2 research outputs found
High Thermoelectric Performance Realized in a BiCuSeO System by Improving Carrier Mobility through 3D Modulation Doping
We
report a greatly enhanced thermoelectric performance in a BiCuSeO
system, realized by improving carrier mobility through modulation
doping. The heterostructures of the modulation doped sample make charge
carriers transport preferentially in the low carrier concentration
area, which increases carrier mobility by a factor of 2 while maintaining
the carrier concentration similar to that in the uniformly doped sample.
The improved electrical conductivity and retained Seebeck coefficient
synergistically lead to a broad, high power factor ranging from 5
to 10 μW cm<sup>–1</sup> K<sup>–2</sup>. Coupling
the extraordinarily high power factor with the extremely low thermal
conductivity of ∼0.25 W m<sup>–1</sup> K<sup>–1</sup> at 923 K, a high <i>ZT</i> ≈ 1.4 is achieved in
a BiCuSeO system
Origin of the High Performance in GeTe-Based Thermoelectric Materials upon Bi<sub>2</sub>Te<sub>3</sub> Doping
As a lead-free material,
GeTe has drawn growing attention in thermoelectrics,
and a figure of merit (<i>ZT</i>) close to unity was previously
obtained via traditional doping/alloying, largely through hole carrier
concentration tuning. In this report, we show that a remarkably high <i>ZT</i> of ∼1.9 can be achieved at 773 K in Ge<sub>0.87</sub>Pb<sub>0.13</sub>Te upon the introduction of 3 mol % Bi<sub>2</sub>Te<sub>3</sub>. Bismuth telluride promotes the solubility of PbTe
in the GeTe matrix, thus leading to a significantly reduced thermal
conductivity. At the same time, it enhances the thermopower by activating
a much higher fraction of charge transport from the highly degenerate
Σ valence band, as evidenced by density functional theory calculations.
These mechanisms are incorporated and discussed in a three-band (L
+ Σ + C) model and are found to explain the experimental results
well. Analysis of the detailed microstructure (including rhombohedral
twin structures) in Ge<sub>0.87</sub>Pb<sub>0.13</sub>Te + 3 mol %
Bi<sub>2</sub>Te<sub>3</sub> was carried out using transmission electron
microscopy and crystallographic group theory. The complex microstructure
explains the reduced lattice thermal conductivity and electrical conductivity
as well