PACS 68. 84.60.Jt Cu 2 ZnSnS 4 (CZTS) thin films were prepared by post-annealing films of metal sulfides of Cu 2 S, ZnS and SnS 2 precursors deposited on soda-lime glass substrates by photo-chemical deposition (PCD) from aqueous solution containing CuSO 4 , ZnSO 4 , SnSO 4 and Na 2 S 2 O 3 . In this study, sulfurization was employed to prepare high quality CZTS thin films. Deposited films of metal sulfides were annealed in a furnace in an atmosphere of N 2 or N 2 +H 2 S(5%) at the temperature of 300˚, 400˚ or 500˚C. The sulfured films showed X-ray diffraction peaks from (112), (220), and (312) planes of CZTS and the peaks became sharp by an increase in the sulfurization temperature. CZTS thin film annealed in atmosphere of N 2 was S-poor. After annealing atmosphere was changed from N 2 into N 2 +H 2 S(5%), the decrease of a compositional ratio of sulfur could be suppressed.1 Introduction Cu 2 ZnSnS 4 (CZTS) has a structure obtained by replacing the indium (In) in chalcopyrite CuInS 2 with zinc (Zn) and tin (Sn), and has very suitable optical properties for an absorber layer of solar cell. Firstly, it has a band gap energy of 1.5 eV which is very close to the optimum value of absorber layer of solar cell. Secondly, it has an absorption coefficient over 10 4 cm -1 which is large enough to constitute thin film solar cell. From these significant features, CZTS is expected to be one of the promising materials for thin film solar cell. This material is non-toxic and the component elements are abundant in the crust of the earth and then inexpensive. Therefore, if we can use CZTS film as absorber of solar cells, we will be free from both of the resource saving problem and the environmental pollution. Photo-chemical deposition (PCD), which is employed in this report, is an interesting thin film growth method of a novelty because films can be grown in a short time and at low cost. There are reports in which ZnS, CdS, ZnSe, PbS and CZTS films were deposited by PCD [7][8][9][10][11][12][13].We reported in a previous paper that a CZTS film prepared by PCD and post-annealed at 400˚C was p-type semiconductor and showed photoconductivity and that X-ray diffraction peaks of CZTS were