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Reduced Recombination and Capacitor-like Charge Buildup in an Organic Heterojunction

Kyra N. Schwarz, Paul B. Geraghty, Valerie D. Mitchell, Saeed-Uz-Zaman Khan, Oskar J. Sandberg, Nasim Zarrabi, Bryan Kudisch, Jegadesan Subbiah, Trevor A. Smith, Barry P. Rand, Ardalan Armin Orcid Logo, Gregory D. Scholes, David J. Jones, Kenneth P. Ghiggino

Journal of the American Chemical Society, Volume: 142, Issue: 5, Pages: 2562 - 2571

Swansea University Author: Ardalan Armin Orcid Logo

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DOI (Published version): 10.1021/jacs.9b12526

Abstract

Organic photovoltaic (OPV) efficiencies continue to rise, raising their prospects for solar energy conversion. However, researchers have long considered how to suppress the loss of free carriers by recombination—poor diffusion and significant Coulombic attraction can cause electrons and holes to enc...

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Published in: Journal of the American Chemical Society
ISSN: 0002-7863 1520-5126
Published: American Chemical Society (ACS) 2020
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URI: https://cronfa.swan.ac.uk/Record/cronfa53277
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Using femtosecond transient spectroscopies, we report the nanosecond grow-in of a large transient 20 Stark effect, caused by nanoscale electric fields of ~487 kV/cm between photogenerated free carriers in the device active layer. We find that particular morphologies of the active layer lead to an energetic cascade for charge carriers, suppressing pathways to recombination, which is ~2000 times less than predicted by Langevin theory. This in turn leads to the build-up of electric charge in donor and acceptor domains&#x2014;away from the interface&#x2014;resistant to bimolecular recombination. 25 Interestingly, this signal is only experimentally obvious in thick films, due to the different scaling of electro-absorption and photo-induced absorption signals in transient absorption spectroscopy. Rather than inhibiting device performance, we show that devices up to 600 nm thick maintain efficiencies of &gt; 8 % because domains can afford much higher carrier densities. 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spelling 2021-09-09T16:55:33.8418973 v2 53277 2020-01-15 Reduced Recombination and Capacitor-like Charge Buildup in an Organic Heterojunction 22b270622d739d81e131bec7a819e2fd 0000-0002-6129-5354 Ardalan Armin Ardalan Armin true false 2020-01-15 SPH Organic photovoltaic (OPV) efficiencies continue to rise, raising their prospects for solar energy conversion. However, researchers have long considered how to suppress the loss of free carriers by recombination—poor diffusion and significant Coulombic attraction can cause electrons and holes to encounter each other at interfaces close to where they were photogenerated. Using femtosecond transient spectroscopies, we report the nanosecond grow-in of a large transient 20 Stark effect, caused by nanoscale electric fields of ~487 kV/cm between photogenerated free carriers in the device active layer. We find that particular morphologies of the active layer lead to an energetic cascade for charge carriers, suppressing pathways to recombination, which is ~2000 times less than predicted by Langevin theory. This in turn leads to the build-up of electric charge in donor and acceptor domains—away from the interface—resistant to bimolecular recombination. 25 Interestingly, this signal is only experimentally obvious in thick films, due to the different scaling of electro-absorption and photo-induced absorption signals in transient absorption spectroscopy. Rather than inhibiting device performance, we show that devices up to 600 nm thick maintain efficiencies of > 8 % because domains can afford much higher carrier densities. These observations suggest that with particular nanoscale morphologies, the bulk heterojunction can go beyond its established role in charge photogeneration, and can act as a capacitor, where adjacent free charges are held away from the interface and can be protected from bimolecular recombination. Journal Article Journal of the American Chemical Society 142 5 2562 2571 American Chemical Society (ACS) 0002-7863 1520-5126 5 2 2020 2020-02-05 10.1021/jacs.9b12526 http://dx.doi.org/10.1021/jacs.9b12526 COLLEGE NANME Physics COLLEGE CODE SPH Swansea University 2021-09-09T16:55:33.8418973 2020-01-15T17:05:36.5143213 Faculty of Science and Engineering School of Biosciences, Geography and Physics - Physics Kyra N. Schwarz 1 Paul B. Geraghty 2 Valerie D. Mitchell 3 Saeed-Uz-Zaman Khan 4 Oskar J. Sandberg 5 Nasim Zarrabi 6 Bryan Kudisch 7 Jegadesan Subbiah 8 Trevor A. Smith 9 Barry P. Rand 10 Ardalan Armin 0000-0002-6129-5354 11 Gregory D. Scholes 12 David J. Jones 13 Kenneth P. Ghiggino 14 53277__16440__bb9b1912fa1b49eb9f5e5be58c95aea8.pdf 53277.pdf 2020-01-27T09:37:55.4674469 Output 1720498 application/pdf Accepted Manuscript true 2021-01-22T00:00:00.0000000 true eng 53277__16441__72eead758350404c8b5f99afcdf6bc8a.pdf 53277_Supporting_Information.pdf 2020-01-27T09:38:33.1736150 Output 2431038 application/pdf Supplemental material true 2021-01-22T00:00:00.0000000 true eng
title Reduced Recombination and Capacitor-like Charge Buildup in an Organic Heterojunction
spellingShingle Reduced Recombination and Capacitor-like Charge Buildup in an Organic Heterojunction
Ardalan Armin
title_short Reduced Recombination and Capacitor-like Charge Buildup in an Organic Heterojunction
title_full Reduced Recombination and Capacitor-like Charge Buildup in an Organic Heterojunction
title_fullStr Reduced Recombination and Capacitor-like Charge Buildup in an Organic Heterojunction
title_full_unstemmed Reduced Recombination and Capacitor-like Charge Buildup in an Organic Heterojunction
title_sort Reduced Recombination and Capacitor-like Charge Buildup in an Organic Heterojunction
author_id_str_mv 22b270622d739d81e131bec7a819e2fd
author_id_fullname_str_mv 22b270622d739d81e131bec7a819e2fd_***_Ardalan Armin
author Ardalan Armin
author2 Kyra N. Schwarz
Paul B. Geraghty
Valerie D. Mitchell
Saeed-Uz-Zaman Khan
Oskar J. Sandberg
Nasim Zarrabi
Bryan Kudisch
Jegadesan Subbiah
Trevor A. Smith
Barry P. Rand
Ardalan Armin
Gregory D. Scholes
David J. Jones
Kenneth P. Ghiggino
format Journal article
container_title Journal of the American Chemical Society
container_volume 142
container_issue 5
container_start_page 2562
publishDate 2020
institution Swansea University
issn 0002-7863
1520-5126
doi_str_mv 10.1021/jacs.9b12526
publisher American Chemical Society (ACS)
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
url http://dx.doi.org/10.1021/jacs.9b12526
document_store_str 1
active_str 0
description Organic photovoltaic (OPV) efficiencies continue to rise, raising their prospects for solar energy conversion. However, researchers have long considered how to suppress the loss of free carriers by recombination—poor diffusion and significant Coulombic attraction can cause electrons and holes to encounter each other at interfaces close to where they were photogenerated. Using femtosecond transient spectroscopies, we report the nanosecond grow-in of a large transient 20 Stark effect, caused by nanoscale electric fields of ~487 kV/cm between photogenerated free carriers in the device active layer. We find that particular morphologies of the active layer lead to an energetic cascade for charge carriers, suppressing pathways to recombination, which is ~2000 times less than predicted by Langevin theory. This in turn leads to the build-up of electric charge in donor and acceptor domains—away from the interface—resistant to bimolecular recombination. 25 Interestingly, this signal is only experimentally obvious in thick films, due to the different scaling of electro-absorption and photo-induced absorption signals in transient absorption spectroscopy. Rather than inhibiting device performance, we show that devices up to 600 nm thick maintain efficiencies of > 8 % because domains can afford much higher carrier densities. These observations suggest that with particular nanoscale morphologies, the bulk heterojunction can go beyond its established role in charge photogeneration, and can act as a capacitor, where adjacent free charges are held away from the interface and can be protected from bimolecular recombination.
published_date 2020-02-05T04:06:09Z
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score 11.016235

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