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

Abstract

Cu5Sn2Se7 (CSS) has a potential application in thermoelectrics in that it consists of affordable, non-toxic, and earth-abundant elements. However, it is less reviewed in thermoelectrics in recent years because it exhibits a metallic-like behavior with a high carrier concentration (n H) (n H ∼ 3.0 × 1021 cm–3). To improve its thermoelectric (TE) performance, an electronic structure- and entropy (ΔS)-driven design of CSS is proposed. By analyzing the electronic structures and ΔS values of CSS alloying with three different species (In, Te, or In2Te3), we determine that the In2Te3-incorporated CSS favors performance optimization. The Hall measurement reveals that the n H of (Cu5Sn2Se7)1–x (In2Te3) x (x = 0.1) reduces to the optimal value (∼8.3 × 1020 cm–3), while the mobility (μ) increases with an increase in x so that the power factor (PF) reaches 12.0 (μW/cm K2), about 20% enhancement. At the same time, the lattice thermal conductivity (κ L) reduces to 0.46 W K–1 m–1 at x = 0.1. As a consequence, the ZT value increases to 0.7 at ∼770 K, which is about 4.7 times that of the pristine Cu5Sn2Se7. The principles applied here can be used as a guidance to design other thermoelectric materials.

High-entropy materials for thermoelectric applications: towards performance and reliability

“…Recently, Yang et al combined the entropy-driven concept and electronic structure design of the (Cu 5 Sn 2 Se 7 ) 1− x (In 2 Te 3 ) x system. 266 They found a very low k L of 0.46 W K −1 m −1 and a ZT of 0.7 at 770 K for (Cu 5 Sn 2 Se 7 ) 0.9 (In 2 Te 3 ) 0.1 , which is 4.7 times higher than that of Cu 5 Sn 2 Se 7 . Bo et al obtained a high ZT of 1.37 at 750 K for Cu 2.91 (MnFeNi) 0.09 Se 0.99 Te 0.01 with a very low k of ∼0.4 W m −1 K −1 at RT 267 and a ZT of 0.84 was obtained at 650 K for Cu 2.9 Ag 0.1 Sb 0.95 Te 0.05 Se 4 .…”

Chemical Composition Modulation Realizing Remarkable Improvement of Thermoelectric Performance in CuInTe2-Based Alloy

“…In this work, however, we propose a chemical composition modulation strategy trying to realize electro-acoustic coordination: , that is, alloying GeTe in CIT at first, aiming to gain degenerated or converged valence bands through improving its structural symmetry. − After that, we introduce a proper Cu deficiency (V Cu ) , to adjust the carrier concentration ( n H ) through unpinning the Fermi level ( F r ) in the madgap and, at the same time, suppress the phonon velocity and/or strengthen the structural anharmonicity through increasing lattice disorder. ,− By utilizing this strategy, we realize the electro-acoustic coordination effectively in the present material and improve the TE performance significantly with the highest ZT value of 1.51 at 838 K. This value ranks at a higher level among the CIT-based materials.…”

“…In this work, however, we propose a chemical composition modulation strategy trying to realize electro-acoustic coordination: 25,26 that is, alloying GeTe in CIT at first, aiming to gain degenerated or converged valence bands through improving its structural symmetry. 27−31 After that, we introduce a proper Cu deficiency (V Cu ) 32,33 to adjust the carrier concentration (n H ) through unpinning the Fermi level (F r ) in the madgap and, at the same time, suppress the phonon velocity and/or strengthen the structural anharmonicity through increasing lattice disorder.…”