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

The thermoelectric (TE) performance of single -layer ABN (A = Zr, Hf; B--Br, 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.