Pressure intrinsically induced thermoelectric enhancement in the SnSe crystal

SnSe is an excellent thermoelectric material due to its high $ZT$ value ($\sim$2.6 along the $b$ direction) at high temperature $\sim$923 K. However, in the temperature range of 300$-$773K, the $ZT$ values are just 0.1$-$0.9. To make this material more efficient, its thermoelectric properties should be large in the entire temperature range. Here, we use DFT calculations to show how pressure intrinsically enhances the thermoelectric properties below 700 K along the three directions ($a$, $b$ and $c$) of the crystal (the low-$T$ SnSe-$Pnma$ phase) due to a significant boost in electrical transport. The estimated $ZT$ values of $p$-type along the $b$ and $c$ directions can reach as high as 3.3 and 2.1 at 6 GPa and 700 K, respectively. At 6 GPa, the $a$ direction shows $n$-type properties and its $ZT$ value is 1.9 at 600 K. It is significant that high-performance both $n$-type and $p$-type conductors could be available in SnSe just through applying pressure. Our work on SnSe under pressure sheds light on a new mechanism for screening high efficiency thermoelectric materials.