Enhanced thermoelectric properties of InSe through simultaneous increase in electrical conductivity and Seebeck coefficient by Cl doping

Post-transition metal chalcogenides, such as SnSe, SnSe2, InSe, In2Se3, and In4Se3, are recently suggested as good candidates for high performance thermoelectric materials. In this present study, we investigated the influence of Cl doping on the electrical and thermal transport of n-type polycrystalline InSe samples in an effort for searching new thermoelectric materials. A series of InSe1-xClx (x = 0, 0.01, 0.03, and 0.05) were synthesized by a conventional solid-state reaction. By Cl doping in the Se site, the power factor is significantly increased to 0.13 mW/mK2 for InSe0.97Cl0.03 from 0.044 mW/mK2 of undoped InSe, primarily owing to the unconventional simultaneous increase in both electrical conductivity and magnitude of Seebeck coefficient. The increase of power factor is discussed in regard with substantial increase of effective mass and weighted mobility by the Cl doping, along with the electronic dispersions calculated by density functional theory. As a result, the thermoelectric figure of merit zT is increased to 0.052 at 690 K in InSe0.97Cl0.03, which is improved by 208% compared to the undoped InSe sample.