Energy‐Level Regulation and Low‐Dimensional Phase Rearrangement via a Multifunctional Spacer Group toward Efficient Sky‐Blue Quasi‐2D Perovskite Light‐Emitting Diodes

Abstract Quasi‐2D perovskite materials have great potential for achieving high‐performance blue perovskite light‐emitting diodes (PeLEDs). Major challenges lie in the need to minimize the energy level mismatch between the blue‐emitting and the charge‐transport materials for better carrier injection, and to suppress low‐dimensional phases in quasi‐2D systems for improved radiation recombination. Here, this work introduces a subtly functionalized compound, methoxylated phenethylammonium bromide (y‐MeO‐PEABr), into the sky‐blue quasi‐2D perovskite. This approach induces an upward shift of the energy levels of the perovskite and reduces the holes injection barrier, thereby achieving a better charge balance. In addition, the introduction of large y‐MeO‐PEA⁺ cations effectively suppresses the formation of undesirable phases in quasi‐2D perovskites, leading to a more concentrated phase distribution and accelerated energy transfer. Specifically, the sky‐blue quasi‐2D PeLED based on 2‐MeO‐PEABr exhibits optimal device performance, obtaining a maximum external quantum efficiency of 10.85% at 486 nm. This work suggests that this method may provide a guide for designing novel organic spacer cations to obtain high‐performance blue quasi‐2D PeLEDs.