Synergistic Optimization of Thermoelectric Performance in Polycrystalline and Crystalline SnS via Na Doping and Se Alloying

Abstract

The development of high-performance and eco-friendly thermoelectric materials is crucial for sustainable energy conversion. Tin sulfide (SnS) has emerged as a promising candidate owing to its low intrinsic thermal conductivity, abundance, and non-toxicity. However, its thermoelectric performance is severely limited by poor electrical conductivity, originating from a wide bandgap and low carrier mobility. Herein, we present a notable improvement in the thermoelectric performance of SnS via a synergistic strategy of Na doping and Se alloying. Na doping optimizes the electrical transport behaviors effectively through boosting the carrier concentration to ~1019 cm-3. Furthermore, Se alloying is crucial for modifying the electronic band structure by narrowing the bandgap and inducing valence band convergence, which enhances the Seebeck coefficient and weighted mobility. Concurrently, mass and strain field fluctuations between S and Se atoms lead to an ultralow lattice thermal conductivity of ~ 0.6 W m-1 K-1 at 873 K. Consequently, a peak ZT of ~ 1.0 is achieved at 873 K in the polycrystalline Sn0.98Na0.02S0.55Se0.45 sample, representing a fourfold improvement over pristine polycrystalline SnS. Moreover, the corresponding crystal sample exhibits a record-high ZT of ~ 1.6 at 623 K, attributed to a remarkable PF of ~ 25 μW cm-1 K-2. This study demonstrates that the synergistic regulation of phonon and charge transport through dual-element doping/alloying and crystal growth is a highly effective strategy for developing thermoelectric materials.