Modulating electrical transport properties of SnSe crystal to improve the thermoelectric power factor by adjusting growth method

Abstract

The SnSe crystal is a promising candidate in the field of thermoelectric materials. In order to elucidate basic physics in the SnSe system, here we report the heavily hole doping SnSe single crystals by the flux method (using alkali halide as solvent). Compared to bad-metal behavior of SnSe grown by the Bridgeman method, the flux-grown SnSe crystals show the metallic conductive behavior consistent with the Landau Fermi liquid (resistivity ρ ∼ T2) with temperatures ranging from 2 to 300 K. Combined angle-resolved photoemission spectroscopy and empirical Landau Fermi liquid theory, screening lengths λ of Coulomb electron–electron interaction U of SnSe grown by the flux method are 6.6 Å and 6.1 eV, which are much higher than those of normal metals. Remarkably, the excellent electrical conductivity (870 S/cm) of the SnSe crystal grown by the flux method at room temperature is attributed to the higher hole concentration (∼3.8 × 1019 cm−3) and large mobility (152.2 cm2 V−1 s−1). Meanwhile, these SnSe crystals still have large Seebeck coefficients (∼190 μV/K). Thus, the SnSe crystals grown by the flux method have an ultrahigh power factor [∼31.5 μW/(cm K2)] at room temperature, which is ten times larger than that of SnSe crystals grown by the Bridgeman method and as best as currently reported results. Our work shows a method for growing heavily hole-doped SnSe crystals, which provides a platform for understanding the electrical properties and improving its thermoelectric performance.

Negative Magnetoresistance in Hopping Regime of Lightly Doped Thermoelectric SnSe

“…When the magnetic field is oriented along the stacking a direction, the magnetoresistance is an order of magnitude larger at low temperatures and high fields than for the field orientation in the bc plane. Negative magnetoresistance with a similar value has been reported in SnSe [ 19 , 26 ] in samples with a higher doping value that falls close to or into a degenerate semiconductor regime and is ascribed to weak antilocalization. However, such a large positive magnetoresistance, as observed in Figure 3 b, has not been seen before.…”

“…Both have higher concentrations of charge carriers, and, as a result, the hopping mechanism is not as pronounced as observed here. Only one study reports negative magnetoresistance at the lowest temperatures [ 26 ], attributed to the same mechanism as here. However, a different model was used there, which does not fit our data.…”

“…A detailed study of the temperature dependence of magnetoresistivity and crystal anisotropy is also missing. Furthermore, we argue that the applicability of the standard Fermi liquid theory proposed in the literature [ 26 ] is questionable in this case due to the very small Fermi surface in the metallic regime.…”

“…There are two reports of magneto-transport on the semiconducting SnSe [ 20 , 26 ]. Both have higher concentrations of charge carriers, and, as a result, the hopping mechanism is not as pronounced as observed here.…”

Camphor sulfonic acid incorporation in SnO2/polyaniline nanocomposites for improved thermoelectric energy conversion

“…Nevertheless, the power factor of conducting polymers is relatively much lower than that of inorganic TE materials due to their lower thermopower ( S ). To date, nearly all the reported power factor values for pure PANI are in the order of 10 −6 W m −1 K −2 or less, 18 and this is nearly three orders of magnitude lower than that of traditional inorganic-based TE materials, such as Pb–Te-based alloys, 19,20 Bi–Te-based alloys, 21,22 Sn–Se-based alloys, 23–25 and Ge-Te-based alloys. 26 Thus, the main challenge is to attain a considerably higher TE power factor for π-conjugated conducting polymers for their use in thermoelectric devices.…”