Preparation and thermoelectric properties of layered Bi<sub>1–<i>x</i></sub>Sb<sub><i>x</i></sub>Se nanocrystalline films

Abstract

<sec>BiSe is found to be a promising near-room-temperature thermoelectric material with higher performance than traditional Bi<sub>2</sub>Se<sub>3</sub> due to its ultra-low intrinsic lattice thermal conductivity. In this work, N-type BiSe nanocrystalline thin films with (00l) preferred orientation are first prepared via vacuum thermal evaporation method, and Bi<sub>1–<i>x</i></sub>Sb<i><sub>x</sub></i>Se nanocrystalline films with different doping concentrations are obtained by Sb co-evaporation. The phases, morphologies, chemical compositions and valences, lattical vibrations, and electrical properties of these films are characterized. It is found that the Sb dopant successfully enters into the crystal lattice and replaces the Bi site of Bi<sub>2</sub>Se<sub>3</sub> quintuple layers and Bi<sub>2</sub> bilayers without selectivity, and the difference of gold properties between Sb atom and Bi atoms leads the carrier concentration to sharply decrease and the Seebeck coefficient in doped BiSe to increase. Meanwhile,</sec><sec>the sizes of nanocrystals in the films decrease and the denser layered structure is formed due to the Sb doping, which is conducive to the carrier transport in the samples, and the in-plane carrier mobility of the films effectively increases from 13.6 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup> (BiSe) to 19.3 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup> (Bi<sub>0.65</sub>Sb<sub>0.35</sub>Se). The maximum room-temperature power factor of 2.18 μW·cm<sup>–1</sup>·K<sup>–2</sup> is obtained in Bi<sub>0.76</sub>Sb<sub>0.24</sub>Se, which is higher than that in undoped BiSe. The results of this work indicate that the BiSe-based thin films have potential applications in room temperature thermoelectric thin film devices.</sec>