This study investigated the influence of stacked structures on the formation of secondary phases, as pertaining to the performance of Cu2ZnSn(S,Se)(4) (CZTSSe) thin film solar cells. Absorber layer precursors of ZnS/Cu/Sn (Sample A) and ZnS/Cu/Sn/Cu/Sn (Sample B) were prepared by sputtering and selenization. Secondary phases of Cu2SnSe3, Cu2-xS and ZnS were observed at the bottom of the absorber layer in Sample A, while only ZnS secondary phases appeared in the absorber layer of Sample B. The structure of stacked precursors was shown to have a significant influence on the formation of secondary phases as well as the crystal quality of the CZTSSe absorber layer. CZTSSe thin film solar cells were prepared from a structure of glass/MoICZTSSe/CdS/ZnO:Al/Al. Sample B demonstrated cell efficiency of 2.4%, which is far superior to the 0.75% efficiency of Sample A. The existence of Cu2-xS and Cu2SnSe3 secondary phases degraded the crystal quality of the absorber layer and increased the number of defects in the crystalline structure. (C) 2015 Elsevier B.V. All rights reserved.