Structural, optical and electrical properties of spray-deposited CZTS thin films under a non-equilibrium growth condition

Spray pyrolysed thin films of quaternary Cu 2 ZnSnS 4 (CZTS) were successfully deposited on soda lime glass substrates at 320 °C under a non-equilibrium condition (by varying Zn, Sn and S precursor concentrations) and without additional sulfurization. The effect of deficiency and enrichment of these three elements (normalized with respect to Cu) on the film's microstrain, optical band-gap and Hall mobility was investigated. A large non-uniform microstrain of (5–6) × 10 −3 and compressive nature were observed for both Zn- and Sn-enriched films from Williamson–Hall analysis of x-ray diffraction (XRD) data. However, a tensile strain of (2–3) × 10 −3 was revealed in Sn-poor and S-rich samples. The optical band-gap ( E g ) in stoichiometric CZTS was found to be 1.45 eV and Hall mobility ( μ H ) in the range 87–92 cm 2 V −1 s −1 was observed for S- and Zn-enriched films. The tensile nature of microstrain and inhomogeneities in E g and μ H were observed with greater magnitude due to the existence of other secondary phases, which were confirmed complementarily by FTIR spectroscopy and XRD.