Quantification of ion migration in CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> 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 (MAPbI<sub>3</sub>) 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<sup>−</sup>) and methylammonium (MA<sup>+</sup>). We find that the concentration of mobile MA<sup>+</sup> ions is one order of magnitude higher than the one of mobile I<sup>−</sup> ions, and that the diffusion coefficient of mobile MA<sup>+</sup> ions is three orders of magnitude lower than the one for mobile I− ions in our samples. This quantification of mobile ions in MAPbI<sub>3</sub> will lead to a better understanding of ion migration and its role in operation and degradation of perovskite solar cells.