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.
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14 March 2019
Research Article|
March 11 2019
The binding energy and dynamics of charge-transfer states in organic photovoltaics with low driving force for charge separation
Special Collection:
Nonlinear Spectroscopy and Interfacial Structure and Dynamics
Yifan Dong
;
Yifan Dong
1
Department of Chemistry and Centre for Plastic Electronics, Imperial College London
, London SW7 2AZ, United Kingdom
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Hyojung Cha
;
Hyojung Cha
1
Department of Chemistry and Centre for Plastic Electronics, Imperial College London
, London SW7 2AZ, United Kingdom
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Jiangbin Zhang
;
Jiangbin Zhang
1
Department of Chemistry and Centre for Plastic Electronics, Imperial College London
, London SW7 2AZ, United Kingdom
2
Cavendish Laboratory, University of Cambridge
, JJ Thomson Avenue, Cambridge CB3 0HE, United Kingdom
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Ernest Pastor
;
Ernest Pastor
1
Department of Chemistry and Centre for Plastic Electronics, Imperial College London
, London SW7 2AZ, United Kingdom
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Pabitra Shakya Tuladhar;
Pabitra Shakya Tuladhar
1
Department of Chemistry and Centre for Plastic Electronics, Imperial College London
, London SW7 2AZ, United Kingdom
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Iain McCulloch;
Iain McCulloch
1
Department of Chemistry and Centre for Plastic Electronics, Imperial College London
, London SW7 2AZ, United Kingdom
3
Physical Sciences and Engineering Division, KAUST Solar Centre (KSC), King Abdullah University of Science and Technology (KAUST)
, Thuwal 23955-6900, Saudi Arabia
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James R. Durrant;
James R. Durrant
a)
1
Department of Chemistry and Centre for Plastic Electronics, Imperial College London
, London SW7 2AZ, United Kingdom
4
SPECIFIC IKC, College of Engineering, Swansea University
, Swansea SA12 7AX, United Kingdom
a)Authors to whom correspondence should be addressed: j.durrant@imperial.ac.uk and a.bakulin@imperial.ac.uk
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Artem A. Bakulin
Artem A. Bakulin
a)
1
Department of Chemistry and Centre for Plastic Electronics, Imperial College London
, London SW7 2AZ, United Kingdom
a)Authors to whom correspondence should be addressed: j.durrant@imperial.ac.uk and a.bakulin@imperial.ac.uk
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a)Authors to whom correspondence should be addressed: j.durrant@imperial.ac.uk and a.bakulin@imperial.ac.uk
Note: This article is part of the Special Topic “Nonlinear Spectroscopy and Interfacial Structure and Dynamics” in J. Chem. Phys.
J. Chem. Phys. 150, 104704 (2019)
Article history
Received:
October 30 2018
Accepted:
February 19 2019
Citation
Yifan Dong, Hyojung Cha, Jiangbin Zhang, Ernest Pastor, Pabitra Shakya Tuladhar, Iain McCulloch, James R. Durrant, Artem A. Bakulin; The binding energy and dynamics of charge-transfer states in organic photovoltaics with low driving force for charge separation. J. Chem. Phys. 14 March 2019; 150 (10): 104704. https://doi.org/10.1063/1.5079285
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