Br doping-induced evolution of the electronic band structure in dimorphic and hexagonal SnSe 2 thermoelectric materials.

SnSe 2 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 SnSe 2 to a fully hexagonal structure. To understand the mechanisms underlying the power factor improvement of Br-doped SnSe 2 , the electronic band parameters of Br-doped dimorphic and hexagonal SnSe 2 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 SnSe 2 . While Br doping significantly improves the mobility of dimorphic SnSe 2 (with the dominant hexagonal phase), it results in a combination of band convergence and band flattening in fully hexagonal SnSe 2 . Br-doped dimorphic SnSe 2 is predicted to exhibit higher thermoelectric performance ( zT ∼0.23 at 300 K) than Br-doped fully hexagonal SnSe 2 ( zT ∼0.19 at 300 K). Characterisation of the other, currently unidentified, structural phases of dimorphic SnSe 2 will enable us to tailor the thermoelectric properties of Br-doped SnSe 2 .