Br doping-induced evolution of the electronic band structure in dimorphic and hexagonal SnSe2 thermoelectric materials

Abstract

SnSe₂ with its layered structure is a promising thermoelectric material with intrinsically low lattice thermal conductivity. However, its poor electronic transport properties have motivated extensive doping studies. Br doping effectively improves the power factor and converts the dimorphic SnSe₂ to a fully hexagonal structure. To understand the mechanisms underlying the power factor improvement of Br-doped SnSe₂, the electronic band parameters of Br-doped dimorphic and hexagonal SnSe₂ should be evaluated separately. Using the single parabolic band model, we estimate the intrinsic mobility and effective mass of the Br-doped dimorphic and hexagonal SnSe₂. While Br doping significantly improves the mobility of dimorphic SnSe₂ (with the dominant hexagonal phase), it results in a combination of band convergence and band flattening in fully hexagonal SnSe₂. Br-doped dimorphic SnSe₂ is predicted to exhibit higher thermoelectric performance (zT ∼0.23 at 300 K) than Br-doped fully hexagonal SnSe₂ (zT ∼0.19 at 300 K). Characterisation of the other, currently unidentified, structural phases of dimorphic SnSe₂ will enable us to tailor the thermoelectric properties of Br-doped SnSe₂.