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

Spray pyrolysed thin films of quaternary Cu2ZnSnS4 (CZTS) were successfully deposited on soda lime glass substrates at 320 degrees 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) x 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) x 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 (mu(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 mu(H) were observed with greater magnitude due to the existence of other secondary phases, which were confirmed complementarily by FTIR spectroscopy and XRD.