Including the finite temperature atomistic evolution into thermoelectric theory

Thermoelectric (TE) materials have enjoyed much attention because of their promise for energy savings and targeted low-power cooling. Bulk monochalcogenides (SnSe) are some of the most effective TE materials [1,2]. Phonon anharmonicity and softening modes play an important role in improved TE performance [3], but so far, theoretical approaches to computing TE properties do not account for such softening explicitly. To address this shortcoming, we use molecular dynamics data for two-dimensional SnSe as inputs for the electronic structure and phonon dispersions at finite temperature. We capture an increase in phonon velocity at the Γ-point and enhanced hole conductivity at the structural transition temperature, accounting for the change in structure and anharmonicity in predicting TE performance explicitly. These ideas enhance our understanding of TE materials, and the procedure is applicable to bulk systems as well.

[1] L.-D. Zhao et al., Nature 508, 373 (2014).
[2] C. W. Li et al., Nature Physics 11, 1063 (2015).
[3] J. P. Heremans, Nature Physics 11, 990 (2015).