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Interplay Between Triplet-, Singlet-Charge Transfer States and Free Charge Carriers Defining Bimolecular Recombination Rate Constant of Organic Solar Cells

Ardalan Armin, James Durrant Orcid Logo, Safa Shoaee Orcid Logo

The Journal of Physical Chemistry C, Volume: 121, Issue: 25, Pages: 13969 - 13976

Swansea University Authors: Ardalan Armin, James Durrant Orcid Logo

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DOI (Published version): 10.1021/acs.jpcc.7b04825

Abstract

Despite the myriad of organic donor:acceptor materials, only few systems have emerged in the life of organic solar cells to exhibit considerable reduced bimolecular recombination, with respect to the random encounter rate given by the Langevin equation. Monte Carlo simulations have revealed that the...

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Published in: The Journal of Physical Chemistry C
ISSN: 1932-7447 1932-7455
Published: American Chemical Society (ACS) 2017
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URI: https://cronfa.swan.ac.uk/Record/cronfa34793
first_indexed 2017-07-27T20:25:56Z
last_indexed 2023-01-11T14:09:11Z
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spelling 2022-12-05T12:04:54.5664712 v2 34793 2017-07-27 Interplay Between Triplet-, Singlet-Charge Transfer States and Free Charge Carriers Defining Bimolecular Recombination Rate Constant of Organic Solar Cells 22b270622d739d81e131bec7a819e2fd Ardalan Armin Ardalan Armin true false f3dd64bc260e5c07adfa916c27dbd58a 0000-0001-8353-7345 James Durrant James Durrant true false 2017-07-27 Despite the myriad of organic donor:acceptor materials, only few systems have emerged in the life of organic solar cells to exhibit considerable reduced bimolecular recombination, with respect to the random encounter rate given by the Langevin equation. Monte Carlo simulations have revealed that the rate constant of the formation of electron–hole bound states depends on the random encounter of opposite charges and is nearly given by the Langevin equation for the domain sizes relevant to efficient bulk heterojunction systems. Recently, three studies suggested that charge transfer states dissociating much faster than their decay rate to the ground state, can result in reduced bimolecular recombination by lowering the recombination rate to the ground state as a loss pathway. A separate study identified another loss pathway and suggested that forbidden back electron transfer from triplet charge transfer states to triplet excitons is a key to achieving reduced recombination. Herein we further explain the reduced bimolecular recombination by investigating the limitations of these two proposals. By solving kinetic rate equations for a BHJ system with realistic rates, we show that both of these previously presented conditions must only be held at the same time for a system to exhibit non-Langevin behavior. We demonstrate that suppression of both of the parallel loss channels of singlet and triplet states can be achieved through increasing the dissociation rate of the charge transfer states; a crucial requirement to achieve a high charge carrier extraction efficiency. Journal Article The Journal of Physical Chemistry C 121 25 13969 13976 American Chemical Society (ACS) 1932-7447 1932-7455 29 6 2017 2017-06-29 10.1021/acs.jpcc.7b04825 COLLEGE NANME COLLEGE CODE Swansea University 2022-12-05T12:04:54.5664712 2017-07-27T15:46:41.8173821 Faculty of Science and Engineering School of Biosciences, Geography and Physics - Physics Ardalan Armin 1 James Durrant 0000-0001-8353-7345 2 Safa Shoaee 0000-0001-8386-2893 3
title Interplay Between Triplet-, Singlet-Charge Transfer States and Free Charge Carriers Defining Bimolecular Recombination Rate Constant of Organic Solar Cells
spellingShingle Interplay Between Triplet-, Singlet-Charge Transfer States and Free Charge Carriers Defining Bimolecular Recombination Rate Constant of Organic Solar Cells
Ardalan Armin
James Durrant
title_short Interplay Between Triplet-, Singlet-Charge Transfer States and Free Charge Carriers Defining Bimolecular Recombination Rate Constant of Organic Solar Cells
title_full Interplay Between Triplet-, Singlet-Charge Transfer States and Free Charge Carriers Defining Bimolecular Recombination Rate Constant of Organic Solar Cells
title_fullStr Interplay Between Triplet-, Singlet-Charge Transfer States and Free Charge Carriers Defining Bimolecular Recombination Rate Constant of Organic Solar Cells
title_full_unstemmed Interplay Between Triplet-, Singlet-Charge Transfer States and Free Charge Carriers Defining Bimolecular Recombination Rate Constant of Organic Solar Cells
title_sort Interplay Between Triplet-, Singlet-Charge Transfer States and Free Charge Carriers Defining Bimolecular Recombination Rate Constant of Organic Solar Cells
author_id_str_mv 22b270622d739d81e131bec7a819e2fd
f3dd64bc260e5c07adfa916c27dbd58a
author_id_fullname_str_mv 22b270622d739d81e131bec7a819e2fd_***_Ardalan Armin
f3dd64bc260e5c07adfa916c27dbd58a_***_James Durrant
author Ardalan Armin
James Durrant
author2 Ardalan Armin
James Durrant
Safa Shoaee
format Journal article
container_title The Journal of Physical Chemistry C
container_volume 121
container_issue 25
container_start_page 13969
publishDate 2017
institution Swansea University
issn 1932-7447
1932-7455
doi_str_mv 10.1021/acs.jpcc.7b04825
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
document_store_str 0
active_str 0
description Despite the myriad of organic donor:acceptor materials, only few systems have emerged in the life of organic solar cells to exhibit considerable reduced bimolecular recombination, with respect to the random encounter rate given by the Langevin equation. Monte Carlo simulations have revealed that the rate constant of the formation of electron–hole bound states depends on the random encounter of opposite charges and is nearly given by the Langevin equation for the domain sizes relevant to efficient bulk heterojunction systems. Recently, three studies suggested that charge transfer states dissociating much faster than their decay rate to the ground state, can result in reduced bimolecular recombination by lowering the recombination rate to the ground state as a loss pathway. A separate study identified another loss pathway and suggested that forbidden back electron transfer from triplet charge transfer states to triplet excitons is a key to achieving reduced recombination. Herein we further explain the reduced bimolecular recombination by investigating the limitations of these two proposals. By solving kinetic rate equations for a BHJ system with realistic rates, we show that both of these previously presented conditions must only be held at the same time for a system to exhibit non-Langevin behavior. We demonstrate that suppression of both of the parallel loss channels of singlet and triplet states can be achieved through increasing the dissociation rate of the charge transfer states; a crucial requirement to achieve a high charge carrier extraction efficiency.
published_date 2017-06-29T07:12:33Z
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score 11.04748

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