Distinct Impact of Alkali-Ion Doping on Electrical Transport Properties of Thermoelectric p-Type Polycrystalline SnSe

Abstract

Recent findings about ultrahigh thermoelectric performance in SnSe single crystals have stimulated related research on this simple binary compound, which is focused mostly on its polycrystalline counterparts, and particularly on electrical property enhancement by effective doping. This work systematically investigated the thermoelectric properties of polycrystalline SnSe doped with three alkali metals (Li, Na, and K). It is found that Na has the best doping efficiency, leading to an increase in hole concentration from 3.2 × 10(17) to 4.4 × 10(19) cm(-3) at room temperature, accompanied by a drop in Seebeck coefficient from 480 to 142 μV/K. An equivalent single parabolic band model was found adequate to capture the variation tendency of Seebeck coefficient with doping levels within a wide range. A mixed scattering of carriers by acoustic phonons and grain boundaries is suitable for numerically understanding the temperature-dependence of carrier mobility. A maximum ZT of ∼0.8 was achieved in 1% Na- or K-doped SnSe at 800 K. Possible strategies to improve the mobility and ZT of polycrystals were also proposed.

Nanoporous PbSe–SiO2 Thermoelectric Composites

“…Instead, considering the nonexponential variation of µ and the presence of nanoporous structures, an additional scattering from boundary barriers is supposed to conform here, as previously observed in a variety of TE materials, for example, PbTe composites28 and SnSe polycrystals 29, 30. The boundary‐barrier scattering is considered as the carrier trapping at grain boundaries with thermally activated dynamics.…”

Heavy Doping by Bromine to Improve the Thermoelectric Properties of n‐type Polycrystalline SnSe

“…Since the electrical resistivity is in inverse proportion to the carrier concentration and mobility, the easiest way is to dope in polycrystalline SnSe for higher carrier concentration, considering the inevitably defects in polycrystals. Relatively high electrical conductivity and ZT values have been achieved in p‐type polycrystalline SnSe doped with Ag, Na, and K, etc 18, 19, 20, 21. Specifically, multiple valence bands have been activated by doping with Na for the further enhanced Seebeck coefficient and TE performance in SnSe.…”

Ideal Strength and Deformation Mechanism in High-Efficiency Thermoelectric SnSe

“…12 SnSe, a simple layered crystal consisting of earth abundant elements, recently attracted much attention surprising the scientific community with the high zT of 2.6 along the b axis in the orthorhombic unit cell and a zT of 2.3 along the c axis. [13][14][15][16][17][18] SnSe behaves as a p-type material with a large energy gap of 0.86 eV, 19 which makes doping SnSe with donor or acceptor atoms not as straightforward as in the case of PbTe and PbSe. However, sodium has been found to be an effective acceptor dopant which can increase the zT from 0.1 to 0.7 at 300 K along the b axis while obtaining a maximum zT of 2.0 at 773 K. 20 Thus, a device ZT, which determines the overall TE conversion efficiency of a device, of 1.34 from 300 to 773 K is obtained, leading to a theoretical conversion efficiency of 16.7% at T c = 300 K and T h = 773 K in hole-doped SnSe.…”