Buried Layer Enhances Interfacial Dipole Toward Ultrabright Blue Perovskite Light‐Emitting Diodes

The emerging micro‐displays and visible light communication demand light‐emitting devices capable of simultaneously achieving high efficiency and ultrahigh brightness under high current injection. Lead‐halide perovskite light‐emitting diodes (PeLEDs) are intrinsically capable of sustaining high efficiency and high brightness, making them highly attractive for micro‐display and visible light communication technologies. While such performance has been well demonstrated in green PeLEDs, blue PeLEDs still lag far behind due to severe nonradiative recombination at high current densities. Herein, we report a potassium thiocyanate (KSCN) interfacial dipole layer strategy for blue PeLEDs that simultaneously improves interfacial energy‐level alignment, suppresses leakage current by forming a compact bottom interface, and regulates the crystallization of perovskite films. Benefiting from the synergistic optimization of interfacial electronic structure and film quality, the resulting devices achieve a maximum external quantum efficiency (EQE) of 17.73% with a narrow emission at 491 nm (FWHM ≈ 15 nm). Meanwhile, the device delivers an ultrahigh luminance of 41890 cd m −2 and improved operational stability with a fivefold increase in lifetime. This work demonstrates that interfacial coordination engineering provides an effective route to simultaneously achieve high efficiency and high brightness in blue PeLEDs.