Thermoelectric properties of the hexagonal- and square-shaped monolayers of ZnO

Two-dimensional thermoelectric materials have been extensively explored in recent years for their potential to recycle waste heat into clean energy. Herein, we investigate the thermoelectric properties of hexagonal- and square-shaped monolayers of ZnO for renewable energy applications. These monolayers have been originated from the 110- and 011-facets of β-BeO type structured ZnO (β-BeO-ZnO). To execute this study, the electronic structures of these monolayers have been obtained within the framework of density functional theory (DFT). The results of electronic structures have been used to obtain the thermoelectric properties against chemical potential and temperature using the semi-classical Boltzmann transport theory (BTT). The high electrical conductivities and substantial Seebeck coefficient equivalent to 1500 μV/K have been recorded for 110-monolayer and 2716.75 μV/K for 011-monolayer. As a result, large thermoelectric power factors (PF) of magnitude 7.96 × 1010 W/mK2s at 0.49 eV for 110- monolayer and 4.63 × 1010 W/mK2s at 1.83 eV recorded for 011-monolayer. The PF of these monolayers has experienced a linear increase with the rise in temperature. Moreover, the thermoelectric figure-of-merit (zT) values have been recorded as ~ 1.02 and ~ 1 for 110- and 011-monolayer. The zT of 011-monolayer has been found to decrease for an increase in temperature beyond 450 K whereas zT of 110-monolayer has been found insensitive to change in temperature. This reveals the potential of ZnO monolayers (110-monolayer in particular) for applications in high-temperature thermoelectric devices.