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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 In2Te3with 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–1m–1at 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 Cu2SnSe4family so far, which proves that the incorporation of In2Te3into CTS is a good proposal.

Guided by the concept of “phonon-liquid electron-crystal”, many n-type argyrodite compounds have been developed as candidates for thermoelectric (TE) materials. In recent years, the p-type Cu8GeSe6(CGS) compound has attracted some attention in TEs due to the presence of very strong atomic vibrational arharmonicity inside the sublattice, which is caused by the weak bonding between Cu ions and [GeSe6]8–. However, its TE performance is still poor, with a ZTvalue of only 0.2 at 623 K. Therefore, in this work, we propose to engineer both the electronic and phonon transports in CGS by incorporating the species In2Te3. This strategy tunes the carrier concentration and at the same time increases the phonon scattering on the point defects (InGe, Ininterstitial, and TeSe) and randomly distributed tetrahedra ([InSe4]5–and [GeTeSe3]4–). As a result, the phase transformation at 329 K in CGS is eliminated, and the peak ZTvalue is enhanced from 0.27 for CGS to ∼0.92 for (Cu8SnSe6)0.9(In2Te3)0.1at 774 K; this thus proves that the incorporation of In2Te3in CGS is an effective way of regulating its TE performance.

The argyrodite compound, Ag8SnSe6(ATS), which is one of the promising thermoelectric (TE) candidates, is receiving growing attention in thermoelectrics recently. However, its TE performance is still low and phases are unstable as the temperature varies. In this work, inspired by entropy engineering, we eliminate the β/γ phase transformation at ∼355 K via alloying Ga, thus extending its high-temperature cubic phase from 320 to 730 K. In the meantime, the power factor (PF) enhances by 10% and lattice thermal conductivity (κL) reduces by 40% at 723 K. As a result, the ZTvalue is boosted to ∼1.15 for Ag8Sn0.5Ga0.5Se6, which stands high among the ATS systems. This proves that the entropy engineering is an effective approach to extend the high-temperature range for the cubic γ-phase and improve its TE performance simultaneously.

γ-In2Se3is selected as a thermoelectric candidate because it has a unique crystal structure and thermal stability at relatively high temperatures. In this work, we have prepared lithiated γ-In2Se3through chemical diffusion and investigated its band structures and thermoelectric performance. After lithiation of γ-In2Se3in a lithium acetate (CH3COOLi) solution at 50 °C for 30 h, we have observed a high Hall carrier concentration (nH) of ≤1.71 × 1018cm–3at room temperature, which is ∼4 orders of magnitude higher than that of pristine γ-In2Se3. The enhancement of nHis directly responsible for the remarkable improvement in electrical conductivity and can be elucidated as the Fermi level (Fr) unpinning and moving toward the conduction band through the dominant interstitial occupation of Li+in the γ-In2Se3lattice. Combined with the minimum lattice thermal conductivity (κL= 0.30–0.34 W K–1m–1) at ∼923 K, the highest ZT value of 0.62–0.67 is attained, which is approximately 9–10 times that of pristine γ-In2Se3, proving that the lithiation in γ-In2Se3is an effective approach to the improvement in thermoelectric performance.