Thermal annealing induced multifold enhancement in thermoelectric power factor of β-Zn4Sb3 thin films

In the present work, thermoelectric parameters electrical conductivity, Seebeck coefficient and power factor of β-Zn₄Sb₃ thin films at room temperature (303 K) were enhanced by 102.56 %, 110.90 % and 712.76 % respectively using post-deposition thermal annealing approach. Multiphase Rietveld refinement analysis was implemented to determine phase quantification, lattice parameters, atomic positions and occupancies, bond lengths & angles and crystal structure of the synthesized material. Maximum electrical conductivity, Seebeck coefficient and power factor values of $1.58\times {10}^{4}S{m}^{-1}$, 232 $\mu V{K}^{-1}$ and 764 $\mu W{m}^{-1}{K}^{-2}$ at 303 K were obtained after annealing of thermally evaporated β-Zn₄Sb₃ thin films for 6 h. Enhancement in electrical conductivity values were attributed to lowered band gap values, reduced defects & grain boundaries, large crystallite sizes and reorientation of growth direction caused by annealing. Enhancement in Seebeck coefficient values were attributed to the energy filtering effects promoted by increasing surface roughness. Structural characteristics of thin films were investigated, revealing reorientation of crystallites growth direction via thermal annealing. Investigation of optical characteristics revealed a band gap energy value of 1.28 eV for without annealed β-Zn₄Sb₃ thin film. Morphological properties of thin film surfaces revealed aggregation of grains due to annealing at elevated temperatures and average thin film thickness of 323 nm was determined. Topographical characteristics of thin films were investigated to visualize 3D surface maps, line profile and determine surface roughness.