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Excitation Dynamics and Losses in Solution Processed Disordered Semiconductors / NASIM ZARRABI

Swansea University Author: NASIM ZARRABI

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DOI (Published version): 10.23889/SUthesis.56943

Abstract

From a technological point of view, organic semiconductor-based devices are of significant interest due to their light weight, ease of processability, conformal flexibility and potentially low cost and low embodied energy pro-duction. Motivated by these quite unique selling points, the performance o...

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Published: Swansea 2021
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
Supervisor: Meredith, Paul ; Armin, Ardalan
URI: https://cronfa.swan.ac.uk/Record/cronfa56943
first_indexed 2021-05-24T08:45:33Z
last_indexed 2021-07-10T03:23:42Z
id cronfa56943
recordtype RisThesis
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spelling 2021-07-09T15:10:47.0924739 v2 56943 2021-05-24 Excitation Dynamics and Losses in Solution Processed Disordered Semiconductors ea5a951b4cfb9243cd46d031d884c8ff NASIM ZARRABI NASIM ZARRABI true false 2021-05-24 From a technological point of view, organic semiconductor-based devices are of significant interest due to their light weight, ease of processability, conformal flexibility and potentially low cost and low embodied energy pro-duction. Motivated by these quite unique selling points, the performance of organic semiconductors has been a subject of multi-disciplinary study for more than 60 years with steady progress in applications such as solar cells, transistors, light emitting diodes and various sensors. One of the main characteristics that governs the performance of organic semiconduc-tors is their low dielectric constants, meaning they are excitonic at room temperature. A second main feature that dictates the charge carrier recom-bination and transport properties is the disordered nature of these semicon-ductors causing low charge carrier mobilities. The work described in this thesis focuses on these defining elements, and particularly their implications on photovoltaic devices. The discussion will start with a review into the main electro-optical phenomena in organic solar cells. Subsequently, a new method is presented for measuring exciton diffusion lengths based upon a low-quencher-content device structure. An anomalously large quenching volume is observed that can be assigned to long-range exciton delocaliza-tion prior to thermalization. These ultra-low-impurity content organic so-lar cells are also very useful as model systems to study and engineer trap states. Using this approach, it is found that mid-gap trap states are a universal feature in organic semiconductor donor-acceptor blends and un-expectedly contribute to charge generation and recombination. This has a profound impact on the thermodynamic limit of organic photovoltaic de-vices. Having demonstrated this important new insight it is further shown that a definitive link exists between a reduced recombination rate compared to the Langevin rate in some exceptional, high performance material sys-tems and a significant increase in the dissociation rate of charge transfer states upon post-processing of the active layer. In sum, the work presented in this thesis delivers important new insight as to the underlying dynamics of exciton generation and diffusion, charge transfer state dissociation, and indeed the ultimate fate of photogenerated free carriers. E-Thesis Swansea Organic Semiconductors, Organic Solar Cells, Organic Photodiodes, Exciton, Diffusion length, Exciton Quenching, Mid-gap Trap Stated, Reciprocity, Open Circuit Voltage losses, Reduced Bimolecular Recombination 17 5 2021 2021-05-17 10.23889/SUthesis.56943 Due to Embargo and/or Third Party Copyright restrictions, this thesis is not available via this service. COLLEGE NANME COLLEGE CODE Swansea University Meredith, Paul ; Armin, Ardalan Doctoral Ph.D Sêr Cymru II Program 2021-07-09T15:10:47.0924739 2021-05-24T09:40:18.7748287 Faculty of Science and Engineering School of Biosciences, Geography and Physics - Physics NASIM ZARRABI 1
title Excitation Dynamics and Losses in Solution Processed Disordered Semiconductors
spellingShingle Excitation Dynamics and Losses in Solution Processed Disordered Semiconductors
NASIM ZARRABI
title_short Excitation Dynamics and Losses in Solution Processed Disordered Semiconductors
title_full Excitation Dynamics and Losses in Solution Processed Disordered Semiconductors
title_fullStr Excitation Dynamics and Losses in Solution Processed Disordered Semiconductors
title_full_unstemmed Excitation Dynamics and Losses in Solution Processed Disordered Semiconductors
title_sort Excitation Dynamics and Losses in Solution Processed Disordered Semiconductors
author_id_str_mv ea5a951b4cfb9243cd46d031d884c8ff
author_id_fullname_str_mv ea5a951b4cfb9243cd46d031d884c8ff_***_NASIM ZARRABI
author NASIM ZARRABI
author2 NASIM ZARRABI
format E-Thesis
publishDate 2021
institution Swansea University
doi_str_mv 10.23889/SUthesis.56943
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 From a technological point of view, organic semiconductor-based devices are of significant interest due to their light weight, ease of processability, conformal flexibility and potentially low cost and low embodied energy pro-duction. Motivated by these quite unique selling points, the performance of organic semiconductors has been a subject of multi-disciplinary study for more than 60 years with steady progress in applications such as solar cells, transistors, light emitting diodes and various sensors. One of the main characteristics that governs the performance of organic semiconduc-tors is their low dielectric constants, meaning they are excitonic at room temperature. A second main feature that dictates the charge carrier recom-bination and transport properties is the disordered nature of these semicon-ductors causing low charge carrier mobilities. The work described in this thesis focuses on these defining elements, and particularly their implications on photovoltaic devices. The discussion will start with a review into the main electro-optical phenomena in organic solar cells. Subsequently, a new method is presented for measuring exciton diffusion lengths based upon a low-quencher-content device structure. An anomalously large quenching volume is observed that can be assigned to long-range exciton delocaliza-tion prior to thermalization. These ultra-low-impurity content organic so-lar cells are also very useful as model systems to study and engineer trap states. Using this approach, it is found that mid-gap trap states are a universal feature in organic semiconductor donor-acceptor blends and un-expectedly contribute to charge generation and recombination. This has a profound impact on the thermodynamic limit of organic photovoltaic de-vices. Having demonstrated this important new insight it is further shown that a definitive link exists between a reduced recombination rate compared to the Langevin rate in some exceptional, high performance material sys-tems and a significant increase in the dissociation rate of charge transfer states upon post-processing of the active layer. In sum, the work presented in this thesis delivers important new insight as to the underlying dynamics of exciton generation and diffusion, charge transfer state dissociation, and indeed the ultimate fate of photogenerated free carriers.
published_date 2021-05-17T04:54:09Z
_version_ 1851367515656028160
score 11.089572

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