Engineering of sub-band in CuGaS2 thin films via Mo doping by chemical spray pyrolysis route

High quality undoped and molybdenum (Mo) doped CuGaS2 (CGS) crystalline thin films were deposited using in-house chemical spray pyrolysis thin film deposition unit. To improve the crystalline quality and prevent the oxidation, deposited thin films were subjected to annealing at various atmospheres (vacuum, nitrogen, and argon). The measured X-ray diffraction peaks were indexed to the standard chalcopyrite tetragonal structure and revealed that no identification of binary phases in the CGS system. Mo doping has strongly influenced the optical properties especially at the bandgaps of CGS thin films. The measured band gaps for undoped, 1%, 2% and 3% Mo-doped CGS thin films were found to be 2.40, 2.38, 2.35, and 2.65 eV, respectively. Interestingly, 1 and 2 wt% Mo-doped CGS thin films give additional characteristic band at 1.45 eV and 1.47 eV, and these could be due to the formation of sub-bandgap in between the conduction and valence band after doping. The photo-response of the prepared films has also been analyzed which demonstrates considerable photocurrent generation for the 1 and 2 wt% Mo-doped CGS thin films. The enhanced photoresponsivity reveals that Mo doped CGS thin films possess potential applications in solar energy utilization.