Live Observations of Non-equilibrium Moisture-induced Phase Segregation in CsMAFA-type Perovskite Revealed by In situ X-ray Diffraction and Operando Liquid-cell Transmission Electron Microscopy
Mohammad Ali Akhavan Kazemi a, Nicolas Folastre a, Parth Raval b, Michel Sliwa c, Olivier Lafon b, Laurent Delevoye b, Arash Jamali a, G.N. Manjunatha Reddy b, Arnaud Demortiere a, Frédéric Sauvage a
a Laboratoire de Réactivité et Chimie des Solides (LRCS) UMR CNRS 7314 - Université de Picardie Jules Verne 33 rue Saint Leu, FR-80039 Amiens Cedex, France
b University of Lille, CNRS, Centrale Lille, Univ. Artois, UMR8181, Unité de Catalyse et Chimie du Solide (UCCS), 59000, Lille, France
c University of Lille, CNRS, UMR8516, Laboratoire de Spectroscopie pour les Intéractions, la Réactivité et l’Environnement (LASIRE), 59000, Lille, France
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Invited Speaker Session, Frédéric Sauvage, presentation 192
Publication date: 20th April 2022

The long-term stability of perovskite solar cells is jeopardized by its sensitiveness to humidity even though technological encapsulation offers a first barrier to shield moisture-induced degradation. Different degradation pathways are activated depending on the perovskite composition for which ex situ characterization techniques provide a comparative view of the degradation before and after a certain ageing time.1 Herein, we exploit the latest advances in in situ X-ray diffraction, real-time electron imaging and liquid-cell transmission electron microscopy to reveal, in live, from early stage to the degradation propagation of triple cation Cs0.05(MA0.17FA0.83)0.95Pb(Br0.17I0.83)3 (CsMAFA) perovskite leading to phase segregation and decomposition.2-3 We reveal two competitive degradation paths leading on one hand to the decomposition of CsMAFA into PbI2 through a dissolution/recrystallization mechanism and on the other hand, to a non-equilibrium phase segregation leading to CsPb2Br5 and a cesium-poor/iodide-rich Cs0.05-x(MA0.17FA0.83)0.95Pb(Br0.17-2yI0.83+2y)3 perovskite. As a consequence of the dissolution/recrystallization mechanism under 85% R.H., such exposure leads to a film containing important heterogeneities in terms of morphology, photoluminescence (PL) intensities and lifetimes. The structural, morphological and chemical changes will be discussed in this communication based on operando liquid-cell TEM combined to SAED analysis and 4D-STEM-ASTAR investigations.


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