Study on the effects of different sulfur vaporization temperature on the properties of CuInS2 thin films

CuInS2 (CIS) absorber thin films were prepared by sulfurization of In/Cu metallic stacked precursor. The precursor thin films were sulfurized using a commercial furnace system in the S2 (s) + Ar atmosphere at 425 °C for 1 h. Effects of different S vapor temperature from 150 to 400 °C on the structural, morphological, compositional and optical properties of CIS thin films were investigated. X-ray diffraction and Raman studies showed that the sulfurized thin films with S vaporization temperature below 300 °C exhibited CIS tetragonal structure with secondary phases such as CuxSy, CuIn5S8, and InxSy. The sulfurized thin films with S vaporization temperature over 350 °C showed a single CIS tetragonal structure. Compositional ratio of CIS thin films showed that Cu/In and S/(Cu + In) ratio in the CIS thin films with S vaporization temperature over 350 °C were 1.0–1.2 and 0.9–1.1, respectively, while compositional ratio deviated from stoichiometry when the sulfurized thin films below S vaporization temperature of 350 °C. Optical study showed that the band gap energy and the absorption coefficient of CIS thin films were estimated from 1.18 eV to 1.5 eV and over 104 cm−1, respectively.