Ionothermal syntheses, structures, and photocurrent responses of two-dimensional layered thiostannates

The transition metal thiostannates, with their diverse structures and rich physical properties, have garnered substantial interest. In this research, two quaternary thiostannates CsCuSnS₃ (1) and Cs₂CdSnS₄ (2) have been synthesized through a facile ionothermal reaction. Both compounds exhibit monoclinic crystal systems with the space group C2/c (no. 15) and possess a two-dimensional layered anionic skeleton. The sandwich-like anionic layer of CsCuSnS₃ is constructed by [CuS₄]_n layer and [SnS₄]_n chains, while Cs₂CdSnS₄ is composed of vertex-sharing of T2 [Cd₂Sn₂S₁₀] cluster. The equilibrium cation Cs⁺ is situated at the inner edge of the layer voids. Remarkably, compounds CsCuSnS₃ (1) and Cs₂CdSnS₄ (2) display appropriate optical band gaps (1.38 eV and 2.50 eV) and good photocurrent response (1.5 μA/cm² and 4.0 μA/cm²) under simulated solar irradiation. Theoretical studies uncover that the electron transfer is mainly contributed by Cu-3d, Cd-4d, Sn-5s, and S-3p states. Moreover, the dimensional reduction from three-dimensional (3D) framework Na₂CdSnS₄ to 2D layered Cs₂CdSnS₄ caused by Cs ⁺ cation is discussed.