Enhanced thermoelectric properties in Ni-Doped Cu2SnS3 thin films via sol–gel synthesis and post-sulfurization

Copper-based chalcogenides have gained increasing attention for thermoelectric applications because of their cost-effectiveness, eco-friendly nature, and inherently low thermal conductivity. In this work, the pristine and Ni-doped Cu2SnS3 films were successfully deposited through a sol–gel-based spin-coating approach, and the effects of Ni incorporation from 5 to 20% relative to Sn on the structural, morphological, and thermoelectric properties were comprehensively studied. The XRD analysis confirmed the formation of polycrystalline Cu2SnS3 with minor secondary phases appearing at higher Ni content, while the crystallite size decreased and micro-strain increased with increasing Ni doping. The SEM coupled with EDX characterization confirmed the formation of compact and well-distributed films, demonstrating uniform incorporation of Ni throughout the matrix. Temperature-dependent thermoelectric investigations conducted in the 300–800K range indicated that Ni incorporation increased the charge carrier density and electrical conductivity, and reduced the Seebeck coefficient value. The 15% Ni-doped Cu2SnS3 film exhibited the maximum thermoelectric performance, with a maximum figure of merit of 0.47 at 800 K. The enhancement was attributed to an optimal balance between enhanced charge carrier transport and reduced total thermal conductivity due to increased phonon scattering from lattice strain and defects. These results highlight Ni-doped Cu2SnS3 thin films as a potential material for high-temperature thermoelectric applications.