Decoupled anisotropic Charge-Phonon Transport Enables Exceptional n-Type Thermoelectric Performance in CuBiSCl$_2$

Abstract

First-principles calculations demonstrate an exceptional decoupling of charge and thermal transport along the \textit{a}-axis in CuBiSCl$_2$. The material achieves superior electron mobility (138 cm$^2$/V$\cdot$s at 300 K) through delocalized Bi-6\textit{p}/S-3\textit{p} networks while maintaining ultralow lattice thermal conductivity (0.40 W/mK at 300 K) via Cu-dominated anharmonic phonon scattering - both optimized along the same crystallographic direction. This simultaneous optimization originates from the anisotropic bonding hierarchy where [BiSCl$_2$]$_n$ ribbons enable efficient charge transport along \textit{a}-axis, while the soft vibrational modes associated with Cu atoms strongly scatter heat-carrying phonons. The resulting high power factor (1.71 mW/mK$^2$ at 700 K) and peak \textit{ZT} of 1.57 establish CuBiSCl$_2$ as a model system that realizes the long-sought "phonon glass-electron crystal" paradigm through crystallographically engineered transport channels.