Effect on partial substitution of Mn2+ ions in perovskite (MA)2Zn1-xMnxCl4 (x=0, 0.1, 0.3, 0.5, 0.7, and 1) mixed crystals through MAS NMR relaxation times

A.R. Lim, J-H Chang
Jeonju University,
Korea

Keywords: solar cell, perovskite, NMR, crystal growth

Summary:

Organic-inorganic hybrid compounds have both organic and inorganic properties. Such compounds have diverse structures and properties and therefore have many potential applications. Organic-inorganic hybrid lead perovskites find applications in solar cells; however, their toxicity and stability remain major drawbacks. Thus, studies are actively developing nontoxic and stable organic-inorganic hybrid compounds. Organic-inorganic hybrid lead-free perovskite compounds show greater promise for applications in solar cells.1, 2 The structures of (MA)2MCl4 compounds, where MA is methyl ammonium (CH3NH3), an organic ion, and M is a divalent metal (M=Mn, Co, Cu, Zn, and Cd), consist of a sequence of alternating organic-inorganic layers. (MA)2Zn1-xMnxCl4 (x=0, 0.1, 0.3, 0.5, 0.7, and 1) lead-free zinc-based perovskite mixed crystals are grown using the slow evaporation method. The crystal structures are defined through X-ray diffraction experiments. This study discusses the effects of the partial replacement of Zn2+ ions with paramagnetic Mn2+ ions in ecofriendly (MA)2Zn1-xMnxCl4 lead-free perovskite crystals through magic angle spinning nuclear magnetic resonance relaxation times. Further, the spin-lattice relaxation time, T1ρ, in the rotating frame is measured for 1H and 13C nuclei of (MA)+ cations to understand the local environments with respect to the Mn2+ ion content, as shown in Figure. The structures and chemical shifts for CH3 and NH3 with x=0.1 and 0.3 were highly similar to those with x=0, whereas those for CH3 and NH3 with x=0.5 and 0.7 were highly similar to those with x=1. Nonetheless, the 1H T1ρ depending on the paramagnetic ion content became shorter because (MA)+ cations were bound to the paramagnetic Mn2+ layer through N-H•••Cl bonds. The main effects were the differences in the metal Zn2+ and Mn2+ ions. The temperature dependence of the T1ρ values for 1H reflected the modulation of the inter-NH3 and inter-CH3 dipolar interactions by (MA)+ cations. The differences in chemical shifts, line widths, and T1ρ for 1H and 13C in (MA)+ cations could potentially be due to differences in the electron structures of the metal ions. Acknowledgment: This research was supported by the Basic Science Research program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (2018R1D1A1B07041593). References [1] J. A. Aramburu, P. G.-Fernandez, N. R. Mathiesen, J. M. G.-Lastra, and M. Moreno, J. Phys. Chem. C 122, 5071 (2018). [2] A. M. Elseman, A. E. Shalan, S. Sajid, M. M. Rashad, A. M. Hassan, and M. Li, ACS Appl. Mater. Interfaces 10, 11699 (2018).