Suppressing Ion Migration in Metal Halide Perovskite via High‐Valent Rare‐Earth Ions Doping Induced Phase Pinning

ABSTRACT Mixed metal halide perovskites (MHPs) enable multi‐band emission for white‐light applications but suffer from instability due to non‐radiative recombination and rapid halogen ion migration. Herein, we propose a high‐valent cation‐doped phase pinning strategy to induce a stable planar heterojunction in all‐inorganic CsPb(Br x I 1‐x ) 3 perovskite microplates. Among a series of selectable cations, Er 3+ proves the most significant inhibitory effect on ion migration. Photoluminescence (PL) and time‐resolved PL (TRPL) spectroscopy reveal that the Er‐doped CsPb(Br x I 1‐x ) 3 microplate exhibits stable dual‐wavelength emission characteristics, accompanied by significantly enhanced PL intensity and prolonged carrier lifetime. The ion migration rate and radiation recombination efficiency were further tuned by adjusting Er concentration and halogen ratios. The finding reveals a viable approach for inhibiting ion migration through the doping of trivalent B‐site cations, providing a basis for optoelectronic devices with multiple emission channels.