Constructing high-performance bulk thermoelectric composites by incorporating uniformly dispersed fullerene sub-nanoclusters

Sub-nanomaterials possess unprecedented size-dependent properties compared to conventional nanomaterials, which endow them with great potential in catalysis, biomedicine, sensors, and so on. However, their applications in thermoelectrics are unknown due to poor thermal stability and low yields. Herein, we construct a series of thermoelectric composites by incorporating highly thermally stable and commercial fullerene sub-nanoclusters (C₆₀ or C₇₀). We find that sub-nanoclusters as the second phase can conduce to optimized carrier concentration through charge transfer at interfaces while the carrier mobility is significantly enhanced due to atom orbital hybridization and size-dependent electrical scattering mechanism. Furthermore, the ultra-low thermal conductivity of C₆₀ due to its distorted chemical bonding and sub-nanometer pore, and the interfacial thermal resistance greatly suppress the phonon transport. Consequently, the 0.15 mol.% C₆₀/Bi_0.4Sb_1.6Te₃ realizes an ultra-high ZT of ∼1.6 at 373 K, an excellent thermoelectric conversion efficiency of ∼7.4 %, and a huge cooling performance of ∼73 K. This work demonstrates the application of sub-nanomaterials in thermoelectrics and may shed light on other fields such as electronic devices, thermal management, and fullerene chemistry.