Thin-film thermoelectrics
(TEs) with unique advantages have triggered
great interest in thermal management and energy harvesting technology
for ambient temperature microscale systems. Although they have exhibited
a good prospect, their unsatisfactory performances still seriously
hamper their widespread application. Tailoring the porous structure
has been demonstrated to be a facile strategy to significantly reduce
thermal conductivity and enhance the figure of merit (ZT) of bulk TE materials; however, it is challenging for thin-film
TEs. Here, the nanoporous Bi2Te3 thin films
with faceted pore shapes and various porosities, pore sizes, and pore
intervals are carefully designed and fabricated by evacuating the
over-stoichiometry Te atoms. The dependence of the carrier mobility
and lattice thermal conductivity on the pore characteristics is investigated.
In the case of the pore interval longer than the electron mean free
path, the porous structure greatly reduces the lattice thermal conductivity
without affecting the electrical conductivity obviously. Phonon specular
backscattering that is highly related to the pore characteristics
is suggested to be mainly responsible for thermal conductivity reduction,
resulting in ∼60% enhancement in ZT at room
temperature, that is, from ∼0.42 for the dense film to ∼0.67
for the nanoporous film. The enhanced ZT value is
comparable to that of commercial bulk TEs and can be further improved
by optimizing the carrier concentrations. This work provides a general
approach to fabricate high-performance chalcogenide TE thin-film materials.