  Silicon is one of the most frequently used chemical elements of the periodic
table in nanotechnology. Two-dimensional (2D) silicene, a silicon analog of
graphene, has been readily obtained to make field-effect transistors since
2015. Recently, as new members of the silicene family, penta-silicene and its
nanoribbon have been experimentally grown on Ag(110) surface with exotic
electronic properties. However, the thermoelectric performance of
penta-silicene has not been so far studied that would hinder its potential
applications of electric generation from waste heat and solid-state Peltier
coolers. Based on the Boltzmann transport theory and ab initio calculations, we
find that penta-silicene shows a remarkable room temperature figure of merit ZT
of 3.4 and 3.0 at the reachable hole and electron concentrations, respectively.
We attribute this high ZT to the superior pudding-mold electronic band
structure and ultralow lattice thermal conductivity. The discovery provides new
insight into the transport property of pentagonal nanostructures and highlights
the potential applications of thermoelectric materials at room temperature.
