Ultra‐Narrow and Stable Blue Perovskite LEDs Enabled by Synergistic Interfacial Modulation With Multifunctional Molecular Bridges

ABSTRACT High‐color‐purity blue perovskite light‐emitting diodes (PeLEDs) using wide bandgap quasi‐two‐dimensional (quasi‐2D) perovskites are limited by buried interface disorder, poor hole injection, broad phase distribution, and nonradiative losses. Here, terminal benzoic‐acid‐functionalized donor–acceptor (D–A) molecules, MPA‐BT‐BA (0F) and fluorinated MPA2FPh‐BT‐BA (2F), are introduced into the hole transport layer as molecular bridges. They reduce energetic disorder in poly(9‐vinylcarbazole) (PVK), facilitate hole transport, coordinate Pb 2+ precursor species, promote interfacial nucleation, and passivate Pb defects. Fluorinated 2F further strengthens hydrogen bonding with organic spacer cations, suppressing low‐ n phases, narrowing phase distribution, and directing energy transfer to the dominant emissive phase. Devices achieve 9.3% external quantum efficiency at 478 nm, an 80 meV (14.73 nm) ultranarrow electroluminescence linewidth, 2.0 V turn‐on voltage, and 41.9 min T 50 lifetime at 100 cd m −2 , highlighting molecular bridge interface engineering for low‐voltage, color‐pure, and operationally stable blue PeLEDs.