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Abstract Mixed‐halide perovskites are considered the most straightforward candidate to realize blue perovskite light‐emitting diodes (PeLEDs). However, they suffer severe halide migration, leading to spectral instability, which is particularly exaggerated in high chloride alloying perovskites. Here, we demonstrate energy barrier of halide migration can be tuned by manipulating the degree of local lattice distortion (LLD). Enlarging the LLD degree to a suitable level can increase the halide migration energy barrier. We herein report an “A‐site” cation engineering to tune the LLD degree to an optimal level. DFT simulation and experimental data confirm that LLD manipulation suppresses the halide migration in perovskites. Conclusively, mixed‐halide blue PeLEDs with a champion EQE of 14.2 % at 475 nm have been achieved. Moreover, the devices exhibit excellent operational spectral stability ( T 50 of 72 min), representing one of the most efficient and stable pure‐blue PeLEDs reported yet.
Zhang et al. (Fri,) studied this question.