Band Structure and Phonon Transport Engineering Realizing Remarkable Improvement in Thermoelectric Performance of Cu₂SnSe₄ Incorporated with In₂Te₃

Cu2SnSe4 (CTS) ternary chalcogenides have potential applications in thermoelectrics for they crystallize in a high-symmetry cubic structure and consist of earth-abundant and eco-friendly elements. However, the pristine CTS does not have optimal thermoelectric (TE) performance (ZT = 0.35 at ∼700 K), so further investigation is required in this regard. In this work, we propose an incorporation of In2Te3 with a defect zinc-blende cubic structure into CTS, aiming to regulate the electronic and phonon transport mechanism simultaneously. The first-principles calculation reveals that the element In favors the residing at a vacancy site as an interstitial atom while Te at the Se site, which leads to band convergence and degeneracy, respectively. As a result, the electrical property improves with a 22% increase in the power factor (PF), and at the same time, the lattice thermal conductivity (κL) reduces to 0.31 W K–1 m–1 at 718 K. Synergistic engineering realizes a remarkable improvement in TE performance with the highest figure of merit (ZT) of 0.92 at 718 K. This value is ∼3 times that of the pristine CTS and stands among the highest in the Cu2SnSe4 family so far, which proves that the incorporation of In2Te3 into CTS is a good proposal.