Efficient Perovskite Nanograin Light‐Emitting Diodes in Green‐to‐Blue Gamut with Co‐Additive Engineering

Abstract Perovskite nanograins exceeding the Bohr exciton diameter show great potential for high‐performance light‐emitting diodes (LEDs) owing to their bandgap homogeneity, spatial charge confinement, and nonlocal interaction. However, it is challenging to directly synthesize proper nanograins along with reduced crystal defects on functional substrate, and the corresponding high‐efficiency perovskite LEDs (PeLEDs) have rarely been reported. In this study, crystallization modulation for perovskites with an effective co‐additive system, including lithium bromide, p‐fluorophenethylammonium bromide, and 18‐crown‐6, is performed. Furthermore, it is demonstrated that the proposed co‐additive system can synergistically retard perovskite crystallization and reduce crystal defects. Consequently, high‐quality perovskite nanograin solids (≈22.8 nm) are obtained with a high photoluminescence quantum yield (≈88%). These superior optical properties contribute to developing efficient green PeLEDs with a champion external quantum efficiency (EQE) of 28.4% and an average EQE of 27.1%. The co‐additive system can be universally applied to mixed‐halide perovskite nanograin LED, presenting a maximum EQE of 24.4%, 21.6%, 17.5%, and 11.1% for the blue device at 496, 488, 478, and 472 nm, respectively, along with a narrow spectral linewidth (17–14 nm) and stable color. These results supplement the research on high‐efficiency perovskite nanograin LEDs for multicolor displays and lighting.