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The relationship between surfaces, interfaces, and bulk properties in organometallic halide materials

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Title: The relationship between surfaces, interfaces, and bulk properties in organometallic halide materials
Authors: Ngiam, Jonathan
Item Type: Thesis or dissertation
Abstract: In this work, organometallic halides as a photovoltaic material are investigated. In particular, photovoltaic devices based on the widely used composition MAPbI3 were subjected to a range of degradation stress tests in which the relationship between electrode layers and interfacial phenomena (e.g. metal diffusion, metal-halide formation) were studied to a greater extent with surface characterisation techniques: Time-of-flight secondary ion mass spectrometry (ToF-SIMS), low-energy ion scattering (LEIS), and X-ray photoelectron spectroscopy (XPS). Additioanlly, given the lack of empirically determined surface stoichiometry and discrepancies in reported quantification from XPS, surface stoichiometry of MAPbI3 and compositional analogues are investigated using LEIS and ToF-SIMS. Results suggest that a Cs-deficient surface (at the first atomic layer) exists for Cs-substituted compositions and extrapolating to pure MAPbI3 composition, suggests an MAdeficient surface; consequently a Pb-I rich surface. A significant effort in determining the effect of organic (processing) additives on surface defect passivation was also undertaken. In particular, surface mass spectra show mass fragments derived from corresponding organic additives. Surface stoichiometry of I and Pb was deduced from LEIS and showed a deviation from pristine MAPbI3. These results support the hypothesised surface bonding mechanism(s) as well as the applicability of these techniques in characterising these materials. The interactions of such ion beams and X-ray irradiation are also discussed and show that certain restrictions exist in using these techniques which are laid out in the following work.
Content Version: Open Access
Issue Date: Jan-2020
Date Awarded: May-2020
URI: http://hdl.handle.net/10044/1/89784
DOI: https://doi.org/10.25560/89784
Copyright Statement: Creative Commons Attribution NonCommercial Licence
Supervisor: McLachlan, Martyn
Stingelin, Natalie
Department: Materials
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Materials PhD theses



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