Please use this identifier to cite or link to this item: https://hdl.handle.net/2440/129896
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Type: Journal article
Title: Anisotropic triplet exciton diffusion in crystalline functionalized pentacene
Author: Hudson, R.J.
Huang, D.M.
Kee, T.W.
Citation: The Journal of Physical Chemistry C: Energy Conversion and Storage, Optical and Electronic Devices, Interfaces, Nanomaterials, and Hard Matter, 2020; 124(43):23541-23550
Publisher: American Chemical Society
Issue Date: 2020
ISSN: 1932-7447
1932-7455
Statement of
Responsibility: 
Rohan J. Hudson, David M. Huang and Tak W. Kee
Abstract: Exciton multiplication through singlet fission (SF) offers scope for next-generation photovoltaic devices to exceed the Shockley–Queisser limit. Organic SF chromophores typically exhibit significant structural anisotropy in their crystal packing, which can impact exciton transport and influence the design of SF-enhanced devices. An improved understanding of the link between structural anisotropy and exciton diffusion is therefore crucial for developing SF-based photovoltaics. Here, we use femtosecond transient absorption spectroscopy to quantify the anisotropic triplet mobility in 6,13-(triisopropylsilylethynyl)pentacene (TIPS-Pn), a prototypical SF chromophore. Bimolecular triplet–triplet annihilation (TTA) in crystalline TIPS-Pn is well-described by a kinetic model that assumes isotropic, three-dimensional triplet exciton diffusion, but with best-fit parameters that do not correspond to any physical parameters of the material. Kinetic models that assume either one-dimensional or anisotropic three-dimensional exciton diffusion describe the annihilation equally well but yield more physically realistic fit parameters, suggesting that triplet diffusion on the subnanosecond time scale occurs mostly along a single axis of the material. These findings highlight the need to treat parameters obtained from fits of experimental data with models of isotropic diffusion with caution for systems with anisotropic packing such as TIPS-Pn. Diffusion coefficients calculated by density functional theory predict that triplet exciton diffusion occurs predominantly along the crystallographic a-axis, with migration in any other direction through the crystal slower by over an order of magnitude. This anisotropic diffusion suggests that fast, directional exciton transport in layers or films of TIPS-Pn may be achieved by control of the chromophore morphology.
Rights: © 2020 American Chemical Society
DOI: 10.1021/acs.jpcc.0c07608
Grant ID: http://purl.org/au-research/grants/arc/LE0989747
http://purl.org/au-research/grants/arc/DP160103797
http://purl.org/au-research/grants/arc/DP190102100
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Chemistry and Physics publications

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