Remarkable Improvement of Thermoelectric Performance in Ga and Te Cointroduced Cu₃SnS₄

Ternary sulfide Cu₃SnS₄ (CTS) receives growing interest in photocatalytic and gas sensing applications; however, limited attention has been paid to the application in thermoelectrics in virtue of its intrinsic high carrier concentration. In this work, a high figure of merit of Ga (ZT) and Te cointroduced CTS with the composition of (Cu₃SnS₄)_1-(Ga₂Te₃) (x = 0.105) has been realized via synergistic optimization of the electronic and thermal transport properties. The incorporation of Ga into CTS results in a downshift of both the conduction and valence bands, which effectively promotes the active hybridization of Sn 5s and S 3p orbitals near the Fermi level (E_F) and optimizes the carrier concentration. In the meantime, the lattice thermal conductivity (κ_L) generally decreases on account of the local internal distortion induced by Ga(Te) substitution at the Cu(S) site. Moreover, the phonon transport is greatly suppressed above ∼725 K attributed to the melting of the second-phase Te on the grain boundaries. Consequently, the highest ZT value of ∼0.96 is obtained at 798 K. This value is ∼3.6 times that of the pristine CTS and ranks the highest in the CTS system to date.