Stepwise Optimization of Thermoelectric Performance in n-Type SnS

Abstract

Tin sulfide (SnS) has been developed as an earth-abundant and eco-friendly compound that exhibits promising thermoelectric (TE) performance. While significant achievements are achieved in p-type SnS, the development of its n-type counterpart remains at a nascent stage, making it rather essential for developing n-type SnS to ensure good compatibility in SnS-based TE devices. In this study, Br is selected as the aliovalent dopant for realizing n-type transport in SnS. Subsequently, isoelectronic Se alloying and vacancy compensation are utilized to further promote the TE performance for n-type SnS. Se alloying can effectively narrow the bandgap of SnS for enhancing carrier concentration and diminishing thermal conductivity by strain and mass field fluctuations, while the excess Sn further compensates intrinsic Sn vacancies, thus optimizing carrier concentration and mobility simultaneously. These results are well verified by microstructure characterization and defect formation energy calculations. Consequently, the maximum ZT value of ≈0.7 and quality factor B of ≈1.02 at 823 K can be obtained after stepwise optimization, which is currently the highest value for n-type SnS thermoelectrics. This study presents a significant progress for n-type SnS and lays an important foundation for constructing all-SnS-based TE devices.