High thermoelectric performance of SnS under high pressure and high temperature

Tin sulfide (SnS) is a promising non-toxic thermoelectric (TE) material to replace SnSe (Se is toxic), due to its similar structure and low thermal conductivity (κ) comparable to SnSe. However, the poor electrical conductivity (σ) of SnS results in lower TE performance. In this work, high pressure was utilized to regulate the electronic structure, thereby mediating the conflict of electron and phonon transport to optimize the TE performance. In situ measurements of thermoelectric properties for SnS under high pressure and high temperature revealed that although the Seebeck coefficient (S) and κ slightly decrease with increasing pressure, the σ dramatically increases with increasing pressure, finally increasing the dimensionless figure of merit (ZT). The σ increases from 2135 S⋅m⁻¹ to 83549 S⋅m⁻¹ as the pressure increases from 1 GPa to 5 GPa at 325 K, representing an increase of an order of magnitude. The high σ of SnS leads to an increase in the PF to 1436 μW⋅m⁻¹⋅K⁻² at 5 GPa and 652 K. The maximum ZT value of 0.77 at 5 GPa and 652 K was obtained, which is 4 times the maximum ZT under ambient pressure and is comparable to that of doped SnS. The increase in σ is due to the fact that pressure modulates the band structure of SnS by narrowing the band gap from 1.013 eV to 0.712 eV. This study presents a valuable guide for searching new high TE performance materials using high pressure.