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Degradation Mechanism of Silver Metal Deposited on Lead Halide Perovskites
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.ORCID iD: 0000-0002-4317-2879
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.ORCID iD: 0000-0002-8249-1469
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.ORCID iD: 0000-0001-9358-8277
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2020 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 12, no 6, p. 7212-7221Article in journal (Refereed) Published
Abstract [en]

Lead halide perovskite solar cells have significantly increased in both efficiency and stability over the last decade. An important aspect of their longterm stability is the reaction between the perovskite and other materials in the solar cell. This includes the contact materials and their degradation if they can potentially come into contact through, e.g., pinholes or material diffusion and migration. Here, we explore the interactions of silver contacts with lead halide perovskites of different compositions by using a model system where thermally evaporated silver was deposited directly on the surface of the perovskites. Using X-ray photoelectron spectroscopy with support from scanning electron microscopy, X-ray diffraction, and UV-visible absorption spectroscopy, we studied the film formation and degradation of silver on perovskites with different compositions. The deposited silver does not form a continuous silver film but instead tends to form particles on a bare perovskite surface. These particles are initially metallic in character but degrade into AgI and AgBr over time. The degradation and migration appear unaffected by the replacement of methylammonium with cesium but are significantly slowed down by the complete replacement of iodide with bromide. The direct contact between silver and the perovskite also significantly accelerates the degradation of the perovskite, with a significant loss of organic cations and the possible formation of PbO, and, at the same time, changed the surface morphology of the iodide-rich perovskite interface. Our results further indicate that an important degradation pathway occurred through gas-phase perovskite degradation products. This highlights the importance of control over the interface materials and the use of completely hermetical barrier layers for the long-term stability and therefore the commercial viability of silver electrodes.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC , 2020. Vol. 12, no 6, p. 7212-7221
Keywords [en]
perovskite solar cells, electrode stability, X-ray photoelectron spectroscopy, interface chemistry, noble metal electrodes
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-407282DOI: 10.1021/acsami.9b20315ISI: 000514256400040PubMedID: 31958007OAI: oai:DiVA.org:uu-407282DiVA, id: diva2:1416363
Funder
Swedish Research Council, VR 2018-04125Swedish Research Council, 2018-06465Swedish Research Council, 2018-04330Swedish Foundation for Strategic Research , RMA15-0130Swedish Energy Agency, P43549-1StandUpÅForsk (Ångpanneföreningen's Foundation for Research and Development)Göran Gustafsson Foundation for Research in Natural Sciences and MedicineAvailable from: 2020-03-23 Created: 2020-03-23 Last updated: 2021-10-07Bibliographically approved
In thesis
1. The life and death of perovskites: Interfacial function and degradation of lead halide perovskites studied by photoelectron spectroscopy
Open this publication in new window or tab >>The life and death of perovskites: Interfacial function and degradation of lead halide perovskites studied by photoelectron spectroscopy
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Perovskiters liv och död : En studie av funktionen och degrationen i blyhalidperovskiters gränsskikt med fotoelektronspektroskopi
Abstract [en]

Lead halide perovskite solar cells are a promising new technology which could soon see widespread commercial application but is partly held back by poor long-term stability. In this thesis, photoelectron spectroscopy (PES) is used to study the dynamical processes at the surface or interfaces of lead halide perovskite materials. Some of these processes are responsible for the different types of degradation while others are essential for the function of the solar cell. The work includes a range of lead perovskite compositions with the general formula APbX3, in which A is a monovalent cation, and often organic (e.g. formamidinium or methylammonium), and X is a halide anion, typically Br- or I-. The compositions can also include mixtures of cations at the A and anions at the X site.

Part of this thesis is dedicated to investigating the degradation of the perovskite surface in response to both intense visible light and X-ray irradiation. The results show that intense illumination induces the decomposition of the perovskite into metallic lead, halide gas and organic halide salt, but also indicate how this process can be suppressed by the addition of small amounts of Cs+ ions and by adjusting the relative amounts of halides. A different process, induced by the X-ray radiolysis of the organic cation, is shown to consume rather than form metallic lead.

Another part of this thesis is dedicated to the investigation of the reactions at the interfaces between the perovskite and silver, copper or SnOx. The results show that both copper and silver react rapidly with the perovskite forming metal halides and that the metal can diffuse into the perovskite. Copper is particularly reactive, leading to the formation of two new compounds and the bulk degradation of the perovskite. The SnOx is significantly more stable but material intermixing results in the formation of a thin interface layer that may hinder charge extraction. 

Finally, a method for measuring both interfacial photovoltage and band alignment in a fully functional perovskite solar cell using hard X-ray photoelectron spectroscopy (HAXPES) is demonstrated. The results showcase the design considerations for the samples and the measurement setup and the potential of this technique. 

In summary, this thesis shows the suitability of PES for studying both the function and degradation of surfaces and interfaces of complex dynamical systems. It serves as a guide for future studies by highlighting challenges and possibilities faced when working with these systems.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2021. p. 75
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 2082
Keywords
lead halide perovskite solar cells, interfacial degradation, heterojunction interfaces, photoelectron spectroscopy, operando
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-454372 (URN)978-91-513-1309-2 (ISBN)
Public defence
2021-11-25, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2021-11-02 Created: 2021-10-07 Last updated: 2021-11-12

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Svanström, SebastianJacobsson, JesperBoschloo, GerritJohansson, ErikRensmo, HåkanCappel, Ute B.
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