Structural properties of CZTS thin films on glass and Mo coated glass substrates: a Rietveld refinement study

Due to the difficulty in analyzing a few properties of CZTS (Cu2ZnSnS4) films coated on opaque substrates, the process conditions are often optimized on normal soda lime glass substrates and then transfer the process to Mo coated soda lime glass (SLG) substrates for device fabrication. This study concentrates on the analysis of structural properties of CZTS films on normal glass and Mo coated SLG substrates. CZTS films were coated on these two substrates by spin coating followed by sulphurization in -N-2 + H2S atmosphere. Phase purity of the films was analyzed by GIXRD and Raman spectroscopy. W-H analysis was used for estimating crystallite size and lattice strain of the films on the two substrates. Detailed structural studies were carried out with Rietveld refinement technique using GSAS package. Kesterite model with space group I4 (SG No: 82) was chosen for the refinement. Formation of kesterite phase on both substrates was confirmed from the refined lattice constant values. Deviation in bond angle with respect to kesterite structure was also analyzed. Different structural parameters were observed for the films on these substrates. The study indicates that it is important to optimize the properties of CZTS film on Mo coated SLG substrate separately, without following the same preparation conditions used for coating film on glass substrates.