Quantification of ion migration in CH3NH3PbI3 perovskite solar cells by transient capacitance measurements

Abstract

Ion migration in halide perovskite films leads to device degradation and impedes large scale commercial applications. We use transient ion-drift measurements to quantify activation energy, diffusion coefficient, and concentration of mobile ions in methylammonium lead triiodide (MAPbI₃) perovskite solar cells, and find that their properties change close to the tetragonal-to-orthorhombic phase transition temperature. We identify three migrating ion species which we attribute to the migration of iodide (I⁻) and methylammonium (MA⁺). We find that the concentration of mobile MA⁺ ions is one order of magnitude higher than the one of mobile I⁻ ions, and that the diffusion coefficient of mobile MA⁺ ions is three orders of magnitude lower than the one for mobile I⁻ ions in our samples. This quantification of mobile ions in MAPbI₃ will lead to a better understanding of ion migration and its role in operation and degradation of perovskite solar cells.