Constructing quasi-layered and self-hole doped SnSe oriented films to achieve excellent thermoelectric power factor and output power density

Thermoelectric (TE) technology can achieve the mutual conversion between electric energy and waste heat, and it has exhibited great prospects in multifunctional energy applications to alleviate the energy crisis. In the recent decade, SnSe has been explored widely because of its potentially high energy harvesting efficiency, green nature, and low cost. However, the relatively poor power factor (PF) derived from the intrinsic low carrier concentration (∼1017 cm-3) limits the output power density of the stoichiometric SnSe devices. Therefore, the advancement of novel optimization strategies for controlling carrier concentration is of utmost importance. Besides, compared with 3D bulks, 2D thin films are more compatible with modern semiconductor technology and have unique advantages in the construction and application of TE micro- and nano-devices. In this study, post-selenization technology were applied to increase the carrier concentration of the a-axis oriented SnSe epitaxial films utilizing the charge transfer and self-hole doped effects. The quasi-layered and self-hole doped films exhibited a high power factor of ∼5.9 µW cm-1 K-2 at 600 K along the in-plane direction when the carrier concentration is enhanced to ∼1018 cm-3 by increasing the selenization time to ∼20 min. The TE generator composed of four P-type film legs demonstrated the ultrahigh maximum power density of ∼83, ∼838 µW cm-2 at the temperature difference of ∼50 and ∼90 K, respectively. Post-selenization can effectively optimize the carrier concentration of SnSe-based materials, which is also feasible to other anion deficient TE films.