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Partially Reversible Photoinduced Chemical Changes in a Mixed-Ion Perovskite Material for Solar Cells
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.ORCID-id: 0000-0002-9432-3112
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Fysiska sektionen, Institutionen för fysik och astronomi, Molekyl- och kondenserade materiens fysik.ORCID-id: 0000-0002-6471-1093
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2017 (Engelska)Ingår i: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, nr 40, s. 34970-34978Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Metal halide perovskites have emerged as materials of high interest for solar energy-to-electricity conversion, and in particular, the use of mixed-ion structures has led to high power conversion efficiencies and improved stability. For this reason, it is important to develop means to obtain atomic level understanding of the photoinduced behavior of these materials including processes such as photoinduced phase separation and ion migration. In this paper, we implement a new methodology combining visible laser illumination of a mixed-ion perovskite ((FAP-bI(3))(0.85)(MAPbBr(3))(0.15)) with the element specificity and chemical sensitivity of core-level photoelectron spectroscopy. By carrying out measurements at a synchrotron beamline optimized for low X-ray fluxes, we are able to avoid sample changes due to X-ray illumination and are therefore able to monitor what sample changes are induced by visible illumination only. We find that laser illumination causes partially reversible chemistry in the surface region, including enrichment of bromide at the surface, which could be related to a phase separation into bromide- and iodide-rich phases. We also observe a partially reversible formation of metallic lead in the perovskite structure. These processes occur on the time scale of minutes during illumination. The presented methodology has a large potential for understanding light-induced chemistry in photoactive materials and could specifically be extended to systematically study the impact of morphology and composition on the photostability of metal halide perovskites.

Ort, förlag, år, upplaga, sidor
AMER CHEMICAL SOC , 2017. Vol. 9, nr 40, s. 34970-34978
Nyckelord [en]
photoelectron spectroscopy, laser illumination, lead halide perovskite, ion migration, phase separation, stability
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
URN: urn:nbn:se:uu:diva-340141DOI: 10.1021/acsami.7b10643ISI: 000413131500043PubMedID: 28925263OAI: oai:DiVA.org:uu-340141DiVA, id: diva2:1178008
Forskningsfinansiär
EU, FP7, Sjunde ramprogrammet, 321319Vetenskapsrådet, 2014-6019Vetenskapsrådet, 2014-6463StandUpStiftelsen för strategisk forskning (SSF), RMA15-0130Tillgänglig från: 2018-01-26 Skapad: 2018-01-26 Senast uppdaterad: 2020-03-26Bibliografiskt granskad
Ingår i avhandling
1. Core-hole Clock Spectroscopy Using Hard X-rays: Exciting States in Condensed Matter
Öppna denna publikation i ny flik eller fönster >>Core-hole Clock Spectroscopy Using Hard X-rays: Exciting States in Condensed Matter
2020 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

This thesis is about how electrons move from one place to another, that is charge transfer dynamics. Charge transfer dynamics is an important property governing chemical and physical changes that form the base for many applications such as electronics, optoelectronics and catalysis. The fundamental aspect is how charge transfer manifests in the constituent materials and their interfaces building up these devices. The basic method used is synchrotron radiation based electron spectroscopies.

Using core-hole clock spectroscopy it is possible to study dynamic processes in the femtosecond and attosecond regimes - here we study the if the core-excited electron decays back into the core hole (local decays), or if the core excited electron have been tunneled away from the atomic site before the core-hole decays. Spectroscopically we can discern the two situations since one of the processes is photon energy dependent and one is not. Knowledge of the life-time of the core hole, and measuring the probability of the core-excited system decaying one way or the other makes it possible to calculate a charge transfer time. Using hard X-rays to create excited state with deep core-holes allow us to study high kinetic energy Auger electrons, also deep core-holes tend to be short lived, which gives access to short time-scales.

Bulk crystals of 2D materials have been used as model systems here owing to their well-known properties. Using those it has been demonstrated that the regime of observable times using the mentioned method can be extended with an order of magnitude compared to previous studies. Our results present themselves on time-scales on par with the atomic unit of time. The highly selective nature of resonant X-ray excitations allows the anisotropic unoccupied electronic structure of bulk 2D crystals to be mapped out, here the example of SnS2 is presented. This shows that this is a direct probe of the unoccupied band structure.

With core-hole clock spectroscopy the charge transfer time dependence on relative concentrations of blends between the low band-gap polymer PCPDTBT, with PCBM (functionalized fullerenes). This is a common prototypical system for organic photovoltaics. The charge transfer time decreases with increasing intermixing, up to a point where is starts getting slower, the same trend as the efficiency of solar cell devices made with the same mixing. The method employed here is chemically specific and probes the local surrounding energy landscape at the site of excitation – this is different from other techniques that utilize optical excitations which are non-local in character.

The synthetization of bulk heterostructures and thin films, and the disentanglement of core-ionized states are also investigated using spectroscopic and scattering techniques.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2020. s. 104
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1921
Nyckelord
core-hole clock, resonant Auger, XPS, black phosphorous, TMDC, perovskite, graphene, coincidences spectroscopy, synchrotron radiation, HAXPES
Nationell ämneskategori
Den kondenserade materiens fysik
Identifikatorer
urn:nbn:se:uu:diva-407540 (URN)978-91-513-0915-6 (ISBN)
Disputation
2020-08-28, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (Engelska)
Opponent
Handledare
Tillgänglig från: 2020-04-27 Skapad: 2020-03-26 Senast uppdaterad: 2020-05-19

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Cappel, Ute B.Svanström, SebastianLanzilotto, ValeriaJohansson, Fredrik O. L.Aitola, KerttuPhilippe, BertrandLeitner, TorstenSvensson, SvanteMårtensson, NilsBoschloo, GerritLindblad, AndreasRensmo, Håkan

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Cappel, Ute B.Svanström, SebastianLanzilotto, ValeriaJohansson, Fredrik O. L.Aitola, KerttuPhilippe, BertrandLeitner, TorstenSvensson, SvanteMårtensson, NilsBoschloo, GerritLindblad, AndreasRensmo, Håkan
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