In this study, Cu2ZnSnS4(CZTS) formation by co-evaporation and subsequent annealing in S-flux was demonstrated using molecular beam epitaxy(MBE) system and the influence of the S-flux annealing temperature on the CZTS formation was investigated. At the films formed by co-evaporation of Cu, Zn, Sn and S at 320 degrees C and subsequent annealing in S-flux at 320-450 degrees C, CZTS and Cu-2 _ S-x phases were detected and those formations were found to have strong dependence on the S-flux annealing temperature. For annealing temperature, detected CZTS has maximum amount at the range of 380-420 degrees C. On the other hand, detected Cu-2 _ S-x is minimum amount at that temperature range. Depth profile of those films showed that significant Cu segregation occurred to the film surface above 400 degrees C of S-flux annealing temperature. These results suggest that the CZTS phase with less secondary phase of Cu-2 _ S-x, which has worse impact on the solar cell performance, is formed in the limited temperature range of 380-420 degrees C of S-flux annealing performed after co-evaporation. 2.25% power conversion efficiency was achieved at the solar cell with CZTS formed by the co-evaporation at 320 degrees C and subsequent S-flux annealing at 400 degrees C. (C) 2017 Elsevier B.V. All rights reserved.