Slow methylammonium migration in methylammonium lead iodide in the dark and under illumination
Alessandro Senocrate a b, Igor Moudrakovski a, Tolga Acartuerk a, Gee Yeong Kim a, Rotraut Merkle a, Ulrich Starke a, Michael Graetzel a b, Joachim Maier a
a Max Planck Institut for Solid State Research, Heisenbergstr. 1, Stuttgart, 70569, Germany
b École Polytechnique Fédérale de Lausanne EPFL, CH
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Oral, Alessandro Senocrate, presentation 078
Publication date: 11th February 2019

Ionic conductivity in methylammonium lead iodide (MAPbI3) and related compounds has received considerable attention after significant ion-induced polarisation phenomena have been observed in perovskite solar cell devices under operation.[1-3] Such polarization processes can affect both charge transport in the bulk of the material and charge extraction at the interfaces of a device, making a comprehensive knowledge of the nature of this process of utmost importance to understand and possibly improve halide-perovskite-based solar cell devices. While the existence of a significant iodine motion in MAPbI3 is now largely accepted,[4] the presence and extent of methylammonium motion is a more controversial topic. Here,[5] we investigate methylammonium transport in methylammonium lead iodide in the dark and under illumination by using tracer diffusion and 1H and 13C solid-state NMR. We observe a perceptible, but very sluggish, MA motion, and we extract the corresponding diffusion coefficient. The derived bulk conductivity is found to be orders of magnitude below the experimental ionic conductivity, corroborating the picture of pure iodine transport in MAPbI3 both in the dark and under illumination.

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