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SnOx Atomic Layer Deposition on Bare Perovskite: An Investigation of Initial Growth Dynamics, Interface Chemistry, and Solar Cell Performance
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solar Cell Technology.ORCID iD: 0000-0002-2402-5427
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. Helmholtz Ctr Berlin, Div Renewable Energies, D-14109 Berlin, Germany.ORCID iD: 0000-0002-4317-2879
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Solar Cell Technology.ORCID iD: 0000-0003-4111-4613
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2021 (English)In: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 4, no 1, p. 510-522Article in journal (Refereed) Published
Abstract [en]

High-end organic–inorganic lead halide perovskite semitransparent p–i–n solar cells for tandem applications use a phenyl-C61-butyric acid methyl ester (PCBM)/atomic layer deposition (ALD)-SnOx electron transport layer stack. Omitting the PCBM would be preferred for manufacturing, but has in previous studies on (FA,MA)Pb(Br,I)3 and (Cs,FA)Pb(Br,I)3 and in this study on Cs0.05FA0.79MA0.16PbBr0.51I2.49 (perovskite) led to poor solar cell performance because of a bias-dependent light-generated current. A direct ALD-SnOx exposure was therefore suggested to form a nonideal perovskite/SnOx interface that acts as a transport barrier for the light-generated current. To further investigate the interface formation during the initial ALD SnOx growth on the perovskite, the mass dynamics of monitor crystals coated by partial p–i–n solar cell stacks were recorded in situ prior to and during the ALD using a quartz crystal microbalance. Two major finds were made. A mass loss was observed prior to ALD for growth temperatures above 60 °C, suggesting the decomposition of the perovskite. In addition, a mostly irreversible mass gain was observed during the first exposure to the Sn precursor tetrakis(dimethylamino)tin(IV) that is independent of growth temperature and that disrupts the mass gain of the following 20–50 ALD cycles. The chemical environments of the buried interface were analyzed by soft and hard X-ray photoelectron spectroscopy for a sample with 50 ALD cycles of SnOx on the perovskite. Although measurements on the perovskite bulk below and the SnOx film above did not show chemical changes, additional chemical states for Pb, Br, and N as well as a decrease in the amount of I were observed in the interfacial region. From the analysis, these states and not the heating of the perovskite were concluded to be the cause of the barrier. This strongly suggests that the detrimental effects can be avoided by controlling the interfacial design.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2021. Vol. 4, no 1, p. 510-522
Keywords [en]
perovskite solar cell, ALD, in situ QCM, HAXPES, interface, SnOx
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-438732DOI: 10.1021/acsaem.0c02405ISI: 000613720100058PubMedID: 33615157OAI: oai:DiVA.org:uu-438732DiVA, id: diva2:1540719
Funder
StandUpSwedish Research Council, VR 2018-04125Swedish Research Council, 2018-06465Swedish Research Council, 2018-04330Swedish Foundation for Strategic Research , RMA15-0130Swedish Energy Agency, P43549-1Swedish Energy Agency, 2017-004796EU, Horizon 2020, 730872Available from: 2021-03-30 Created: 2021-03-30 Last updated: 2024-01-15Bibliographically 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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