The effect of organic cation dynamics on the optical properties in (PEA)2(MA)Pb2I7 perovskite dimorphs

Lekina, Y., Dintakurti, S.S.H., Febriansyah, B. , Bradley, D., Yan, J., Shi, X., England, Jason, White, T., Hanna, J.V. and Shen, Z.X. (2021) The effect of organic cation dynamics on the optical properties in (PEA)2(MA)Pb2I7 perovskite dimorphs. Journal of Materials Chemistry C, 9 (47). pp. 17050-17060. ISSN 2050-7534

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Two-dimensional (2D) phenylethyl ammonium (PEA+)-methyl ammonium (MA+) lead iodide ((PEA)2(MA)[Pb2I7]) hybrid perovskite exists as temperature-dependent dimorphs exhibiting an ill-defined phase transition occurring over the 150-200 K range. Raman scattering, photoluminescence, optical absorbance and solid state MAS NMR spectroscopic methods are employed to investigate the structural complexity, disorder and structure/function of this system. The Raman and 1H MAS NMR data indicate that the lower bounds of the phase transition at ∼150 K are characterised by attenuated rotational modes and slower motional dynamics throughout the disordered MA+ organic sublattice, inducing a strengthening of the MA+⋯I hydrogen bonds and a 5 meV increase in the excitonic and photoluminescence energies. It is evident that different recombination mechanisms are dominant for the room temperature and low temperature phases reflecting the importance of MA+ dynamics in the optical properties of the material. Single crystal X-ray studies are unable to position the organic cations within the Pb2I7 framework; however, 1H/13C MAS NMR measurements describe elements of local structural disorder based on conformational isomerism within the PEA+ sublattice. Concomitant I- and Pb2+ migration and [Pb2I7]3- framework defects create stacking disorder, dislocations and dispersed octahedral tilting leading to additional disorder and distributed MA+ and PEA+ cation dynamics.

Keywords:Dynamics, Hydrogen bonds, Iodine compounds, Layered semiconductors, Optical properties, Perovskite, Photoluminescence, Positive ions, Single crystals, Spectroscopic analysis, Stereochemistry, Temperature, Complexity functions, MAS NMR, Optical absorbance, Organic cations, Spectroscopic method, Structural complexity, Structure functions, Sub-lattices, Temperature dependent, Two-dimensional, Lead compounds
Subjects:F Physical Sciences > F200 Materials Science
F Physical Sciences > F120 Inorganic Chemistry
F Physical Sciences > F100 Chemistry
Divisions:College of Science > School of Chemistry
ID Code:51885
Deposited On:04 Oct 2022 09:28

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