Efficient Perovskite Light‐Emitting Diodes Using Polycrystalline Core–Shell‐Mimicked Nanograins

Abstract Making small nanograins in polycrystalline organic–inorganic halide perovskite (OIHP) films is critical to improving the luminescent efficiency in perovskite light‐emitting diodes (PeLEDs). 3D polycrystalline OIHPs have fundamental limitations related to exciton binding energy and exciton diffusion length. At the same time, passivating the defects at the grain boundaries is also critical when the grain size becomes smaller. Molecular additives can be incorporated to shield the nanograins to suppress defects at grain boundaries; however, unevenly distributed molecular additives can cause imbalanced charge distribution and inefficient local defect passivation in polycrystalline OIHP films. Here, a kinetically controlled polycrystalline organic‐shielded nanograin (OSN) film with a uniformly distributed organic semiconducting additive (2,2′,2′′‐(1,3,5‐benzinetriyl)‐tris(1‐phenyl‐1‐ H ‐benzimidazole), TPBI) is developed mimicking core–shell nanoparticles. The OSN film causes improved photophysical and electroluminescent properties with improved light out‐coupling by possessing a low refractive index. Finally, highly improved electroluminescent efficiencies of 21.81% ph el −1 and 87.35 cd A −1 are achieved with a half‐sphere lens and four‐time increased half‐lifetime in polycrystalline PeLEDs. This strategy to make homogeneous, defect‐healed polycrystalline core–shell‐mimicked nanograin film with better optical out‐coupling will provide a simple and efficient way to make highly efficient perovskite polycrystal films and their optoelectronics devices.