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Posted On: 06/27/2017 1:28:11 PM
Post# of 22463
Resolving ultrafast exciton migration in organic solids at the nanoscale
Samuel B. Penwell, Lucas D. S. Ginsberg, Rodrigo Noriega, Naomi S. Ginsberg
(Submitted on 26 Jun 2017)
The effectiveness of molecular-based light harvesting relies on transport of optical excitations, excitons, to charg-transfer sites. Measuring exciton migration has, however, been challenging because of the mismatch between nanoscale migration lengths and the diffraction limit. In organic semiconductors, common bulk methods employ a series of films terminated at quenching substrates, altering the spatioenergetic landscape for migration. Here we instead define quenching boundaries all-optically with sub-diffraction resolution, thus characterizing spatiotemporal exciton migration on its native nanometer and picosecond scales without disturbing morphology. By transforming stimulated emission depletion microscopy into a time-resolved ultrafast approach, we measure a 16-nm migration length in CN-PPV conjugated polymer films. Combining these experiments with Monte Carlo exciton hopping simulations shows that migration in CN-PPV films is essentially diffusive because intrinsic chromophore energetic disorder is comparable to inhomogeneous broadening among chromophores. This framework also illustrates general trends across materials. Our new approach's sub-diffraction resolution will enable previously unattainable correlations of local material structure to the nature of exciton migration, applicable not only to photovoltaic or display-destined organic semiconductors but also to explaining the quintessential exciton migration exhibited in photosynthesis.
https://arxiv.org/abs/1706.08460
Samuel B. Penwell, Lucas D. S. Ginsberg, Rodrigo Noriega, Naomi S. Ginsberg
(Submitted on 26 Jun 2017)
The effectiveness of molecular-based light harvesting relies on transport of optical excitations, excitons, to charg-transfer sites. Measuring exciton migration has, however, been challenging because of the mismatch between nanoscale migration lengths and the diffraction limit. In organic semiconductors, common bulk methods employ a series of films terminated at quenching substrates, altering the spatioenergetic landscape for migration. Here we instead define quenching boundaries all-optically with sub-diffraction resolution, thus characterizing spatiotemporal exciton migration on its native nanometer and picosecond scales without disturbing morphology. By transforming stimulated emission depletion microscopy into a time-resolved ultrafast approach, we measure a 16-nm migration length in CN-PPV conjugated polymer films. Combining these experiments with Monte Carlo exciton hopping simulations shows that migration in CN-PPV films is essentially diffusive because intrinsic chromophore energetic disorder is comparable to inhomogeneous broadening among chromophores. This framework also illustrates general trends across materials. Our new approach's sub-diffraction resolution will enable previously unattainable correlations of local material structure to the nature of exciton migration, applicable not only to photovoltaic or display-destined organic semiconductors but also to explaining the quintessential exciton migration exhibited in photosynthesis.
https://arxiv.org/abs/1706.08460
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