Synergistic Optimization of Carrier Transport and Lattice Thermal Conductivity in Bi-Alloyed SnSe for Mid-Temperature Thermoelectric Performance

Polycrystalline SnSe is a promising material for thermoelectric applications due to its ease of processing, robust mechanical strength, and scalability. Herein, we report the thermoelectric properties of spark-plasma-sintered n-type Bi-alloyed SnSe across the entire compositional range (x = 0 to 1). With Bi-alloying, we demonstrate a 4550-fold enhancement in electrical conductivity from 0.21 S/cm (x = 0) to 955.9 S/cm (x = 0.75). A 55% reduction in lattice thermal conductivity, ∼0.52 W/mK at 300 K, is achieved for x = 0.25. The combined alloying-induced mass disorder and enhanced phonon scattering, particularly of low-frequency modes affirmed by sound velocity measurements, is the primary mechanism for suppression of lattice thermal conductivity. The optimal composition Sn0.25Bi0.75Se exhibited a thermoelectric power factor as high as 537 μW/mK2 with a figure of merit zT of ∼0.14 at 466 K. Our results demonstrate that Bi-alloying is an effective strategy to tune both electrical and thermal transport, advancing SnSe as a potential high-performance candidate for mid-temperature thermoelectric applications.