Multinuclear Magnetic Resonance Tracking of Hydro, Thermal, and Hydrothermal Decomposition of CH3NH3PbI3

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• 作者：Abdelrahman M. AskarGuy M. Bernard ; Benjamin Wiltshire ; Karthik Shankar ; Vladimir K. Michaelis
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：January 19, 2017
• 年：2017
• 卷：121
• 期：2
• 页码：1013-1024
• 全文大小：630K
• ISSN：1932-7455

文摘

An NMR investigation of methylammonium lead iodide, the leading member of the hybrid organic–inorganic perovskite class of materials, and of its putative decomposition products as a result of exposure to heat and humidity, has been undertaken. We show that the ²⁰⁷Pb NMR spectra of the compound of interest and of the proposed lead-containing decomposition products, CH₃NH₃PbI₃·H₂O, (CH₃NH₃)₄PbI₆·2H₂O, and PbI₂, have distinctive chemical shifts spanning over 1400 ppm, making ²⁰⁷Pb NMR an ideal tool for investigating this material; further information may be gained from ¹³C and ¹H NMR spectra. As reported in many investigations of CH₃NH₃PbI₃ on films, the bulk material hydrates in the presence of high relative humidity (approximately 80%), yielding the monohydrated perovskite CH₃NH₃PbI₃·H₂O. This reaction is reversible by heating the sample to 341 K. We show that neither (CH₃NH₃)₄PbI₆·2H₂O nor PbI₂ is observed as a decomposition product and that, in contrast to many studies on CH₃NH₃PbI₃ films, the bulk material does not decompose or degrade beyond CH₃NH₃PbI₃·H₂O upon prolonged exposure to humidity at ambient temperature. However, exposing CH₃NH₃PbI₃ concurrently to heat and humidity, or directly exposing it to liquid water, leads to the irreversible formation of PbI₂. In spite of its absence among the decomposition products, the response of (CH₃NH₃)₄PbI₆·2H₂O to heat was also investigated. It is stable at temperatures below 336 K but then rapidly dehydrates, first to CH₃NH₃PbI₃·H₂O and then to CH₃NH₃PbI₃. The higher stability of the bulk material as reported here is a promising advance, since stability is a major concern in the development of commercial applications for this material.