Which ions migrate in operating perovskite devices and why
In plain words
Charged atoms (ions) and empty atomic sites in perovskites drift under electric fields and light, causing current-voltage hysteresis and device degradation. Which species move, how fast, and why light speeds them up is not settled.
Precise statement
Determine the dominant mobile species (halide vacancies, halide interstitials, organic cations) in MAPbI3 and FAPbI3 under operation, their densities and activation energies (reported values span approximately 0.1 to 0.6 eV), and the mechanism of light-enhanced ionic conductivity. Measurements must separate ionic from electronic signals (e.g. impedance with tracer diffusion) and be matched to first-principles migration barriers. An answer is the identified species with activation energies and the photo-enhancement mechanism.
What would settle it
Isotope or tracer diffusion measurements in the dark and under light, consistent with computed barriers for a single identified species.