Promising thermoelectric performance towards single-layer β-ABN (A = Zr, Hf; BBr, I)

The thermoelectric (TE) performance of single-layer ABN (A = Zr, Hf; BBr, I) was systematically investigated by first-principles approach and Boltzmann transport theory. The results show that four monolayers possess high stability, as well as low cleavage energies of 0.30–0.41 J/m2, which provide a reliable approach to obtain the monolayers by mechanical exfoliation. Owing to strong optical-acoustic phonon coupling and low frequency (2.31–2.78 THz) of low-lying phonons, they exhibit low lattice thermal conductivities of 2.14–2.77 W/mK. Besides, monolayer ABN are indirect semiconductors with band-gaps of 1.52–2.97 eV, and their optimal power factor (PF) reaches 15.96 − 19.47 mW/K2m. As a result, monolayer ABN deliver TE figure of merit (ZT) of 0.25–0.31 at 300 K, and increase further to 1.15–1.80 at 700 K, demonstrating that they are promising candidates as low-medium temperature TE materials.