Promising thermoelectric performance in earth abundant SnS: local Sn distortion and modular misfit nanostructures

Abstract

Tin sulphide (SnS), a promising and earth-abundant thermoelectric material, offers a low-cost and non-toxic substitute to SnSe and SnTe but remains less explored and requires enhancement in thermoelectric performance in the polycrystal sample for practical applications. Here, we elucidate the origin of the intrinsically low lattice thermal conductivity (κ_lat) of SnS through synchrotron X-ray pair distribution function (X-PDF) analysis, which reveals local Sn distortion along the crystallographic b-axis. To further maximize the thermoelectric performance, Sn vacancies were introduced into polycrystalline SnS, which effectively increases the p-type carrier concentration. This resulted in improved electrical conductivity in Sn_0.985S. The formation of line defects and modular misfit SnS–SnS₂ nano-heterostructures in the SnS matrix leads to strong scattering of heat-carrying acoustic phonons, reducing κ_lat to 0.22 W m⁻¹ K⁻¹ at 873 K. Consequently, a peak thermoelectric figure of merit (zT) of ∼0.8 was achieved at 873 K. A single-leg thermoelectric device fabricated from Sn_0.985S delivered an output power density of ∼10 mW cm⁻² with a temperature difference of 400 K.