High thermoelectric performance of Co-doped Cu₂SnS₃-attapulgite nano-composites achieved by synergetic manipulation of electrical and thermal transport properties

Mohite-type Cu₂SnS₃ has merged as a promising environmentally-friendly thermoelectric candidate. When heavily hole-doped, it exhibits a large power factor (PF) by virtue of a high electrical conductivity (σ), which results in an undesired high electronic thermal conductivity (κ_e) that limits the ZT value. In the present work, nanocomposites of Co-doped Cu₂Sn_0.8Co_0.2S₃ embedded with fibrous in-situ-dehydrated attapulgite (D-ATT) nanorods are prepared, and the effect of D-ATT on the thermoelectric properties are investigated. Results show that, with the incorporation of D-ATT, σ is lowered effectively as expected as a primary result of charge compensation caused by a donor effect of D-ATT, which gives rise to an optimal reduction of κ_e by 50% in the studied temperature range, accompanied with an enhanced Seebeck coefficient (S) and high PFs maintained at ~9.4 μW cm⁻¹ K⁻² at 773 K. Meanwhile, the lattice thermal conductivity is strongly suppressed due to the intensified phonon scattering with ATT addition, leading to an ultralow value of 0.27 W m⁻¹ K⁻¹ at 773 K. Finally, a maximal ZT of ~1.0 has been achieved in the sample with 0.2 wt% D-ATT at 773 K, which stands a new record for Cu₂SnS₃-based TE materials.