Abstract Halide ion mobility in metal halide perovskites remains an intriguing phenomenon, influencing their optical and photovoltaic properties. Selective injection of holes through electrochemical anodic bias has allowed us to probe the effect of hole trapping at iodide (0.9 V) and bromide (1.15 V) in mixed halide perovskite (CH3NH3PbBr1.5I1.5) films. Upon trapping holes at the iodide site, the iodide gradually gets expelled from the mixed halide film (as iodine and/or triiodide ion), leaving behind reformed CH3NH3PbBr3 domains. The weakening of the Pb-I bond following the hole trapping (oxidation of iodide site) and its expulsion from the lattice in the form of iodine, provided further insight into the photoinduced segregation of halide ions in mixed halide perovskite films. Transient absorption spectroscopy revealed that the iodide expulsion process leaves a defect rich perovskite lattice behind as charge carrier recombination in the reformed lattice is greatly accelerated. The selective mobility of iodide species provide insight into the photoinduced phase segregation and its implication in the stable operation of perovskite solar cells.
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