, the band gap of the layers was reduced from about 2.4 eV to 2.0 eV. We found that as a result of annealing at 400 °C for 1.5 h in Ar atmosphere, the sample which was initially grown at 310 °C with the highest copper content, totally transformed into the polycrystalline monoclinic chalcocite phase (Cu₂S) with 3D nanoporous architecture.