A thin-film solar cell based on a Cu 2 ZnSnS 4 (CZTS) absorber layer deposited by pulsed laser deposition has been fabricated with an Al:ZnO (n-type) window layer and a CdS buffer layer. Some peaks attributed to ( 112), ( 200), ( 220), and (312) planes of CZTS appeared in an X-ray diffraction pattern of a thin film. The composition of the film was Sn-rich and the band gap energy was approximately 1.5 eV. A CZTS film annealed at 500 C in an atmosphere of N 2 had optical characteristics suitable for use in an absorber layer of a thin-film solar cell and was used for a solar cell. The CZTS thin-film solar cell with an active area of 0.092 cm 2 showed an open-circuit voltage of 546 mV, a short-circuit current of 6.78 mA/cm 2 , a fill factor of 0.48, and a conversion efficiency of 1.74%.

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

Cu 2 ZnSnS 4 (CZTS) precursors were prepared by pulsed laser deposition while controlling the energy density to eliminate grains of Cu-Sn-S compounds. The precursor prepared with an energy density of 0.7 J/cm 2 was flat and of better quality than the precursor prepared with an energy density of 1.5 J/cm 2 . The precursors were annealed in N 2 þ H 2 S (5%) atmosphere. As a result of annealing, the decrease of the compositional ratio of sulfur was suppressed and the films became nearly stoichiometric. Some peaks in the an X-ray diffraction pattern of thin films are attributed to ( 112), ( 220), (312), and ( 200) planes of CZTS. The direct band-gap energy of the film annealed at 500 C was about 1.5 eV, which is very close to the optimum value for a solar-cell absorber, and hence was used for a solar cell. The CZTS thin film solar cell with an active area of 0.12 cm 2 showed an open-circuit voltage of 336 mV, a short-circuit current of 6.53 mA/cm 2 , a fill factor of 0.46, and a conversion efficiency of 0.64%.

Cu 2 ZnSnS 4 thin films were grown epitaxially on GaP substrates by pulsed laser deposition (PLD). The band gap of the films was about 1.5 eV from the absorption spectra. In XRD patterns, two CTZS peaks, (004) and (008), were observed at the vicinity of GaP peaks of (200) and (400), respectively. The Cu 2 ZnSnS 4 thin films deposited at substrate temperatures of 350 and 400 °C were nearly stoichiometric and showed 4 poles observed at about 48° in pole figure measurement, indicating that the samples were oriented in plane.

Cu2ZnSnS4 thin films were prepared by photo-chemical deposition (PCD) from aqueous solution containing CuSO4, ZnSO4, SnSO4 and Na2S2O3. The compositional ratio of the films was dependent little on pH of aqueous solution and the surface of the samples became smooth by use of aqueous filter. A sample annealed at 400°C was a p-type semiconductor and showed photoconductivity. This is the first observation of photo-conductivity from semiconductor films deposited by PCD, to the best of our knowledge.