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Spectroscopic Investigation of the Effect of Microstructure and Energetic Offset on the Nature of Interfacial Charge Transfer States in Polymer: Fullerene Blends

Stoichko Dimitrov Orcid Logo, M. Azzouzi, J. Wu, J. Yao, Y. Dong, P. Shakya Tuladhar, B. C. Schroeder, E. R. Bittner, I. McCulloch, Jenny Nelson Orcid Logo, James Durrant Orcid Logo

Journal of the American Chemical Society, Volume: 141, Issue: 11, Pages: 4634 - 4643

Swansea University Authors: Stoichko Dimitrov Orcid Logo, Jenny Nelson Orcid Logo, James Durrant Orcid Logo

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DOI (Published version): 10.1021/jacs.8b11484

Abstract

Despite performance improvements of organic photovoltaics, the mechanism of photoinduced electron–hole separation at organic donor–acceptor interfaces remains poorly understood. Inconclusive experimental and theoretical results have produced contradictory models for electron–hole separation in which...

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Published in: Journal of the American Chemical Society
ISSN: 0002-7863 1520-5126
Published: 2019
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URI: https://cronfa.swan.ac.uk/Record/cronfa49219
first_indexed 2019-03-18T13:59:31Z
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Inconclusive experimental and theoretical results have produced contradictory models for electron&#x2013;hole separation in which the role of interfacial charge-transfer (CT) states is unclear, with one model identifying them as limiting separation and another as readily dissociating. Here, polymer&#x2013;fullerene blends with contrasting photocurrent properties and enthalpic offsets driving separation were studied. By modifying composition, film structures were varied from consisting of molecularly mixed polymer&#x2013;fullerene domains to consisting of both molecularly mixed and fullerene domains. Transient absorption spectroscopy revealed that CT state dissociation generating separated electron&#x2013;hole pairs is only efficient in the high energy offset blend with fullerene domains. In all other blends (with low offset or predominantly molecularly mixed domains), nanosecond geminate electron&#x2013;hole recombination is observed revealing the importance of spatially localized electron&#x2013;hole pairs (bound CT states) in the electron&#x2013;hole dynamics. A two-dimensional lattice exciton model was used to simulate the excited state spectrum of a model system as a function of microstructure and energy offset. The results could reproduce the main features of experimental electroluminescence spectra indicating that electron&#x2013;hole pairs become less bound and more spatially separated upon increasing energy offset and fullerene domain density. Differences between electroluminescence and photoluminescence spectra could be explained by CT photoluminescence being dominated by more-bound states, reflecting geminate recombination processes, while CT electroluminescence preferentially probes less-bound CT states that escape geminate recombination. 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spelling 2023-02-14T16:43:48.7023897 v2 49219 2019-03-18 Spectroscopic Investigation of the Effect of Microstructure and Energetic Offset on the Nature of Interfacial Charge Transfer States in Polymer: Fullerene Blends 9fc26ec1b8655cd0d66f7196a924fe14 0000-0002-1564-7080 Stoichko Dimitrov Stoichko Dimitrov true false e0e41c0bb2b9cae677f7fbbf88abe590 0000-0003-1048-1330 Jenny Nelson Jenny Nelson true false f3dd64bc260e5c07adfa916c27dbd58a 0000-0001-8353-7345 James Durrant James Durrant true false 2019-03-18 Despite performance improvements of organic photovoltaics, the mechanism of photoinduced electron–hole separation at organic donor–acceptor interfaces remains poorly understood. Inconclusive experimental and theoretical results have produced contradictory models for electron–hole separation in which the role of interfacial charge-transfer (CT) states is unclear, with one model identifying them as limiting separation and another as readily dissociating. Here, polymer–fullerene blends with contrasting photocurrent properties and enthalpic offsets driving separation were studied. By modifying composition, film structures were varied from consisting of molecularly mixed polymer–fullerene domains to consisting of both molecularly mixed and fullerene domains. Transient absorption spectroscopy revealed that CT state dissociation generating separated electron–hole pairs is only efficient in the high energy offset blend with fullerene domains. In all other blends (with low offset or predominantly molecularly mixed domains), nanosecond geminate electron–hole recombination is observed revealing the importance of spatially localized electron–hole pairs (bound CT states) in the electron–hole dynamics. A two-dimensional lattice exciton model was used to simulate the excited state spectrum of a model system as a function of microstructure and energy offset. The results could reproduce the main features of experimental electroluminescence spectra indicating that electron–hole pairs become less bound and more spatially separated upon increasing energy offset and fullerene domain density. Differences between electroluminescence and photoluminescence spectra could be explained by CT photoluminescence being dominated by more-bound states, reflecting geminate recombination processes, while CT electroluminescence preferentially probes less-bound CT states that escape geminate recombination. These results suggest that apparently contradictory studies on electron–hole separation can be explained by the presence of both bound and unbound CT states in the same film, as a result of a range of interface structures. Journal Article Journal of the American Chemical Society 141 11 4634 4643 0002-7863 1520-5126 20 3 2019 2019-03-20 10.1021/jacs.8b11484 COLLEGE NANME COLLEGE CODE Swansea University UKRI, EP/M025020/1 2023-02-14T16:43:48.7023897 2019-03-18T11:37:37.7062753 Faculty of Science and Engineering School of Biosciences, Geography and Physics - Physics Stoichko Dimitrov 0000-0002-1564-7080 1 M. Azzouzi 2 J. Wu 3 J. Yao 4 Y. Dong 5 P. Shakya Tuladhar 6 B. C. Schroeder 7 E. R. Bittner 8 I. McCulloch 9 Jenny Nelson 0000-0003-1048-1330 10 James Durrant 0000-0001-8353-7345 11 49219__17564__38d1b045c58c409e83a618994cd1a814.pdf 49219VOR.pdf 2020-06-23T15:19:11.9870375 Output 3316247 application/pdf Version of Record true Released under the terms of a Creative Commons Attribution License (CC-BY). true eng http://pubs.acs.org/page/policy/authorchoice_ccby_termsofuse.html
title Spectroscopic Investigation of the Effect of Microstructure and Energetic Offset on the Nature of Interfacial Charge Transfer States in Polymer: Fullerene Blends
spellingShingle Spectroscopic Investigation of the Effect of Microstructure and Energetic Offset on the Nature of Interfacial Charge Transfer States in Polymer: Fullerene Blends
Stoichko Dimitrov
Jenny Nelson
James Durrant
title_short Spectroscopic Investigation of the Effect of Microstructure and Energetic Offset on the Nature of Interfacial Charge Transfer States in Polymer: Fullerene Blends
title_full Spectroscopic Investigation of the Effect of Microstructure and Energetic Offset on the Nature of Interfacial Charge Transfer States in Polymer: Fullerene Blends
title_fullStr Spectroscopic Investigation of the Effect of Microstructure and Energetic Offset on the Nature of Interfacial Charge Transfer States in Polymer: Fullerene Blends
title_full_unstemmed Spectroscopic Investigation of the Effect of Microstructure and Energetic Offset on the Nature of Interfacial Charge Transfer States in Polymer: Fullerene Blends
title_sort Spectroscopic Investigation of the Effect of Microstructure and Energetic Offset on the Nature of Interfacial Charge Transfer States in Polymer: Fullerene Blends
author_id_str_mv 9fc26ec1b8655cd0d66f7196a924fe14
e0e41c0bb2b9cae677f7fbbf88abe590
f3dd64bc260e5c07adfa916c27dbd58a
author_id_fullname_str_mv 9fc26ec1b8655cd0d66f7196a924fe14_***_Stoichko Dimitrov
e0e41c0bb2b9cae677f7fbbf88abe590_***_Jenny Nelson
f3dd64bc260e5c07adfa916c27dbd58a_***_James Durrant
author Stoichko Dimitrov
Jenny Nelson
James Durrant
author2 Stoichko Dimitrov
M. Azzouzi
J. Wu
J. Yao
Y. Dong
P. Shakya Tuladhar
B. C. Schroeder
E. R. Bittner
I. McCulloch
Jenny Nelson
James Durrant
format Journal article
container_title Journal of the American Chemical Society
container_volume 141
container_issue 11
container_start_page 4634
publishDate 2019
institution Swansea University
issn 0002-7863
1520-5126
doi_str_mv 10.1021/jacs.8b11484
college_str Faculty of Science and Engineering
hierarchytype
hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Biosciences, Geography and Physics - Physics{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Biosciences, Geography and Physics - Physics
document_store_str 1
active_str 0
description Despite performance improvements of organic photovoltaics, the mechanism of photoinduced electron–hole separation at organic donor–acceptor interfaces remains poorly understood. Inconclusive experimental and theoretical results have produced contradictory models for electron–hole separation in which the role of interfacial charge-transfer (CT) states is unclear, with one model identifying them as limiting separation and another as readily dissociating. Here, polymer–fullerene blends with contrasting photocurrent properties and enthalpic offsets driving separation were studied. By modifying composition, film structures were varied from consisting of molecularly mixed polymer–fullerene domains to consisting of both molecularly mixed and fullerene domains. Transient absorption spectroscopy revealed that CT state dissociation generating separated electron–hole pairs is only efficient in the high energy offset blend with fullerene domains. In all other blends (with low offset or predominantly molecularly mixed domains), nanosecond geminate electron–hole recombination is observed revealing the importance of spatially localized electron–hole pairs (bound CT states) in the electron–hole dynamics. A two-dimensional lattice exciton model was used to simulate the excited state spectrum of a model system as a function of microstructure and energy offset. The results could reproduce the main features of experimental electroluminescence spectra indicating that electron–hole pairs become less bound and more spatially separated upon increasing energy offset and fullerene domain density. Differences between electroluminescence and photoluminescence spectra could be explained by CT photoluminescence being dominated by more-bound states, reflecting geminate recombination processes, while CT electroluminescence preferentially probes less-bound CT states that escape geminate recombination. These results suggest that apparently contradictory studies on electron–hole separation can be explained by the presence of both bound and unbound CT states in the same film, as a result of a range of interface structures.
published_date 2019-03-20T07:41:52Z
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score 11.04748

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