Guo, Junjun;
(2023)
Spectroscopy and morphology study of polymer/ fullerene and nonfullerene organic photovoltaic blends.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Solution-processable organic solar cells (OSC) have attracted considerable attention in recent years with rapid increases in device efficiency. The improvement is primarily a consequence of newly designed non-fullerene acceptors (NFAs), providing a series of options to match with the donor and covering a broader spectral range than the fullerenes. My thesis aims to study the charge and triplet photogeneration in fullerene and non-fullerene based OSCs. Triplet states are traditionally considered harmful to device stability and performance, but their recent discovery in high-performing non-fullerene OSCs brings their exact role in device performance into question. Furthermore, charge photogeneration mechanisms in non-fullerene acceptor OSC blends, particularly with minimal LUMO level offsets, still need to be fully understood. Millisecond and picosecond transient absorption spectroscopy mainly study the charge photogeneration and recombination process. Atomic force microscopy and grazing incident X-ray diffraction are used to study the morphology of films. In the first results chapter, chapter 3, charge photogeneration is explored in temperature dependence aggregated polymer with fullerene blend films. Bimodal polarons are generated in polymer-dominated domains and mixed domains influenced by fullerene induced ordering. In addition, polymer triplet formation was identified for the first time in this high-performing PffBT4T-based polymer blend system via charge back recombination. Chapter 4 studied charge photogeneration in the polymer PffBT4T-C9C13 blended with four different NFAs (ITIC, ITIC-Th, ITIC-2F and Y6). Triplet states are detected in three ITIC blend systems, and the ITIC-2F blend film shows the highest charge to triplet population ratio. Triplet extinction coefficient has been calculated in both NFA solutions and films, which is further used to quantify the triplet population in polymer:NFA blend films. The correlation between triplet and charge population is further investigated regarding film morphology. In Chapter 5, Charge photogeneration and recombination are investigated in polymer PM6 with three novel PDFC NFA blend systems, two showing high fill factor and high device performance. An energy transfer process from the polymer singlet state to the NFA under the polymer dominant excitation was observed in all three blend systems.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Spectroscopy and morphology study of polymer/ fullerene and nonfullerene organic photovoltaic blends |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2023. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10171336 |
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