Investigating the effects of post-synthetic treatments of MAPbI 3 on its lattice structure and cation dynamics using X-ray diffraction and solid-state NMR Jessica Dawber 1, 2 , Julien Trébosc 3 , Mark Green 1 , Olivier Lafon 2 1 University of Kent, UK, 2 Univ. Lille, CNRS, UMR 8181-UCCS-Unité de Catalyse et Chimie de Solide, France, 3 Univ. Lille, CNRS, FR 2638 – IMEC – Fédération Chevreul, France Hybrid perovskites, consisting of an organic cation inside a metal halide scaffold, arose in 2009 1 as low-cost photovoltaic devices. Methylammonium lead iodide (MAPbI 3 ) is one of the most extensively studied hybrid perovskite materials since it exhibits high photovoltaic conversion efficiencies (> 25%), while substantially reducing production costs over existing technologies. 2-4 However, thermal and moisture stability issues, along with structural variability over the general operating temperatures of a perovskite solar cell (15 – 70 °C) 5 , affect their overall photovoltaic performance. 6 Our research involves developing post-synthetic annealing treatments the material structure in the bulk. We show that post-treatment of MAPbI 3 under various conditions alters the motions of the cation (measured by solid-state NMR), which correlate to the change in tilting of the PbI 6 octahedra observed in X-ray diffraction. This exhibits the importance of using a combination of techniques to characterise the structural modifications in the treated phases, while also demonstrating the synergy between the structure and dynamics in these systems. This allows for the opportunity of a range of new related hybrid perovskite materials through topotactic transformations, that can have properties tuned according to the requirements of their application. References 1. Kojima, et al., JACS 2009, 131, 6050.H. Im, et al., Nanoscale, 2011 2. Chen, et al., ACS Energy Lett., 2019, 4, 6, 1258–1259 3. M. Lee, et al., Scientific Reports , 2012, 2, 59
4. 1T. Weller, et al., Chem. Commun. , 2015, 51, 4180—4183 5. Slonopas, et al., Journal of Applied Physics , 2016, 119, 074101
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