Opposites Attract, Muons as Direct Probes for Iodide Diffusion in Methyl Ammonium Lead Iodide

The volume of research into organo-lead hailde perovskites is increasing rapidly, with perovskite solar cell efficiencies reaching as high as 22 percent. There is considerable evidence that mobile ions in the perovskite strongly influence the properties of the solar cell, with the majority of studies carried out on whole cells under bias. Here we use muon spin relaxation to directly probe iodide diffusion in methyl ammonium lead iodide (MAPI). This is the first time that has been used to detect iodide diffusion in any material and the results provide valuable insight into the movement of ions in lead halide perovskites. The experiment was carried out in the dark with no external biases applied and allowed us to calculate a diffusion coefficient of 1.6 x10-14 cm2/s for iodide in MAPI at 300 K.