Toolsets for assessing ionic migration in halide perovskites

Summary

Halide perovskites, known for their tunable and exceptional optoelectronic properties, have been extensively explored for photovoltaics, light-emitting diodes, photodetectors, and memristors. With solar cell efficiencies closing on theoretical limits, stabilization of perovskite devices—especially via control of the ionic activity within the device—is a research gap that needs to be addressed before its commercialization. Solar cell stability is directly linked to ionic defects, and their effective passivation is essential for curbing ionic migration and associated deleterious effects. However, techniques to quantify and directly observe ionic migration are limited by the soft ionic lattice nature of the perovskite as well as its mixed ionic-electronic conductivity. This review examines both theoretical and experimental approaches to understand intrinsic and extrinsic ionic motion in halide perovskites at the material and device level. In addition to elemental and molecular analysis techniques that directly identify the ion in motion, spectroscopy techniques that measure properties associated with local stoichiometry changes have also been deployed. Measurement artifacts, strategies to mitigate their occurrence, as well as ways to differentiate electronic and ionic components related to specific techniques, are evaluated. Strict environmental control during measurement is highlighted due to perovskite's sensitivity to external factors such as humidity, light, electric field, and heat.