Knitting Interconnected Perovskite Grains with A Π‐Conjugated Passivator for Blue Light‐Emitting Diodes

Metal halide perovskite light‐emitting diode (PeLED) is the most promising candidate for next‐generation display technology. However, the development of the blue PeLEDs is far behind the expectations. Mixed‐halide perovskites demonstrate to be the most facile method to realize blue emission, which confronts serious spectra stability problem arising from the halide segregation. Here, a polymerizable passivator is introduced into the Cl/Br‐mixed perovskites, which can simultaneously cross‐link perovskite grains by interconnecting halides through hydrogen bonding, and transport the carriers through its π‐conjugated backbone. Consequently, this cross‐linked blue perovskite film demonstrates a significantly improved spectra stability under various external stimuli of high humidity, UV radiation, and electrical field, and the corresponding PeLED yields a decent external quantum efficiency of 12.0% at high brightness of 3390 cd m −2 with the emission at 478 nm. Notably, this work provides a unique cross‐link agent with in situ polymerizability to address the ion migration and phase segregation issues without sacrificing the conducting capacity in mixed‐halide perovskites.