Temperature-Dependent Ionic Conductivity and Properties of Iodine-Related Defects in Metal Halide Perovskites

The properties of charged point defects in semiconductors such as metal halide perovskites play a critical role in the efficiency and stability of solar cells. Still, the formation and migration enthalpies as well as formation entropies of ionic defects in metal halide perovskites have not yet been determined experimentally. Through impedance spectroscopy, along with a quantification of the ionic defect properties, we demonstrate an approach to obtain ion migration and formation enthalpies as well as formation entropy changes in different metal halide perovskite thin films. We investigate lead-based perovskites that contain different cations (Cs, methylammonium (MA), and formamidinium (FA)) such as MAPbI3, CsPbI3, and a mixture of all Cs0.05(FA0.83MA0.17)0.95Pb(I0.9Br0.1)3. We assign the most dominant, common defect responsible for ion conductivity to iodide vacancy and compare its defect properties in terms of entropy and enthalpy changes in all measured perovskite compositions. Our approach is relevant for ionic conductors in general.