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

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

doi:10.1021/jacs.8b11484

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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

, M. Azzouzi, J. Wu, J. Yao, Y. Dong, P. Shakya Tuladhar, B. C. Schroeder, E. R. Bittner, I. McCulloch, Jenny Nelson

, James Durrant

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

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

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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
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first_indexed	2019-03-18T13:59:31Z
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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. 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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 EEN 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 Engineering COLLEGE CODE EEN 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
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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	2019-03-20T04:00:02Z
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score	11.012678

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

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