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Photochemical Stability of Organic Solar Cells: The Role of Electron Acceptors / Emily M. Speller

DOI (Published version): 10.23889/Suthesis.50959

Abstract

Environmental stability remains to be a critical barrier for the commercialisation (along with cost) of organic solar cells, and understanding the roles of material degradation is the key to address this challenge. The thesis investigates the photochemical stability (namely under illumination and ai...

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Published: 2018
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
URI: https://cronfa.swan.ac.uk/Record/cronfa50959
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first_indexed 2019-06-28T14:55:50Z
last_indexed 2019-10-21T16:56:53Z
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spelling 2019-07-01T14:58:17.0302456 v2 50959 2019-06-28 Photochemical Stability of Organic Solar Cells: The Role of Electron Acceptors 2019-06-28 Environmental stability remains to be a critical barrier for the commercialisation (along with cost) of organic solar cells, and understanding the roles of material degradation is the key to address this challenge. The thesis investigates the photochemical stability (namely under illumination and air) of well established fullerene-based acceptors and some cutting edge non-fullerene acceptors, and their impact upon organic solar cell performance.Fullerene photo-oxidation was found to have a general and detrimental effect to poly-mer:fullerene organic cell performance for a range of device architectures, benchmark polymers and benchmark fullerenes. This photo-oxidation was found to correlate to the degree of aggregation, whereby the more aggregated the fullerene the more resistant it was to photo-oxidation. The photo-oxidation was found to substantially reduce elec-tron mobility through the formation of trap states. In donor polymer:fullerene films the photochemical stability of both the polymer and fullerene were related to the degree of aggregation, and correlated with a decrease in device stability. Transient absorption spec-troscopy (TAS) revealed fullerene photo-oxidation occurs primarily due to singlet oxygen generation via the fullerene triplet states for photo-inactive polymer:fullerene films and via the polymer triplet states for photo-active polymer:fullerene films.An energetic origin of acceptor photochemical stability was also determined. Generally, it was found that fullerenes with a lower lowest unoccupied molecular orbital (LUMO) underwent less photo-oxidation and device performance degraded less. For both fullerene and non-fullerene acceptors, the lower the LUMO level of the acceptor, the more stable the polymer:acceptor film. This relationship was shown to be strongly mediated by the yield of superoxide formation via the acceptor LUMO level.The work presented herein establishes relationships between electron acceptor struc-tural/nanomorphological/electronic properties with material/device stability, thereby pav-ing the way toward achieving long-term environmental stability of low-cost organic solar cells with minimal encapsulation. E-Thesis Organic photovoltaics, third generation photovoltaics, photochemical stability, fullerene receptors, non fullerene receptors 31 12 2018 2018-12-31 10.23889/Suthesis.50959 A selection of third party content is redacted or is partially redacted from this thesis. COLLEGE NANME COLLEGE CODE Swansea University Doctoral Ph.D National Research Network in Advanced Engineering and Materials NRN093 2019-07-01T14:58:17.0302456 2019-06-28T11:07:14.8172122 Faculty of Science and Engineering School of Engineering and Applied Sciences - Uncategorised Emily M. Speller 1 0050959-28062019112626.pdf Speller_Emily_PhD_Thesis_Final_Redacted.pdf 2019-06-28T11:26:26.3930000 Output 50094914 application/pdf Redacted version - open access true 2019-06-27T00:00:00.0000000 true
title Photochemical Stability of Organic Solar Cells: The Role of Electron Acceptors
spellingShingle Photochemical Stability of Organic Solar Cells: The Role of Electron Acceptors
,
title_short Photochemical Stability of Organic Solar Cells: The Role of Electron Acceptors
title_full Photochemical Stability of Organic Solar Cells: The Role of Electron Acceptors
title_fullStr Photochemical Stability of Organic Solar Cells: The Role of Electron Acceptors
title_full_unstemmed Photochemical Stability of Organic Solar Cells: The Role of Electron Acceptors
title_sort Photochemical Stability of Organic Solar Cells: The Role of Electron Acceptors
author ,
author2 Emily M. Speller
format E-Thesis
publishDate 2018
institution Swansea University
doi_str_mv 10.23889/Suthesis.50959
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 Engineering and Applied Sciences - Uncategorised{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Uncategorised
document_store_str 1
active_str 0
description Environmental stability remains to be a critical barrier for the commercialisation (along with cost) of organic solar cells, and understanding the roles of material degradation is the key to address this challenge. The thesis investigates the photochemical stability (namely under illumination and air) of well established fullerene-based acceptors and some cutting edge non-fullerene acceptors, and their impact upon organic solar cell performance.Fullerene photo-oxidation was found to have a general and detrimental effect to poly-mer:fullerene organic cell performance for a range of device architectures, benchmark polymers and benchmark fullerenes. This photo-oxidation was found to correlate to the degree of aggregation, whereby the more aggregated the fullerene the more resistant it was to photo-oxidation. The photo-oxidation was found to substantially reduce elec-tron mobility through the formation of trap states. In donor polymer:fullerene films the photochemical stability of both the polymer and fullerene were related to the degree of aggregation, and correlated with a decrease in device stability. Transient absorption spec-troscopy (TAS) revealed fullerene photo-oxidation occurs primarily due to singlet oxygen generation via the fullerene triplet states for photo-inactive polymer:fullerene films and via the polymer triplet states for photo-active polymer:fullerene films.An energetic origin of acceptor photochemical stability was also determined. Generally, it was found that fullerenes with a lower lowest unoccupied molecular orbital (LUMO) underwent less photo-oxidation and device performance degraded less. For both fullerene and non-fullerene acceptors, the lower the LUMO level of the acceptor, the more stable the polymer:acceptor film. This relationship was shown to be strongly mediated by the yield of superoxide formation via the acceptor LUMO level.The work presented herein establishes relationships between electron acceptor struc-tural/nanomorphological/electronic properties with material/device stability, thereby pav-ing the way toward achieving long-term environmental stability of low-cost organic solar cells with minimal encapsulation.
published_date 2018-12-31T04:02:40Z
_version_ 1763753235205586944
score 11.014224

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