Large Exciton Diffusion Coefficients in Two Dimensional Covalent Organic Frameworks with Different Domain Sizes Revealed by Ultrafast Exciton Dynamics
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 Lab. (ANL), Argonne, IL (United States)
- 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, Vol. 142, Issue 35
- Country of Publication:
- United States
- Language:
- English
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