Simultaneous Enhancement of Density of States and Phonon Scattering for Excellent Performance of Cu2SnSe3

As an environmentally friendly thermoelectric material, Cu₂SnSe₃ has drawn much attention. However, the thermoelectric conversion efficiency of Cu₂SnSe₃ is still too low to satisfy wide applications due to the high electrical resistivity ρ and low thermopower S. Herein, we show that around a 7-fold drop of electrical resistivity and 2.5-fold increase in thermopower (at room temperature) were simultaneously achieved by doping Co at Sn sites due to the increased hole concentration and enhanced density of states (DOS), enabling a dramatic power factor boost. Consequently, PF = 8.7 μW cm^–1 K^–2 was achieved at 848 K for Cu₂Sn_0.92Co_0.08Se₃. Moreover, both the substitution of Cu with Yb and the formation of Cu vacancies caused by Yb doping can lead to further enhancement of DOS, which gives a 1.5 times increase in S. In addition, as large as a 31% reduction (at 300 K) of lattice thermal conductivity was obtained because of the enhanced phonon scattering by point defects (Co_Sn^–, Yb_Cu²⁺, and V_Cu^–) and Yb₂Se₂O nanoprecipitates. As a result, a high ZT = 1.23 was achieved at 848 K for the Cu_1.94Yb_0.06Sn_0.92Co_0.08Se₃ sample, which is about 2.5 times larger than that of the pristine sample.