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

Abstract

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.

Improved Thermoelectric Performance of Cu2SnSe4 by Proper Decoupling Between Electron and Phonon Through Replacement of Sn with In

“…That is why we observed a big drop in mobility at x = 0.05 (see Figure 3b). Although the interstitial In atom in CTS has the potential to reduce the mobility as well due to the band convergence, according to the previous investigation, [ 33 ] the activation energy ( E A ) rapidly decreases from 22 m eV ( x = 0.05) to 1.2 m eV ( x = 0.2) with an increase in x , estimated according to the slope of each straight line in Figure 5a,b. This suggests that the localized bondage to the carrier weakens and the transport between the electron and phonon decouples rapidly.…”

“…Whereas the conventional band transport mechanism should not have such a big impact on μ. [33] The electrical properties of the materials (Cu 2 Sn 1Àx In x Se 4 ) (x ¼ 0-0.2) are presented in Figure 6 as a function of temperature. It is observed that the Seebeck coefficients (α) are all positive, indicating that the majority of carriers are holes.…”

Electronic Structure- and Entropy-Driven Design of Thermoelectric Chalcogenide Cu5Sn2Se7 Leading to the Optimization of Carrier Concentration and Reduction in Thermal Conductivity

“…In the meantime, the authors found that p-type doping on the Sn site has little influence on the upper valence band (VB), according to those observed in Cu 2 SnSe 3 systems. − We noticed that in the band structure of CSS, its Fermi level (Fr) is in the deep part of the valence band . What should be further noted is that there is also an energy gap (∼0.5 eV) above Fr with the bonding states partially non-occupied. , In this regard, the structure of CSS, unlike those of Cu 2 SnSe 3 , , Cu 2 SnSe 4 , and other Cu-containing chalcogenides, , might be favorable to the regulation of the conduction band (CB) if proper dopants are incorporated.…”

“…This is because the element In (Te) is energetically favorable to reside at the Sn (Se) site. 10,13 On the other hand, the binary In 2 Te 3 or Ga 2 Te 3 having its inherent structural vacancy 14−16 is often used as a dopant to tune the carrier concentration of materials, similar to those observed in InSb, 17 (Sn,Ge)Te, 18,19 CuGaTe 2 , 20 significantly than the single element In or Te does. It is thus effective to regulate both the phonon and electronic transport mechanisms.…”

“…1 What should be further noted is that there is also an energy gap (∼0.5 eV) above Fr with the bonding states partially non-occupied. 1,8 In this regard, the structure of CSS, unlike those of Cu 2 SnSe 3 , 8,9 Cu 2 SnSe 4 , 10 and other Cucontaining chalcogenides, 11,12 might be favorable to the regulation of the conduction band (CB) if proper dopants are incorporated.…”