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Direct measurements of interfacial photovoltage and band alignment in perovskite solar cells using hard X-ray photoelectron spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Condensed Matter Physics of Energy Materials.ORCID iD: 0000-0001-7351-8183
Kungliga Tekniska Högskolan.ORCID iD: 0000-0003-1671-9979
Kungliga Tekniska Högskolan.ORCID iD: 0000-0002-6469-3374
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2023 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 15, no 9, p. 12485-12494Article in journal (Refereed) Published
Abstract [en]

A heterojunction is the key junction for charge extraction in many thin film solar cell technologies. However, the structure and band alignment of the heterojunction in the operating device are often difficult to predict from calculations and, due to the complexity and narrow thickness of the interface, are difficult to measure directly. In this study, we demonstrate a technique for direct measurement of the band alignment and interfacial electric field variations of a fully functional lead halide perovskite solar cell structure under operating conditions using hard X-ray photoelectron spectroscopy (HAXPES). We describe the design considerations required in both the solar cell devices and the measurement setup and show results for the perovskite, hole transport, and gold layers at the back contact of the solar cell. For the investigated design, the HAXPES measurements suggest that 70% of the photovoltage was generated at this back contact, distributed rather equally between the hole transport material/gold interface and the perovskite/hole transport material interface. In addition, we were also able to reconstruct the band alignment at the back contact at equilibrium in the dark and at open circuit under illumination.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2023. Vol. 15, no 9, p. 12485-12494
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-454370DOI: 10.1021/acsami.2c17527ISI: 000949872700001PubMedID: 36847773OAI: oai:DiVA.org:uu-454370DiVA, id: diva2:1598008
Funder
Swedish Research Council, VR 2016-04590Swedish Research Council, VR 2018-04125Swedish Research Council, VR 2018-04330Swedish Research Council, VR 2018-06465Swedish Energy Agency, P50626-1Swedish Energy Agency, P43549-1Göran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of TechnologySwedish Foundation for Strategic Research, RMA15-0130Carl Tryggers foundation , CTS 18:59Available from: 2021-09-28 Created: 2021-09-28 Last updated: 2023-04-17Bibliographically 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, SebastianGarcía-Fernández, AlbertoSloboda, TamaraJacobsson, T JesperZheng, FuguoJohansson, FredrikCeolin, DenisRueff, Jean-PascalLicheng, SunAitola, KerttuRensmo, HåkanCappel, Ute B
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