Theoretical Study of Thermoelectric Properties of Covalent Organic Frameworks with Slipped Arrangement

Abstract

In this study, Density Functional Theory and the Boltzmann transport equation are applied to calculate the semiclassical thermoelectric transport properties of phthalocyanine (PC) covalent organic frameworks with different central metals in the macrocycle MPc-COFs, (M = Co, Cu, and Zn), which have a slipped-AA stacking of 2D polymer sheets. The weakening of pi-pi stacking increased the role ofin-planeintramolecular through-bond carrier transfer involving sigma/pi interactions, leading to significant anisotropy of transport coefficients in the studied compounds, which are also affected by the nature of the transition metals. The maximum values of thermopower for Co-Pc COF (770 mu V/K) and Cu-Pc COF (- 423 mu V/K) were found along thein-planedirection. However, for ZnPc-COF, the maximum positive value of the Seebeck coefficient (156 mu V/K) was found along the stacking direction, while the maximum value of the thermopower along thein-planedirection was equal to - 315 mu V/K. The electronic fitness function was calculated to estimate the thermoelectric performance of the studied compounds for bothp- andn-type doping at 300 and 800 K. The maximum values of the electronic fitness function are observed for Cu-Pc and Zn-Pc COFs along the stacking direction at 800 K for bothp- andn-type doping, while forp-doped Co-Pc COF the maximum value of this function was found along thein-planedirection.