dr. Artem Bakulin : Real-Time Observation of Organic Cation Motion in Methylammonium Lead Iodide Persovskites

Abstract

The introduction of mobile and polarisable organic moiety as a cation in three-dimensional lead-iodide perovskites brings fascinating optoelectronic properties to these materials. However the extent of organic cation orientational mobility and the molecular mechanism behind its motion are still unclear. I will present an ultrafast two-dimensional vibrational spectroscopy experiments on methylammonium (MA) lead iodide which directly resolves the rotation of the organic cations within the MA PbI3 lattice. Our results reveal two characteristic time constants of motion. Using ab-initio molecular dynamics simulations, we identify these as a fast (~300-fs) ‘wobbling’ and rotation around the CN axis, and a relatively slow jump-like reorientation of molecular dipole with respect to the iodide lattice.