Similar Structural Dynamics for the Degradation of CH3NH3PbI3 in Air and in Vacuum |
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| Authors: | Dr Alessandra Alberti Dr Ioannis Deretzis Dr Giovanna Pellegrino Dr Corrado Bongiorno Dr Emanuele Smecca Dr Giovanni Mannino Dr Filippo Giannazzo Prof Guglielmo Guido Condorelli Dr Nobuya Sakai Prof Tsutomu Miyasaka Dr Corrado Spinella Dr Antonino La Magna |
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| Affiliation: | 1. CNR‐IMM Zona Industriale, Strada VIII 5, 95121, Catania (Italy);2. Università degli Studi di Catania and INSTM UdR Catania, Viale Andrea Doria 6, 95125 Catania (Italy);3. Toin University of Yokohama, Graduate School of Engineering, 1614 Kuroganecho, Aoba, Yokohama, 225‐8503 (Japan) |
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| Abstract: | We investigate the degradation path of MAPbI3 (MA=methylammonium) films over flat TiO2 substrates at room temperature by means of X‐ray diffraction, spectroscopic ellipsometry, X‐ray photoelectron spectroscopy, and high‐resolution transmission electron microscopy. The degradation dynamics is found to be similar in air and under vacuum conditions, which leads to the conclusion that the occurrence of intrinsic thermodynamic mechanisms is not necessarily linked to humidity. The process has an early stage, which drives the starting tetragonal lattice in the direction of a cubic atomic arrangement. This early stage is followed by a phase change towards PbI2. We describe how this degradation product is structurally coupled with the original MAPbI3 lattice through the orientation of its constituent PbI6 octahedra. Our results suggest a slight octahedral rearrangement after volatilization of HI+CH3NH2 or MAI, with a relatively low energy cost. Our experiments also clarify why reducing the interfaces and internal defects in the perovskite lattice enhances the stability of the material. |
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| Keywords: | crystal growth X‐ray diffraction electron microscopy perovskite phases solid‐state structures |
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