Westbrook, Robert John Eric;
(2020)
Functional Characterisation of Perovskite Films for Solar Cell Applications.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
The world is currently faced with an energy dilemma; as global demand for power continues to soar, pressure is mounting to move away from fossil fuels towards low-carbon alternatives. In this setting, highly efficient, low-cost photovoltaics, which turn solar photons into electricity offer an attractive solution. The efficiency of such photovoltaics is essentially underpinned by the competition between extraction and recombination of photogenerated charges. In this thesis, we use a combination of transient optical, structural and device characterisation techniques to elucidate the key factors governing these two processes in perovskite solar cells. In Chapter 3, we address the issue of charge extraction at perovskite|hole transport layer interfaces. We find that a remarkably small driving energy (∆E ∼ 0.1 eV) between the perovskite valence band and the highest occupied molecular orbital (HOMO) of the hole transport layer is required to induce efficient hole injection (> 75%). We also find that the rate of recombination of injected holes in Cs0.05(MA0.17FA0.83)0.95PbI3 systems is slower compared to MAPbI3. In Chapter 4, we show that passivation of perovskite with phenethylammonium iodide results in an enhancement of the efficiency from 12.95% to 16.73% and an improvement in stability – taken as the time for efficiency to drop to 80% of its initial value – from a few hours to over 21 days. Optical characterisation reveals that a bilateral passivation mechanism is behind these improvements, where iodide anions fill iodide vacancies and the phenethylammonium cation induces a 2D heterostructure. Finally, we bring these two strands of research together in Chapter 5 by correlating the extent of passivation from transport layers with an enhancement in the interfacial charge injection yield. Throughout, we make constant reference to the impact of our findings on perovskite solar cell device parameters and set out design rules for their optimum efficiency and stability.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Functional Characterisation of Perovskite Films for Solar Cell Applications |
| Event: | UCL (University College London) |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/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 > 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.ucl.ac.uk/id/eprint/10113114 |
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