Theoretical Study of Intrinsic and Extrinsic Point Defects and Their Effects on Thermoelectric Properties of Cu₂SnSe₃

Current understanding of the intrinsic point defects and potential extrinsic dopants in p-type Cu₂SnSe₃ is limited, which hinders further improvement of its thermoelectric performance. Here, we show that the dominant intrinsic defects in Cu₂SnSe₃ are Cu_Sn and V_Cu under different chemical conditions, respectively. The presence of V_Cu will damage the hole conduction network and reduce hole mobility. Besides, we find that the substitution of Al, Ga, In, Cd, Zn, Fe, and Mn for Sn can inhibit the formation of V_Cu; introducing Cu_Sn, Fe_Sn, Mn_Sn, and Ni_Cu defects can significantly enhance electronic density of states near the Fermi level due to the contribution of 3d orbitals. Therefore, increasing the Cu content and/or introducing the above beneficial dopants appropriately are expected to cause enhancement of carrier mobility and/or thermopower of Cu₂SnSe₃. Furthermore, introducing Ag_Cu, Al_Sn, Zn_Sn, Ge_Sn, and Mn_Sn defects can induce large mass and strain field fluctuations, lowering lattice thermal conductivity remarkably. Present results not only deepen one's insights into point defects in Cu₂SnSe₃ but also provide us with a guide to improve its thermoelectric properties.