Abstract: The coupling of charge carrier and phonon transport limits the application of Ag₂Se as a low-toxic near-room-temperature thermoelectric material. Strategies that reduce the thermal conductivity via enhancing the phonon scattering usually lead to reduced carrier mobility due to high grain boundary potential barrier. In this study, we developed a cell-membrane-mimic grain boundary engineering strategy for decoupling the charge carrier and phonon scattering through decorating high-dielectric-constant rutile TiO₂ at Ag₂Se grain boundaries to enable the charge carrier/phonon selective permeability. The nano-sized TiO₂ with high dielectric permittivity can secure the charge carrier transport by shielding the interfacial Coulomb potential to lower the energy barrier of grain boundaries, rendering an enhanced power factor. Additionally, benefited from the enhanced phonon scattering by TiO₂ nanoparticles, a significantly decreased lattice thermal conductivity of ∼0.20 W m^-1 K^-1 and a high zT of ∼0.97 at 390 K are obtained in the Ag₂Se-based nanocomposites. This work demonstrates that such cell-membrane-mimic grain boundary engineering strategy may shed light on developing high-performance thermoelectric materials.

Key words: Thermoelectric, Ag₂Se, Grain boundary decoration, High-dielectric-constant, TiO₂