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 intrinsically low lattice thermal conductivity (κlat) 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 in polycrystalline SnS, which effectively increases the p-type carrier concentration. This resulted in improved electrical conductivity in Sn0.985S. Formation of line defects and modular misfit SnS-SnS2 nano-heterostructures in SnS matrix scatter heat-carrying acoustic phonons tremendously, reducing κlat to 0.22 W/m•K at 873 K. Consequently, a peak thermoelectric figure of merit (zT) of ~0.8 at 873 K was achieved. A single-leg thermoelectric device fabricated from Sn0.985S delivered an output power density of ~10 mW/cm² with temperature difference of 400 K.