This supplementary material provides detailed information on the preparation, characterization, and thermoelectric properties of Bi0.5Sb1.5Te3 samples with and without excess tellurium (Te). The materials were prepared through melt spinning, spark plasma sintering, and various characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDS). The samples were characterized for their microstructure, crystal structure, and thermoelectric properties, including electrical conductivity, Seebeck coefficient, thermal conductivity, and figure of merit (zT). The anisotropic properties of the samples were also investigated, and the thermal diffusivity, heat capacity, and lattice thermal conductivity were calculated. Additionally, the compatibility factor and dislocation arrays embedded in grain boundaries were analyzed. The results demonstrate the high performance of Te-excess samples in thermoelectric applications.This supplementary material provides detailed information on the preparation, characterization, and thermoelectric properties of Bi0.5Sb1.5Te3 samples with and without excess tellurium (Te). The materials were prepared through melt spinning, spark plasma sintering, and various characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDS). The samples were characterized for their microstructure, crystal structure, and thermoelectric properties, including electrical conductivity, Seebeck coefficient, thermal conductivity, and figure of merit (zT). The anisotropic properties of the samples were also investigated, and the thermal diffusivity, heat capacity, and lattice thermal conductivity were calculated. Additionally, the compatibility factor and dislocation arrays embedded in grain boundaries were analyzed. The results demonstrate the high performance of Te-excess samples in thermoelectric applications.