Crystal symmetry modification enables high-ranged in-plane thermoelectric performance in n-type SnSe crystals

SnSe crystal has witnessed significant advancements as a promising thermoelectric material over the past decade. Its in-plane direction shows robust mechanical strength for practical thermoelectric applications. Herein, we optimize the in-plane thermoelectric performance of n-type SnSe by crystal symmetry modification. In particular, we find that Te and Mo alloying continuously enhances the crystal symmetry, thereby increasing the carrier mobility to ~ 422 cm²V^-1 s^-1. Simultaneously, the conduction bands converge with the symmetry modification, further improving the electrical transport. Additionally, the lattice thermal conductivity is limited to ~ 1.1 W m^-1 K^-1 due to the softness of both acoustic and optical branches. Consequently, we achieve a power factor of ~ 28 μW cm^-1 K^-2 and ZT of ~ 0.6 in n-type SnSe at 300 K. The average ZT reaches ~ 0.89 at 300-723 K. The single-leg device based on the obtained n-type SnSe shows a remarkable efficiency of ~ 5.3% under the ΔT of ~ 300 K, which is the highest reported in n-type SnSe. This work demonstrates the substantial potential of SnSe for practical applications of power generation and waste heat recovery.