Realizing high thermoelectric performance in hot-pressed polycrystalline AlxSn1-xSe through band engineering tuning

SnSe-based thermoelectric materials are being explored since they have potential high thermoelectric figure of merit. We synthesized polycrystalline AlxSn1-xSe (x = 0.01, 0.02, 0.03 and 0.04) by hot-pressing method, and combined theoretical estimation with experimental measurement to investigate the influence of Al doping on thermoelectric properties of SnSe. It was found that dopant Al can effectively adjust the band structure of SnSe by introducing intermediate band. Al doping with low content (x = 0.01 and 0.02) can introduce a single intermediate band close to the valence band maximum or conduction band minimum, achieving band engineering optimization. In high temperature region (498 K < T < 823 K), the electronic transport properties significantly enhance with thermal excitation. The lattice thermal conductivity reduces with the Al atomic point defect scattering, leading to a low thermal conductivity of 0.47 W m−1K−1 in Al0.04Sn0.96Se at 823 K. As a result, a high ZT of 0.84 at 823 K is obtained from the Al0.04Sn0.96Se perpendicular to the pressing direction, which is 58.5% larger than that of SnSe. In addition, dopant Al can adjust the anisotropy of polycrystalline SnSe. The anisotropy of electronic properties are enhanced with low doping level (x = 0.01, 0.02) and suppressed with high doping level (x = 0.03, 0.04).