Temperature driven n- to p-type conduction switching in SnSe and its mitigation through Zn doping with added advantage of Improved thermoelectric performance

Abstract

Tin selenide (SnSe) has emerged as a surprising new p-type thermoelectric material with exceptionally low thermal conductivity, leading to impressive thermoelectric performance. However, the presence of thermally conducting & electrically insulating SnO2 at the grain boundaries of SnSe supresses its desirable thermoelectric properties. In this work we report temperature dependence of Seebeck coefficient for polycrystalline SnSe which exhibits an unusual reversible change in conduction from n- to p-type at ~ 565 K. The n-type conduction near room temperature is attributed to the Se deficiency as well as SnO2 present at grain boundaries. At high temperature formation of Sn vacancies leads to p-type conduction. The Zn doping at Sn site (Sn1−xZnxSe) establishes the usual p-type conduction in the entire temperature range along with the lowering of thermal conductivity, resulting in a figure-of-merit of ~ 0.15 at 700 K, which is nearly 275% higher than that for pristine SnSe.