P-Type PbTe is an outstanding high temperature thermoelectric material with zT of 2 at high temperatures due to its complex band structure which leads to high valley degeneracy. Lead-free SnTe has a similar electronic band structure, which suggests that it may also be a good thermoelectric material. However, stoichiometric SnTe is a strongly p-type semiconductor with a carrier concentration of about 1 × 10²⁰ cm⁻³, which corresponds to a minimum Seebeck coefficient and zT. While in the case of p-PbTe (and n-type La₃Te₄) one would normally achieve higher zT by using high carrier density in order to populate the secondary band with higher valley degeneracy, SnTe behaves differently. It has a very light, upper valence band which is shown in this work to provide higher zT than doping towards the heavier second band. Therefore, decreasing the hole concentration to maximize the performance of the light band results in higher zT than doping into the high degeneracy heavy band. Here we tune the electrical transport properties of SnTe by decreasing the carrier concentration with iodine doping, and increasing the carrier concentration with Gd doping or by making the samples Te deficient. A peak zT value of 0.6 at 700 K was obtained for SnTe_0.985I_0.015 which optimizes the light, upper valence band, which is about 50% higher than the other peak zT value of 0.4 for Gd_zSn_1−zTe and SnTe_1+y which utilize the high valley degeneracy secondary valence band.

Solid solution is a potential way to optimize thermoelectric performance for its low thermal conductivity compared to those of the constituent compounds because of the phonon scattering from disordered atoms. Tin(II) sulfide (SnS) shows analogous band structure and electrical properties with tin selenide (SnSe), which was the motivation for investigating the thermoelectric performance of SnS and SnS–SnSe solid solution system. SnS compound and SnS_1−xSe_x (0 < x < 1) solid solution were fabricated using the melting method and they exhibited anisotropic thermoelectric performance along the parallel and perpendicular to the pressing directions. For the SnS compound, the maximum zT_∥ value is 0.19 at 823 K along the parallel to pressing direction, which is higher than that along the perpendicular to the pressing direction (zT_⊥ = 0.16). The zT values of SnS_0.5Se_0.5 and SnS_0.2Se_0.8 were higher than those of the SnS compound and a maximum zT value of 0.82 was obtained for SnS_0.2Se_0.8 at 823 K, which is more than four times higher than that of SnS.

Lead-free polycrystalline SnSe is a promising thermoelectric compound consisting of earth-abundant elements. However, the poor electrical transport property for low intrinsic defect concentration (3 × 10¹⁷ cm⁻³) limits the usage of the stoichiometric SnSe compound. In this work, Na₂Se as an acceptor was doped into SnSe in order to optimize the electrical transport properties, especially to increase the carrier concentration. As a result, the carrier concentrations increased and saturated at about 1.0 × 10¹⁹ cm⁻³ for Na_0.01Sn_0.99Se at 300 K, and a maximum power factor of 0.48 mW m⁻¹ K⁻² was obtained. A maximum zT value of 0.75 was obtained at 823 K for Na_0.01Sn_0.99Se along the direction perpendicular to the sintering pressure, which is 25% higher than that (0.6) of the undoped SnSe compound.

An ideal dielectric epoxy nanocomposite with high thermal conductivity is successfully fabricated utilizing aminopropyltrimethoxysilane-functionalized BNNTs.