期刊
JOURNAL OF PHYSICAL CHEMISTRY A
卷 122, 期 6, 页码 1560-1573出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpca.7b11558
关键词
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资金
- Canadian Universities - National Research Council Canada
- Bruker BioSpin
- Natural Sciences and Engineering Research Council (NSERC) of Canada
- SABIC
In light of the intense recent interest in the methylammonium lead halides, CH3NH3PbX3 (X = Cl, Br, and I) as sensitizers for photovoltaic cells, the dynamics of the A methylammonium (MA) cation in these perovskite salts has been reinvestigated as a function of temperature via H-2, N-14 and Pb-207 NMR spectroscopy. In the cubic phase of all three salts, the MA cation undergoes pseudoisotropic tumbling (picosecond time scale). For example, the correlation time, tau(2), for the C-N axis of the iodide salt is 0.85 +/- 0.30 ps at 330 K. The dynamics of the MA cation are essentially continuous across the cubic H tetragonal phase transition; however, H-2 and N-14 NMR line shapes indicate that subtle ordering of the MA cation occurs in the tetragonal phase. The temperature dependence of the cation ordering is rationalized using a six-site model, with two equivalent sites along the c-axis and four equivalent sites either perpendicular or approximately perpendicular to this axis. As the cubic 4-tetragonal phase transition temperature is approached, the six sites are nearly equally populated. Below the tetragonal H orthorhombic phase transition, H-2 NMR line shapes indicate that the C-N axis is essentially frozen.
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