The binding energy and dynamics of charge-transfer states in organic photovoltaics with low driving force for charge separation

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Title: The binding energy and dynamics of charge-transfer states in organic photovoltaics with low driving force for charge separation
Authors: Dong, Y
Cha, H
Zhang, J
Pastor, E
Tuladhar, PS
McCulloch, I
Durrant, JR
Bakulin, AA
Item Type: Journal Article
Abstract: Recent progress in organic photovoltaics (OPVs) has been enabled by optimization of the energetic driving force for charge separation, and thus maximization of open-circuit voltage, using non-fullerene acceptor (NFA) materials. In spite of this, the carrier dynamics and relative energies of the key states controlling the photophysics of these systems are still under debate. Herein, we report an in-depth ultrafast spectroscopic study of a representative OPV system based on a polymer donor PffBT4T-2OD and a small-molecule NFA EH-IDTBR. Global analysis of the transient absorption data reveals efficient energy transfer between donor and acceptor molecules. The extracted kinetics suggest that slow (∼15 ps) generation of charge carriers is followed by significant geminate recombination. This contrasts with the "reference" PffBT4T-2OD:PC71BM system where bimolecular recombination dominates. Using temperature-dependent pump-push-photocurrent spectroscopy, we estimate the activation energy for the dissociation of bound charge-transfer states in PffBT4T-2OD:EH-IDTBR to be 100 ± 6 meV. We also observe an additional activation energy of 14 ± 7 meV, which we assign to the de-trapping of mobile carriers. This work provides a comprehensive picture of photophysics in a system representing new generation of OPV blends with a small driving force for charge separation.
Issue Date: 11-Mar-2019
Date of Acceptance: 19-Feb-2019
URI: http://hdl.handle.net/10044/1/69275
DOI: https://doi.org/10.1063/1.5079285
ISSN: 0021-9606
Publisher: AIP Publishing
Journal / Book Title: Journal of Chemical Physics
Volume: 150
Issue: 10
Copyright Statement: © 2019 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in [J. Chem. Phys. 150, 104704 (2019); doi: 10.1063/1.5079285] and may be found at [https://doi.org/10.1063/1.5079285]
Sponsor/Funder: The Royal Society
Funder's Grant Number: UF130178
Keywords: Science & Technology
Physical Sciences
Chemistry, Physical
Physics, Atomic, Molecular & Chemical
Chemistry
Physics
SOLAR-CELLS
EFFICIENCY
RECOMBINATION
GENERATION
MORPHOLOGY
Chemical Physics
02 Physical Sciences
03 Chemical Sciences
09 Engineering
Publication Status: Published
Conference Place: United States
Embargo Date: 2020-03-11
Article Number: 104704
Online Publication Date: 2019-03-11
Appears in Collections:Chemistry
Faculty of Natural Sciences



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