First-principles calculations to investigate thermoelectric properties of new monolayers of ZnO

Zinc Oxide (ZnO) in two-dimensional morphology has emerged as a potential cost-effective material for applications in thermoelectric devices. Herein, we examine the thermoelectric behavior of two new types of ZnO monolayers (namely ZnO(NaCl) and ZnO(GeP)) originated from the rocksalt (NaCl) and GeP-type structures using the first-principles approach. The designed monolayers exhibited large Seebeck coefficients of magnitude 1700 mu V/K and 2800 mu V/K respectively for single-layered ZnO(NaCl) and ZnO(GeP). The substantial Seebeck coefficients and high electrical conductivities recorded for single-layered ZnO(NaCl) and ZnO(GeP) have resulted in large thermoelectric power factors (PF) of magnitude 8.40 x 1010 W/mk2s and 7.19 x 1010 W/ mk2s respectively. The p-type doping is seen to improve the PF of ZnO(NaCl) whereas the PF of ZnO(GeP) is enhanced by n-type doping. The PFs recorded for both monolayers are found to increase with the rise in temperature which is useful for thermoelectric applications at high temperatures. Moreover, significant figure-of-merit (zT) values equivalent to 1.04 and 0.98 have been recorded respectively for ZnO(NaCl) and ZnO(GeP) monolayers at room temperature. The recorded zT of both monolayers has been found independent of temperature which suggests them suitable for high-temperature thermoelectric applications.