Phonon-Limited Electron Transport in a Highly Conductive Two-Dimensional Covalent Organic Framework: A Computational Study

Two-dimensional covalent organic frameworks (2D COFs) represent an emerging class of organic 2D materials with promising applications in electronics and optoelectronics. However, the current understanding of their charge transport mechanism associated with electron–phonon (e–ph) coupling still remains very limited. Here, by first-principles calculations, we present a computational study on the mechanism of electron transport as a result of e–ph coupling in a C 2 N- h 2D monolayer, a prototypical highly conductive 2D COF available in experiments. We obtain power-law behaviors of full-phonon-scattered electron mobility vs temperature, demonstrating that band transport is operational in the system for both low and high temperatures. Unusual phonon scatterings of electrons are revealed to be determined by optical rather than acoustic phonons at room temperature, which is quite different from the case of many other 2D materials and bulk inorganic/organic materials. This can be rationalized by the small optical-phonon energy as well as the different landscapes of e–ph coupling for acoustic and optical phonons in reciprocal space. Moreover, electron mobility as large as about 10 3 cm 2 V –1 s –1 is predicted for the C 2 N- h 2D monolayer at room temperature, and it can reach up to 10 5 cm 2 V –1 s –1 at low temperatures by doping engineering. This work provides a deep insight into the charge transport mechanism and a guideline for improving charge mobility in highly conductive 2D COFs.