Influence of Dopants on Grain Growth and Electrical Transport Properties in Spin-Coated CsSnI<sub>3</sub> for Thermoelectric Applications

We conducted ion-substitution doping experiments on CsSnI3 to enhance its electrical properties for thermoelectric applications. While CsPbI3 is widely known as a printable semiconductor for solar cells, Sn-based halide perovskites are expected to be promising thermoelectric materials due to their inherently high carrier density, which originates from the characteristic self-doping effect caused by the instability of Sn2+. A CsSnI3 solution was spin-coated onto a glass substrate, and the resulting films exhibited electrical conductivity after annealing at 130°C. Various dopants, including Bi, Sb, Ni, In, and Cu, were introduced at different concentrations to improve electrical conductivity, and the formation of Sn-based halide perovskites was confirmed by X-ray diffraction analysis. A positive correlation was observed between grain size and electrical conductivity, and it was found that dopants with smaller ionic radii play a significant role in promoting grain growth. Among the tested dopants, In-, Sb-, and Ni-doped samples exhibited higher electrical conductivity, whereas Bi-doped samples showed comparatively lower conductivity, which could be explained by the difference in grain size.