Fabrication And Characterization Of Cu₂SnS₃ And Cu₂ZnSn S₄ Photovoltaic Material

Cu2SnS3(CTS) and Cu2ZnSnS4(CZTS), are considered as a potential candidate of indium-free thin film solar cells absorber layer due to their characters of p-type semiconductor, direct band gap, high absorption coefficient, non-toxic and abundant-component. To achieve these outstanding properties, it still needs to improve processes to fabricate CTS and CZTS layers with suitable crystallization.In this dissertation, CTS thin films were fabricated by sulfurizing different kinds of metallic precursors. Columnar grains were obtained with optimized conditions. CZTS was prepared by sulfurization of co-electrodeposited Cu-Zn-Sn metallic precursor.(1) CTS with columnar grains were synthesized by sulfurizing Cu/Sn stacked metallic precursor. The Cu/Sn ratio in the sulfurized thin films was adjusted stoichiometric value, which is a key point to obtain desirable CTS material because the loss of Sn usually occurs at elevated sulfurization temperature.(2) CTS with highly dense crystallinity were fabricated through sulfurization of Cu-Sn alloy precursors. The Cu-Sn precursors were sputtered by using single Cu-Sn target with Cu/Sn ratio of 1.88. This approach is cost-efficient and simple, because the corresponding sputtering process does not need the control of sputtering parameters to obtain a precursor with specific Cu/Sn ratio. In addition, the phenomenon of Sn loss while high temperature sulfurizing as previously reported did not occur in this process. The band gap of Cu2Sn(S,Se)3 was adjusted by varying ratio of S/Se in annealing process. Similar Cu2SnS3 thin film can also be synthesized on Mo layer.(3) One-step annealing process of Cu metallic precursor at a mixture vapor of S, Sn and SnS to prepare CTS was carried out for the first time. Moreover, this innovative approach was proved successfully.(4) CZTS was obtained by single-step co-electrodeposition method of Cu-Zn-Sn precursor, which followed by annealing in sulfur vapor. These results grain experience for mass production of Cu2ZnSnS4 as well as Cu2SnS3.