Weak Polar Optical Phonon Scattering Decouples Electron and Phonon Transport in Layered Thermoelectric Materials

High-performance thermoelectric (TE) materials are crucial for efficient waste-heat recovery and solid-state cooling technologies. A persistent challenge in TE materials design arises from the strong interdependence among the electrical conductivity (σ), Seebeck coefficient (S), and lattice thermal conductivity (κ_L). Layered compounds can effectively suppress κ_L along the cross-plane direction owing to weak interlayer interactions; however, they often suffer from low carrier mobility (μ) caused by limited band dispersion and strong polar optical phonon (POP) scattering. Here, we perform high-throughput density functional theory calculations to screen 236 layered semiconductors and identify candidates with low effective mass (m*) and weak POP scattering. We identify 23 compounds with high cross-plane μ, among which 14 exhibit large power factors (S²σ). Notably, GaGe₂Te stands out with exceptionally high cross-plane σ and power factor, enabled by a favorable combination of small m* and a small ionic dielectric constant. Simultaneously, GaGe₂Te exhibits an ultralow cross-plane κ_L of 0.57 W m^-1 K^-1 at 300 K, originating from weak interlayer bonding and pronounced phonon anharmonicity. These results demonstrate an effective strategy to decouple electron and phonon transport in layered materials by mitigating POP scattering, thereby providing a promising pathway toward high-performance thermoelectric materials.