Halide Ion Migration in Halide Perovskites and Its Impact on the Photovoltaic Stability*

The intrinsic ionic defects, specifically halide ion vacancies, often dictate the mobility of halide species within the metal halide perovskite film during the operation of solar cells. Of particular interest is the halide ion mobility in mixed halide perovskites, which offer an insight into the halide ion migration. The origin of processes leading to halide migration is investigated using mixed halide perovskite films. Both hole trapping at I-site and the defect mediated migration influence the mobility of iodide species under photoirradiation. The iodide species migrating toward the grain boundaries render the mixed halide film phase-segregated under photoirradiation.Ways to suppresses the halide ion mobility through introduction of Cs at the A-site will be discussed.