Resolving different scattering effects on the thermal and electrical transport in doped SnSe

Recently, it has been found that crystalline tin selenide (SnSe) holds great potential as a thermoelectric material due to its ultralow thermal conductivity and moderate electronic transport performance. As the thermoelectric application usually requires doped materials, dopants play an essential role in both the thermal and electrical transport properties in SnSe, but such an effect has never been clearly elucidated in previous theoretical and experimental studies. Here, we performed a rigorous first-principles analysis on the thermal and electrical transport in doped SnSe. Three phonon scattering mechanisms, including phonon-phonon, phonon-dopant, and phonon-electron interactions, were considered. The electron-phonon scattering is considered in the calculation of charge carrier transport properties using a mode specific calculation. Although intrinsic SnSe holds extremely low lattice thermal conductivity due to strong anharmonicity, the dopants can further reduce the lattice thermal conductivity. However, phonon-electron scattering is much weaker even at high carrier concentrations and thus has little effect on the lattice thermal conductivity. In comparison, the electronic thermal conductivity is not negligible when the carrier concentration is higher than 10(19) cm(-3), and the values can be as high as 1.55, 1.45, and 1.77 W m(-1) K-1 on a, b, and c axes, respectively, for 10(20) cm(-3) electron concentration at 300 K. The strong anisotropy of electrical transport is observed, and it is attributed to the complex electronic band structure. The Lorenz number of SnSe is also calculated and it is dependent on crystal orientations, carrier concentrations, and carrier types. The simple estimation of electronic thermal conductivity using the Wiedemann-Franz law can cause large uncertainties for doped SnSe.