Unraveling the Effect of Defects, Domain Size, and Chemical Doping on Photophysics and Charge Transport in Covalent Organic Frameworks

We present a novel theoretical approach to understanding the effect of electronic defects, domain size, and chemical dopants on the infrared spectral line shape and three-dimensional charge transport of positively charged polarons (“holes”) in doped (and undoped) Covalent Organic Frameworks (COFs). The simulated spectra are in excellent agreement with very recent measurements conducted on Iodine doped COF films. Through a detailed systematic analysis, we can also determine the polaron coherence lengths both along the 2D COF plane (intraframework) and through the molecular columns (interframework). The coherence lengths are important quantities in determining the anisotropic charge mobilities and conductivities in such films and are therefore of major interest in understanding the operation of organic electronic devices such as transistors and solar cells. By obtaining the first quantitative agreement with iodine doped TANG-COF, we identify well defined spectral signatures that provides conclusive evidence on why doped COFS have so far shown lower bulk conductivity compared to doped polythiophenes.