Ultralow Lattice Thermal Conductivity and Thermoelectric Properties of Monolayer Tl₂O

We report first-principles results on the thermal and thermoelectric properties of monolayer Tl₂O. The lattice thermal conductivity and electronic transport coefficients are obtained by semiclassical Boltzmann transport theory. Monolayer Tl₂O is found to be a semiconductor with a direct band gap of 1.62 eV. The lattice thermal conductivity turns out to be ultralow, for example, 0.17 W/mK at 300 K. Combined with a high power factor, this results in excellent thermoelectric performance. For example, at 500 K the p-type and n-type thermoelectric figures of merit reach peak values of 0.96 and 0.94 at hole and electron concentrations of 1.2 × 10¹¹ and 0.8 × 10¹¹ cm^-2, respectively.