Enhanced thermoelectric properties and high carrier mobility of two-dimensional SbBiSY2 (Y = Se, Te) and their Janus monolayers

• 2D SbBiSY 2 (Y = Te, Se) and Janus SbBiSYZ (Y ≠ Z = S, Se, Te) monolayers are indirect band gap semiconductors. • These materials show ultralow lattice thermal conductivity of 0.17–1.89 W/mK at 300 K. • Thermoelectric figure of merit (ZT) of these monolayers reaches up to 2.16 at 300 K. • The calculated conversion efficiency η m a x (%) of these monolayers are in the range of 31–74%. The electronic transport and thermoelectric characteristics of SbBiSY 2 (Y = Se, Te) and their Janus monolayers are investigated utilizing Boltzmann transport equation (BTE) and electron–phonon dynamics through first-principles computations. Ab initio molecular dynamics (AIMD) simulation, and phonon spectra calculations validate the thermodynamic and dynamic stabilities of these monolayers. These monolayers are semiconductor in nature with carrier mobility reaching up to 204 cm 2 V −1 s −1 . The lattice thermal conductivity ( κ l ) , at ambient temperature are calculated to be 1.89 W/mK, 1.08 W/mK, and 0.81 W/mK, 0.56 W/mK, 0.17 W/mK for SbBiSTe 2 , SbBiSSe 2 , and Janus SbBiSTeSe, SbBiSTeS, SbBiSSeS monolayers, respectively. The thermoelectric figure of merit, ZT, is significantly enhanced, primarily owing to low values of lattice thermal conductivity and high Seebeck coefficient. The ZT reaches up to 0.44, 0.98, 1.30, 1.16 and 2.16, respectively for SbBiSTe 2 , SbBiSSe 2 and Janus SbBiSTeSe, SbBiSTeS, and SbBiSSeS monolayers for p-type carrier at ambient temperature. These characteristics makes these monolayers to be promising candidates for thermoelectric applications.