Boosting Thermoelectric Performance of Cu₂SnSe₃ <i>via</i> Comprehensive Band Structure Regulation and Intensified Phonon Scattering by Multidimensional Defects

Abstract

As an eco-friendly thermoelectric material, Cu₂SnSe₃ has recently drawn much attention. However, its high electrical resistivity ρ and low thermopower <i>S</i> prohibit its thermoelectric performance. Herein, we show that a widened band gap and the increased density of states are achieved <i>via</i> S alloying, resulting in 1.6 times enhancement of <i>S</i> (from 170 to 277 μV/K). Moreover, doping In at the Sn site can cause a 19-fold decrease of ρ and a 2.2 times enhancement of <i>S</i> (at room temperature) due to both multivalence bands' participation in electrical transport and the further enhancement of the density of states effective mass, which allows a sharp increase in the power factor. As a result, PF = 9.3 μW cm^-1 K^-2 was achieved at ∼800 K for the Cu₂Sn_0.82In_0.18Se_2.7S_0.3 sample. Besides, as large as 44% reduction of lattice thermal conductivity is obtained <i>via</i> intensified phonon scattering by In-doping-induced formation of multidimensional defects, such as Sn vacancies, dislocations, twin boundaries, and CuInSe₂ nanoprecipitates. Consequently, a record high figure of merit of ZT = 1.51 at 858 K is acquired for Cu₂Sn_0.82In_0.18Se_2.7S_0.3, which is 4.7-fold larger than that of pristine Cu₂SnSe₃.