Enhanced thermoelectric performance of n-type Bi2Te3 alloyed with low cost and highly abundant sulfur

Abstract

Bi2Te3 is one of the most promising thermoelectric (TE) materials. Effect of doping to decouple the electrical and thermal properties has been studied over a long decade. Here, sulfur (S), being highly abundant and non-toxic, has been used as dopant in Bi2Te3 material. Structural study reveals that highly doped S i.e., Bi2Te2S has highest dislocation density due to the enhanced point defect, which increases lattice strain. We analyzed that the combine effect of point and bulk defects significantly lead the TE performance and established a strong correlation between structure and properties. These provide a moderate Seebeck coefficient of ~240 μV/K and strong channel for scattering of low/mid frequency phonons that showed smaller lattice thermal conductivity ~0.53 W/mK (40% decrease with respect to Bi2Te3) for Bi2Te2S at 413 K. Although, there is a slight decrease in electrical conductivity with S doping but significant reduction in lattice thermal conductivity leads to an enhanced ZT value of 1.12 for Bi2Te2S. Enhanced ZT value for Bi2Te2S is rationalized by competing effect of Seebeck coefficient, electrical conductivity, and lattice thermal conductivity.