Quaternary Cu2ZnSnS4 (CZTS) thin films with different S/(Cu+Zn+Sn) molar ratio have been deposited by homemade chemical spray pyrolysis unit. Secondary phase formation in CZTS thin films with respect to various S/(Cu+Zn+Sn) molar ratio was investigated. XRD and micro Raman results revealed that CZTS thin films belongs to kesterite crystal structure with a preferred orientation along (1 1 2) plane. Films deposited at x = 2, 1.72, 1.33 contain binary and ternary phases in addition to CZTS. High purity single phase CZTS was obtained at x = 0.80. The surface morphology of the films is found to be smooth. The optical absorption spectra showed that the absorption coefficient of the CZTS thin films is larger than 10^4 cm−1 in the visible region and the optical band gap varies from 2.05 eV to 1.45 eV. CZTS thin films were used as a photocatalyst to examine the effect of secondary phases in the decolorization of the Rhodamine B (RhB) dye under visible light. It was found that the presence of secondary phase significantly affects the photocatalytic performance of CZTS thin films. © 2018 Elsevier B.V., All rights reserved.