Atomistic design of two-dimensional covalent organic frameworks with high thermoelectric performance

Abstract

Very recently, burgeoning two-dimensional covalent organic framework-based materials have been proven to exhibit decent performance for potential thermoelectric applications. Nevertheless, hitherto formulating systematic atomistic-level materials design strategies for two-dimensional covalent organic frameworks with enhanced thermoelectric performance still remains a formidable challenge. Here, on the basis of ab initio computations, and taking 17 representative two-dimensional covalent organic frameworks as examples, an atomistic understanding is established to uncover the complex correlation among the macroscopic thermoelectric properties, nontrivial transport processes, and basic chemical structures, and concurrently, general materials design guidelines are offered. We reveal that the ratio of contributions of linker and knot parts to the valence bands can be treated as a strong predictor to assess the thermoelectric performance of covalent organic frameworks. Our results corroborate that a small ratio of the contributions of the linker and knot parts to the valence bands brings about a large band dispersion, weak interactions of charge carriers with lattice vibrations, high hole mobility, and thus an outstanding thermoelectric power factor. Furthermore, our findings reveal that for two-dimensional covalent organic frameworks, introducing benzene rings, replacing the heterocycles with benzene rings, reducing the number of nitrogen heterocycles, and avoiding benzoquinone structures in the linker parts help in realizing their charge-carrier delocalization, and thus a decent power factor.