Cobalt atom incorporation regulates grain structure and thermoelectric properties in Bi₂Te₃ thin films

Cobalt-doped Bi₂Te₃ thin films were fabricated via sustainable manufacturing of the direct current magnetron co-sputtering with Co contents ranging from 0 to 8.2 at.%. Magnetic doping is introduced as a viable strategy to regulate microstructure and transport properties in thermoelectric coatings for use in the renewable energy. The incorporation of cobalt results in grain refinement from ∼16 nm to 5 nm and promotes the in-situ formation of nanoscale CoTe₂ phases, as confirmed by high-resolution TEM. These nanophases suppress grain coarsening and enhance interfacial density, thereby increasing carrier scattering. Electrical measurements reveal that Co doping increases carrier concentration while maintaining the Seebeck coefficient up to 2.5 at.%, a behavior explained by single parabolic band modeling with an effective mass of ∼1.7 mₑ. This suggests that magnetic scattering and band structure stability together enable decoupling of electrical conductivity and thermopower. The optimized film achieves a power factor of 260 μW m⁻¹ K⁻² at 300 K. The as-deposited films exhibit tunable electrical properties and well-defined nanostructures without thermal post-treatment. These findings provide new insights into how magnetic dopants mediate phase formation, defect structures, and transport dynamics in layered thermoelectric systems, and establish a scalable platform for designing multifunctional coatings applicable to energy harvesting, microelectronic integration, and active thermal management.