Large Exciton Diffusion Coefficients in Two Dimensional Covalent Organic Frameworks with Different Domain Sizes Revealed by Ultrafast Exciton Dynamics

Journal Article · Wed Sep 02 04:00:00 EDT 2020 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/jacs.0c05404· OSTI ID:1756858

Flanders, Nathan C.; Kirschner, Matthew S.; Kim, Pyosang; Fauvell, Thomas; Evans, Austin; Helweh, Waleed; Spencer, Austin; Schaller, Richard D.; Dichtel, William R.; Chen, Lin X.

Large singlet exciton diffusion lengths are a hallmark of high performance in organic-based devices such as photovoltaics, chemical sensors, and photodetectors. In this study, exciton dynamics of a two-dimensional covalent organic framework, 2D COF-S, is investigated using ultrafast spectroscopic techniques. After photoexcitation, the COF-S exciton decays via three pathways: (1) excimer formation (4 +/- 2 ps), (2) excimer relaxation (160 +/- 40 ps), and (3) excimer decay (>3 ns). Excitation fluence-dependent transient absorption studies suggest that COF-5 has a relatively large diffusion coefficient (0.08 cm(2)/s). Furthermore, exciton-exciton annihilation processes are characterized as a function of COF-S crystallite domain size in four different samples, which reveal domain-size-dependent exciton diffusion kinetics. These results reveal that exciton diffusion in COF-S is constrained by its crystalline domain size. These insights indicate the outstanding promise of delocalized excitonic processes available in 2D COFs, which motivate their continued design and implementation into optoelectronic devices.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: U.S. Army Research Laboratory - U.S. Army Research Office (ARO); USDOE Office of Science - Office of Basic Energy Sciences - Chemical Sciences, Geosciences, and Biosciences Division; National Science Foundation (NSF)
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1756858
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 35 Vol. 142; ISSN 0002-7863
• Country of Publication: United States
• Language: English