An enhanced Seebeck coefficient and high thermoelectric performance in p-type In and Mg co-doped Sn1−xPbxTe via the co-adjuvant effect of the resonance level and heavy hole valence band

Abstract

Recently, tin telluride (SnTe) has drawn much attention as a potential candidate for thermoelectric power generation. Herein, we report the high thermoelectric performance in SnTe achieved through a two-step design (a) reduction in lattice thermal conductivity via solid solution alloying and (b) enhancement of the Seebeck coefficient (S) via the modification of the electronic structure through co-doping. First, we demonstrate that the introduction of Pb into the position of Sn in SnTe decreases the excess of p-type carrier concentration in SnTe. Notably, the Sn_0.70Pb_0.30Te sample exhibits a κ_latt value of ∼0.67 W m⁻¹ K⁻¹ at 300 K, which is close to the theoretical minimum limit of the κ_latt in SnTe, which results mainly from scattering of heat carrying phonons by solid solution point defects. Secondly, we achieve an S value of 121 μV K⁻¹ at 300 K, which increases to ∼241 μV K⁻¹ at 710 K for In and Mg co-doped Sn_0.70Pb_0.30Te, which is the highest Seebeck coefficient among all the state-of-the-art SnTe based materials known so far. Indium acts as a resonant dopant, leading to a remarkable enhancement in the Seebeck coefficient mainly near room temperature, whereas Mg doping enables the valence band convergence in Sn_0.70Pb_0.30Te, which is confirmed by density functional theory (DFT) calculations of its electronic structure. As a result of co-doping, a remarkable enhancement in the Seebeck coefficient over a wide range of temperatures is achieved due to the synergistic effect of resonance level formation and valence band convergence. Hence, we have achieved a maximum zT of 1 at 710 K for In and Mg co-doped Sn_0.70Pb_0.30Te. Notably, an average zT (zT_avg) of ∼0.6 is achieved in the temperature range of 300–710 K for the Sn_0.655Mg_0.04In_0.005Pb_0.30Te sample.