Growth and characterization of Cu2ZnSnSe4 thin films by a two-stage process

Polycrystalline Cu2ZnSnSe4 (CZTSe) thin films were prepared by a two-stage process namely thermal evaporation of stacked layers Cu/ZnSe/Sn/Se on soda-lime glass substrates held at different substrate temperatures (Ts) in the range 523–723 K followed by annealing the stack in selenium atmosphere at 723 K for an hour. The effect of Ts on the growth and properties of these films were analyzed by studying their structural, microstructural and optical properties. XRD studies revealed the structure to be kesterite with a=0.569 nm and c=1.139 nm. Raman spectroscopy is used as a complimentary tool to know the presence of possible secondary phases. The crystallinity of the films improved with increase in the substrate temperature. Spectral transmittance studies of these films revealed two optical transitions with direct band gaps of ∼1.0 eV and 1.4 eV which are attributed to CZTSe and CZTSe with minor ZnSe, as the annealed stack might be inhomogeneous.