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 (nH) (nH ∼ 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 nH 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 (κL) 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.