Investigation of the structural and optical properties of ACZTS solid solution

Multinary chalcogenides Ⅰ₂-Ⅱ-Ⅳ-X₄ materials made from ecofriendly and abundant elements, namely Cu₂ZnSn(S,Se)₄ have received wide attention in the photovoltaic field. Recently, many researchers have focused on studying the behavior of their characteristic features through substituting of one or two of CZTS(e) constituents with isoelectronic elements in order to reduce the propensity of the system to form unwanted defects which hinder the improvement of photoelectric conversion capacity of this material. In this work, (Ag_xCu_1-x)₂ZnSnS₄ solid solution were synthetized via solid state method under vacuum. The impact of Ag substitution on the structural and optical properties of the as-prepared ACZTS samples has been systematically investigated. According to X-ray diffraction (XRD) analysis, a noticeable change in the structural features of (Ag_xCu_1-x)₂ZnSnS₄ samples has been observed. The diffraction lines are slightly shifted to lower angles with increasing Ag content, and the dominant tetragonal phase with a kesterite (CZTS) type-structure is gradually shifted into tetragonal perquitasite-type AZTS structure as a result of the appearance of peaks associated with the letter structure. The lattice constants of (Ag_xCu_1-x)₂ZnSnS₄ deviate from Vegard's law as a consequence of defects formation during the synthesis. UV-Vis diffuse reflectance measurements showed that optical properties could be tuned by varying the Ag content, however, due to the presence of secondary phases, the variation of the band gap does not depend linearly on Ag concentrations.

Our study provides a useful path for better understanding the effect of Ag-substitution on the structural and optical properties of CZTS.