Efficient Red Perovskite LEDs with Iodine Management via Volatile Additive I2

Abstract Perovskite light‐emitting diodes (PeLEDs) face a tough challenge that halogen vacancy defects limit device performance, while the introduction of additional agents to passivate defects may potentially compromise the stability of the structure and increase the complexity of the system. Here, elemental iodine (I 2 ) is employed as an additive, utilizing its ability to create an iodine‐rich condition and to transform into I − ions for passivating iodine vacancy defects, while its volatile nature ensures no residue and avoids the introduction of extraneous elements. This approach also alters the perovskite's surface energy and subsequently regulates its crystallization kinetics, which results in a more well‐crystallized perovskite with vertically‐aligned organic spacer layers, in turn promoting the transport of charge carriers. On the basis of this strategy, PeLEDs with efficiencies of 32.5% and 29.5% for deep‐red (678 nm) and pure‐red (649 nm) have been achieved, respectively.