Highly Improved Thermoelectric Performance in Periodically Ablated BiSbTe: WSe₂ Nanostructured Films

An innovative technique has been developed to combine two different layered materials, bismuth antimony telluride (BiSbTe) and tungsten diselenide (WSe₂), which are well-known for their great efficacy in waste heat recovery and extremely low thermal conductivity, respectively. To enhance the thermoelectric properties even more, WSe₂ as a secondary target is encapsulated periodically in the primary target Bi_1.5Sb_0.5Te₃ using a pulse laser deposition technique. The WSe_2, for the first time, is co-ablated with the BiSbTe at four distinct deposition temperatures, resulting in hetero-nanocomposite thin films. Various characterization techniques are employed to determine thermoelectric properties. Both x-ray diffraction (XRD) and Raman spectroscopy validate the existence of WSe₂ and Te as heterogeneous phases. The sharp XRD peaks observed indicate strong crystallinity and evidence that the crystals are grown in a highly c-oriented manner. The electrical transport properties are greatly improved due to the optimized hole concentration, resulting in significantly high electrical conductivity in hundreds to thousands of S cm^-1 for the samples grown at 573 K and 723 K, respectively. Furthermore, the room temperature and temperature-dependent Seebeck coefficient measurements exhibit highly optimized values, providing evidence of a satisfactory trade-off between the thermoelectric parameters. The overall outcome is a significant increase in the power factor which is computed up to 156 μW cm^-1 K^-2, demonstrating outstanding room temperature thermoelectric performance. In addition to electrical characteristics, the specimens have a low electronic thermal conductivity, k_e. The calculated room temperature k_e values are 0.10 W m^-1K^-1 and 0.87 W m^-1K^-1for the samples grown at 573 K and 723 K, respectively. Additionally, a qualitative measurement of lattice thermal conductivity was conducted through Raman spectroscopy under different laser power conditions, providing enough room for the highly improved figure of merit value. The enhanced thermoelectric transport characteristics of the periodically encapsulated WSe₂ in the BiSbTe matrix place it among the best thermoelectric materials with excellent performance for thermoelectric conversion, such as solid-state refrigeration and power generation.