The earth-abundant, less environmental impact Cu2ZnSnS4 (CZTS) thin film solar cells are fabricated by using a sulfurization technique. The CZTS film possesses promising characteristic optical properties; band-gap energy of about 1.5 eV and large absorption coefficient in the order of 104 cm-1. All constituents of this CZTS film, which are abundant in the crust of the earth, are non-toxic. Therefore, by using CZTS film practically as the absorber of thin film solar cells, we will be free from both of the resource saving problem and the environmental pollution. We believe that the key words of the after next generation have to be abundant and non-toxic. CZTS is one of the most promising materials for thin film solar cells.
In this study, CZTS absorber layers were synthesized by the sulfurization technique of sputtered precursors. In our previous report, we have clarified that the off-stoichiometry composition of Cu-poor and Zn-rich is desirable to achieve high conversion efficiency. By using CZTS compound target that provide such active composition, we could use a simple single sputtering method to prepare CZTS absorber. In our laboratory, a two stages process of precursor preparation followed by sulfurization is a major fabrication method from the start of this study. We think that this method is suitable for a mass production. Therefore, the sulfurization process as well as the composition control is a quite important issue. In this paper, TG/DTA system available in the H2S atmosphere is introduced to optimize the sulfurization condition. When we examined the sulfurization condition, we used both the results of XRF composition measurements and TG/DTA thermal analysis. It was confirmed that the raising rate of the substrate temperature within the certain temperature region affected significantly to the film properties.
Nagaoka National College of Technology, Japan Science and Technology Agency-CREST
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