Thermoelectric materials, as clean energy materials, can directly convert thermal energy into electrical energy. These materials have received significant attention owing to their environmentally friendly nature. Skutterudite thermoelectric materials feature excellent electrical properties and great potential for environmentally friendly and industrial applications. The thermal performance optimization of skutterudite is mainly achieved through framework atom substitution, lattice void filling, and recombination of nano second-phase. In this study, the significant optimization of the thermal properties of S0.05Co4Sb11.6Te0.4 with fullerene-C-60 as a nano second-phase composite material was reported. At 773 K, the N-type 0.10C(60)-S0.05Co4Sb11.6Te0.4 (0.10C(60)-SKD) polycrystalline material featured a dimensionless figure of merit zT value of 1.34, which is 31% higher than that of the matrix material. The overall optimization of the thermoelectric properties of the material was achieved through the high-pressure and high-temperature (HPHT) synthesis method, combined with electronegative S element filling, Te element substitution, and the recombination of C-60 nano second-phase. The experimental results indicated that the incorporation of C-60 resulted in the formation of finer grains in the composite material with significant lattice distortion, dislocations, and abundant grain boundaries in its microstructure. Various phonon scattering mechanisms occurred within the material, effectively reducing the lattice thermal conductivity of the material. The stable structure of C-60 molecules added to the matrix material can optimize the mechanical properties of the material. The composite sample with a C-60 amount of 0.20 exhibited a Vickers hardness of 7.01(1) GPa. This study employed the HPHT method for the direct synthesis of C-60 composite samples within 30 min and provides insights into improving the thermoelectric properties of skutterudite.
