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

Abstract

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 207 Pb NMR spectra of the compound of interest and of the proposed leadcontaining decomposition products, CH 3 NH 3 PbI 3 •H 2 O, (CH 3 NH 3) 4 PbI 6 •2H 2 O, and PbI 2 , have distinctive chemical shifts spanning over 1400 ppm, making 207 Pb NMR an ideal tool for investigating this material; further information may be gained from 13 C and 1 H NMR spectra. As reported in many investigations of CH 3 NH 3 PbI 3 on films, the bulk material hydrates in the presence of high relative humidity (approximately 80%), yielding the monohydrated perovskite CH 3 NH 3 PbI 3 •H 2 O. This reaction is reversible by heating the sample to 341 K. We show that neither (CH 3 NH 3) 4 PbI 6 •2H 2 O nor PbI 2 is observed as a decomposition product and that, in contrast to many studies on CH 3 NH 3 PbI 3 films, the bulk material does not decompose or degrade beyond CH 3 NH 3 PbI 3 •H 2 O upon prolonged exposure to humidity at ambient temperature. However, exposing CH 3 NH 3 PbI 3 concurrently to heat and humidity, or directly exposing it to liquid water, leads to the irreversible formation of PbI 2. In spite of its absence among the decomposition products, the response of (CH 3 NH 3) 4 PbI 6 •2H 2 O to heat was also investigated. It is stable at temperatures below 336 K but then rapidly dehydrates, first to CH 3 NH 3 PbI 3 •H 2 O and then to CH 3 NH 3 PbI 3. 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.

Evolution of Photoluminescence, Raman, and Structure of CH3NH3PbI3 Perovskite Microwires Under Humidity Exposure

“…Density functional theory calculations and XRD investigations have related these reflections at low angle to the monohydrate phase MAPbI 3 ·H 2 O [21, 24, 43]. Moreover, a recent study with multinuclear magnetic resonance of MAPbI 3 powder at 80% RH determined that the monohydrate phase was the only intermediate hydrate product formed, with no signal of the dihydrate compound even prolonging the exposure to 3 weeks [26]. Thus, we can assign the new peaks to the monohydrate compound MAPbI 3 ·H 2 O.…”

“…Degradation due to humid ambient air is a key issue. In the presence of water vapor, MAPbI 3 forms an intermediate monohydrate phase and/or dihydrate phase, then decomposes into the precursor materials lead iodide (PbI 2 ) solid and aqueous methylammonium iodide (CH 3 NH 3 I, MAI), and ultimately, MAI could further decompose into volatile methylamine (CH 3 NH 2 ), hydrogen iodide (HI), and iodide (I 2 ) [20–26]. …”

Surface Termination of CsPbBr3 Perovskite Quantum Dots Determined by Solid-State NMR Spectroscopy

“…[24][25][26][27][28][29] Indeed, solid-state NMR spectroscopy has proven to be a valuable tool to study cation dynamics [30][31][32][33][34][35] and the structure of bulk lead halide perovskites. 31,[36][37][38][39][40][41][42] To the best of our knowledge, solid-state NMR spectroscopy has only been applied to study lead halide perovskite QDs in a handful of cases. Piveteau et al 43 recorded DNP enhanced spectra of 133 Cs from perovskite CsPbBr3 QDs.…”

Local Structure and Dynamics in Methylammonium, Formamidinium, and Cesium Tin(II) Mixed-Halide Perovskites from 119Sn Solid-State NMR

“…38 In particular, solid-state NMR can be used to evidence A-/B-site cation incorporation, 39−45 halide mixing, 46−49 and dopinginduced phase segregation processe, 40,41,43,46 and to study interfacial passivation mechanisms, 50−52 cation and anion dynamics, 39,53−59 and degradation processes. 60 The local structure of tin halide perovskites has been previously investigated in CsSnBr 3 , 61 MASnI 3 , 62 and FASnI 3 62 using pair distribution function (PDF) analysis. Given the prevalence of tin NMR studies of other groups of materials, it is surprising that it has not yet been applied to tin(II) halide perovskites.…”