Sb deficiencies control hole transport and boost the thermoelectric performance of p-type AgSbSe2

Abstract

Silver antimony selenide, AgSbSe₂, a Te free analogue of AgSbTe₂, has been known to show a promising thermoelectric performance when it is doped with monovalent (M⁺) and divalent (M²⁺) cations in the Sb sublattice. Here, we report a significant enhancement of the thermoelectric performance of p-type nonstoichiometric AgSbSe₂ through Sb deficiencies. Sb deficiencies markedly increase the carrier concentration in AgSbSe₂ without the addition of any foreign dopant, which in turn enhances electrical conductivity in the 300–610 K temperature range. Enhancement in the electrical transport results in a remarkable improvement in the power factor (σS²) values up to ∼6.94 μW cm⁻¹ K⁻² at 610 K in AgSb_1−xSe₂. Notably, we have achieved a nearly constant σS² value of ∼6 μW cm⁻¹ K⁻² in the 400–610 K temperature range in Sb deficient samples. Additionally, AgSbSe₂ exhibits ultra-low thermal conductivity due to phonon scattering because of bond anharmonicity and a disordered cation sub-lattice. With superior electronic transport and ultra-low thermal conductivity, a peak ZT value of ∼1 at 610 K was achieved for the AgSb_0.9925Se₂ and AgSb_0.99Se₂ samples. A maximum thermoelectric conversion efficiency (η_max) of ∼8% was calculated by considering a virtual thermoelectric module consisting of the present p-type AgSb_1−xSe₂ and previously reported n-type AgBiSe_2−xCl_x, by maintaining a temperature difference of ΔT = 400 K.