A new strategy for preparation of Cu2ZnSn(SxSe1-x)(4) (CZTSSe) thin film solar cells by a two-step sulfurization of Cu-Zn-Sn-Se precursors is introduced. The growth evolution of the CZTSSe films has been characterized compositionally and structurally and the growth mechanism has been revealed. A single-phase CZTSSe film without any secondary phase was observed with a solar cell efficiency of 8.55%. A sulfur rich CZTSSe layer was obtained at grain boundaries which is proposed to be beneficial by forming a hole barrier at grain boundary to reduce the recombination. This solar cell is further characterized using photoluminescence (PL) and capacitance-voltage (C-V) and drive-level capacitance profiling (DLCP) technology.