  Due to their great potential in electronics, optoelectronics and
piezoelectronics, Janus transition metal dichalcogenide (TMD) monolayers have
attracted increasing research interest, the MoSSe of which with sandwiched
S-Mo-Se structure has been synthesized experimentally. In this work, the
biaxial strain dependence of electronic structures and transport properties of
Janus PtSSe monolayer is systematically investigated by using generalized
gradient approximation (GGA) plus spin-orbit coupling (SOC). Calculated results
show that SOC has a detrimental effect on power factor of PtSSe monolayer,
which can be understood by considering SOC effects on energy bands near the
Fermi level. With $a/a_0$ from 0.94 to 1.06, the energy band gap firstly
increases, and then decreases, which is due to the position change of
conduction band minimum (CBM). It is found that compressive strain can increase
the strength of conduction bands convergence by changing relative position of
conduction band extrema (CBE), which can enhance n-type $ZT_e$ values.
Calculated results show that compressive strain can also induce the flat
valence bands around the $\Gamma$ point near the Fermi level, which can lead to
high Seebeck coefficient due to large effective masses, giving rise to better
p-type $ZT_e$ values. The calculated elastic constants with $a/a_0$ from 0.94
to 1.06 all satisfy the mechanical stability criteria, which proves that the
PtSSe monolayer is mechanically stable in the considered strain range. Our
works further enrich studies of Janus TMD monolayers, and can motivate farther
experimental works.
