Crystal quality studies of CuInS2 films prepared by spray pyrolysis

Raman spectroscopy and XRD methods were applied to determine the phase composition and crystal quality of copper indium sulfide (CIS) films grown by spray pyrolysis. The aim of the study was to develop a low-cost preparation technique for solar cell quality materials. The Cu/In molar ratio in spray solution (0.8–1.1) and post-deposition heat treatment conditions were taken as variables.According to XRD, KCN-etched films from Cu-rich solutions result in single phase CuInS2. The A1 phonon modes at 290 and 300 cm−1 in Raman spectra show that CIS films deposited at 370 °C consisted of chalcopyrite (CH) and Cu–Au (CA) ordered phases of CuInS2. Both XRD and Raman studies showed the presence of an extra phase in as-deposited films using Cu/In=0.8–1.0, which could belong to CuIn5S8. Thermal treatments reduced the amount of secondary phase and improved the crystallinity of the films. The heat treatment at 525 °C in H2S led to an increase in CH content with a decrease in the FWHM of A1 mode. Furthermore, the rise of the quality factor (I(CH)/I(CH)+I(CA)) up to 62% was observed, indicating the formation of CuInS2 films with better crystal quality.