Journal
ADVANCED FUNCTIONAL MATERIALS
Volume 25, Issue 13, Pages 2038-2046Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.201403005
Keywords
electronic structures; organic semiconductors; density functional theory; excitons; optical spectroscopy; singlet fission
Categories
Funding
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
- Scientific Discovery through Advanced Computing (SciDAC) Partnership program - U.S. Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences
- Defense Advanced Research Projects Agency Young Faculty Award [N66001-12-1-4228]
- David and Lucile Packard Foundation Fellowship for Science and Engineering
- Natural Sciences and Engineering Research Council, Canada
- National Science Foundation [DGE 1106400]
- Israel Science Foundation
- Helmsley Foundation
- Wolfson Foundation
- Lise Meitner Minerva Center for Computational Chemistry
- United States-Israel Binational Science Foundation (BSF)
- Office of Science of the U.S. Department of Energy [DE-AC02-05CH11231, DE-AC02-06CH11357]
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Theory and experiment are combined to investigate the nature of low-energy excitons within ordered domains of 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-PEN) polycrystalline thin films. First-principles density functional theory and many-body perturbation theory calculations, along with polarization-dependent optical absorption spectro-microscopy on ordered domains, show multiple low-energy absorption peaks that are composed of excitonic states delocalized over several molecules. While the first absorption peak is composed of a single excitonic transition and retains the polarization-dependent behavior of the molecule, higher energy peaks are composed of multiple transitions with optical properties that can not be described by those of the molecule. The predicted structure-dependence of polarization-dependent absorption reveals the exact inter-grain orientation within the TIPS-PEN film. Additionally, the degree of exciton delocalization can be significantly tuned by modest changes in the solid-state structure and the spatial extent of the excitations along a given direction is correlated with the degree of electronic dispersion along the same direction. These findings pave the way for tailoring the singlet fission efficiency of organic crystals by solid-state structure.
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