Nanostructured Ferecrystal Intergrowths with TaSe 2 Unveiled High Thermoelectric Performance in n -Type SnSe.

Ferecrystals, a distinctive class of misfit layered compounds, hold significant promise in manipulating the phonon transport owing to their two-dimensional (2D) natural superlattice-type structure and turbostratic (rotational) disorder present between the constituent layers. Integrating these 2D intergrowth structures as nanodomains embedded in a bulk thermoelectric matrix is a formidable challenge in synthetic chemistry, yet offers groundbreaking opportunities for efficient thermoelectrics. Here, we have achieved an exceptionally high thermoelectric figure of merit, zT ∼ 2.2, at 823 K in n -type Ta and Br-codoped SnSe, by successfully incorporating [(SnSe) 1.15 ] 7 (TaSe 2 ) 1 ferecrystals with [110] SnSe//[100] TaSe 2 orientation, as nanostructures with modulations in few nm in bulk SnSe solid-state matrix. While the presence of ferecrystal nanostructures induces strong scattering of heat-carrying phonons resulting in an ultralow lattice thermal conductivity (κ L ) of ∼0.18 W m -1 K -1 at 773 K, the Ta and Br codoping strategy increases the concentration of n -type charge carriers for enhanced electrical conductivity. Our approach provides a new pathway for damping the phonon transport and enhancing the thermoelectric performance in 2D layered materials.