Enhancing thermoelectric performance via synergistic regulation of band structure and microstructure in Cu-doped WS₂ polycrystalline films

Thermoelectric materials have great potential in the energy recovery and environmental protection, and thermoelectric films can also effectively achieve heat dissipation of the chip through thermoelectric refrigeration. WS₂ films show good thermoelectric performance in prediction, but the figure of merit (ZT) of the synthesized WS₂ films still needs improvement. In this work, Cu was doped into WS₂ films by magnetron sputtering combined with chemical vapor deposition and sulfurization annealing. Cu doping narrowed the band gap and increased the hole concentration from 5.6 × 10¹⁹ cm⁻³ to 2.2 × 10²¹ cm⁻³, greatly improved the electrical properties of WS₂ film. At 300 K, the electrical conductivity and power factor of Cu-doped films increased by 1086 % and 575 % compared to pristine WS₂, respectively. In addition, Cu doping reduced the grain size and introduced more grain boundaries, which decreased the in-plane thermal conductivity to as low as 0.22 W m⁻¹ K⁻¹ at 300 K. The coupling of the electrical and thermal properties optimization greatly improved ZT. The ZT value of Cu_5.5-WS₂ films is as high as 0.181 at 425 K. This work provides a new idea for improving the thermoelectric performance of transition metal dichalcogenides (TMDCs) films.