Modulating Thermoelectric and Optical Properties of Bi2Te3 Monolayers Via Band Engineering.

Modulation of the band structure is essential for achieving superior thermoelectric (TE) and optical properties in semiconductor materials. Based on first-principles calculations and Boltzmann transport theory, this work comprehensively explores the modulation of the TE and optical properties of Bi2Te3 monolayers through atomic substitution with S, Se, Y, and La. The results demonstrate that while substituting the middle-layer Te atoms with S or Se largely enhances the electrical transport of the Bi2Te3 monolayer by boosting carrier mobility, this approach also deteriorates its lattice thermal conductivity by facilitating phonon propagation. In contrast, substituting the Bi atomic layer with Y or La significantly suppresses phonon transport, with the BiLaTe3 monolayer achieving an ultralow lattice thermal conductivity of 0.21 W m-1 K-1 at 500 K owing to the short phonon relaxation time and low group velocity. Consequently, the p-type Bi2Te2Se and n-type BiLaTe3 monolayers exhibit maximum ZT values of 3.66 and 1.00 at 500 K, respectively, which are 2.1 times and 1.5 times those of the corresponding Bi2Te3 monolayer. Besides, optical analysis indicates that with the exception of the BiLaTe3 monolayer, all other monolayers present high optical absorption peaks within the visible spectrum. These findings highlight that Bi2Te3 monolayers modified by atomic substitution show promising prospects in optical absorption and thermoelectric devices.