Morphological characteristics in polycrystalline tungsten diselenide regulating transport properties lead to predominant thermoelectric performance

Abstract

We studied a polycrystalline p-type WSe2 semiconductor for thermoelectric applications. The polycrystalline WSe2 nanocompound was prepared via a thermal reaction process of tungsten and selenium elements and it was sintered to produce a bulk structure using spark plasma sintering equipment. The resulting bulk specimen showed different morphological aspects, in which we observed irregularly-shaped grains along the direction perpendicular to the sintering pressing direction (i.e., along transversal direction) while finding thin layers along the parallel direction (i.e., along longitudinal direction). The specimen recorded a significantly low longitudinal thermal conductivity possibly because longitudinal phonon transport should be hindered due to the thin layers. Electron transport along the longitudinal direction might not be greatly interrupted by the morphological characteristics because the specimen recorded high carrier mobility along the direction resulting in lower electrical resistivity than that of a single crystalline equivalent. The specimen also showed moderate carrier concentration, which led to a plausible Seebeck coefficient. Since the specimen exhibited the significantly low thermal conductivity with the electrical properties, it recorded a higher figure of merit than the equivalent, which is the highest thermoelectric performance for p-type WSe2 in bulk phase ever developed.