The characteristics and formation mechanism of Cu₂SnS₃-based solar cells synthesized using practical method

The demand for affordable solar cells has encouraged the development of thin-film solar cell (TFSC) technology, which employs low-cost, readily-available, and non-toxic photovoltaic (PV) materials like Cu2ZnSnS4 (CZTS). Since CZTS is a quaternary semiconductor compound, the growth and synthesis of a single-phase CZTS are challenging due to the formation of secondary phases like ZnS and Cu2SnS3 (CTS), which affect the material's PV properties. Several studies have investigated the possibility of using ternary semiconductor compounds like CTS as an alternative PV material. This research aims to synthesize CTS compound powder using a practical method and to analyze CTS's properties and phase formation mechanism. CTS was synthesized in a solid-state reaction using copper (Cu), sulfur (S), and tin (Sn) elemental powders with various precursor compositions, including stoichiometric, S-rich, Sn-rich, and Cu-poor compositions. The experiment begins with mixing Cu, Sn, and S powders in stoichiometric composition using mortar-pestle and rotary mixing for three hours at 500:rpm, followed by annealing at various temperatures to determine the optimal synthesis parameter by investigating the CTS formation mechanism during the annealing. Then, CTS with other compositions was synthesized at optimal annealing temperature to examine the effect of the precursor composition on the purity and crystallinity of CTS material. The synthesized CTS was characterized based on thermal analysis, X-ray powder diffraction, and UV-VIS diffuse reflectance spectroscopy results. The result showed that CTS crystallization commenced at 340°C due to the reaction between Cu2-xS, S, and SnS. The optimal annealing temperature ranges between 340-420°C and 507-600°C. CTS with a Cu-poor composition in the precursor has better crystallinity and fewer secondary phases, resulting in a higher quality CTS. Diffuse reflectance spectroscopy reveals that the band gap of CTS powder is 1.67 eV, showing that the synthesized CTS is appropriate for a solar cell material.