Advancements in Blue Perovskite Light‐Emitting Diodes Enabled by Diammonium‐Based Structural Modulation

ABSTRACT Metal halide perovskite light‐emitting diodes (PeLEDs) have undergone a meteoric rise in performance, with near‐infrared, red, and green devices consistently achieving external quantum efficiencies (EQEs) exceeding 30%. Despite these triumphs, the realization of high‐performance and spectrally stable blue PeLEDs remains a significant bottleneck, largely due to high defect densities, severe phase instability, and field‐induced ion migration in wide‐bandgap systems. This review provides a comprehensive synthesis of diammonium cation regulation as a primary and transformative strategy to bridge the “Blue Gap” by directly “Stitching” the inorganic framework and suppressing ion migration. Furthermore, recognizing that diammonium modulation alone cannot fully eliminate all intrinsic non‐radiative losses, we systematically summarize universal optimization strategies developed across conventional blue PeLEDs, including phase distribution control, compositional engineering, additive processing, post‐treatment, as well as device architecture design and optimization, establishing them as a transferable toolbox to synergize with diammonium systems. Finally, a strategic roadmap for the rational design of diammonium‐regulated perovskites is proposed to accelerate the commercialization of stable, full‐color perovskite‐based display and lighting technologies.