Efficient Inverted Blue Perovskite Light‐Emitting Diodes Based on Bulk Crystal‐Splitting Fabricated FAPbBr x Cl 3‐x Nanocrystal Films

Abstract Inverted n‐i‐p architectures using metal oxide electron transport layers, such as zinc oxide, are widely studied in perovskite light‐emitting diodes (PeLEDs) for their high mobility, transparency, and environmental compatibility. However, high‐performance blue inverted PeLEDs based on 3D mixed‐halide materials remain underdeveloped due to severe ion migration, which limits their spectral stability and external quantum efficiency (EQE). In this study, an innovative top‐down approach is developed to construct bright blue FAPbBr x Cl 3‐x nanocrystal films by splitting the bulk crystal, thereby suppressing ion migration. The benzylphosphonic acid (BPA) molecules etch the large perovskite grains into small nanocrystals and simultaneously anchor on their surface, resulting in pronounced carrier confinement and restricted ion migration pathways. Furthermore, the effective passivation provided by BPA molecules increase the activation energy of nonradiative recombination, thereby enhancing the photoluminescence efficiency of the film. The above merits contribute to excellent spectral stability during PeLED operation and endow two orders of magnitude enhancement in EQEs of the inverted device, yielding peak values of 3.68% (470 nm), 4.97% (478 nm), and 7.87% (490 nm), respectively. The efficiencies represent the state‐of‐the‐art performance in inverted blue PeLEDs, highlighting the critical role of suppressing phase separation in improving efficiency.